|
|||||||||
|
|
|
|
|
|
|
|
|
|
|
HEMATOPOIESIS
From the Renal Unit, Massachusetts General Hospital,
Harvard Medical School, Charlestown, and the Dana-Farber Cancer
Institute, Boston, MA.
CD43 is an abundant, heavily glycosylated molecule expressed
specifically on the surface of leukocytes and platelets. When leukocytes are at rest, CD43 acts to prevent both homotypic and heterotypic interactions. However, during leukocyte activation CD43
expression is repressed, facilitating the intercellular contact required for chemotaxis, phagocytosis, aggregation, adhesion to endothelium, and transendothelial migration. Consequently, CD43 repression plays a vital role both in innate and acquired immunity. Here we report that a dramatic down-regulation of CD43 mRNA levels occurs during activation of the leukocytic cell line K562. This repression coincides with repression of the transcriptional activity of
the CD43 gene promoter. We have determined that
heterogeneous nuclear ribonucleoprotein K (hnRNP-K) and Pur CD43 is a heavily glycosylated transmembrane
molecule that plays a critical role in leukocyte activation and
adhesion.1-3 The importance of CD43 is demonstrated by 2 immunodeficiency diseases, Wiskott-Aldrich syndrome (WAS) and the early
stages of HIV infection.4-9 The etiology of both diseases
involves the development of defects in CD43. Patients with WAS, which
is an X chromosome-linked, recessive disorder, express defective CD43
on the surface of their T lymphocytes. Affected males are subject to
recurring opportunistic infections and do not respond to carbohydrate
antigens, reflecting defects in T lymphocyte function. In addition,
patients suffer from eczema and thrombocytopenia with platelets of
reduced size and function. With regard to HIV infection, the finding
that all affected individuals have circulating anti-CD43 antibodies has
led to the suggestion that these autoantibodies contribute to severe
immunodeficiency.8
CD43 is composed of 381 amino acids divided between a 235-residue
extracellular region, a 23-residue transmembrane region, and a
123-amino acid C-terminal intracellular region.10,11 The
extracellular region contains approximately 84 sialylated O-linked
carbohydrate units and appears by electron microscopy to be a rodlike
structure extending 45 nm from the cell surface.12 Comparison of the rat, mouse, and human sequences indicates that the
intracellular domain has been highly conserved during evolution, suggesting a critical function. The intracellular domain anchors CD43
to the cytoskeleton by binding actin, ezrin, and
moesin.13,14
When leukocytes are at rest, CD43 maintains their circulation within
the bloodstream by preventing intercellular adhesion. This function is
achieved by virtue of the size and strong negative charge of the
extracellular domain.15-18 During leukocyte activation, CD43 expression is dramatically down-regulated, allowing intercellular interactions mediated by molecules such as the The proadhesive function of CD43 is indicated by its identification as
a counterreceptor for galectin-1, intercellular adhesion molecule 1 (ICAM-1), and the macrophage adhesion molecule
sialoadhesin.29-32 In addition, antibodies to CD43 have
been shown to activate monocytes, B lymphocytes, and dendritic, mast,
and natural killer cells.33-39 CD43 binds major
histocompatibility complex (MHC) class I molecules and activates T
lymphocytes in a manner independent of both the T lymphocyte
receptor/CD3 complex and CD28.40-43 The activation signals
of this pathway are mediated through phosphorylation of the
intracellular domain of CD43 and its physical interaction with the
tyrosine kinases Fyn and Lck and the serine/threonine kinase
STANK.44-47 Activation signals transduced by CD43 lead to phosphorylation of Shc, induction of the formation of a Shc/Grb2 complex, tyrosine phosphorylation of Vav, mitogen-activated protein kinase activation, and nuclear translocation of ERK2.48
Ultimately, these CD43-mediated signals induce the DNA-binding activity
of the transcription factors AP-1, nuclear factor of activated T cells (NF-AT), and nuclear factor- CD43 is clearly vital to the function of leukocytes. Of particular
importance is CD43 repression because this mediates leukocyte adhesion
under both physiologic and pathologic circumstances. Regulation of the
transcriptional activity of the CD43 gene is the
first level at which CD43 expression is controlled. Therefore, we have
investigated the possibility that CD43 repression is mediated by
transcriptional events. We have previously reported that
transcriptional repression of the CD43 promoter occurs
during activation of the monocytic cell line U937 and that this is
mediated by the transcription factor Pur Cells and culture media
Northern blot analysis
Southern blot analysis DNA was subjected to electrophoresis through a 1% agarose gel and transferred to a Hybond N+ nylon membrane (Amersham Pharmacia Biotech). This membrane was then hybridized with the oligonucleotide LUC-2, which had been radiolabeled at its 5' end and which specifically interacts with the coding region of the firefly luciferase gene. LUC-2 was labeled using T4 polynucleotide kinase and [32P]-adenosine triphosphate (ATP). The nucleotide
sequence of LUC-2 is: 5'-ATAGCCTTATGCAGTTGCTCT-3'.
Following hybridization, membranes were washed and subjected to autoradiography.
Plasmid construction The activity of the CD43 promoter was assessed using the expression vector pATLuc54 that contains a promoterless firefly luciferase reporter gene. The polymerase chain reaction (PCR) was used to generate a fragment of the CD43 gene representing nucleotides 2 to +99
relative to the most 5' of the 2 major transcription initiation
sites.55 This fragment was then subcloned into the filled-in HindIII site of pATLuc to generate
p43Wt.50,56 The correct orientation and nucleotide
sequence of the CD43 promoter within p43Wt was verified by
DNA sequencing.57 K562 cells carrying within their genome
the 2/+99 region of the CD43 gene linked to the
luciferase reporter were produced using the plasmid
p43Wt/Zeo. This plasmid was generated by inserting between the
SalI and PstI sites of p43Wt the
XhoI/PstI fragment of pCMV/Zeo (Invitrogen Life
Technologies) containing the zeocin-resistance gene. Prior to transfection, p43Wt/Zeo was linearized by digestion with
PstI such that the zeocin gene lay downstream and
head-to-tail relative to the luciferase gene. The hnRNP-K
expression constructs, full-length hnRNP-K, glutathione
S-transferase (GST)-RNP-K, and the equivalent vectors empty of
hnRNP-K-coding sequences were kindly provided by David
Levens (National Institutes of Health, Bethesda, MD).52 The Pur expression construct, pHAPur1, was kindly provided by Edward
Johnson (Mount Sinai School of Medicine, New York, NY) and the empty
vector equivalent, pHA, produced by religation following liberation of
the Pur sequence by RsrII and
EcoRI digestion.
Reverse transcriptase-PCR Total RNA was prepared from K562 cells carrying within their genome the CD43 promoter fused to the luciferase reporter. A GeneRacer Kit (Invitrogen Life Technologies) was used to ligate the RNA oligonucleotide GeneRacer RNA Oligo to the 5' end specifically of full-length mRNA within the total RNA mixture. This ligated mRNA was then converted to cDNA using reverse transcriptase (RT) and the GeneRacer Oligo dT Primer. Next, this cDNA was used as the template in a PCR with the oligonucleotides GeneRacer 5' Primer, which represents the DNA equivalent of the 5' end of the GeneRacer RNA Oligo, and LUC-4, which hybridizes to the coding strand of the luciferase gene. The resulting PCR products were then used as templates in a second round of PCR using the oligonucleotides GeneRacer 5' Nested Primer, which represents the DNA equivalent of the 3' end of the GeneRacer RNA Oligo, and LUC-2, which hybridizes to the coding strand of the luciferase gene 5' to the LUC-4 hybridization site. The products of this second reaction were then cloned using the TOPO TA Cloning Kit for Sequencing (Invitrogen Life Technologies). Clones containing the luciferase coding region were identified by filter hybridization. The radiolabeled probe used in this analysis was a 720 bp EcoRI/PstI fragment isolated from the plasmid p43Wt/Zeo, which spans the CD43 promoter and the 5' end of the luciferase reporter gene. Clones containing the luciferase-coding region were analyzed by DNA sequencing. The nucleotide sequences of the oligonucleotides used in RT-PCR were:GeneRacer RNA Oligo: 5'-CGACUGGAGCACGAGGACACUGACAUGGACUGAAGGAGUAGAAA-3'; GeneRacer Oligo dT Primer: 5'-GCTGTCAACGATACGCTACGTAACGGCATGACAGTG(T)18-3'; GeneRacer 5' Primer: 5'-CGACTGGAGCACGAGGACACTGA-3'; GeneRacer 5' Nested Primer: 5'-GGACACTGACATGGACTGAAGGAGTA-3'; LUC-2: 5'-ATAGCCTTATGCAGTTGCTCT-3'; and LUC-4: 5'-CACTACGGTAGGCTGCGAAATGTTCATACTGTT-3'. Transfection K562 cells were transfected by electroporation as previously described.58,59 Cells were transiently transfected with 23 µg of p43Wt together with 2 µg of the plasmid pRSV- (Promega, Madison, WI), which contains the lacZ gene encoding
-galactosidase. Each transfection of p43Wt was performed in parallel
with a transfection of the promoterless luciferase plasmid
pATLuc. Transfected cells were then either left untreated or treated
with PMA for 12 hours before harvesting and lysis. Luciferase and
-galactosidase activities were subsequently determined using
reagents purchased from Promega and Tropix (Bedford, MA), respectively.
Luciferase and -galactosidase activities, assessed as light output,
were measured using a Moonlight Luminometer (Analytical Luminescence
Laboratory, San Diego, CA), which integrated peak luminescence 10 seconds after injection of assay buffer. The levels of
-galactosidase activity resulting from different transfections were
taken as reflective of relative transfection efficiency and used to
correct the measurements of luciferase activity. Transrepression by
hnRNP-K in PMA-treated K562 cells was assessed by transient
transfections in which 8 µg of pATLuc or p43Wt were mixed with 1 µg
of pRSV- and 16 µg of either full-length hnRNP-K or the equivalent
vector empty of hnRNP-K-coding sequences. Full-length
hnRNP-K contains the human hnRNP-K-coding region downstream
of the cytomegalovirus (CMV) promoter. After correction for
transfection efficiency, the level of luciferase activity directed by
pATLuc in the presence of full-length hnRNP-K was used to divide the
levels of luciferase activity directed by p43Wt also in the presence of
full-length hnRNP-K. This calculation yielded the fold above background
activity of p43Wt in the presence of hnRNP-K. Equivalent calculations
of luciferase activity in the presence of the CMV vector empty of the
hnRNP-K-coding region assessed nonspecific effects caused
by the vector backbone. The figures resulting from this second set of
calculations represented the fold above background activity of p43Wt in
the absence of hnRNP-K. K562 cells carrying stably within their genome
the CD43 promoter linked to the luciferase
reporter were transfected as described above except p43Wt was omitted
and the concentration of pRSV-, full-length hnRNP-K, and its parent
varied as described in Figure 6 and Figure 8. In experiments assessing
the role of Pur, 6 µg of the Pur expression construct pHAPur1
or 6 µg of its empty parent pHA were used.
Affinity purification Streptavidin MagneSphere paramagnetic particles (200 µg; Promega) were washed 2 times in 1 mL of phosphate-buffered saline (PBS) containing 0.1% bovine serum albumin (BSA), then mixed on a rotating wheel for 30 minutes with 1 mL of 0.2 M NaCl containing 10 µg of a version of the oligonucleotide CD43 PyRo SS56 that was biotinylated at its 3' end. The particles were then washed twice in 1 × washing buffer (75 mM NaCl, 20 mM Tris [tris(hydroxymethyl)aminomethane]-HCl, pH 7.5, 1 mM EDTA [ethylenediaminetetraacetic acid], 15% glycerol, 0.05% IGEPAL CA-630). DNA affinity particles were mixed for 30 minutes at room temperature on a rotating wheel with 500 µL of a binding mixture consisting of 1 × binding buffer (70 mM KCl, 5 mM NaCl, 20 mM Tris-HCl, pH 7.5, 0.5 mM EDTA, 1 mM dithiothreitol [DTT] and 10% glycerol), 300 µg of nuclear extract prepared from Jurkat cells, and 0.2 µg/µL of poly(dI-dC). The particles were captured with a magnetic stand and washed 3 times with 1 mL of 2 × binding buffer containing 0.2 µg/µL of poly(dI-dC). Bound protein was then eluted by adding 50 µL of washing buffer containing 1 M NaCl. The eluate was then subjected to electrophoretic mobility shift assay (EMSA) and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis.Protein identification by MALDI-TOF-MS Affinity purified protein from Jurkat nuclear extracts was subjected to SDS-PAGE and stained with Coomassie blue. The stained band was excised from the gel and then cut into small but uniform pieces. The gel was dehydrated with acetonitrile and rehydrated with 100 mM ammonium bicarbonate. Protein was protected from oxidation by incubation at 56°C for 1 hour with 10 mM DTT and the amino terminus protected by treatment with 10 mM iodoacetamide in 100 mM ammonium bicarbonate. Next, gel pieces were subjected to 2 rounds of washing with ammonium bicarbonate and subsequent drying with acetonitrile followed by a 12-hour incubation at 37°C with 12.5 ng/µL of trypsin in 50 mM ammonium bicarbonate.60,61 The masses of the trypsin-digested peptides were determined by matrix-assisted laser desorption/ionization time-of-flight mass spectroscopy (MALDI-TOF-MS) using a Voyager DE-PRO instrument (Perseptive Biosystems, Framingham, MA). Protein identification was achieved by mass fingerprinting using the Mascot database created by Matrix Science (London, United Kingdom).Expression and purification of recombinant GST proteins The construct GST-RNP-K and its parent vector empty of hnRNP-K sequences were introduced into the Escherichia coli strain XL-2 (Stratagene, La Jolla, CA). Bacteria were grown in 50 mL of Lauria broth at 37°C until they reached an optical density at 600 nm of 0.6, then recombinant protein expression was induced for 7 hours with 0.5 mM isopropyl-D-thiogalactopyranoside (IPTG). Bacteria were washed
twice in PBS and resuspended in 1 mL of 1 × binding buffer (70 mM
KCl, 5 mM NaCl, 20 mM Tris-HCl, pH 7.5, 0.5 mM EDTA, 1 mM DTT, and 10%
glycerol) containing complete proteinase inhibitors (Roche Diagnostics,
Indianapolis, IN). Bacterial lysates were prepared by sonication and
clarified by centrifugation. These preparations were then incubated for
30 minutes at room temperature with 200 µL of glutathione-sepharose
beads (Amersham Pharmacia Biotech). Beads were washed 3 times with 1 mL
of PBS containing complete inhibitors and bound proteins eluted by
adding 800 µL of 50 mM Tris-HCl, pH 8.0, 5 mM reduced glutathione.
Finally, proteins were concentrated by centrifugation on a centricon 30 filter unit (Millipore, Bedford, MA) for 15 minutes at
5000g.
EMSA Oligonucleotides were labeled using T4 polynucleotide kinase and purified through Micro Bio-Spin 6 columns (Bio-Rad Laboratories, Hercules, CA). DNA/protein-binding reactions were carried out in a 20 µL volume. Protein preparations were incubated with or without a molar excess of unlabeled specific or nonspecific competitor oligonucleotides at 4°C for 10 minutes in 1 × binding buffer (70 mM KCl, 5 mM NaCl, 20 mM Tris-HCl, pH 7.5, 0.5 mM EDTA, 1 mM DTT, and 10% glycerol) with 2.4 µg/µL of poly(dI-dC). Radiolabeled oligonucleotides were then added and the incubation continued for 20 minutes. DNA/protein complexes were resolved by electrophoresis through 4% or 6% polyacrylamide gels with 4.5 mM Tris-HCl, pH 7.5, 4.5 mM boric acid, 0.1 mM EDTA (0.5 × TBE) and visualized by autoradiography. The oligonucleotides used in the EMSA analyses were: CD43 PyRo SS56: 5'-GGGCCCACTTCCTTTCCCCTTG-3'; CD43 PyRo SSUB: 5'-GGGCCCACUUCCUUUCCCCUUGB-3' (U is bromouracil; B, biotin); CD43 Mut-1156: 5'-GGGCCCACTTCCTTCATATATG-3'; and NS-SS56: 5'-GAGTTAGCTCACTCATTAGG-3'.UV cross-linking The UV cross-linking was performed using the oligonucleotide CD43 PyRo SSUB. This oligonucleotide was the same as the PyRo1-binding probe CD43 PyRo SS56 except that it was biotinylated at its 3' end and its deoxythymidines were substituted with 5-bromo-2'-deoxyuridine. Then 30 µg of Jurkat nuclear extract were preincubated for 5 minutes in 50 µL of EMSA-binding buffer containing 2.4 µg/µL of poly(dI-dC), 105 cpm of radiolabeled CD43 PyRo SSUB were added and binding performed for 20 minutes on ice in 1.5 mL microcentrifuge tubes. The tubes were then opened and placed in a UV cross-linker (Stratagene) and exposed to 254 nm UV light for 10 minutes. Next, 100 µL of washed streptavidin-coated magnetic particles were added and cross-linked CD43 PyRo SSUB-protein complexes were captured by rotation for 20 minutes at room temperature. Streptavidin particles were sedimented with a magnetic stand, washed 5 times with 500 µL of EMSA-binding buffer, and then resuspended in 25 µL of EMSA buffer containing 2% SDS and 5% 2-mercaptoethanol. Samples were boiled for 5 minutes and centrifuged to pellet the magnetic particles. The supernatant was then analyzed by electrophoresis through a 12% SDS-polyacrylamide gel and subsequent autoradiography.
Down-regulation of CD43 mRNA levels during K562 activation During activation, leukocytes increase in their adhesive capacity mediated in part by a down-regulation of CD43 expression. We have shown that 48 hours after activation of the monocytic cell line U937 with phorbol ester there is a 69% reduction in CD43 mRNA levels.50 A more dramatic reduction in CD43 mRNA levels follows activation of the pre-erythroid/premegakaryocytic cell line K562 (Figure 1). Within 6 hours of K562 cells being activated with phorbol ester the steady-state levels of CD43 mRNA become barely detectable.
Repression of CD43 promoter activity during K562 activation Previous studies have indicated that the cis-acting elements responsible for directing the leukocytic expression of the CD43 gene are located in the proximal promoter region.50,56,62,63 Transfection experiments using the expression construct p43Wt, which contains the CD43 promoter spanning nucleotides2 to +99, indicate that the proximal promoter
also contains the elements required for CD43 repression
during K562 activation. Specifically, we found that expression of p43Wt
is repressed by 39% on PMA-mediated activation of K562 cells (Figure
2).
Identification of a putative repressor of the CD43 promoter We have previously determined that the uncloned single-stranded DNA-binding activity PyRo1 interacts with the CD43 promoter and is induced concomitant with CD43 repression during U937 activation.56 Consequently, PyRo1 represents a potential means by which CD43 repression is effected. To determine the function of PyRo1 we undertook its molecular cloning. PyRo1 was purified from Jurkat T lymphocytic cells by affinity capture and digested with trypsin and its resulting peptides subjected to analysis by mass spectrometry. The fragmentation patterns produced from the PyRo1 peptides were then compared with those of known proteins deposited in the Mascot database created by Matrix Science. The most significant match to a known human protein was with heterogeneous nuclear ribonucleoprotein K (hnRNP-K).64 Next, a fusion protein of hnRNP-K and glutathione S-transferase (GST) was produced in bacteria. The fusion protein was purified and shown to bind a radiolabeled single-stranded oligonucleotide representing the PyRo1-binding site within the CD43 gene promoter (Figure 3). This binding was effectively competed by an unlabeled excess of the PyRo1-binding site. However, binding failed to be competed with an identical molar excess of a mutant version of the binding site, which fails to support PyRo1 interaction.56 These studies demonstrate that the DNA-binding characteristics of PyRo1 and hnRNP-K are indistinguishable. In addition, UV cross-linking demonstrated that the apparent molecular mass of PyRo1 is in the range of 50 to 65 kDa (Figure 4), which is comparable to that reported for hnRNP-K.65 Originally, hnRNP-K was identified as an RNA-binding protein and recently its consensus RNA-binding site was determined as 5-'UC3-4(U/A)2-3'.64,66 The single-stranded DNA equivalent of this consensus is present in the PyRo1-binding site within the CD43 promoter, and mutation analysis has demonstrated that this sequence is critical for PyRo1 binding.56 Consequently, by the criteria of molecular cloning, molecular mass analysis and nucleic acid-binding characteristics, PyRo1 and hnRNP-K are indistinguishable.
Repression of the CD43 gene promoter by hnRNP-K Following identification of hnRNP-K as a candidate mediator of CD43 repression, we sought to determine if this factor could indeed function in such a capacity. Transfection of 16 µg of a plasmid expressing hnRNP-K indicated that in PMA-treated K562 cells hnRNP-K does indeed repress the transcriptional activity of p43Wt. The level of this repression averaged 38% (Figure 5). It has been reported that the effects of hnRNP-K on transcriptional activity are dependent on chromosomal structures.67 Consequently, we generated a pool of K562 cell lines in which the2/+99 CD43 promoter linked to the
luciferase reporter was randomly integrated into the genome.
Transfection of the hnRNP-K expression plasmid into this stable cell
line pool subsequently treated with PMA repressed
luciferase reporter gene activity by an average of 62% (Figure 6). Consequently, hnRNP-K
significantly represses the CD43 promoter either in a
chromosomal or extrachromosomal context.
Repression mediated by hnRNP-K is dependent on DNA methylation Previous studies have demonstrated that in nonhematopoietic cells the CD43 promoter is maintained in an inactive state by DNA methylation.75,76 This finding suggested that methylation may also influence CD43 repression in hematopoietic cells as they undergo differentiation. Therefore, we tested whether hnRNP-K repression of the CD43 promoter was dependent on methylation. The pool of stable cell lines containing the CD43 promoter linked to luciferase was treated for 48 hours with the DNA methyltransferase inhibitor 5-azacytidine.77 These treated cells were then transfected with the hnRNP-K expression plasmid and incubated for 12 hours in the presence of PMA and 5-azacytidine. Under these circumstances, the CD43 promoter was repressed by only 17% (Figure 6). Without a 48-hour pretreatment but with a 12-hour treatment with 5-azacytidine and PMA immediately after transfection, hnRNP-K repressed the CD43 promoter by 50%. In cells treated only with PMA after transfection, hnRNP-K represses the CD43 promoter by 62% (Figure 6). These results indicate that exposure of the hnRNP-K expression plasmid to 5-azacytidine for 12 hours influences its ability to effect repression by only 12%. In contrast, exposure of the CD43 promoter to 5-azacytidine for 48 hours reduces the repressive capacity of hnRNP-K by 33%. Consequently, repression of the CD43 promoter by hnRNP-K is substantially dependent on this promoter being methylated.Determination of the transcription start site of the CD43 gene when linked to luciferase and integrated within the genome of K562 Transcription of the CD43 gene has been shown to be initiated at 2 major sites between which lies the binding site for hnRNP-K.55 This factor is known to bind RNA and has been implicated in mediating RNA stability and transport.68-74 Consequently, if transcription of the CD43/luciferase gene is initiated at the upstream of the 2 potential start sites, the effect of hnRNP-K on luciferase activity may reflect mechanisms mediated by RNA binding rather than transcriptional control mechanisms. Due to this reasoning, we identified the transcription start site of the CD43/luciferase gene present in the genome of K562 using RT-PCR coupled with rapid amplification of cDNA ends (RACE) technology. Southern blot analysis of the RT-PCR products resulting from this procedure revealed a single discrete cDNA containing the luciferase-coding region (Figure 7). Cloning and sequencing of this cDNA determined that the downstream of the 2 potential transcription start sites is used by the CD43 promoter when linked to luciferase and integrated within K562. Therefore, the transcript produced from this promoter does not contain a binding site for hnRNP-K. Consequently, repression of the CD43/luciferase fusion gene by hnRNP-K is likely mediated by transcriptional mechanisms as opposed to mechanisms involving RNA binding such as decreased RNA stability or transport.
hnRNP-K acts together with Pur interacts with the
CD43 promoter immediately upstream of the region that we
show here binds hnRNP-K.50 In the promonocytic cell line
U937 treated with PMA, Pur represses the CD43 promoter.
Therefore, it was of interest to determine whether Pur also mediates
repression within K562 cells and whether it works with or against
hnRNP-K. In transfection experiments using expression plasmids
constitutively expressing hnRNP-K or Pur, we found that alone,
Pur represses the CD43/luciferase gene present within the
K562 genome by 36% (Figure 8). However,
when recombinant Pur is expressed together with recombinant hnRNP-K,
repression of the CD43 promoter is increased to 51%.
Consequently, hnRNP-K and Pur appear to work together to effect
repression.
On the surface of resting leukocytes CD43 prevents cellular
interaction. However, during leukocyte activation the glycosylation pattern of CD43 changes and there is a down-regulation of the overall
amount of CD43 expressed on the cell surface. These alterations in both
the qualitative and quantitative expression of CD43 result in the
promotion of both homotypic and heterotypic leukocyte interactions. Using in vitro models of leukocyte activation we have found that down-regulation of CD43 is mediated by repression of the
transcriptional activity of the CD43 gene promoter.
Previously, we demonstrated that the transcription factor Pur Pur
The site within the CD43 promoter that binds hnRNP-K lies
adjacent to a site that interacts with Sp1.50,63,76 This
Sp1-binding site overlaps the region that binds Pur In addition to DNA remodeling, Pur A third mechanism by which hnRNP-K and Pur Previous studies have shown that in nonhematopoietic cells the CD43 gene is maintained in a transcriptionally inactive state by methylation of CpG dinucleotides within the promoter.75 These methylated dinucleotides are then able to bind the methyl-CpG-binding protein MeCP2.76 We have shown that repression of the CD43 promoter by hnRNP-K is dependent on DNA methylation. This finding suggests that repression of the CD43 promoter during hematopoietic differentiation may be mediated by an increase in its degree of methylation. Such an increase could result in the recruitment of methyl-CpG-binding proteins or the more effective recruitment of hnRNP-K or both. Beyond CD43 repression, leukocyte adhesion is induced by up-regulation
of the
We would like to thank David Levens for providing full-length hnRNP-K, GST-RNP-K, and the equivalent vectors empty of hnRNP-K coding sequences. In addition, we would like to thank Edward Johnson and Sharon Barr for providing the expression vector pHAPur1.
Submitted November 9, 2001; accepted July 15, 2002.
Supported by National Institutes of Health grants DK43351 and DK50779. N.D.S. was supported by a postdoctoral grant awarded by the Association pour la Recherche sur le Cancer. Additional support was provided by grant DAMD17-00-1-0255. In regard to this grant the US Army Medical Research Acquisition Activity (820 Chandler St, Fort Detrick, MD 21702) is the awarding and administering acquisition office.
The publication costs of this article were defrayed in part by page charge payment. Therefore, and solely to indicate this fact, this article is hereby marked "advertisement" in accordance with 18 U.S.C. section 1734.
Reprints: Carl Simon Shelley, Renal Unit, Massachusetts General Hospital, 149 13th St, Charlestown, MA 02129; e-mail: shelley{at}receptor.mgh.harvard.edu.
1. Ostberg JR, Barth RK, Frelinger JG. The Roman god Janus: a paradigm for the function of CD43. Immunol Today. 1998;19:546-550[CrossRef][Medline] [Order article via Infotrieve]. 2. Remold-O'Donnell E, Rosen FS. Sialophorin (CD43) and the Wiskott-Aldrich syndrome. Immunodefic Rev. 1990;2:151-174[Medline] [Order article via Infotrieve]. 3. Rosenstein Y, Santana A, Pedraza-Alva G. CD43, a molecule with multiple functions. Immunol Res. 1999;20:89-99[Medline] [Order article via Infotrieve]. 4. Parkman R, Remold-O'Donnell E, Kenney DM, Perrine S, Rosen FS. Surface protein abnormalities in lymphocytes and platelets from patients with Wiskott-Aldrich syndrome. Lancet. 1981;ii:1387-1389.
5.
Remold-O'Donnell E, Kenney DM, Parkman R, Cairns L, Savage B, Rosen FS.
Characterization of a human lymphocyte surface sialoglycoprotein that is defective in Wiskott-Aldrich syndrome.
J Exp Med.
1984;159:1705-1723
6.
Ardman B, Sikorski MA, Settles M, Staunton DE.
Human immunodeficiency virus type 1-infected individuals make autoantibodies that bind to CD43 on normal thymic lymphocytes.
J Exp Med.
1990;172:1151-1158
7.
Lefebvre JC, Giordanengo V, Limouse M, et al.
Altered glycosylation of leukosialin, CD43, in HIV-1-infected cells of the CEM line.
J Exp Med.
1994;180:1609-1617
8.
Giordanengo V, Limouse M, Desroys du Roure L, et al.
Autoantibodies directed against CD43 molecules with an altered glycosylation status on human immunodeficiency virus type 1 (HIV-1)-infected CEM cells are found in all HIV-1+ individuals.
Blood.
1995;86:2302-2311 9. Gallego MD, Aguado E, Kindelan JM, Pena J, Santamaria M, Molina IJ. Altered expression of CD43-hexasaccharide isoform on peripheral HIV-infected individuals. AIDS. 2001;15:477-481[CrossRef][Medline] [Order article via Infotrieve].
10.
Pallant A, Eskenazi A, Mattei M-G, et al.
Characterization of cDNAs encoding human leukosialin and localization of the leukosialin gene to chromosome 16.
Proc Natl Acad Sci U S A.
1989;86:1328-1332
11.
Shelley CS, Remold-O'Donnell E, Davis AE III, et al.
Molecular characterization of sialophorin (CD43), the lymphocyte surface sialoglycoprotein defective in Wiskott-Aldrich syndrome.
Proc Natl Acad Sci U S A.
1989;86:2819-2823 12. Cyster JG, Shotton DM, Williams AF. The dimensions of the T lymphocyte glycoprotein leukosialin and identification of linear protein epitopes that can be modified by glycosylation. EMBO J. 1991;10:893-902[Medline] [Order article via Infotrieve].
13.
Serrador JM, Nieto M, Alonso-Lebrero JL, et al.
CD43 interacts with moesin and ezrin and regulates its redistribution to the uropods of T lymphocytes at the cell-cell contacts.
Blood.
1998;91:4632-4644
14.
Yonemura S, Hirao M, Doi Y, et al.
Ezrin/radixin/moesin (ERM) proteins bind to the positively charged amino acid cluster in the juxta-membrane cytoplasmic domain of CD44, CD43, and ICAM-2.
J Cell Biol.
1998;140:885-895 15. Brown WRA, Barclay AN, Sunderland CA, Williams AF. Identification of a glycoprotein-like molecule at the cell surface of rat thymocytes. Nature. 1981;289:456-460[CrossRef][Medline] [Order article via Infotrieve].
16.
Ardman B, Sikorski MA, Staunton DE.
CD43 interferes with T-lymphocyte adhesion.
Proc Natl Acad Sci U S A.
1992;89:5001-5005 17. Manjunath N, Johnson RS, Staunton DE, Pasqualini R, Ardman B. Targeted disruption of CD43 gene enhances T lymphocyte adhesion. J Immunol. 1993;151:1528-1534[Abstract].
18.
Dragone LL, Barth RK, Sitar KL, Disbrow GL, Frelinger JG.
Disregulation of leukosialin (CD43, Ly48, sialophorin) expression in the B-cell lineage of transgenic mice increases splenic B-cell number and survival.
Proc Natl Acad Sci U S A.
1995;92:626-630
19.
Carlsson SR, Fukuda M.
Isolation and characterization of leukosialin, a major sialoglycoprotein on human leukocytes.
J Biol Chem.
1986;261:12779-12786
20.
Piller F, Piller V, Fox RI, Fukuda M.
Human T-lymphocyte activation is associated with changes in O-glycan biosynthesis.
J Biol Chem.
1988;263:15146-15150 21. Remold-O'Donnell E, Rosen FS. Proteolytic fragmentation of sialophorin (CD43): localization of the activation-inducing site and examination of the role of sialic acid. J Immunol. 1990;145:3372-3378[Abstract].
22.
Campanero MR, Pulido R, Alonso JL, et al.
Down-regulation by tumor necrosis factor-
23.
Ba
24.
Ellies LG, Jones AT, Williams MJ, Ziltener HJ.
Differential regulation of CD43 glycoforms on CD4+ and CD8+ T lymphocytes in graft-versus-host disease.
Glycobiology.
1994;4:885-893 25. Remold-O'Donnell E, Parent D. Two proteolytic pathways for down-regulation of the barrier molecule CD43 of human neutrophils. J Immunol. 1994;152:3595-3605[Abstract]. 26. Tomlinson Jones A, Federsppiel B, Ellies LG, et al. Characterization of the activation-associated isoform of CD43 on murine T lymphocytes. J Immunol. 1994;153:3426-3439[Abstract].
27.
Ellies LG, Tao W, Fellinger W, Teh HS, Ziltener HJ.
The CD43 130-kD peripheral T-cell activation antigen is downregulated in thymic positive selection.
Blood.
1996;88:1725-1732 28. Weber S, Babina M, Hermann B, Henz BM. Leukosialin (CD43) is proteolytically cleaved from stimulated HMC-1 cells. Immunobiology. 1997;197:82-96[Medline] [Order article via Infotrieve]. 29. Rosenstein Y, Park JK, Hahn WC, Rosen FS, Bierer BE, Burakoff SJ. CD43, a molecule defective in Wiskott-Aldrich syndrome, binds ICAM-1. Nature. 1991;354:233-235[CrossRef][Medline] [Order article via Infotrieve].
30.
Baum LG, Pang M, Perillo NL, et al.
Human thymic epithelial cells express an endogenous lectin, galectin-1, which binds to core 2 O-glycans on thymocytes and T lymphoblastoid cells.
J Exp Med.
1995;181:877-887 31. Perillo NL, Pace KE, Seilhamer JJ, Baum LG. Apoptosis of T cells mediated by galectin-1. Nature. 1995;378:736-739[CrossRef][Medline] [Order article via Infotrieve].
32.
Van den Berg TK, Nath D, Ziltener HJ, et al.
CD43 functions as a T cell counterreceptor for the macrophage adhesion receptor sialoadhesin (Siglec-1).
J Immunol.
2001;166:3637-3640 33. Vargas-Cortes M, Axelsson B, Larsson A, Berzins T, Perlmann P. Enhancement of human spontaneous cell-mediated cytotoxicity by a monoclonal antibody against the large sialoglycoprotein (CD43) on peripheral blood lymphocytes. Scand J Immunol. 1988;27:661-671[CrossRef][Medline] [Order article via Infotrieve].
34.
Nong YH, Remold-O'Donnell E, LeBien TW, Remold HGA.
A monoclonal antibody to sialophorin (CD43) induces homotypic adhesion and activation of human monocytes.
J Exp Med.
1989;170:259-267 35. Wiken M, Bjorck P, Axelsson B, Perlmann P. Studies on the role of CD43 in human B-cell activation and differentiation. Scand J Immunol. 1989;29:353-361[CrossRef][Medline] [Order article via Infotrieve]. 36. Wiken M, Bjorck P, Axelsson B, Perlmann P. Enhancement of human B-cell proliferation by a monoclonal antibody to CD43. Scand J Immunol. 1989;29:363-370[CrossRef][Medline] [Order article via Infotrieve]. 37. Kuijpers TW, Hoogerwerf M, Kuijpers KC, Schwartz BR, Harlan JM. Cross-linking of sialophorin (CD43) induces neutrophil aggregation in a CD18-dependent and a CD18-independent way. J Immunol. 1992;149:998-1003[Abstract]. 38. Weber S, Ruh B, Dippel E, Czarnetzki BM. Monoclonal antibodies to leucosialin (CD43) induce homotypic aggregation of the human mast cell line HMC-1: characterization of leucosialin on HMC-1 cells. Immunology. 1994;82:638-644[Medline] [Order article via Infotrieve]. 39. Fanales-Belasio E, Zambruno G, Cavani A, Girolomoni G. Activation of immature dendritic cells via membrane sialophorin (CD43). Adv Exp Med Biol. 1997;417:207-212[Medline] [Order article via Infotrieve].
40.
Mentzer SJ, Remold-O'Donnell E, Crimmins MAV, Bierer BE, Rosen FS, Burakoff SJ.
Sialophorin, a surface sialoglycoprotein defective in Wiskott-Aldrich syndrome, is involved in human T lymphocyte proliferation.
J Exp Med.
1987;165:1383-1392 41. Park JK, Rosenstein YJ, Remold-O'Donnell E, Bierer BE, Rosen FS, Burakoff SJ. Enhancement of T-cell activation by the CD43 molecule whose expression is defective in Wiskott-Aldrich syndrome. Nature. 1991;350:706-709[CrossRef][Medline] [Order article via Infotrieve].
42.
Sperling AI, Green JM, Mosley RL, et al.
CD43 is a murine T cell costimulatory receptor that functions independently of CD28.
J Exp Med.
1995;182:139-146
43.
Stöckl J, Majdic O, Kohl P, Pickl WF, Menzel JE, Knapp W.
Leukosialin (CD43)-major histocompatibility class I molecule interactions involved in spontaneous T cell conjugate formation.
J Exp Med.
1996;184:1769-1779 44. Chatila TA, Geha RS. Phosphorylation of T cell membrane proteins by activators of protein kinase C. J Immunol. 1988;140:4308-4314[Abstract]. 45. Silverman LB, Wong RCK, Remold-O'Donnell E, et al. Mechanism of mononuclear cell activation by anti-CD43 (sialophorin) agonistic antibody. J Immunol. 1989;142:4194-4200[Abstract].
46.
Pedraza-Alva G, Mérida LB, Burakoff SJ, Rosenstein Y.
CD43-specific activation of T cells induces association of CD43 to fyn kinase.
J Biol Chem.
1996;271:27564-27568 47. Wang W, Link V, Green JM. Identification and cloning of a CD43-associated serine/threonine kinase. Cell Immunol. 2000;205:34-39[CrossRef][Medline] [Order article via Infotrieve].
48.
Pedraza-Alva G, Mérida LB, Burakoff SJ, Rosenstein Y.
T cell activation through the CD43 molecule leads to Vav tyrosine phosphorylation and mitogen-activated protein kinase pathway activation.
J Biol Chem.
1998;273:14218-14224
49.
Santana MA, Pedraza-Alva G, Olivares-Zavaleta N, et al.
CD43-mediated signals induce DNA binding activity of AP-1, NF-AT, and NF
50.
Shelley CS, Da Silva N, Teodoridis JM.
During U937 monocytic differentiation repression of the CD43 gene promoter is mediated by the single-stranded DNA binding protein Pur
51.
Bergemann AD, Ma Z-W, Johnson EM.
Sequence of cDNA comprising the human pur gene and sequence-specific single-stranded DNA-binding properties of the encoded protein.
Mol Cell Biol.
1992;12:5673-5682
52.
Tomonaga T, Levens D.
Heterogeneous nuclear ribonucleoprotein K is a DNA-binding transactivator.
J Biol Chem.
1995;270:4875-4881
53.
Tso JY, Sun XH, Kao TH, Reece KS, Wu R.
Isolation and characterization of rat and human glyceraldehyde-3-phosphate dehydrogenase cDNAs: genomic complexity and molecular evolution of the gene.
Nucleic Acids Res.
1985;13:2485-2502
54.
Shelley CS, Farokhzad OC, Arnaout MA.
Identification of cell-specific and developmentally regulated nuclear factors that direct myeloid and lymphoid expression of the CD11a gene.
Proc Natl Acad Sci U S A.
1993;90:5364-5368 55. Shelley CS, Remold-O'Donnell E, Rosen FS, Whitehead AS. Structure of the human sialophorin (CD43) gene. Biochem J. 1990;270:569-576[Medline] [Order article via Infotrieve].
56.
Farokhzad OC, Teodoridis JM, Park H, Arnaout MA, Shelley CS.
CD43 gene expression is mediated by a nuclear factor which binds pyrimidine-rich single-stranded DNA.
Nucleic Acids Res.
2000;28:2256-2267
57.
Sanger F, Nicklen S, Coulson AR.
DNA sequencing with chain-terminating inhibitors.
Proc Natl Acad Sci U S A.
1977;74:5463-5467
58.
Potter H, Weir L, Leder P.
Enhancer-dependent expression of human kappa immunoglobulin genes introduced into mouse pre-B lymphocytes by electroporation.
Proc Natl Acad Sci U S A.
1984;81:7161-7165
59.
Shelley CS, Arnaout MA.
The promoter of the CD11b gene directs myeloid-specific and developmentally regulated expression.
Proc Natl Acad Sci U S A.
1991;88:10525-10529 60. Rosenfeld J, Capdevielle J, Guillemot JC, Ferrara P. In-gel digestion of proteins for internal sequence analysis after one- or two-dimensional gel electrophoresis. Anal Biochem. 1992;203:173-179[CrossRef][Medline] [Order article via Infotrieve]. 61. Wilm M, Mann M. Analytical properties of the nanoelectrospray ion source. Anal Chem. 1996;68:1-8[Medline] [Order article via Infotrieve].
62.
Kudo S, Fukuda M.
A short, novel promoter sequence confers the expression of human leukosialin, a major sialoglycoprotein on leukocytes.
J Biol Chem.
1991;266:8483-8489 63. Kudo S, Fukuda M. Transcriptional activation of human leukosialin (CD43) gene by Sp1 through binding to a GGGTGG motif. Eur J Biochem. 1994;223:319-327[Medline] [Order article via Infotrieve].
64.
Matunis MJ, Michael WM, Dreyfuss G.
Characterization and primary structure of the poly(C)-binding heterogeneous nuclear ribonucleoprotein complex K protein.
Mol Cell Biol.
1992;12:164-171 65. Dejgaard K, Leffers H, Rasmussen HH, et al. Identification, molecular cloning, expression and chromosome mapping of a family of transformation upregulated hnRNP-K proteins derived by alternative splicing. J Mol Biol. 1994;236:33-48[CrossRef][Medline] [Order article via Infotrieve].
66.
Thisted T, Lyakhov DL, Liebhaber SA.
Optimized RNA targets of two closely related triple KH domain proteins, heterogeneous nuclear ribonucleoprotein K and 67. Lau JS, Baumeister P, Kim E, et al. Heterogeneous nuclear ribonucleoproteins as regulators of gene expression through interactions with the human thymidine kinase promoter. J Cell Biochem. 2000;79:395-406[CrossRef][Medline] [Order article via Infotrieve]. 68. Piñol-Roma S, Dreyfuss G. Shuttling of pre-mRNA binding proteins between nucleus and cytoplasm. Nature. 1992;355:730-732[CrossRef][Medline] [Order article via Infotrieve]. 69. Piñol-Roma S, Dreyfuss G. hnRNP proteins: localization and transport between the nucleus and the cytoplasm. Trends Cell Biol. 1993;3:151-155[CrossRef][Medline] [Order article via Infotrieve].
70.
Michael WM, Siomi H, Choi M, et al.
Signal sequences that target nuclear import and nuclear export of pre-mRNA binding proteins.
Cold Spring Harbor Symp Quant Biol.
1995;60:663-668
71.
Kiledjian M, Wang X, Liebhaber SA.
Identification of two KH domain proteins in the 72. Visa N, Alzhanova-Ericsson AT, Sun X, et al. A pre-mRNA binding protein accompanies the RNA from the gene through the nuclear pores and into polysomes. Cell. 1996;84:253-264[CrossRef][Medline] [Order article via Infotrieve]. 73. Michael WM, Eder PS, Dreyfuss G. The K nuclear shuttling domain: a novel signal for nuclear import and nuclear export in the hnRNP K protein. EMBO J. 1997;16:3587-3598[CrossRef][Medline] [Order article via Infotrieve]. 74. Dreyfuss G, Kim VN, Kataoka N. Messenger-RNA-binding proteins and the messages they carry. Nat Rev Mol Cell Biol. 2002;3:195-205[CrossRef][Medline] [Order article via Infotrieve].
75.
Kudo S, Fukuda M.
Tissue-specific transcriptional regulation of human leukosialin (CD43) gene is achieved by DNA methylation.
J Biol Chem.
1995;270:13298-13302
76.
Kudo S.
Methyl-CpG-binding protein MeCP2 represses Sp1-activated transcription of the human leukosialin gene when the promoter is methylated.
Mol Cell Biol.
1998;18:5492-5499
77.
Creusot F, Acs G, Christman JK.
Inhibition of DNA methyltransferase and induction of Friend erythroleukemia cell differentiation by 5-azacytidine and 5- aza-2'-deoxycytidine.
J Biol Chem.
1982;257:2041-2048 78. Yagil G. Paranemic structures of DNA and their role in DNA unwinding. Crit Rev Biochem Mol Biol. 1991;26:475-559[Medline] [Order article via Infotrieve].
79.
Darbinian N, Gallia GL, Khalili K.
Helix-destabilizing properties of the human single-stranded DNA- and RNA-binding protein Pur 80. Michelotti GA, Michelotti EM, Puller A, Duncan RC, Eick D, Levens D. Multiple single-stranded cis elements are associated with activated chromatin of the human c-myc gene in vivo. Mol Cell Biol. 1996;16:2656-2669[Abstract]. 81. Michelotti EF, Michelotti GA, Aronsohn AI, Levens D. Heterogeneous nuclear ribonucleoprotein K is a transcription factor. Mol Cell Biol. 1996;16:2350-2360[Abstract].
82.
Takimoto M, Tomonaga T, Matunis M, et al.
Specific binding of heterogeneous ribonucleoprotein particle protein K to the human c-myc promoter, in vitro.
J Biol Chem.
1993;268:18249-18258
83.
Tretiakova A, Steplewski A, Johnson EM, Khalili K, Amini S.
Regulation of myelin basic protein gene transcription by Sp1 and Pur
84.
Du Q, Melnikova IN, Gardner PD.
Differential effects of heterogeneous nuclear ribonucleoprotein K on Sp1- and Sp3-mediated transcriptional activation of a neuronal nicotinic acetylcholine receptor promoter.
J Biol Chem.
1998;273:19877-19883
85.
Denisenko ON, O'Neill B, Ostrowski J, Van Seuningen I, Bomsztyk K.
Zik1, a transcriptional repressor that interacts with the heterogeneous nuclear ribonucleoprotein particle K protein.
J Biol Chem.
1996;271:27701-27706 86. Denisenko ON, Bomsztyk K. The product of the murine homolog of the Drosophila extra sex combs gene displays transcriptional repressor activity. Mol Cell Biol. 1997;17:4707-4717[Abstract].
87.
Shelley CS, Teodoridis JM, Park H, Farokhzad OC, Böttinger EP, Arnaout MA.
During differentiation of the monocytic cell line U937, Pur
© 2002 by The American Society of Hematology.
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
 |
|
 |
|
  T. Revil, J. Pelletier, J. Toutant, A. Cloutier, and B. Chabot Heterogeneous Nuclear Ribonucleoprotein K Represses the Production of Pro-apoptotic Bcl-xS Splice Isoform J. Biol. Chem., August 7, 2009; 284(32): 21458 - 21467. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 R. Gonzalez-Lamothe, P. Boyle, A. Dulude, V. Roy, C. Lezin-Doumbou, G. S. Kaur, K. Bouarab, C. Despres, and N. Brisson The Transcriptional Activator Pti4 Is Required for the Recruitment of a Repressosome Nucleated by Repressor SEBF at the Potato PR-10a Gene PLANT CELL, November 1, 2008; 20(11): 3136 - 3147. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 P. A. Fowler, N. J. Dora, H. McFerran, M. R. Amezaga, D. W. Miller, R. G. Lea, P. Cash, A. S. McNeilly, N. P. Evans, C. Cotinot, et al. In utero exposure to low doses of environmental pollutants disrupts fetal ovarian development in sheep Mol. Hum. Reprod., May 1, 2008; 14(5): 269 - 280. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 L. G. Wang, E. M. Johnson, Y. Kinoshita, J. S. Babb, M. T. Buckley, L. F. Liebes, J. Melamed, X.-M. Liu, R. Kurek, L. Ossowski, et al. Androgen Receptor Overexpression in Prostate Cancer Linked to Pur{alpha} Loss from a Novel Repressor Complex Cancer Res., April 15, 2008; 68(8): 2678 - 2688. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
C.-C. Wei, S.-L. Zhang, Y.-W. Chen, D.-F. Guo, J. R. Ingelfinger, K. Bomsztyk, and J. S. D. Chan Heterogeneous Nuclear Ribonucleoprotein K Modulates Angiotensinogen Gene Expression in Kidney Cells J. Biol. Chem., September 1, 2006; 281(35): 25344 - 25355. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
A. M. Knapp, J. E. Ramsey, S.-X. Wang, K. E. Godburn, A. R. Strauch, and R. J. Kelm Jr. Nucleoprotein Interactions Governing Cell Type-dependent Repression of the Mouse Smooth Muscle {alpha}-Actin Promoter by Single-stranded DNA-binding Proteins Pur{alpha} and Purbeta J. Biol. Chem., March 24, 2006; 281(12): 7907 - 7918. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 M. Lynch, L. Chen, M. J. Ravitz, S. Mehtani, K. Korenblat, M. J. Pazin, and E. V. Schmidt hnRNP K Binds a Core Polypyrimidine Element in the Eukaryotic Translation Initiation Factor 4E (eIF4E) Promoter, and Its Regulation of eIF4E Contributes to Neoplastic Transformation Mol. Cell. Biol., August 1, 2005; 25(15): 6436 - 6453. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
 |
 |
 |
|||||||
 |
 |
 |
 |
 |
 |
 |
 |
||
| Copyright © 2002 by American Society of Hematology Online ISSN: 1528-0020 | |||||||||
act together to repress the
transcriptional activity of the CD43 gene
promoter
Top
Abstract
Introduction
B (NF-
il V, Strominger JL.
CD43, the major sialoglycoprotein of human leukocytes, is proteolytically cleaved from the surface of stimulated lymphocytes and granulocytes.
Proc Natl Acad Sci U S A.
1993;90:3792-3796