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Blood, Vol. 95 No. 4 (February 15), 2000:
pp. 1451-1455
PHAGOCYTES
From the Department of Medicine and Department of Pediatrics and
Medical Genetics, Cedars-Sinai Medical Center, UCLA School of Medicine,
Los Angeles, CA.
Familial Mediterranean fever (FMF) is a recessively inherited
disorder characterized by recurrent, self-limited attacks of fever and
serositis and by infiltration of affected tissues by large numbers of
neutrophils. A candidate gene for FMF was identified by positional
cloning and named "MEFV." The corresponding protein was
named "pyrin." To elucidate the currently unknown function of
pyrin, we characterized its tissue distribution, regulation of
expression during hematopoietic differentiation, and subcellular localization. Reverse transcription-polymerase chain reaction analysis,
followed by hybridization with an internal oligonucleotide, demonstrated expression of MEFV in different populations of
peripheral blood cells. Among hematopoietic cell lines, MEFV
was almost exclusively expressed in cells of the myeloid lineage.
Furthermore, MEFV messenger RNA was strongly expressed within
24 hours of dimethyl sulfoxide-induced granulocytic differentiation of
HL-60 cells. Analysis of complementary DNA from human solid
tumor-derived cell lines revealed expression of MEFV in
several cell lines derived from colon and prostate cancers. Expression
of MEFV fused to enhanced green fluorescent protein showed that
pyrin localized in distinct patches in the cytoplasm, forming a
perinuclear cap. Taken together, MEFV is predominantly
expressed in myeloid cells and upregulated during myeloid
differentiation, and the corresponding protein, pyrin, is expressed in
the cytoplasm.
(Blood. 2000;95:1451-1455)
Familial Mediterranean fever (FMF) is a hereditary
disease characterized by periodic episodes of fever accompanied by
acute inflammatory attacks of serosal or synovial
membranes.1,2 A massive influx of neutrophils into the
affected tissues occurs during these attacks. This enormous invasion of
neutrophils to the sites of inflammation plays a major role in the
inflammatory process, although the regulating factors remain unknown.
Recently, a gene linked to FMF was identified by positional
cloning.3,4 The gene was named "MEFV," and
the predicted protein was called either "pyrin" or
"marenostrin." MEFV is located on chromosome 16p13.3 and
consists of at least 10 exons. Analysis of the predicted amino acid
sequence revealed the presence of 2 potential nuclear localization
signals as well as a basic domain and a B-box-type zinc finger motif.
Similarly, a coiled-coil domain and a B30.2 globular domain, which are
implicated in dimerization and protein-protein interactions,
respectively, were predicted from the MEFV
sequence.3,4
Several missense mutations in the MEFV gene have been described
in patients with FMF.3-5 FMF patients display decreased
C5a-inhibitor activity,6,7 and an investigative group has
hypothesized that pyrin might regulate expression of C5a-inhibitor
activity.8 So far, this C5a-inhibitor activity has not been
cloned, and a direct connection to pyrin awaits further investigation.
To date, the function of pyrin and its role in the pathogenesis of FMF
remain unknown. Pyrin may act as a regulator of inflammatory stimuli in
neutrophils in FMF as well as in other diseases.
Here, we investigated expression of MEFV messenger RNA (mRNA)
in hematopoietic and nonhematopoietic tissues and cell lines. Induction
of MEFV mRNA during granulocytic differentiation is demonstrated in HL-60 cells incubated with dimethyl sulfoxide (DMSO).
Expression of pyrin as an EGFP (enhanced green fluorescent protein)
fusion protein reveals cytoplasmic, perinuclear localization of the
pyrin protein.
Cell culture
Separation of peripheral blood neutrophils
Sorting of peripheral blood leukocytes by flow cytometry First, mononuclear cells were separated from heparinized blood by Ficoll-Paque (Pharmacia Biotech, Piscataway, NJ) density gradient centrifugation. Individual populations of peripheral blood leukocytes were further isolated by flow cytometry (FACStar, Becton Dickinson, Mountain View, CA) using monoclonal mouse antibodies against CD19 and CD3 conjugated to fluorescein isothiocyanate and PE, respectively (Dako, Carpinteria, CA).Reverse transcription and polymerase chain reaction Total RNA was isolated using TRIzol reagent (Gibco BRL, Gaithersburg, MD) according to the method described by Chomczynski and Sacchi11; 2 µg of total RNA were reverse transcribed using SuperscriptII (Gibco BRL) and random primers (Gibco BRL) according to the manufacturer's instructions. Polymerase chain reaction (PCR) was performed with Taq DNA polymerase (Gibco BRL) under standard conditions using MEFV-specific oligonucleotides (5'-ATCCAACTCCTCCACCAGAA-3' and 5'-AGTGTTGGGC-ATTCAGTCAG-3') that amplify a 690-base pair (bp) fragment. All PCR primer pairs span an exon/intron boundary to allow discrimination between complementary DNA (cDNA)- and DNA-generated fragments. Oligonucleotides specific for -actin (5'-TACATGGCTGGGGTGTTGAA-3' and
5'-AAGAGAGGCATCCTCACCCT-3') amplify a 218-bp fragment, and
oligonucleotides for lactoferrin
(5'-GTTCAGTGGTGCGCCGTATC-3' and
5'-CACCACAGCCACGGCATAAT-3') generate a 279-bp fragment.
Each cycle of PCR consisted of denaturation (1 minute at 95°C),
annealing (1 minute at 60°C, 55°C, or 64°C for
MEFV, lactoferrin, and -actin, respectively), and extension
(1 minute at 72°C) and was repeated 22 to 30 times, as
indicated in "Results." PCR-amplified DNA fragments were
visualized by ethidium bromide staining after agarose gel electrophoresis.
Hybridization with an internal oligonucleotide Gel-separated PCR products were blotted onto a positively charged nylon membrane (Boehringer Mannheim, Indianapolis, IN, or Amersham Life Science, Arlington Heights, IL) by capillary transfer in 20xSCC. Prehybridization (30-45 minutes) and hybridization (1-2 hours) occurred at 42°C in DIG (digoxigenin) Easy-Hyb solution (Boehringer Mannheim). As a hybridization probe, internal oligonucleotides specific for MEFV 5'-GACAGC-ATGGATCCTGGGAGCCTGCAAG-3', lactoferrin 5'-CCCTTGATGGTGGTTTCA-TATACGA-3', or -actin
5'-ATCGAGCACGGCATCGTCAC-3' were labeled with DIG using the
DIG 3' End Labeling Kit (Boehringer Mannheim). Washes were
repeated twice in 2xSCC for 5 minutes at room temperature
and in 0.5xSCC for 5 minutes at 42°C. The membrane was
blocked (1% blocking reagent in maleic acid buffer) for 30 minutes
prior to incubation with anti-DIG antibodies coupled to alkaline
phosphatase (30 minutes). After washing twice in maleic acid buffer,
detection was performed by incubating with the chemiluminescent substrate CDP-Star (Tropix, Bedford, MA). Autoradiographic film (X-OMAT/AR, Eastman Kodak, Rochester, NY) was exposed to the blot for
several seconds up to 30 minutes.
Cloning and expression of an EGFP-pyrin fusion protein In a 2-step cloning procedure, the cDNAs of EGFP and pyrin were cloned into the pcDNA3.1(+) vector (Invitrogen, Carlsbad, CA). First, PCR-amplified EGFP cDNA (Clontech, Palo Alto, CA) was cloned into the vector using recognition sites for restriction endonucleases HindIII and KpnI. Second, the full-length cDNA of pyrin was amplified by PCR using Pfu polymerase (Stratagene, La Jolla, CA) and the following primers that contain recognition sites for BglII and EcoRI, respectively: 5'-GCATATAGATCTATGGCTAAGACCCCTAG-3' and 5'-GCATATGAATTCGGCAT-TCAGTCAGGCC-3'. PCR fragments were digested, gel-purified, and cloned in frame 3' of EGFP cDNA into the EcoRI and BglII sites of a pCDNA3.1(+) expression vector. Transformants were tested for the correct insert by restriction enzyme digestion and DNA sequencing. Either EGFP or EGFP-pyrin plasmid (15 µg) were transfected into COS-1 cells using Superfect reagent (Qiagen, Valencia, CA). Transfected cells were plated on cover slips and analyzed 2 to 3 days after transfection by fluorescent microscopy using a 510-nm filter.Western blot Transfected cells were lysed in radioimmunoprecipitation assay (RIPA) buffer containing protease inhibitors on day 2 after transfection and separated by SDS-PAGE on a 4% to 15% acrylamide gradient gel. Proteins were transferred onto a nitrocellulose membrane and detected with a monoclonal anti-GFP antibody (Clontech). Incubation with a secondary goat anti-mouse antibody coupled to horseradish peroxidase and subsequent incubation with ECL1 and ECL2 substrate (Amersham Life Science) was followed by exposure to autoradiographic film (Biomax-MR, Eastman Kodak) for several seconds or minutes.
Hematopoietic expression of MEFV MEFV was recently identified as a disease-related gene in patients with FMF.3,4 So far, little is known about its function. To begin to address this issue, we studied the expression of MEFV mRNA in different tissues and cell lines. Expression of MEFV mRNA previously was described in peripheral blood leukocytes.3,4 In this report, we analyzed MEFV expression in different populations of peripheral blood leukocytes. PCR was performed using specific oligonucleotides for MEFV, lactoferrin, and -actin. Hybridization with gene-specific internal
oligonucleotides confirmed the specificity of the PCR products.
MEFV mRNA could be amplified in neutrophils, monocytes, and
also weakly in CD19+ B cells and CD3+ T cells
(Figure 1). Amplification of -actin
served as a control for cDNA quality (Figure 1). Lactoferrin is a
specific granule marker and was chosen to exclude potential
contamination of neutrophils to the other cell populations. Only
neutrophils showed strong expression of lactoferrin mRNA, whereas
CD19+ B lymphocytes, CD3+ T cells, and
monocytes were negative for lactoferrin mRNA (Figure 1).
Induction of MEFV expression during granulocytic
differentiation
MEFV expression in nonhematopoietic cells and cell lines
Intracellular localization of the pyrin protein
Expression of mutated pyrin does not alter its localization
FMF is an inherited disease that is characterized by recurrent
attacks of fever. Positional cloning identified MEFV, the gene that is likely to cause FMF.3,4 So far, the function of the corresponding protein, named pyrin, remains unknown. Analysis of the
predicted amino acid sequence of pyrin suggested that pyrin might be
expressed as a nuclear factor that could regulate
transcription.3,4,12 In contrast to this prediction, we
demonstrate that the EGFP-pyrin fusion protein is expressed in the
cytoplasm of COS-1 cells. To exclude that EGFP may interfere with
nuclear localization, we expressed a known nuclear protein, cyclin A1,
fused 3' of EGFP, and found that it was clearly expressed in the
nucleus. Our data suggest that pyrin is expressed in the cytoplasm and
therefore may evoke functions other than a transcription factor.
Alternatively, the intracellular localization of pyrin may change in
response to appropriate stimuli, and pyrin might be translocated into
the nucleus upon stimulation. For example, signal transducers and activators of transcription (STAT) proteins are expressed as monomeric cytoplasmic proteins and, in response to growth factors, they dimerize
and translocate into the nucleus to act as transcription factors.13 Also, the transcription factor NF Submitted March 15, 1999; accepted October 12, 1999.
Supported by grants from the National Institutes of Health, U.S. Army,
and the C. and H. Koeffler and the Parker Hughes Funds. N. Tidow is
recipient of a fellowship of the Deutsche Forschungsgemeinschaft. H. P. Koeffler holds the Mark Goodson Chair in Oncology Research and is a
member of the Jonsson Cancer Center.
This work is in memory of Dr Marge Goldberg, an indefatigable assistant
and a champion of individuals with familial Mediterranean fever.
Reprints: Nicola Tidow, Davis Bldg, RM5005, Division of
Hematology/Oncology, Cedars-Sinai Medical Center/UCLA School of
Medicine, 8700 Beverly Blvd, Los Angeles, CA 90048.
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.
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