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Blood, Vol. 95 No. 8 (April 15), 2000:
pp. 2666-2671
NEOPLASIA
MUC1 is activated in a B-cell lymphoma by the
t(1;14)(q21;q32) translocation and is rearranged and amplified in
B-cell lymphoma subsets
Vadim G. Dyomin,
Nallasivam Palanisamy,
Kenneth O. Lloyd,
Katerina Dyomina,
Suresh C. Jhanwar,
Jane Houldsworth, and
R. S. K. Chaganti
From the Cell Biology Program, the Immunology Program, and the
Department of Human Genetics, Memorial Sloan-Kettering Cancer
Center, New York, NY.
 |
Abstract |
The band 1q21 is among the most common sites affected by chromosomal
translocations in lymphoid, myeloid, epithelial, and sarcomatous
lesions. In non-Hodgkin's lymphoma (NHL), translocations and
duplications affecting this chromosomal site are frequently, but not
exclusively, seen in association with primary abnormalities such as the
t(14;18)(q32;q21) and t(8;14)(q24;q32) translocations, suggesting a
role for 1q21 rearrangements in tumor progression. We report here the
characterization and cloning of breakpoints in a case of extranodal
ascitic B-cell lymphoma with a t(1;14)(q21;q32) translocation. The
breakpoints on the der(1) and der(14) chromosomes were mapped by
fluorescence in situ hybridization and Southern blot analysis and
cloned using an IGHG (C ) probe. The translocation linked the
IGHG4 switch (S4) sequences of the productively rearranged allele to chromosome 1 sequences downstream of MUC1, leaving
the MUC1 transcriptional unit intact. MUC1 was markedly
overexpressed in the tumor at the mRNA and protein levels relative to
lymphoma cell lines lacking a 1q21 rearrangement. Presumably,
MUC1 transcription is aberrantly regulated by the IGHA
(C ) 3' enhancer element retained on the same chromosome.
Screening of a panel of B-cell lymphomas by Southern blot analysis
identified a subset with a 3' MUC1 breakpoint and another
with low-level amplification of MUC1. MUC-1 mucin has
previously been shown to be frequently overexpressed in human epithelial cancers and to be associated with tumor progression and poor
clinical outcome. Thus, MUC1 activation by chromosomal translocation, rearrangement, and amplification, identified here for
the first time in NHL, is consistent with its suggested role in tumorigenesis.
(Blood. 2000;95:2666-2671)
© 2000 by The American Society of Hematology.
| |
Introduction |
The chromosomal band 1q21 is the third most frequent
site of rearrangement in non-Hodgkin's lymphoma (NHL).1-3
Translocations and duplications affecting this chromosomal site are
usually detected along with other translocations, such as
t(14;18)(q32;q21) and t(8;14)(q24;q32), that are considered to be
primary genetic alterations in NHL. These data have suggested that 1q21
abnormalities may be associated with tumor progression.1-3
Rearrangement breaks affecting band 1q21 are also common in leukemia,
sarcoma, and epithelial tumors.4 Thus, identification of
the genes involved in 1q21 rearrangements is of importance to the
understanding of tumorigenesis in multiple lineages. Recently, a
candidate gene, BCL9, was cloned from a case of acute
lymphoblastic leukemia (ALL) with a t(1;14)(q21;q32)
translocation.5 However, BCL9 rearrangements were
rare in NHL,5 suggesting that other genes at this band may
be involved in 1q21 rearrangements in lymphomas. We report here the
cloning of a t(1;14)(q21;q32) translocation breakpoint in a B-cell
lymphoma. The translocation linked sequences 2.4 kbp 3' of the
MUC1 gene on chromosome 1 to the IGHG4 switch
(S4) region on chromosome 14. MUC1 was markedly
overexpressed in the tumor with respect to lymphoma cell lines that did
not contain a 1q21 rearrangement. This observation is consistent with
aberrant activation of MUC1 expression by an IGH
enhancer, a mechanism of gene activation well established in other
14q32-associated translocations in B-cell leukemias and
lymphomas.6 Screening of a large panel of B-cell lymphomas
by Southern blot analysis using probes derived from the MUC1
genomic locus identified a subset with recurrent DNA rearrangements
clustering 3' of the MUC1 gene and another subset with
multiple MUC1 gene copies. MUC-1 mucin has previously been
shown to be frequently overexpressed in human epithelial cancers and
associated with tumor progression and poor clinical
outcome.7-10 MUC1 activation by chromosomal translocation, a novel phenomenon in lymphomas, is thus consistent with
its previously recognized role in tumorigenesis.
| |
Materials and methods |
Tumor specimens and cell lines
Case 2385 was from a patient with an extranodal ascitic lymphoma at
presentation that exhibited the G-banded karyotype: 47-50, XY,+X,
t(1; 14)(q21;q32),add(6)(q21),+7,+10,der(10)t(?;10)(?;p15)t(?;2)(?;p11.2), add(11)(q23),+13,add(15)(p13),der(17)t(?;17)(?;q25)t(?;8)(?;q13),add (18)(q21)[cp20].
The tumor cells were positive for CD19, CD20, and CD21 with  clonal
excess and µ-chain expression, confirming B-lineage derivation. Other
B-cell NHL specimens used in this study were derived from the ongoing
prospective ascertainment and cytogenetic analysis of NHL cases at the
Memorial Sloan-Kettering Cancer Center.2 Two groups were
analyzed for MUC1 rearrangement and copy number. One group that
exhibited a 1q21 rearrangement by G-banding karyotype analysis
comprised 72 B-cell lymphomas of all histologic types (small
lymphocytic, follicular, diffuse small noncleaved, diffuse large cell,
and immunoblastic). In the second group of 106 biopsies, 27 cases were
cytogenetic failures, 7 cases yielded normal metaphases, and 72 cases
were clonally abnormal but did not exhibit a 1q21 aberration. In this
group, 12 had follicular histologies and 94 were diffuse large-cell
lymphomas. OSI-Ly 3, a B-cell lymphoma cell line, and OSI-Ly 12, a
T-cell lymphoma cell line11 (gift of Mark Minden) that did
not contain 1q21 rearrangements, were maintained as suspension cultures.
DNA probes
The probes used for fluorescence in situ hybridization (FISH),
Southern blotting, and genomic library screening comprised the
following: a 5.5-kbp BamHI-HindIII fragment containing
IGHJ (JH), a 1.3-kbp EcoRI fragment containing the
first 2 exons of IGHM (Cµ), a 7-kbp
HindIII-BamHI fragment containing IGHG1
(C), and a 13-kbp HindIII fragment containing IGHA1
(C ). The PAC clones 288D9 and 35A12 containing, respectively, the
BCL9 and MUC1 loci were obtained from Genome Systems
(St Louis, MO), and the YAC clone 876B11, mapping 8 cM
telomeric to BCL9, was obtained from Research Genetics
(Huntsville, AL).
Fluorescence in situ hybridization
DNA probes were labeled with biotin-14-dATP (Gibco BRL, Rockville,
MD) and hybridized to metaphase spreads from normal human lymphocytes
and tumor cells as previously described.12 Hybridization signals and the corresponding chromosomal bands were visualized with
fluorescein isothiocyanate-conjugated avidin (Oncor, Gaithersburg, MD)
after staining with 4',6-diamidino-2-phenylindole dihydrochloride.
Southern and Northern blot analyses
Genomic DNA was extracted and subjected to restriction enzyme
digestion, gel electrophoresis, and Southern blot analysis as previously described, using normal placental DNA as
control.13 Mapping of subcloned genomic fragments was
performed by Southern blot analysis of monochromosomal cell hybrid DNA
(Coriell Cell Repositories, Camden, NJ). DNA copy number was estimated
relative to a control probe (D2S48) as previously
described.14 Total RNA was extracted from the ascitic fluid
or cultured lymphoma cell lines, electrophoresed, and hybridized as
previously described.15 Northern filters were initially
hybridized with a probe derived from the tandem repeat segment of
MUC1 cDNA,16 followed by THBS3 (generated
by polymerase chain reaction [PCR]), and then with GAPDH to
control for loading. Multiple-tissue Northern filters were obtained
from Clontech (Palo Alto, CA).
Molecular cloning of the translocation breakpoint
A genomic library of the tumor DNA was constructed in  GEM-11
phage vector (Promega, Madison, WI) by partial Sau3A
digestion,17 and was screened using the probes detailed
above. Fragments of phage clones were subcloned in pBluescript.
Polymerase chain reaction
PCR was performed in a 50-µL reaction volume using AmpliTaq
DNA-polymerase (Perkin-Elmer, Norwalk, CT) under the following conditions: 94°C (1 minute) followed by 30 cycles of 94°C (30 seconds), 60°C (30 seconds), 72°C (2 minutes), and a
final extension at 72°C (10 minutes). The following primers were
used to isolate PACs from the Genome Systems PAC library:
5'-TTTGTGGACTTGGGTATCAATGA-3' and 5'-AAAAACAGAAAA
GAATCCTGGGAGAAG-3' for BCL9;
5'-CCCACCAATTTCTCGGACACTTCTCA-3' and
5'-GTCCAGTTCAGGATCCCC GCTATCTC-3' for germline chromosome 1 region containing MUC1. The primers
5'-ACCTGGGACCTGAGCTGTGATTTCCT-3' and
5'-GACACCCACCTTCCCAACATCCTTTC-3', derived from sequences on chromosomes 14 and 1, respectively, were used for cloning the breakpoint on der(1). The isolated PAC 35A12 and YAC 876B11 were confirmed to be nonchimeric by FISH analysis of normal human metaphases.
Flow cytometric analysis
Expression of MUC-1 mucin on live ascitic fluid cells and cultured
cell lines was assayed by FACS as described.18 Cells were
either incubated with normal mouse serum or with a mouse monoclonal
antihuman MUC-1 mucin antibody (HMFG-2)19 as a
primary antibody. FITC-conjugated rabbit antimouse
IgG (H+L) was used as a secondary antibody for detection.
| |
Results |
Mapping of translocation breakpoints by FISH
To determine whether BCL9 was affected by the
t(1;14)(q21;q32) translocation in tumor 2385, PAC 288D9 was used as a
probe in FISH analysis of tumor metaphases. Hybridization signals were observed on the normal chromosome 1 and the der(1)
chromosome, but not on the der(14) chromosome, indicating that the
breakpoint was distal to BCL9 (data not shown). In contrast,
YAC 876B11, which mapped distal to BCL9, hybridized to normal
chromosome 1 and the der(14) chromosome, but not to the
der(1) chromosome, narrowing the breakpoint region to
approximately 8 cM telomeric to BCL9 (data not
shown). The JH probe hybridized only to the der(1) chromosome without a
signal either on the der(14) or on the apparently normal chromosome 14, suggesting a deletion of this region in the latter (Figure
1A). The C probe hybridized to the
der(1) and der(14) chromosomes and to the apparently normal chromosome
14 (Figure 1B). The C probe hybridized to both copies of C in
each homolog; therefore, this result indicated that the breakpoint in
the der(14) chromosome occurred in an approximately 150-kbp region
between C1 and C2, with C1 translocated to der(1) and C2
retained on the der(14) chromosome. The C probe was detected on the
apparently normal chromosome 14 and the der(1) chromosome, but not on the der(14) chromosome (Figure 1C). Absence of C signal on the der(14) chromosome suggested that the breakpoint was within or
downstream of C4 (Figure 1D). These results indicated the translocation breakpoint to be in the region containing C4, C , and C2.
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| Fig 1.
FISH analysis of the t(1;14) translocation in tumor 2385.
Metaphase chromosome spreads from tumor 2385 were hybridized with the
IGH gene probes JH (A), C (B), and C (C). The IGH
locus map is shown (D). Lines above the map indicate the target regions
for hybridization by the JH, Cµ, C, and C probes.
|
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Mapping the translocation breakpoints by Southern blot analysis
Southern blot analysis using the JH probe revealed a single
rearranged band in the BamHI digest of tumor DNA (Figure
2A). A band of the same size was detected
by hybridization with the Cµ probe as expected for a productive
rearrangement in a µ-chain producing tumor (Figure 2B). Consistent
with the FISH data, a germline BamHI fragment containing JH and
Cµ sequences was not detected, indicating a deletion of this region.
Because the only copy of JH mapped to the der(1) chromosome, it was
concluded that the translocation affected the productive IGH
allele with a breakpoint centromeric to JH. No rearrangement was
detected in Southern blot analysis using the C probe (data not
shown), whereas the C (Figure 2C) and C (Figure 2D) probes
detected rearranged bands; these 2 rearrangements were selected for
molecular cloning.
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| Fig 2.
Southern blot analysis of tumor 2385 DNA.
DNA extracted from normal placenta (N) and tumor fluid (2385) were
digested with the respective enzymes. The blots were hybridized with
the IGH gene probes JH (A), Cµ (B), C (C), and C (D).
Arrows indicate rearranged bands in the tumor DNA. Size markers are
given in kbp.
|
|
Cloning of the translocation breakpoints
A genomic library of the tumor DNA partially digested with
Sau3A was constructed and screened with the C and C
probes. Positive clones were analyzed by Southern blotting, FISH,
restriction enzyme mapping, and partial sequencing. A C-positive
phage clone containing a 6-kbp C-positive BglII fragment
corresponding to the BglII rearranged band in the tumor DNA
(Figure 2C) was isolated. These clones contained an intrachromosomal
breakpoint linking IGHA1 switch (S1) sequences to the
IGHD region downstream of the D3-3 segment (data not shown).
The ensuing deletion included the JH and Cµ regions and, together
with FISH data described above, established a nonproductive IGH
allele on the karyotypically normal chromosome 14.
FISH of the C-positive phage clone g401 to normal human metaphases
revealed signals on both chromosomes 1 and 14 (Figure 3A), confirming that this clone contained
sequences from both chromosomes. A repeat-free, non-IGH,
1.1-kbp PstI-PstI fragment (PP1) was isolated from
clone g401 and used as a probe in Southern blot analysis. Hybridization
of this probe to a somatic cell hybrid DNA panel established that it
was derived from chromosome 1 (Figure 3B). When hybridized to an
EcoRI digest of tumor 2385 DNA, it recognized the same
rearranged band as the C probe (Figure 2D), confirming the clonal
nature of the interchromosomal breakpoint in clone g401 (Figure 3C).
PAC 35A12, which was obtained by screening a PAC library using
g401-derived chromosome 1 sequences, hybridized to the normal
chromosome 1 as well as to the der(1) and der(14) chromosomes in the
tumor (Figure 3D).
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| Fig 3.
Analysis of the breakpoint-containing clone g401.
Normal metaphase spreads were hybridized with the phage clone g401 (A).
A repeat-free fragment derived from g401 (PP1) was hybridized to a
somatic cell hybrid panel (B) and to tumor DNA (C). Arrow indicates the
rearranged band in tumor DNA. Size markers are given in kbp. Tumor
metaphase spreads were hybridized with a chromosome 1 PAC (PAC 35A12)
that spanned the breakpoint (D).
|
|
Restriction mapping and partial sequencing of the breakpoint region
showed that the translocation occurred between S4 and C4 (Figure
4). Sequence analysis revealed a 27-bp
deletion in C immediately 3' of the breakpoint. An additional
1.5-kbp deletion, including exons 1-2 of C, and a 51-bp duplication
5' of exon 3 were also noted (data not shown). Partial deletion
of the target for the C probe is consistent with the lack of signal
on der(14) with this probe in the FISH experiment described above.
Restriction mapping and sequence analysis of subcloned PAC fragments
showed that sequences from the 5' part of clone g401 were
colinear to the corresponding germline region of chromosome 1 (Figure
4).
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| Fig 4.
Restriction maps and sequences of the breakpoint regions
on normal and derivative chromosomes.
The respective regions of germline chromosomes 1 and 14 are shown, with
sites of breakpoint indicated by arrows. The location of PP1 is
indicated. Sequences shown are chromosome 14, a germline IGHG4
heavy chain switch region (GenBank accession number 56,796); chromosome
1; PAC 35A12; der(14); phage clone g401; and der(1), a PCR product
amplified as detailed in "Materials and
methods."
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To clone the reciprocal breakpoint on the der(1) chromosome by PCR, a
primer pair was designed such that a forward primer from chromosome 14 (an S4 sequence) and a reverse primer based on the germline
chromosome 1 sequence proximal to the breakpoint identified on the
der(14) chromosome would amplify a DNA fragment from the tumor DNA. As
expected, the PCR reaction did not yield a band with placental DNA, but
a 930-bp band was amplified from the tumor DNA (data not shown).
Sequence analysis of the PCR product revealed sequences colinear with
S4 and germline chromosome 1, as predicted for the reciprocal
breakpoint region on the der(1) chromosome. A 12-bp deletion of S4
sequence and a duplication of a CATT tetramer originating from
chromosome 1 were found in the immediate vicinity of the breakpoint
(Figure 4).
Identification of transcriptional units in the breakpoint region
Because IGH gene-associated translocations result in
aberrant activation of genes immediately adjacent to the breakpoint, we
sought to identify transcriptional units in the breakpoint region.
Repeat-free restriction fragments derived from the breakpoint region on
chromosome 1 were hybridized to human multiple tissue Northern blots.
Northern hybridization analysis using the PP1 probe revealed a 2.7-kb
transcript expressed predominantly in human brain (data not shown). A
number of human and mouse cDNA clones homologous to the PP1 sequence
were identified by searching EST databases. A more detailed sequence
analysis showed that the PP1 fragment contained the last exon of the
human homolog of the putative mouse gene Y. The partial
sequences of both human and mouse homologs contained a continuing
open-reading frame with no homology to any known protein. The exon
contained in the PP1 fragment measured 1050-bp and did not account for
the entire 2.7-kb transcript observed in the Northern hybridization
analysis. The 5' end of gene Y containing the ATG codon
is presumably retained on the der(1) chromosome and remains to be
cloned and characterized. Gene Y was not considered a candidate
for an activated gene because its open-reading frame was disrupted by
the t(1;14)(q21;q32) translocation in the tumor.
Immediately centromeric to gene Y, 2 genes, MUC1 and
THBS3,20 were identified. In tumor 2385, the
THBS3 gene, which encodes thrombospondin 3, a glycoprotein that
mediates cell-to-cell and cell-to-matrix interactions, showed an mRNA
expression level similar to that of the lymphoma cell lines (data not
shown). The MUC1 gene encodes a high molecular weight
glycoprotein containing multiple copies of a tandemly repeated 20-amino
acid mucin-like domain.21,22 Allelic differences in the
number of repeat units have been observed that account for differences
in the size of MUC1 mRNA species (4kb-7kb).21 In tumor 2385, marked expression
of a single mRNA species was observed in comparison to both lymphoma
cell lines (Figure 5A). Flow cytometric
analysis using a MUC-1 mucin-specific antibody revealed marked
expression in tumor 2385, no expression in K562 cells as previously
reported,23 and low levels in the lymphoma cell lines
(Figure 5B). The 3' end of MUC1 was located 2.4 kbp
telomeric to the der(14) chromosomal breakpoint. MUC1, with a
telomeric-to-centromeric direction of transcription, remained intact in
the translocated allele. The presence of an immunoglobulin 3'
C enhancer sequence, presumably retained on the same chromosome, suggests a mechanism for MUC1 gene deregulation. Since MUC-1
mucin has previously been implicated in human cancer and found to be overexpressed in tumor 2385, it was considered to be the target gene
deregulated and activated by the t(1;14)(q21;q32) translocation in this
case.
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| Fig 5.
Elevated expression of MUC-1 mucin in tumor 2385.
Total RNA extracted from tumor 2385 and lymphoma cell lines OCI-Ly 3 and OCI-Ly 12 were hybridized with an MUC1 tandem repeat probe
and subsequently with GAPDH to control for loading (A).
Expression of MUC-1 mucin in K562, OCI-Ly 3, OCI-Ly 12, and tumor 2385 cells by flow cytometric analysis (B). Live cells were incubated either
with normal mouse serum (gray line) or a MUC-1 mucin antibody (HMFG-2)
(black line) and quantitated by FACS analysis. MUC-1 mucin
staining is plotted as a histogram.
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Translocation breakpoint cluster near MUC1 in B-cell
lymphoma
The incidence of MUC1 rearrangements was ascertained by
Southern blot analysis of 2 groups of B-cell lymphoma using the PP1 fragment as the probe. One group comprised 72 biopsies that included all histologic types (small lymphocytic, follicular, diffuse small noncleaved, diffuse large cell, and immunoblastic), each of which exhibited a rearrangement affecting band 1q21 by G-banding analysis. In this group, 4 tumors (6%) exhibited MUC1 DNA rearrangements (Figure 6A). These comprised 1 each of
diffuse small cleaved (177), follicular mixed (1992), immunoblastic
(1366), and extranodal ascitic (2385) lesions. Case 1992 was a relapsed
tumor, whereas the remaining were ascertained at presentation. The
second group comprised 106 biopsies. Of these, 12 had follicular
histologies and 94 were diffuse large-cell lymphomas that were either
cytogenetic failures (27 cases), yielded only normal metaphases (7 cases), or were clonally abnormal but without a 1q21 aberration (72 cases). In this group, 1 diffuse mixed lymphoma that exhibited only a normal karyotype (913) showed a MUC1 rearrangement (Figure 6A).
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| Fig 6.
Rearrangement and increased copy number of MUC1
in B-cell NHL.
Tumor DNA was digested with the respective enzymes and hybridized with
the PP1 probe. Rearranged bands in the tumor DNA compared to normal
placenta (N) are indicated by arrows (A). Size markers are given in
kbp. The calculated copy numbers of MUC1 are listed relative to
normal placenta (N) using the hybridization signal from the probe D2S48
to control for loading (B).14 The numbers of tumors in each
study group with 1 to 3 (normal) and 4 to 6 (increased) copy numbers of
MUC1 are shown (C).
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Increased copy number of MUC1 in B-cell lymphoma
We also assayed for copy number changes of MUC1 in the 2 groups of B-cell lymphoma biopsies evaluated for rearrangements. Seven
(10%) in the first group and 11 (10%) in the second group showed 4 to
6 copies of MUC1 (Figures 6B, 6C). We have previously found
that this level of copy number increase represents either nondisjunctional gain of the chromosomal region or a low level of
amplification of the gene.14
| |
Discussion |
The third most common site of chromosomal rearrangement in B-cell
lymphoma after bands 14q32 and 18q21 is band 1q21. This site exhibits a
promiscuous pattern of rearrangement involving multiple other
chromosomal sites.1,2 Translocations, duplications, and
amplifications affecting 1q21 are usually, but not exclusively, seen in
lymphomas in addition to primary abnormalities such as t(14;18)(q32;q21) and t(8;14)(q24;q32), suggesting that 1q21-associated abnormalities may play a role in tumor progression.1-3
Rearrangements involving this chromosomal site have also been noted in
other tumor systems; thus, the gene(s) involved in 1q21 rearrangements may play an important role in tumor biology per se. Previous studies have identified BCL9 as a gene possibly deregulated in
1q21-associated translocations. However, only 1 lymphoma with a DNA
rearrangement involving this gene was identified,5
indicating the presence of additional gene(s) that may be more relevant
in lymphoma translocations. We report here the identification of
MUC1 as a gene recurrently involved in 1q21-associated
rearrangements in B-cell lymphomas.
In tumor 2385, the t(1;14)(q21;q32) translocation resulted in linkage
of the S4 region to the region 3' of the MUC1 gene, 8 cM distal to BCL9. Interestingly, the IGH allele
involved in the translocation also was the productively rearranged
allele, an event not previously reported. The karyotypically normal
chromosome 14 in this tumor did in fact have a deletion that resulted
in a nonproductive IGH allele. Sequence analysis of the cloned
der(14) chromosomal breakpoint revealed that it was located within a
poorly characterized gene Y. Based on the transcript size and
direction of transcription of gene Y, it was predicted that the
translocation would result in disruption of this gene. Hence, gene
Y was discounted as a candidate for the gene activated in the
translocation. The transcriptional unit of the immediately adjacent
MUC1 gene was found to be intact in the rearranged allele and
thus became a candidate for the involved gene. Indeed, the steady state
levels of MUC1 mRNA and protein in this tumor were elevated
compared to lymphoma cell lines that did not exhibit a 1q21
rearrangement. Presumably, this elevated MUC1 expression
resulted from aberrant activation by the 3' C enhancer
sequence retained on the der(14) chromosome.
We show that the MUC1 region is rearranged in 6% of tumors
with a documented 1q21 cytogenetic aberration. Thus, although
recurring, this molecular breakpoint does not account for all the
1q21-associated cytogenetic breakpoints. We also found increased copy
numbers of the MUC1 region in 10% of B-cell lymphomas of all
histologies. The amplification itself was of a relatively low level (4 to 6 copies), and its effect on MUC1 expression remains to be
determined. Of significance, however, is the observation that up to
16% of B-cell lymphomas show a molecular perturbation of the
MUC1 region that can potentially lead to its deregulated
overexpression. The clinical significance of these perturbations
remains to be established.
The MUC-1 mucin protein can be expressed as a transmembrane or secreted
protein as a result of alternate splicing. Short MUC-1 mucin isoforms,
MUC-1/Y and MUC-1/Z, devoid of tandem repeats, have also been
described.16,24 MUC-1 mucin has previously been implicated
in human carcinogenesis. It is frequently overexpressed in both
epithelial7-10 and nonepithelial
tumors,16,23,25 and is associated with cell invasiveness
and poor outcome. An important role for MUC1 in tumorigenesis
has been demonstrated in Muc-1 null mice, which show a delayed
progression of primary tumors.26 Therefore, a role for
MUC1 in the progression of NHL is consistent with 1q21 as a
site of secondary chromosomal abnormalities in these tumors. Although
the precise role of MUC-1 mucin protein in tumorigenesis is not well
understood, a few putative functions have been proposed that may confer
cells overexpressing MUC-1 mucin a selective advantage. MUC-1 mucin has
been shown to inhibit cell adhesion mediated by integrin and E-cadherin
that may facilitate metastatic expansion of tumors.27 High
serum levels of the secreted form of MUC-1 mucin, frequently found in
patients with epithelial tumors, can suppress T-cell proliferative
responses blocking T cells in an "anergic" state.28
The MUC-1/Y isoform has a cytokine receptor-like domain and has been
suggested to play a role in signal transduction.29
The mechanisms shown to date that are responsible for MUC-1 mucin
overexpression in epithelial tumors include gene
amplification30 or activation by transcription
factors.31 We now show deregulation of MUC1
expression by chromosomal translocation. Translocations affecting band
1q21 are frequent in leukemias, lymphomas, sarcomas, and epithelial
tumors,1-4 which may indicate a previously unrecognized mechanism for MUC1 deregulation in these tumor types. Aberrant, high expression of MUC-1 mucin on the surface of cancer cells makes it
an attractive target gene for immunotherapy of epithelial tumors.32,33 The possibility that its expression may also
be frequently deregulated in NHL makes it a target for
immunotherapeutic approaches for the treatment of lymphomas.
| |
Footnotes |
Submitted September 29, 1999; accepted December 16, 1999.
Supported by National Institutes of Health-National Cancer Institute
grants CA34775 and CA66999 (R.S.K.C.) and CA52477 (K.O.L.).
Reprints: R. S. K. Chaganti, Memorial Sloan-Kettering Cancer
Center, 1275 York Avenue, New York, NY 10021; e-mail: chagantr{at}mskcc.org.
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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Abstract
Introduction