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1 Istituto di Ricovero e Cura a Carattere Scientifico H. "Casa Sollievo della Sofferenza" Laboratory of Gene Therapy and Oncology, San Giovanni Rotondo (FG), Italy;
2 Interdisciplinary Center for Biomedical Research, Laboratory for Molecular Medicine and Biotechnology, Università Campus BioMedico, Rome, Italy; and
3 Otolaryngology Head and Neck Surgery and
4 Wilmer Ophthalmological Institute, Johns Hopkins University School of Medicine, Baltimore, Maryland
| ABSTRACT |
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| INTRODUCTION |
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Posterior uveal melanoma is a relatively rare tumor, but it is associated with a high visual morbidity and can pose a serous treat to life (2)
. About 30% of patients will develop distant metastases within 10 years of successful management of the local tumor (3)
. The most common genetic abnormality in uveal melanoma is the loss of one copy of chromosome 3. Cytogenetic and comparative genomic hybridization studies have demonstrated monosomy 3 in
50% of cases (4, 5, 6, 7, 8)
. Complete or partial deletions of chromosome 3 have been detected by microsatellite marker analysis (9
, 10)
. In our allelotype of 50 uveal melanomas,
60% of tumors had LOH of all markers on chromosome 3 consistent with monosomy or isodisomy 3 (11)
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Genetic abnormalities of chromosome 3 and, in particular 3p, are also critical to the development of in several other tumor types, including small cell lung carcinoma, breast cancer, ovarian cancer, adenocarcinoma of the cervix, renal cell carcinoma, and head and neck tumors (12) . Several regions on chromosome 3p are frequently rearranged in tumors and are therefore believed to contain TSGs. Two of these regions are located on the centromeric portion of the short arm (12) . The 3p12-13 region contains the gene ROBO1/DUTT1 and the 3p14.2 region spans the FHIT gene. Three other hot spots for rearrangements were reported on 3p21. The first is located on 3p21.1-p21.2 and includes the gene BAP1 that binds the RING finger domain of the BRCA1 gene. The second is the lung cancer TSG region (LUCA) that includes the RASSF1 gene frequently hypermethylated in cancer. The third is located on 3p21.3 and contains the DLC1 gene found deleted in a number of small cell lung cancer cell lines and primary tumors. The telomeric region 3p25-26, containing the VHL gene, has also been reported to be frequently rearranged (12) .
Although monosomy or isodisomy 3 are very common in uveal melanoma, only a few partial deletions of this chromosome have been described (13 , 14) . To gain more insight into the patterns of chromosome 3 deletion and possible genes involved in the carcinogenesis of uveal melanoma, we analyzed 21 tumors from our allelotype cohort that did not show monosomy 3, with a total of 41 microsatellite markers (11) . We identified a 1.4-Mb shared MRD on chromosome 3p25.1-p25.2 between markers D3S3610 and D3S1554 that contains 9 National Center for Biotechnology Information reference sequences and a number of predicted genes.
| MATERIALS AND METHODS |
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Fine Deletion Mapping.
Twenty-one uveal melanomas from the original allelotype cohort (15 tumors with retention of all tested markers on 3p, 4 tumors with LOH of 3p or 3q, and 2 tumors noninformative for markers on 3p or 3q) were tested (11)
. DNA from normal and tumor tissues were analyzed for LOH by amplification of STS microsatellite markers using PCR and the conditions described below.
For an initial screening, 27 primer pairs (Research Genetics. Huntsville, AL) were analyzed: 14 on chromosomal arm 3p (D3S1270, D3S1597, D3S1263, D3S1252, D3S1286, D3S3510, D3S1293, D3S1283, D3S1007, D3S1358, D3S1578, D3S1234, D3S1210, D3S1284) and 13 on chromosomal arm 3q (D3S2318, D3S1251, D3S1603, D3S1546, D3S1310, D3S1292, D3S1238, D3S1764, D3S1268, D3S3715, D3S1580, D3S2748, D3S1311). The microsatellite markers were chosen to span
5-Mb intervals on chromosome 3p and
8-Mb intervals on chromosome 3q. The relative positions of the markers were determined using the Human Genome Working Draft Sequence Browser November 2002 (Ref. 16
; Fig. 1
).6
Markers D3S1597, D3S1284, D3S1292 and D3S1268 had been previously used in the allelotype (11)
. The common regions of loss on 3p were further mapped with additional 14 microsatellite markers (D3S1259, D3S3701, D3S656, D3S3610, D3S100, D3S2385, D3S1585, D3S1554, D3S1479, D3S1360, D3S1076, D3S1295, D3S3635, D3S3507). In total, each tumor was tested with 41 markers. The MRD identified on chromosome 3p25.1-p25.2 was defined using only tumors with at least two consecutive losses.
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50% of one of the two alleles was documented visually by two independent observers (P. P. and S. L. M.) in the tumor as compared with the corresponding normal tissue. | RESULTS |
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The chromosomal region 3p25.3-p24.3 between markers D3S1263 and D3S3510 was further mapped with 10 additional microsatellite chosen at
0.5-Mb intervals (Fig. 2A)
. Four additional markers were used to map the 3p14-12 region (Fig. 2B)
. With the additional markers, 4 more tumors (UM22, UM13, UM14, and UM26) were found to have LOH in the common region of loss on 3p25.3-24.3, and 2 more tumors (UM14 and UM57) were found to have LOH in the common region of loss on 3p14-11. In total, the 3p chromosomal arm was mapped with 28 STS microsatellite markers, and 15 of the 21 uveal melanomas (71%) harbored LOH of at least one marker.
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| DISCUSSION |
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Chromosomal arm 3p abnormalities are frequently found in tumors. At least six major regions of chromosomal rearrangement have been described, and they are often multiple and discontinuous (12) . We defined a common region of loss on 3p14-12, which maps to the centromeric region of chromosome 3 and includes two of these frequently rearranged regions, 3p12-13, and the 3p14.2. The latter contains the putative TSG FHIT gene that spans the FRA3B fragile site. However, occurrence of intragenic mutations in FHIT are very rare, thus some researches have argued that FHIT abnormalities may only represent alterations in the fragile site. One tumor, UM31, showed loss of the pericentromeric region of the chromosome suggesting the presence of a complex rearrangement that cannot be further characterized by microsatellite analysis.
Frequent allelic losses on 3p25-26, corresponding to our MRD, have been reported in lung, renal, breast, and other solid tumors, and in vitro studies indicate that this region is able to suppress growth of tumor cells (19) . The VHL gene, located on 3p25.3, is associated with a familial cancer syndrome characterized by kidney cancer and multiple benign tumors, but it is telomeric to our 3p25.1-p25.2 region (20) .
In a previous study of uveal melanoma, Tschentscher et al. (10) defined by comparative genomic hybridization and microsatellite analysis a 2.2-Mb MRD on 3p25-26 between markers D3S2450-D3S3691. On the human draft sequence, their markers map to 3p25.3-3p26.1 (6.7-8.9 on the physical map), a region slightly telomeric to our 3p25.1-p25.2 MRD (10) . This conflict may simply be explained by the presence of two TSGs closely spaced and both important in the tumorigenesis of uveal melanoma. Even if we conservatively define our telemetric boundary by D3S656 and 3 tumors (UM6, UM28, UM35), our MRD does not overlap that of Tschentscher et al. (10) . If the 6 tumors with partial deletion of 3p in the study by Tschentscher et al. (10) are considered, 5 of them show allelic losses in areas that include our MRD.
Two uveal melanomas (UM10 and UM50) showed loss of all informative markers on chromosomal arm 3p except for one marker, D3S1252, included in the 1.4-Mb MRD (Figs. 2A
and 3
). This pattern of apparent retention of at least one marker, flanked by loss of at least two other markers, is the previously described criteria for a homozygous deletion as determined by microsatellite analysis (17)
. This apparent retention, shown to represent homozygous deletion of this marker by correlation with Southern blot and FISH analyses, is caused by amplification of a small amount of residual normal DNA, which remains after careful microdissection of uveal melanomas (17)
. The homozygous deletion of the region corresponding to marker D3S1252 further limits the region of interest to 100 Kb (between markers D3S2385 and D3S1585) and suggests that a TSG may exist in the region between markers D3S2385 and D3S1585.
Analysis of our 1.4-Mb MRD with the University of California-Santa Cruz at Genome Browser (16) indicates the presence of 9 National Center for Biotechnology Information reference sequences. Of those, five have known function. The xeroderma pigmentosum complementation group C (XPC) gene is involved in the DNA excision repair pathway and is associated with the Xeroderma pigmentosum syndrome in which both cutaneous and uveal melanomas have been described previously (21 , 22) . The WNT7A gene belongs to the wingless-type mouse mammary tumor virus integration site (WNT) family and seems to be involved in embryo development (23) . The expression of WNT7A was recently found to be reduced in lung cancer (24) . The other three genes encode an extracellular matrix protein FBLN2 (25) , a novel member of the histone deacetylase family HDAC11 (26) , and a protein LSM3 that binds the U6 snRNA, an essential element of spliceosome in humans (27) . Each of these genes represents a good candidate for mutational screening in uveal melanoma. In addition to these genes, four other poorly characterized RefSeq proteins map in the MRD, and the presence of other genes in the D3S2385-D3S1554 region is suggested by UNIgene Cluster analysis and gene prediction computer programs.
Allelic losses in the 3p25-26 region that do not overlap the VHL gene have been described in several tumor types (12) . In uveal melanoma, we have identified a 1.4-Mb MRD on 3p25.1-p25.2, the smallest reported MRD at this site. Deletions described in studies of breast cancer and oral cancer overlap our MRD (28 , 29) , and it is quite possible that a TSG on 3p25.1-p25.2 may be involved in other important tumor types in addition to uveal melanoma. Follow-up mutational analysis of candidate genes in the region will be needed to identify this putative TSG.
| FOOTNOTES |
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The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
Requests for reprints: Shannath L. Merbs.
5 The abbreviations used are: TSG, tumor suppressor gene; LOH, loss of heterozygosity; MRD, minimal region of deletion; STS, sequence-tagged site. ![]()
6 Internet address: http://www.ucsc.edu. ![]()
Received 5/14/03. Revised 8/10/03. Accepted 9/16/03.
| REFERENCES |
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