We prospectively screened (through chart review) 913 consecutive patients who were seen at the Massachusetts General Hospital (MGH) Melanoma Clinic over a 6-month period (December 1997 to August 1998) and identified 519 patients with invasive melanomas. TheMGHMelanoma Clinic is a referral-based clinic for patients with a history of melanomaand high-risk individuals with a history of atypical moles or a family history of melanoma. We identified 172 patients whowere or had been diagnosed as having an invasive or metastatic melanoma before they were 40 years old. The diagnoses did not have to have been rendered during the ascertainment period; the average interval between melanoma diagnosis and the study visit was 5.9 years (range, 0 [time at diagnosis] to 30 years). Only diagnoses that were histologically confirmed by a member of the MGH Dermatopathology Unit were included. Patients with a diagnosis of melanoma in situ were excluded, given the occasional ambiguity between melanoma in situ and severely dysplastic nevus. At the time of the clinic visit, each of the 172 patients was provided with a detailed letter describing the study. Those patients expressing interest then underwent an extended discussion regarding the study content and risks. A total of 49 patients (28%) consented to the study and, in accordance with a protocol approved by the Dana Farber Cancer Institute and theMGHInstitutional Review Board, donated 20mLof blood for genetic analysis. The blood samples were coded, and the confidentiality of the patients was maintained. The results were not available to the patients. Medical and family histories and demographic details of participants were recorded through chart review and direct interview. All 49 patients were white and were unrelated to one another. Forty-three blood specimens from normal, healthy blood donors at heMGHblood bank were used for analysis of the polymorphism.

To screen genes involved in P15NK4b regulation during cell cycle, differential display method was applied to compare mRNAs from G1 synchronized cells of MLIK6, which overexpressed P15INK4b gene, and itscontrol MLC2. By using thisapproach, 15 cDNA fragments that were preferentially expressed in MLIK6 cells, but not in MLC2 cells, were screened out. A novel gene named P15RS was identified with further analysis. Combining the sequence from DD-PCR, homology analysis against EST database and RACE, a 4404 bp complete cDNA sequence of P15RS was generated. Sequence analysis revealed that P15RS cDNA encoded a 312-aminoacid peptide containing a RAR domain that is involved in regulation of nuclear pre-mRNA, which suggests that P15RS may be a nuclear regulation protein. Genomic sequence analysis demonstrated that human P15RS gene was localized on chromosome 18q12 with seven exons and six introns. Expressing antisense P15RS in MLIK6 cells can up-regulate the expression of cyclinD1 and cyclinE. These data indicate that P15RS may act as a negative regulator in G1 phase.

Both inactivation of the tumor suppressor gene, PTEN/MMAC1, and oncogenic activation of RAS have been described in human cutaneous melanoma. In mice, activation of a RAS-containing pathway is a necessary step in the pathogenesis of murine melanomas. Because PTEN negatively regulates on the downstream effects of phosphatidylinositol-3-kinase (PI3-K), we hypothesized that the loss of PTEN/MMAC1 and the activation of RAS may be largely equivalent because RAS is a known positive upstream regulator of PI3-K. We expanded our previous survey of PTEN/MMAC1 mutations and analyzed the RAS status of 53 cutaneous melanoma cell lines, 18 glioma cell lines, and 17 uncultured cutaneous melanoma metastasis. Overall, 51% of the cell lines had alterations in either PTEN/MMAC1 or RAS. We found 16 cell lines (30%) with alterations in PTEN/MMAC1 and 11 cell lines (21%) with activating NRAS mutations; only 1 cell line had concurrent alterations in both genes. Moreover, glioma cell lines with a high frequency of PTEN/MMAC1 inactivation had no identifiable RAS alterations. Ectopic expression of PTEN in several cutaneous melanoma cell lines suppressed colony formation irrespective of PTEN/MMAC1 status; urthermore, PTEN expression in cell lines carrying activated RAS also suppressed colony formation. The relative reciprocity of PTEN/MMAC1 abrogation and NRAS activation suggests that the two genetic changes, in a subset of cutaneous melanomas, are functionally overlapping.

A novel p53-related gene, p73, was recently isolated and cytogenetically mapped to chromosome region 1p36. Functionally, p73 expression induces p21waf and suppresses tumor cell growth. We mapped p73 using radiation hybrids and localized the gene to an interval that putatively harbors a melanoma tumor suppressor locus. We then analyzed p73 transcripts from 24 melanoma cell lines using reverse transcription-PCR/single strand conformation polymorphism and identified nine polymorphic sequence changes (three novel and six previously published polymorphisms); furthermore, we found evidence of biallelic transcription in our cell lines. However, we did not detect any deleterious mutations. These data suggest that the p73 gene is unlikely to be essential in melanoma tumorigenesis.