P53 in human melanoma fails to regulate target genes associated with apoptosis and the cell cycle and may contribute to proliferation.

BACKGROUND: Metastatic melanoma represents a major clinical problem. Its incidence continues to rise in western countries and there are currently no curative treatments. While mutation of the P53 tumour suppressor gene is a common feature of many types of cancer, mutational inactivation of P53 in melanoma is uncommon; however, its function often appears abnormal. METHODS: In this study whole genome bead arrays were used to examine the transcript expression of P53 target genes in extracts from 82 melanoma metastases and 6 melanoma cell lines, to provide a global assessment of aberrant P53 function. The expression of these genes was also examined in extracts derived from diploid human melanocytes and fibroblasts. RESULTS: The results indicated that P53 target transcripts involved in apoptosis were under-expressed in melanoma metastases and melanoma cell lines, while those involved in the cell cycle were over-expressed in melanoma cell lines. There was little difference in the transcript expression of P53 target genes between cell lines with null/mutant P53 compared to those with wild-type P53, suggesting that altered expression in melanoma was not related to P53 status. Similarly, down-regulation of P53 by short-hairpin RNA (shRNA) had limited effect on P53 target gene expression in melanoma cells, whereas there were a large number of P53 target genes whose mRNA expression was significantly altered by P53 inhibition in melanocytes. Analysis of whole genome gene expression profiles indicated that the ability of P53 to regulate genes involved in the cell cycle was significantly reduced in melanoma cells. Moreover, inhibition of P53 in melanocytes induced changes in gene expression profiles that were characteristic of melanoma cells and resulted in increased proliferation. Conversely, knockdown of P53 in melanoma cells resulted in decreased proliferation. CONCLUSIONS: These results indicate that P53 target genes involved in apoptosis and cell cycle regulation are aberrantly expressed in melanoma and that this aberrant functional activity of P53 may contribute to the proliferation of melanoma.

Frequency of the Common MYH Mutations (G382D and Y165C) in MMR Mutation Positive and Negative HNPCC Patients.

Recently mutations in the MYH gene have been associated with a milder form of adenomatous polyposis which is characterized by a variable level of colonic polyps ranging from a few to several hundred. In the context of HNPCC it is not unusual to identify patients with a smattering of polyps. The MYH gene product is involved in DNA repair and indeed the hMSH2/hMSH6 complex (both genes being essential elements of the DNA mismatch repair pathway) is required to stimulate MYH activity. We reasoned that because of the clinical similarity of a subset of HNPCC patients to those described with MYH mutations and the role of the hMSH2/hMSH6 complex in the activation of MYH protein that MYH mutations may account for a small proportion of HNPCC patients. In a study of 442 HNPCC patients we identified MYH mutations at the same frequency as that expected in the general population. Nevertheless, two HNPCC families were identified harbouring biallelic changes in MYH.

Mutation analysis of the MYH gene in an Australian series of colorectal polyposis patients with or without germline APC mutations.

The MYH gene has recently been shown to be associated with a recessive form of colorectal adenomatous polyposis. Two common mutations in the MYH gene have been identified that lend themselves to rapid screening. We have examined a series of 302 individuals comprising 120 control subjects, 120 patients diagnosed with adenomatous polyposis but without germline mutations in the APC gene and 62 patients diagnosed with familial adenomatous polyposis all harbouring confirmed causative APC germline mutations. The results reveal that MYH accounts for 16 percent of polyposis patients without germline mutations in the APC gene and that it does not appear to be a modifier gene in FAP patients diagnosed with APC germline mutations.