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Frequent genomic alterations have been observed in melanomas, suggesting that genetic changes play a pivotal role in melanoma progression. To further characterize the potential oncogenes and tumor suppressor genes underlying these changes, we carried out array CGH analysis using genomic DNA from a collection of melanoma cell lines derived from primary and metastatic lesions from individual patients and sex-matched, pooled reference DNA differentially-labeled with Cy3 and Cy5 fluorescent dyes. The Bac library that we used is composed of 4134 clones that span the human genome at a spacing interval of approximately 1 Mb. Through this array CGH analysis, a region on chromosome 7p22 was found to be frequently amplified in melanoma (43.5%). This amplification event was confirmed by real-time PCR analysis. The copy number changes determined by taqman range from 3 copies to 16 copies. The boundaries of this amplicon were mapped by real-time PCR analysis, and was found to contain multiple genes, including CARD11, a positive regulator for NF-kappaB activation, and GNA12, a guanine nucleotide-binding protein. The expression of the genes within the amplicon was investigated by Affymatrix analysis and GNA12 seemed to be overexpressed. This was confirmed by real-time RT-PCR analysis, by comparing the ratio of GNA12 mRNA to beta-ACTIN mRNA in tumor samples to the ratio in normal melanocytes. Using 2.5 fold as cutoff, the overexpression rate in tumors was determined to be at 41.5% (17/41) with highest overexpression at 6 fold. The encoded protein guanine nucleotide binding protein (G protein) alpha 12, has been shown to be highly efficient in transforming NIH 3T3 mouse fibroblasts by overexpression alone, suggesting that this amplification event at 7p22 plays a functional role in melanoma formation and progression.

[Proc Amer Assoc Cancer Res, Volume 46, 2005]