SELECTIVE INCREASE IN SPECIFIC ALTERNATIVE SPLICE VARIANTS OF TYROSINASE IN MURINE MELANOMAS - A PROJECTED BASIS FOR IMMUNOTHERAPY

Melanomas tend to become less pigmented in the course of malignant pro gression, Thus, as proliferation increases, the tumors are decreasingl y characterized by the tissue-specific phenotype of normally different iated melanocytes, To learn whether the decline in melanization is ass ociated with a shift from constitutive to alternative splicing of some pigment gene pre-mRNAs, melanomas were collected from Tyr-SV40E trans genic mice of the standard C57BL/6 strain, The mRNAs of the tyrosinase gene, which has a key role in melanogenesis, were analyzed by quantit ative reverse transcriptase-PCR in 34 samples from 16 cutaneous tumors and 9 metastases, The cutaneous tumors included some cases with disti nct melanotic and amelanotic zones, which were separately analyzed, Al l tyrosinase transcripts found in the melanomas were also found in nor mal skin melanocytes. However, the Delta 1b and Delta 1d alternatively spliced transcripts, due to deletions within the first exon, were spe cifically augmented in most of the tumors over their very low levels i n skin; the exceptions were some all-amelanotic tumors in which no tyr osinase transcripts were detected, The level of Delta 1b rose as high as 11.3% of total tyrosinase mRNAs as compared with 0.6% in skin; Delt a 1d reached 4.0% as compared with 0.8% in skin, Expression of these s plice variants was highest in the melanotic components of zonal primar y tumors, relatively lower in their amelanotic components, and still l ower in all-amelanotic primary tumors and amelanotic metastases, The i ncrease in Delta 1b and Delta 1d transcripts may be predicted to incre ase the levels of unusual peptides, which could have antigenic potenti al in the tumors, especially in the relatively early phases of maligna ncy, Analyses of the alternative transcripts of other pigment genes ma y identify additional candidate antigens, ultimately enabling melanoma cells in all phases of the disease to be represented as a basis for i mmune intervention.