Up-regulation of specific tyrosinase mRNAs in mouse melanomas with the c(2j) gene substituted for the wild-type tyrosinase allele: Utilization in design of syngeneic immunotherapy models

The expression of cell-specialization genes is likely to be changing in tumor cells as their differentiation declines. Functional changes in these genes might yield unusual peptide epitopes with anti-tumor potential and could occur without modification in the DNA sequence of the gene. Melanomas undergo a characteristic decline in melanization that may reflect altered contributions of key melanocytic genes such as tyrosinase. Quantitative reverse transcriptase-PCR of the wild-type (C) tyrosinase gene in transgenic (C57BL/6 strain) mouse melanomas has revealed a shift toward alternative splicing of the pre-mRNA that generated increased levels of the Delta 1b and Delta 1d mRNA splice variants. The spontaneous c(2j) albino mutation of tyrosinase (in the C57BL/6 strain) changes the pre-mRNA splicing pattern. In c(2j)/c(2j) melanomas, alternative splicing was again increased. However, while some mRNAs (notably Delta 1b) present in C/C were obligatorily absent, others (Delta 3 and Delta 1d) were elevated. In c(2j)/c(2j) melanomas, the percentage of total tyrosinase transcripts attributable to Delta 3 reached approximately 2-fold the incidence in c(2j)/c(2j) or C/C skin melanocytes. The percentage attributable to Delta 1d rose to approximately 2-fold the incidence in c(2j)/c(2j) skin, and to 10-fold that in C/C skin. These differences provide a basis for unique mouse models in which the melanoma arises in skin grafted from a C/C or c(2j)/c(2j) transgenic donor to a transgenic host of the same or opposite tyrosinase genotype. Immunotherapy designs then could be based on augmenting those antigenic peptides that are novel or overrepresented in a tumor relative to the syngeneic host.