The long-term goal of this program is to identify the intraspecies allelic forms at cellular oncogene loci and define the functional consequence of these polymorphisms and their interactions with endogenous retrovirus elements and in the multistep process of oncogenesis. The recent characterization of the feline endogenous retrovirus elements and c-myc oncogene locus, and isolation of two allelic forms of this gene with sequence alterations in the 3' coding region enable initiation of the study in the outbred domestic cat species. There is preliminary evidence that one type of homozygosity at the c-myc locus is rarely found while the other type of homozygosity which is commonly occurring in the cat population is associated with increased frequency of lymphomas. The model system is highly suitable for the study as the domestic cat has the highest incidence of lymphoma-leukemias of any animal, and it is possible that unique characteristics like the distribution of c-myc alleles and horizontal infection by feline leukemia virus may be related to increased susceptibility of the species to leukemogenesis. The specific objectives are: 1) to confirm the c-myc allele distribution pattern and examine association of one type of homozygosity with lymphoma incidence; 2) to determine if the allelic differences observed in the third exon, which are likely to alter the structure of the c-myc protein, exhibit differential transforming abilities when the genes are introduced into susceptible cells and appropriately expressed; and 3) to determine if genetic rearrangements including transposition next to endogenous retrovirus elements or transduction by ecotropic virus show allele-specificity for activation and consequent biological activity. The experimental approach will include construction of recombinant DNA containing appropriate endogenous retrovirus elements linked to a test gene, construction of c-myc alleles flanked by retroviral promoter-enhancer elements, and isolation of naturally rearranged c-myc DNA from identified lymphoma tissues or cells. Functional studies will involve DNA transfection on suitable fibroblast cell system using constructed DNA alone or in combination with other activated oncogene DNA demonstrating a synergistic effect, focus assays, single cell cloning and related methodologies. Polymorphic variants will be characterized by restriction enzyme mapping, and DNA sequencing of cloned DNAs will be done to define the observed biological activity in terms of nucleic acid sequence, and if appropriate, deduced amino acid sequence of the regions showing restriction length polymorphisms.
