Elevated expression of an endogenous retroviral long terminal repeat in a mouse colon tumor.

We have previously identified a number of cloned poly(A)+ RNA sequences in a cDNA library, each of whose expression is markedly altered in a dimethylhydrazine-induced mouse colon tumor as compared to the normal colon. Transcripts which hybridize to one of the cloned cDNAs, pMCT-1, have now been shown to be elevated in expression in three mouse leukemia cell lines as well, and induction of differentiation in one of these lines (DS-19) is associated with a substantial decrease in expression of these transcripts. By hybridization and sequence analysis, pMCT-1 has been found to contain a region homologous to a long terminal repeat of an intracisternal A particle sequence. Intracisternal A sequences are endogenous, retroviral genomes repeated several thousandfold and dispersed in the mouse genome. The data show that the transcripts which are homologous to this long terminal repeat are highly heterogeneous, suggesting that many intracisternal type A particle transcriptional units may be expressed in the colon tumor and leukemia cell lines.