Expression of long terminal repeat (LTR) sequences in carcinogen-induced murine skin carcinomas.

RNA sequences homologous to the Long Terminal Repeat (LTR) sequence of Moloney Murine Leukemia Virus proviral DNA are expressed in murine squamous cell carcinomas of the skin induced by chemical carcinogens. These transcripts range in size from 8.2 to less than 2.4 kb but their size profile varies between individual tumors. These RNAs are not detected in the poly A+ RNA fraction obtained from the epidermis of control mice or carcinogen induced skin papillomas. The poly A+ RNAs from the livers and spleens of some of the mice with skin carcinomas also revealed LTR related sequences, whereas these RNAs were not detected in the livers and spleens of control mice or of carcinogen-treated mice that did not develop carcinomas. Thus, chemical carcinogenesis in mouse skin is associated with constitutive expression of endogenous retrovirus related sequences in the carcinomas as well as in certain apparently normal host tissues.