Expression of retroviral sequences and oncogenes in murine hepatocellular tumors

The expression of endogenous retroviral sequences and of three cellular oncogenes was examined in three hepatocellular adenomas and in four carcinomas induced in male C57BL/6JDp X C3Hf/Dp F1 (hereafter called B6C3F1) mice by a single dose of nitrosodiethylamine, in five carcinomas that arose spontaneously in male C3Hf mice, and in the livers of normal age-matched control mice. In all of these adenomas and carcinomas, there was increased expression of Moloney murine leukemia virus- and intracisternal A particle-related sequences. The retrovirus-like VL30 sequence was expressed at significant levels in the normal liver of these mice and increased expression of this sequence was found in only 4 of the 12 tumors examined. Expression of endogenous mouse mammary tumor virus-related sequences was not detected in the normal livers or in any of the liver tumors. With respect to cellular oncogenes, increased expression of c-myc was seen in all of the B6C3F1 tumors. Two of five normal liver samples and all of the tumors of the C3Hf mice displayed significant expression of c-myc. There was a slight increase in expression of c-Ha-ras in some of the tumors. Increased expression of c-fos was found in only 1 of the 12 tumors. Taken together, these studies indicate that both carcinogen-induced and spontaneous liver tumor formation in mice is associated with abnormalities in the expression of endogenous retrovirus-related DNA sequences and also specific cellular oncogenes.