The objective of this project is to characterize the role of retroviral associated oncogenes in both the formation and/or maintenance of hepatocellular carcinoma (HCC). The experimental systems presently under study are (a) a human hepatoma cell line, HEP G2 and (b) an in vivo rat model for chemically-induced hepatocellular carcinoma. The results obtained with the HEP G2 study include the tumorigenic characterization of this cell line which may be associated with elevated levels of c-myc transcripts coupled to the expression of an """"""""activated"""""""" N-ras gene. The greatly increased steady-state level of c-myc transcripts in HEP G2 cells is the result of increased gene transcription and not the result of a specific stabilization of the c-myc message. Early preneoplastic changes were examined by isolating preneoplastic foci hepatocytes (which lack the cell-surface asialoglycoprotein receptor) in addition to later stage preneoplastic nodules and hepatocellular carcinomas. Utilizing this system, we have examined the expression of genes that are associated with hepatocyte proliferation [ornithine decarboxylase (ODC)], differentiation [albumin (ALB)] and oncofetal development [myc, raf, Ha-ras, P53 and alpha-fetoprotein (AFP)] during the development of HCC in carcinogen-treated Fischer rats by Northern blot analysis. ODC transcripts were not increased in liver foci but were increased in nodules and HCC. Myc transcripts, however, were increased in liver foci, nodules and HCC. AFP and P53 transcripts were not detected in liver foci, barely detectable in nodules and variably expressed in HCC, whereas ALB transcripts were decreased by approximately 50% in all HCC. Ha-ras and raf transcripts were variably expressed in all samples and could be correlated with a particular stage of HCC development. The data suggest that increases in steady-state levels of myc transcripts may be an early event in HCC development and may not be related to hepatocyte proliferation, but rather to alterations in the differentiation state.
