The development of chemically induced hepatocellular carcinoma in the rat proceeds through a series of premalignant changes that may ultimately progress to a primary malignant tumor. Using the selection technique based on diminished binding of preneoplasic hepatocytes to tissue culture plates precoated with asialofetuin, we have isolated poly(A+)RNA from early preneoplastic foci as well as preneoplastic persistent nodules and primary hepatocellular carcinoma induced by the Solt-Farber protocol in the Fischer rat. The steady-state poly(A+)RNA levels of genes traditionally associated with growth, differentiation and/or transformation were then determined to address the question of their temporal expression in the multistep nature of cancer development.
Ornithine decarboxylase- and P53-specific transcripts did not significantly change in preneoplastic foci but were increased in later-stage preneoplastic nodules and hepatocellular carcinoma. Albumin-specific transcripts were decreased in all hepatocellular carcinoma but there was no consistent coordinated increase in α-fetoprotein-specific transcripts. c-myc and raf transcripts increased at the very early preneoplastic foci stage and continued to increase throughout the neoplastic process. No L-myc or N-myc transcripts could be detected in any RNA sample. c-Ha-ras-specific transcripts were essentially unaltered in all RNA samples whereas no c-Ki-ras or N-ras transcripts could be detected throughout the neoplastic process. In addition, no dominant-acting transforming mutations in the ras gene family were detected by DNA transfection experiments using NIH/3T3 cells.