Sequential analysis of chemically induced hepatoma development in rats by two dimensional electrophoresis

Using the Solt-Farber hepatocarcinogenesis model, a large population of preneoplastic and neoplastic nodules were induced in male Fischer 344 rats. Total cellular polypeptides from normal liver and individual preneoplastic and neoplastic nodules were analyzed for both qualitative and quantitative changes using computer assisted high resolution two-dimensional electrophoresis. Approximately 800–1000 cytosolic and 1200–1400 membrane associated polypeptides were readily separated and detected using an ultrasensitive silver stain. The polypeptide patterns were remarkably similar for each tissue and only four qualitative polypeptide differences were noted. One cytosolic polypeptide, 6.8/57 (designated pl/ M r × 10-3), and three membrane associated polypeptides, 6.25/41, 6.75/24, and 6.05/21, were expressed in both preneoplastic and neoplastic nodules but not in normal liver. No qualitative polypeptide differences were detected among the individual preneoplastic or individual neoplastic nodules or between preneoplastic and neoplastic nodules. Numerous quantitative changes in both known markers for hepatocarcinogenesis and in as yet unidentified polypeptides were noted. In particular, the Ya subunit of glutathione S -transferase B, the Yb subunit of glutathione S -transferase A, as well as the three isoelectric point variants of the Yp subunit of glutathione S -transferase P were increased 2-, 4-, and 7-fold, respectively, in preneoplastic and neoplastic nodules. Whereas DT-diaphorase was increased 2–3-fold in hyperplastic nodules as compared to normal liver, no differences in the expression of albumin were noted. Although no differences were observed in the expression of aldehyde dehydrogenase in preneoplastic and neoplastic nodules, polypeptide b (6.9/54) was shifted slightly toward the basic region in normal liver. α-Fetoprotein was not detected in either preneoplastic or neoplastic nodules. In addition to these changes in known markers, comparison of 500–800 cytosolic and 750–1000 membrane associated polypeptides showed that roughly 4–10% of the polypeptides were undergoing quantitative changes of at least 4-fold during these stages of hepatocarcinogenesis. Thirty (10 cytosolic and 20 membrane) polypeptides were significantly down-regulated while 22 (7 cytosolic and 15 membrane) polypeptides were up-regulated in both preneoplastic and neoplastic nodules. In all cases the direction and magnitude of change were the same in both preneoplastic and neoplastic nodules with the exception of three polypeptides. Membrane associated polypeptides 1055 and 1221 remained unchanged in preneoplastic nodules while decreased in the neoplastic nodules, while polypeptide 319 increased in preneoplastic nodules but returned to normal levels in neoplastic nodules. In no other cases did a particular polypeptide increase (or decrease) in a preneoplastic nodule while decreasing (or increasing) in a neoplastic nodule.