Inhibition of proliferation of normal, preneoplastic, and neoplastic rat hepatocytes by transforming growth...

The influences of purified transforming growth factor beta (TGF-beta) on proliferation of normal, preneoplastic, and neoplastic rat hepatocytes were examined in primary monolayer culture with or without prior stimulation with epidermal growth factor (EGF). Hepatocytes from normal livers or discrete preneoplastic nodules or carcinomas generated in F344 rats by the Solt-Farber model were isolated and cultured in serum-free modified Williams' E. medium for up to 72 h. Proliferation was quantified by labeling index by [3H]thymidine autoradiography. The majority of normal hepatocytes became labeled in response to EGF (20 ng/ml) between 24 and 72 h. TGF-beta had a dose-dependent inhibitory effect which was virtually complete at concentrations above 0.5 ng/ml added at 0 h together with EGF. Hepatocytes from all nodule and carcinoma populations were less stimulated by EGF but also strongly inhibited by TGF-beta. Hepatocytes isolated from normal livers 24 h after partial hepatectomy were similarly inhibited by TGF-beta. The minimal initial exposure period for TGF-beta to maximally inhibit was 2 h. TGF-beta added at various times between 8 and 48 h after EGF partially inhibited the labeling index to levels that were constant but substantially greater than the labeling index at the time TGF-beta was added. A proportion of hepatocytes from normal and nodular livers became resistant to the inhibitory effects of TGF-beta between 48 and 72 h, suggesting that the inhibitory effect is transient. TGF-beta added at 0 h also virtually completely inhibited the labeling of normal and nodular hepatocytes that were not exposed to EGF. These studies demonstrate that TGF-beta is a potent negative regulator of proliferation of normal, regenerating, preneoplastic, and neoplastic hepatocytes. This suggests that persistent proliferation of neoplastic hepatocytes in vivo cannot be explained by a difference in response to TGF-beta.