Changes in TGF-beta receptors of rat hepatocytes during primary culture and liver regeneration: increased expression of TGF-beta receptors associated with increased sensitivity to TGF-beta-mediated growth inhibition.

Abstract

To clarify the role of transforming growth factor-beta (TGF-beta) and its receptors in hepatocyte growth, we studied the expression of TGF-beta1 and its receptors and the sensitivity to growth inhibition by TGF-beta1 protein in rat hepatocytes derived from resting and regenerating livers. In hepatocytes derived from resting livers, mRNAs for TGF-beta type II receptor (TbetaR-II), insulin-like growth factor-II/mannose 6-phosphate receptor (IGF-II/M-6-PR), and TGF-beta1 increased with time in primary culture. The cell surface TGF-beta receptor proteins (TbetaR-I, II, and III), examined by the receptor affinity-labeling assay using 125I-TGF-beta1, also increased, especially after 48 hr of culture. Hepatocytes were more sensitive to inhibition of DNA synthesis, when the TGF-beta1 protein was added at later times in culture, corresponding to the presence of increased TGF-beta receptors. In hepatocytes from regenerating livers after a partial hepatectomy (PH), an increase of TbetaR-I, TbetaR-II, TbetaR-III, IGF-II/M-6-PR, and TGF-beta1 mRNAs was found, compared with hepatocytes from resting livers. Similarly, using TGF-beta receptor affinity-labeling assay, hepatocytes from PH livers were found to have an increase in TbetaR-I, II, and III proteins, with a peak at 4 days post-PH, compared with hepatocytes from resting livers. When TGF-beta1 protein was added for a short period (6 or 24 hr) after cell attachment to hepatocyte cultures, it inhibited DNA synthesis more effectively in hepatocytes from regenerating compared with resting livers. Our results show that hepatocyte TGF-beta receptors and sensitivity to growth inhibition by TGF-beta1 protein change together and are modulated during liver regeneration, as well as during the conditions of primary culture.