Growth hormone signaling pathway leading to the induction of dna synthesis and proliferation in primary cultured hepatocytes of adult rats

Background: We investigated the signal transduction pathway associated with growth hormone (GH)-stimulated DNA synthesis and proliferation in primary cultured hepatocytes. Methods: Adult rat hepatocytes were isolated from normal livers by two-step in situ collagenase perfusion to facilitate disaggregation of the adult rat liver. Then hepatocytes were cultured in serum-free Williams’ medium E supplemented with GH (1-100 ng/ml) in the presence or absence of test reagents. GH-induced hepatocyte DNA synthesis and proliferation were determined, and the phosphorylation activities of Janus kinase (JAK) 2 (JAK2) (p125 kDa), p95-kDa RTK, and ERK1/2 were measured by western blotting. Results: Hepatocytes grown in serum-free defined medium proliferated within 5 h of culture in the presence of GH (100 ng/ml) in a concentration- and time-dependent manner (EC50 75 ng/ml). These proliferative effects of GH were almost completely blocked by an anti-GH receptor monoclonal antibody (85 ng/ml) and an anti-insulin-like growth factor (IGF)-I receptor monoclonal antibody. In addition, the proliferative effects of GH were significantly blocked by a JAK2 inhibitor (TG101209, 10−6 M), as well as specific signal-transducing inhibitors of phospholipase C (PLC; U-73122, 10−6 M), RTK (AG538, 10−6 M), phosphoinositide 3-kinase (PI3K; LY294002, 10−6 M), mitogen-activated protein kinase kinase/extracellular signal-regulated kinase (MEK/ERK; PD98059, 10−6 M), and mammalian target of rapamycin (mTOR; rapamycin, 10 ng/ml). GH significantly induced the phosphorylations of JAK2 (p125 kDa), p95-kDa IGF-I receptor tyrosine kinase (RTK), and ERK2 in this order according to western blotting analysis. Conclusions: The proliferative action of GH is mediated by two main signaling pathways. One includes activation of the GH receptor/JAK2/PLC/Ca2+ pathway, and the other involves activation of the p95-kDa IGF-I RTK/PI3K/ERK2/mTOR pathway in primary cultures of adult rat hepatocytes.This is an open access journal with with free of charge submission and non-commercial download. At the time of submission, authors will be asked to transfer the copyright to the accepted article to the Journal of Pharmacy and Pharmaceutical Sciences. The author may purchase the copyright for $500 upon which he/she will have the exclusive copyright to the article. Nevertheless, acceptance of a manuscript for publication in the Journal is with the authors' approval of the terms and conditions of the Creative Commons copyright license Creative Common license (Attribution-ShareAlike) License for non-commercial uses