Effects of insulin-like growth factor I and II on DNA synthesis and proliferation in primary cultures of adult rat hepatocytes

Abstract

We compared the effects of insulin-like growth factor I (IGF-I) and II (IGF-II) on DNA synthesis and proliferation and investigated various signal transduction mechanisms involved in insulin-like growth factor-induced mitogenesis in primary cultures of adult rat hepatocytes. IGF-I stimulated hepatocyte DNA synthesis and proliferation with an EC 50 of 75 ng/ml within 4 h of culture. These effects were sensitive to the IGF-I concentration and cell density. Hepatocyte proliferation induced by IGF-I was potentiated by metaproterenol (10 −6 M) as well as by 8-bromo-cAMP, phorbol 12-myristate 13-acetate (PMA; 10 −8 M) and was inhibited by U-73122 (1-(-[[17β-3-methoxyestra-1, 3, 5 (10)-triene-17-yl] amino] hexyl]-1 H pyrrol-2, 5-dione)), genistein, wortmannin, PD98059 (2′-amino-3′-methoxyflavone) and rapamycin. The IGF-I effect was independent of pertussis toxin (100 ng/ml). IGF-II also dose dependently stimulated hepatocyte DNA synthesis and proliferation with an EC 50 of 0.75 ng/ml within 4 h of culture. However, these effects were not dependent on the initial plating density. The stimulatory effects of IGF-II were potentiated by UK-14304 (5-bromo-6-[2-imidazolin-2-ylamino]-quinoxaline) (10 −5 M) and inhibited by phenylephrine, PMA, metaproterenol, 8-bromo-cAMP, PD98059, rapamycin, and pertussis toxin. The IGF-II effects were not affected by genistein, U-73122, and wortmannin. These results suggest that IGF-I and IGF-II rapidly stimulate the DNA synthesis and proliferation of adult rat hepatocytes by separate mechanisms.