β-estradiol stimulation of DNA synthesis requires different PKC isoforms in HEPG2 and MCF7 cells

The role exerted by protein kinase C (PKC) on estrogen-induced DNA synthesis has been investigated in hepatic and mammary gland cells, HepG2 and MCF7. 17-beta -estradiol stimulated DNA synthesis in HepG2 and MCF7 cells, maximal effect occurring at 10 nM. DNA synthesis stimulation was prevented by anti-estrogen ICl 182,780 and by inhibitor of PKC, Ro 31-8220. The rapid estradiol effects in MCF7 cells were determined by following the inositol trisphosphate (IP3) production and PKC-V. membrane translocation. After estradiol treatment the increase of IP3 production, prevented by anti-estrogen or by phospholipase C (PLC) inhibitor (neomycin), was present in MCF7 cells. In MDA cells, devoid of estrogen receptor, no effect was observed. The PKC-alpha presence on the membranes appeared unchanged in MCF7 cells. The PLC inhibitors, neomycin and U73,122, and PKC-alpha down regulator, phorbol 12-myristate 13-acetate (PMA), were able to prevent estradiol-induced DNA synthesis in hepatoma cells, but ineffective in mammary cells; wortmannin, an inhibitor of phosphoinositide 3-kinases (P13-K), blocked DNA synthesis in both cell lines. These data show that beta -estradiol, via an estrogen receptor-mediated mechanism, activates more signal transduction pathways, and consequently different PKC isoforms in two responsive cell lines. In both cell lines P13-K/PKC pathway is functional to the estrogen regulation of DNA synthesis, whereas in HepG2 cells the parallel involvement of the PLC/PKC-alpha. pathway is present. The reported results indicate that the DNA synthesis stimulation by beta -estradiol requires the estrogen receptor and utilises one or more activated pathways in dependence on the cell equipment. (C) 2001 Wiley-Liss, inc.