Protein Kinase C Inhibitors Enhance Differentiation of Rat Adipocyte Precursor Cells in Serum-Free Culture

Abstract

The involvement of protein kinase C in differentiation of rat adipocyte precursor cells in serum-free culture was evaluated by using various protein kinase inhibitors. Induction of adipose conversion, which was maximal after 10 days of culture in the presence of 5 micrograms/ml insulin, 10 micrograms/ml transferrin, and 200 pM triiodothyronine, was inhibited by the addition of protein kinase C inhibitors, H-7 and staurosporine, in a dose-dependent fashion with the maximal effect at 10 microM and 10 nM, respectively. Inhibition of adipocyte differentiation by 12-O-tetradecanoylphorbol 13-acetate (10(-8) M), an activator of protein kinase C, was reversed by a concomitant addition of either 10 microM H-7 or 10 nM staurosporine. HA1004, a potent inhibitor of cAMP- and cGMP-dependent protein kinases, with minimal inhibitory activity on protein kinase C, did not affect adipose conversion. Furthermore, H-89, another isoquinoline derivative with a selective inhibitory action on cAMP-dependent protein kinase, was without effect on cellular differentiation. These results indicate that the potentiation of adipogenesis by H-7 and staurosporine is mediated by suppression of protein kinase C and that protein kinase C is involved in adipocyte differentiation in an inhibitory fashion.