Induction of apoptosis through the PKC pathway in cultured dermal papilla fibroblasts

The dermal papilla (DP) consists of a discrete population of specialized fibroblasts that are important in the morphogenesis of the hair follicle in the embryo and in the control of the hair growth cycle in the adult. This mitotically quiescent and long-lived cell population expresses gene products that promote cell survival such as Bcl-2, and thus normally might be protected from apoptosis. We investigated whether cultured DP fibroblasts are able to undergo apoptosis by treatment with the protein kinase inhibitor staurosporine. Involvement of the PKC signaling pathway in DP fibroblast survival/death was investigated by inhibition (staurosporine and Bisindolylmaleimide (Bis) treatment) or activation (TPA; 12-O-tetradecanoylphorbol-13-acetate treatment) of PKC and characterization of DP-expressed PKC isoforms by RT-PCR. We determined that cultured DP fibroblasts undergo apoptosis, in a dose-related manner, when treated with staurosporine but not when treated with Bis, an inhibitor with narrow PKC isoform specificity. TPA confers partial and transient resistance to staurosporine-induced DP apoptosis. Staurosporine and Bis each induced G1 arrest, whereas TPA treatment of cultured DP resulted in increased entry into S-phase. The differential responses to individual inhibitors and activators of PKC may be related to the multiple PKC isoforms that DP fibroblasts express. Flow cytometric analysis indicates that the mechanism of staurosporine-induced apoptosis may be through decrease of Bcl-2 in treated DP cells or through modulation of cell cycle regulators. Correlation between sensitivity to induction of apoptosis and proliferation suggests that dermal papilla cells may normally be protected from apoptosis in vivo by their mitotically quiescent state.