STAUROSPORINE INDUCES A SEQUENTIAL PROGRAM OF MOUSE KERATINOCYTE TERMINAL DIFFERENTIATION THROUGH ACTIVATION OF PKC ISOZYMES

Staurosporine (stsp) induces assembly of cornified envelopes in mouse keratinocyte cultures, To clarify whether this effect is the consequen ce of a coordinated differentiation program similar to that observed i n epidermis, we assessed the expression of multiple differentiation-sp ecific markers in stsp-treated keratinocytes, In medium containing 0.0 5 mM Ca2+, in which the basal cell phenotype is normally maintained, s tsp induced dose-dependent increases in keratin 1, epidermal and kerat inocyte transglutaminases, SPR-1, loricrin, and profilaggrin mRNA, Bas ed on nuclear run-on analysis, stsp-mediated marker expression was fou nd to be due at least in part to increased transcription, Since protei n kinase C (PKC) activation is required for keratinocyte differentiati on, we tested whether stsp influenced this signaling pathway, Stsp ind uced the translocation of multiple PKC isoforms from the cytosol to me mbrane and/or cytoskeletal fractions, inducing isozyme downregulation within 24 h, Moreover, AP-1 DNA binding activity was elevated in stsp- treated keratinocytes, consistent with the notion that this agent infl uences keratinocyte-specific gene expression via the PKC pathway, Stsp -mediated marker expression was inhibited by the PKC inhibitor GF 1092 03X, In cells pre-treated with bryostatin 1 to selectively down-modula te specific PKC isoforms, stsp-induced loricrin, filaggrin, and SPR-1 expression was suppressed when PKC alpha, epsilon, and/or delta were d ownregulated, suggesting that these isozymes may be necessary for mark er expression in response to this agent, Thus, in addition to its effe cts on cornified envelope assembly, stsp induces a coordinate program of differentiation-specific keratinocyte gene expression that is media ted at least in part by the PKC signaling pathway.