PKC regulation of microfilament network organization in keratinocytes defined by a pharmacological study with PKC activators and inhibitors.

The modulation by PKC activators and inhibitors of adhesion, spreading, migration, actin cytoskeleton organization, and focal complex formation in keratinocytes attaching to type I collagen was studied. Two actin microfilament networks, stress fibers and cortical actin, could be distinguished on the basis of cellular distribution and opposite regulation by growth factors, tyrosine kinase inhibitors, and PKC activators. Stress fiber formation was stimulated by growth factors and by PMA (100 ng/ml) and these stimulations were blocked by tyrosine kinase inhibitors (0.3 mM genistein and 1 microM herbimycin A). By contrast, the cortical network occurred in quiescent cells, was unaffected by tyrosine kinase inhibitors, and was broken down after PKC activation by PMA. Spreading, migration, and actin polymerization were completely blocked while adhesion efficacy was significantly decreased by three specific PKC inhibitors. Half-inhibition of migration was obtained with 0.025, 1, and 3 microM concentrations of calphostin C, chelerytrine chloride, and D-erythrosphingosine, respectively, which are concentrations close to those known to inhibit the PKC kinase function in vitro. Paxillin clustering, which was observed even in the presence of tyrosine kinase inhibitors, disappeared only when actin polymerization was completely impaired, i.e., in cells treated with PKC inhibitors or with both tyrosine kinase inhibitors and PMA, which indicated that focal complex formation was highly dependent on microfilament reorganization. The analysis of these data underscores a major regulation function of PKC in the molecular events involved in growth factor and adhesion-dependent regulation of microfilament dynamics.