PKCδ Clustering at the Leading Edge and Mediating Growth Factor-Enhanced, but not ECM-Initiated, Dermal Fibroblast Migration

We have previously shown that the immobilized extracellular matrices (ECMs) initiate cell migration and soluble growth factors (GFs) further enhance ECM-initiated cell migration. GFs alone cannot initiate cell migration. To further investigate the specificity of the two signaling mechanisms, we focused on the protein kinase C (PKC) family genes in primary human dermal fibroblasts (DFs). We here show that platelet-derived growth factor-BB (PDGF-BB) strongly stimulates membrane translocation and leading edge clustering of protein kinase Cδ (PKCδ). In contrast, attachment to collagen matrix alone does not cause the translocation. Although the kinase function of PKCδ is dispensable for initial membrane translocation, it is critical for its sustained presence at the cells's leading edge. Blockade of endogenous PKCδ signaling with dominant-negative kinase-defective PKC (PKCδ-KD) or PKCδ-small interfering RNA (siRNA) completely inhibited PDGF-BB-stimulated DF migration. In contrast, neither PKCδ-KD nor PKCδ-siRNA affected collagen-induced initiation of DF migration. Overexpression of a constitutively activated PKCδ (PKCδ-R144/145A) partially mimics the effect of PDGF-BB. However, PKCδ-KD, PKCδ-siRNA, or PKCδ-R144/145A does not affect PDGF-BB-stimulated activation of p38 mitogen-activated protein kinase, extracellular signal-regulated kinase1/2, or c-Jun N-terminal kinase. Instead, inhibition of PKCδ blocks PDGF-BB-stimulated activation of signal transducer and activator of transcription 3 (Stat3). This study unveiled the specificity of PKCδ in the control of DF migration