Functional suppression of E-cadherin by protein kinase Cδ

Protein kinase C (PKC) δ, a member of the novel PKC subfamily, has been shown to have an important role in cell proliferation, differentiation, apoptosis and cell motility. In this study, we investigated the effect of green fluorescent protein (GFP)-PKCδ and GFP-PKCα on cell-cell junctions of Madin-Darby canine kidney (MDCK) cells and found that only GFP-PKCδ suppressed the homophilic interactions between the ectodomains of E-cadherins, accompanied by a weaker cell-cell adhesion. The kinase-deficient mutant of GFP-PKCδ retained its localization at cell-cell junctions but failed to suppress the function of E-cadherin. In addition, we demonstrated that the hinge region (residues 280-347) that links the regulatory domain and the catalytic domain of PKCδ is essential for both its kinase activity and the targeting of cell-cell junctions. A PKCδ mutant with the deletion of amino acids 280-323 within the hinge region, which is catalytically active but defective in the targeting of cell-cell junctions, failed to suppress the function of E-cadherin. Moreover, expression of GFP-PKCδ in MDCK cells expedited the detachment of cells from their neighbors and facilitated cell scatter induced by hepatocyte growth factor. By contrast, the GFP-PKCδ mutants including the kinase-deficient mutant and the truncated mutant lacking residues 280-323 suppressed hepatocyte-growth-factor-induced cell scattering. Finally, siRNA-mediated knockdown of endogenous PKCδ in MDCK cells was found to delay the onset of cell-cell detachment and cell scattering induced by hepatocyte growth factor. Taken together, our results demonstrate that the catalytic activity of PKCδ and its localization to cell-cell junctions are necessary for PKCδ to suppress the function of E-cadherin, which thereby facilitates scattering of epithelial cells in response to extracellular cues.