The Protein Kinase C Cascade Regulates Recruitment of Matrix Metalloprotease 9 to Podosomes and Its Release and Activation

Podosomes are transient cell surface structures essential for degradation of extracellular matrix during cell invasion. Protein kinase C (PKC) is involved in the regulation of podosome formation; however, the roles of individual PKC isoforms in podosome formation and proteolytic function are largely unknown. Recently, we reported that PDBu, a PKC activator, induced podosome formation in normal human bronchial epithelial cells. Here, we demonstrate that phorbol-12,13-dibutyrate (PDBu)-induced podosome formation is mainly mediated through redistribution of conventional PKCs, especially PKC alpha, from the cytosol to the podosomes. Interestingly, although blocking atypical PKC zeta did not affect PDBu-induced podosome formation, it significantly reduced matrix degradation at podosomes. Inhibition of PKC zeta reduced recruitment of matrix metalloprotease 9 (MMP-9) to podosomes and its release and activation. Downregulation of MMP-9 by small interfering RNA (siRNA) or neutralization antibody also significantly reduced matrix degradation. The regulatory effects of PKC zeta on matrix degradation and recruitment of MMP-9 to podosomes were PKC zeta kinase activity dependent. PDBu-induced recruitment of PKC zeta and MMP-9 to podosomes was blocked by inhibition of novel PKC with rottlerin or PKC delta siRNA. Our data suggest that multiple PKC isozymes form a signaling cascade that controls podosome formation and dynamics and MMP-9 recruitment, release, and activation in a coordinated fashion.