Protein kinase Cζ is up-regulated in osteoarthritic cartilage and is required for activation of NF-κB by tumor necrosis factor and interleukin-1 in articular chondrocytes

Protein kinase C zeta(PKC zeta) is an intracellular serine/threonine protein kinase that has been implicated in the signaling pathways for certain inflammatory cytokines,including interleukin-1 (IL-1) and tumor necrosis factor alpha(TNF-alpha), in some cell types. A study of gene expression in articular chondrocytes from osteoarthritis (OA) patients revealed that PKC zeta is transcriptionally up-regulated in human OA articular cartilage clinical samples. This finding led to the hypothesis that PKC zeta may be an important signaling component of cytokine-mediated cartilage matrix destruction in articular chondrocytes, believed to be an underlying factor in the pathophysiology of OA. IL-1 treatment of chondrocytes in culture resulted in rapidly increased phosphorylation of PKC zeta, implicating PKC zeta activation in the signaling pathway. Chondrocyte cell-based assays were used to evaluate the contribution of PKC zeta activity in NF-kappa B activation and extracellular matrix degradation mediated by IL-1, TNF, or sphingomyelinase. In primary chondrocytes, IL-1 and TNF-alpha caused an increase in NF-kappa B activity resulting in induction of aggrecanase-1 and aggrecanase-2 expression, with consequent increased proteoglycan degradation. This effect was blocked by the pan-specific PKC inhibitors RO 31-8220 and bisindolylmaleimide I, partially blocked by Go 6976, and was unaffected by the PKC zeta- sparing inhibitor calphostin C. A cell-permeable PKC zeta pseudosubstrate peptide inhibitor was capable of blocking TNF- and IL-1-mediated NF-kappa B activation and proteoglycan degradation in chondrocyte pellet cultures. In addition, overexpression of a dominant negative PKC zeta protein effectively prevented cytokine-mediated NF-kappa B activation in primary chondrocytes. These data implicate PKC zeta as a necessary component of the IL-1 and TNF signaling pathways in chondrocytes that result in catabolic destruction of extracellular matrix proteins in osteoarthritic cartilage.