Regulation of human neutrophil-mediated cartilage proteoglycan degradationby phosphatidylinositol-3-kinase

The ability of neutrophils to degrade cartilage proteoglycan suggests that the neutrophils that accumulate in the joints of rheumatoid arthritis patie nts are mediators of tissue damage. The regulatory mechanisms which are rel evant to the proteoglycan-degrading activity of neutrophils are poorly unde rstood. Since phosphatidylinositol 3-kinase (PI3-K), protein kinase C (PKC) . the extracellular signal-regulated protein kinase (ERK)1/ERK2 and cyclic adenosine monophosphate (cAMP) have been reported to regulate neutrophil re spiratory burst and/or degranulation, a role for these signalling molecules in regulating proteoglycan degradation was investigated. Preincubation of human neutrophils with GF109203X (an inhibitor of PKC), PD98059 (an inhibit or or MEK, the upstream regulator of ERK1/ERK2) or with forskolin or dibuty ryl cAMP, failed to suppress proteoglycan degradation of opsonized bovine c artilage. In contrast, preincubation of neutrophils with wortmannin or LY29 4002, specific inhibitors of PI3-K, inhibited proteoglycan degradation. inc ubation of neutrophils with cartilage resulted in the activation of PI3-K i n neutrophils. consistent with a role for PI3-K in proteoglycan degradation . Activation of PI3-K and proteoglycan degradation was enhanced by tumour n ecrosis factor-alpha. Degradation caused by neutrophils from the synovial f luid of rheumatoid arthritis patients was also inhibited by wortmannin. The se data demonstrate that the proteoglycan degradative activity of neutrophi ls required PI3-K but not PKC or the ERK1/ERK2/ERK5 cascades and was insens itive to increases in intracellular cAMP concentrations.