Regulation of matrix metalloproteinase-9 (MMP-9) in TNF-stimulated neutrophils: novel pathways for tertiary granule release

Matrix metalloproteinase‐9 (MMP‐9) is present in the tertiary granules of neutrophils and is rapidly released following stimulation. We examined the pathways that regulate tumor necrosis factor (TNF)‐mediated MMP‐9 release and found this to be dependent on the TNF receptor I. TNF rapidly activated extracellular signal‐regulated kinase and p38 mitogen‐activated protein kinases, but neither of these pathways was critical for MMP‐9 release. Many neutrophil responses to TNF require β2‐integrin‐dependent signaling and subsequent Src family kinase activation. In conrast, we found that MMP‐9 release from tertiary granules was only partially affected by blocking β2‐integrin‐mediated adhesion. Similarly, blocking Src family kinases with the inhibitor PP2 only attenuated TNF‐induced MMP‐9 release. Blocking β2‐integrin‐mediated adhesion and Src family kinases did not result in additive inhibition of MMP‐9 release. In contrast, inhibiting protein kinase C (PKC) with a pan‐specific inhibitor blocked greater than 85% of MMP‐9 release. Inhibitors against specific PKC isoforms suggested a role for PKC α and PKC δ in maximal MMP‐9 release. These data suggest that MMP‐9 release from tertiary granules uses β2‐integrin‐independent signaling pathways. Furthermore, PKC isoforms play a critical role in regulating tertiary granule release.