JNK and PI3K differentially regulate MMP-2 and MT1-MMP mRNA and protein in response to actin cytoskeleton reorganization in endothelial cells.

Increased production and activation of matrix metalloproteinase-2 (MMP-2) are critical events in skeletal muscle angiogenesis and are known to occur in response to mechanical stresses. We hypothesized that reorganization of the actin cytoskeleton would increase endothelial cell production and activation of MMP-2 and that this increase would require a MAPK-dependent signaling pathway in endothelial cells. The pharmacological actin depolymerization agent cytochalasin D increased expression of MMP-2 and membrane type 1-matrix metalloproteinase (MT1-MMP) mRNA, and this was reduced significantly in the presence of the JNK inhibitor SP600125. Activation of JNK by anisomycin was sufficient to induce expression of both MMP-2 and MT1-MMP mRNA in quiescent cells. Downregulation of c-Jun, a downstream target of JNK, with small interference (si)RNA inhibited MMP-2 expression in response to anisomycin. Inhibition of phosphoinositide 3-kinase (PI3K), but not JNK, significantly decreased the amount of active MMP-2 following cytochalasin D stimulation with a concurrent decrease in MT1-MMP protein. Physiological reorganization of actin occurs during VEGF stimulation. VEGF-induced MMP-2 protein production and activation, as well as MT1-MMP protein production, depended on PI3K activity. VEGF-induced MMP-2 mRNA expression was reduced by inhibition of JNK or by treatment with c-Jun siRNA. In summary, our results provide novel insight into the signaling cascades initiated in the early stages of angiogenesis through the reorganization of the actin cytoskeleton and demonstrate a critical role for JNK in regulating MMP-2 and MT1-MMP mRNA expression, whereas PI3K regulates protein levels of both MMP-2 and MT1-MMP.