Okadaic acid induces matrix metalloproteinase‐9 expression in fibroblasts: crosstalk between protein phosphatase inhibition and β‐adrenoceptor signalling

BACKGROUND AND PURPOSE Interactions between protein phosphatase inhibition and matrix metalloproteinase (MMP)‐9 expression have implications for tissue remodelling after injury. Stimulation of β‐adrenoceptors could affect such interactions as isoprenaline increases protein phosphatase 2A (PP2A) activity and MMP‐9 abundance. We investigated the effect of okadaic acid (OA) on MMP‐9 expression to assess interactions between phosphatase inhibition and β‐adrenoceptor signalling in fibroblasts. EXPERIMENTAL APPROACH Fibroblasts were exposed to OA alone and in combination with isoprenaline. Effects on MMP‐9 expression and intracellular signalling were studied using promoter assays, Western blot analysis and siRNA methodologies. KEY RESULTS Okadaic acid increased MMP‐9 abundance in human cardiac ventricular fibroblasts, NIH3T3 fibroblasts and hepatic stellate cells. This effect was unaffected by PP2A knockdown in NIH3T3 cells. OA increased phosphorylation of NF‐κB, but not NF‐κB promoter activity, IκBα degradation, or nuclear translocation of p65‐NF‐κB. Exposure to SB202190 (p38 MAPK), U0126 (ERK1/2) and NF‐κB III inhibitor revealed that OA induced MMP‐9 activity through p38 MAPK. Isoprenaline inhibited OA‐mediated MMP‐9 expression in NIH3T3, in a β‐arrestin 2‐ and PP2A‐dependent manner. Mutation of the activator protein‐1 (AP‐1) and NF‐κB binding sites demonstrated that OA‐induced MMP‐9 activity was mediated through the AP‐1 but not NF‐κB sites. The latter mediated the inhibitory effect of isoprenaline on OA‐induced MMP‐9 promoter activity. CONCLUSION AND IMPLICATIONS Okadaic acid induced MMP‐9 activity through p38 MAPK and was inhibited by isoprenaline via a pathway involving β‐arrestin 2, PP2A and an NF‐κB binding motif. These findings elucidate how phosphoprotein phosphatases and adrenoceptors may modulate tissue remodelling by affecting fibroblast function.