Role of MMP-2 in oxidant-mediated regulation of Ca²⁺ uptake in microsomes of bovine pulmonary artery smooth muscle

Abstract

Treatment of bovine pulmonary artery smooth muscle microsomes with tert-butylhydroperoxide (t-buOOH) (300 µM) markedly stimulated matrix metalloproteinase-2 (MMP-2) activity and enhanced Ca²⁺-ATPase activity and ATP-dependent Ca²⁺ uptake. Pre-treatment with vit. E (1 mM) and tissue inhibitor of metalloproteinase-2 (TIMP-2) (50 µg/ml) prevented t-buOOH-induced stimulation of MMP-2 activity, Ca²⁺-ATPase activity and ATP-dependent Ca²⁺ uptake. In contrast, Na⁺-dependent Ca²⁺ uptake was inhibited by t-buOOH and the inhibition was reversed by vit. E (1 mM) and TIMP-2 (50 µg/ml). However, t-buOOH-triggered changes in MMP-2 activity, and ATP- and Na+-dependent Ca²⁺ uptake were not reversed upon pre-treatment of the microsomes with a low concentration of 5 µg/ml of TIMP-2, which on the contrary reversed MMP-2 (1 µg/ml)-mediated alteration on these parameters. The inhibition of Na+-dependent Ca²⁺ uptake by MMP-2 under t-buOOH treatment overpowered the stimulation of ATP-dependent Ca²⁺ uptake in the microsomes. Combined treatment of the microsomes with low doses of MMP-2 (0.5 µg/ml) and t-buOOH (100 mM) augmented Ca²⁺-ATPase activity and ATP-dependent Ca²⁺ uptake, but inhibited Na+-dependent Ca²⁺ uptake, compared to that elicited by either MMP-2 (0.5 µg/ml) or t-buOOH (100 µM). Pre-treatment with TIMP-2 (50 µg/ml) reversed the effects of MMP-2 (0.5 µg/ml) and/or t-buOOH (100 mM). Although pre-treatment with 5 µg/ml of TIMP-2 reversed the effects produced by MMP-2 (0.5 µg/ml), but it did not inhibit the responses elicited by t-buOOH (300 µM) or t-buOOH (100 mM) plus MMP-2 (0.5 mg/ml) in the microsomes. Treatment with TIMP-2 (5 mg/ml) inhibited MMP-2 (1 mg/ml) activity (assessed by [14C]-gelatin degradation), whereas treatment of t-buOOH (300 µM) with TIMP-2 (5 µg/ml) abolished the inhibitory effect of TIMP-2 (5 µg/ml) on MMP-2 (1 µg/ml) activity (assessed by [14C]-gelatin degradation). Overall, these results suggested that t-buOOH inactivated TIMP-2, the ambient inhibitor of MMP-2, leading to activation of the ambient proteinase, MMP-2 which subsequently stimulated Ca²⁺-ATPase activity and ATP-dependent Ca²⁺ uptake, but inhibited Na⁺-dependent Ca²⁺ uptake, resulting in a marked decrease in Ca²⁺ uptake in the microsomes.