Abstract

SB203580 [4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)1H-imidazole] is widely used as a specific inhibitor of p38 mitogen-activated protein kinase (MAPK). Here we report that SB203580, which blocked p38 kinase activation elicited by anisomycin, increased the phosphorylation and activity of cytosolic phospholipase A₂ (cPLA₂) and arachidonic acid (AA) release in quiescent vascular smooth muscle cells from rabbit aortae. SB203580 also increased the activity of calcium (Ca²⁺)/camodulin-dependent kinase II (CaMKII) and ERK1/2 MAPK. The increase in CaMKII activity and cPLA₂phosphorylation caused by SB203580 was attenuated by CaMKII inhibitor KN-93, indicating involvement of CaMKII in cPLA₂phosphorylation by this compound. Since KN-93 also inhibited SB203580-induced ERK1/2 activation, it appears that ERK1/2 activation is also mediated by CaMKII. SB203580-induced cPLA₂phosphorylation was inhibited by depletion of Ca²⁺ from the medium, by the voltage-operated Ca²⁺ channel blocker nifedipine, and by the calmodulin inhibitor W-7. cPLA₂translocation from cytoplasm to the nuclear envelope caused by SB203580 was also inhibited in the absence of extracellular Ca²⁺. Other p38 kinase inhibitors, SB202190 and PD169316, failed to alter CaMKII, ERK1/2, and cPLA₂ activity or cPLA₂translocation to the nuclear envelope. These data suggest that SB203580 not only inhibits p38 kinase activity but also increases Ca²⁺ influx through voltage-sensitive Ca²⁺channels, which promotes cPLA₂ translocation to the nuclear envelope, and by interacting with calmodulin, activates CaMKII and cPLA₂ and releases AA.