Inhibition of the MEK1/ERK pathway reduces arachidonic acid release independently of cPLA(2) phosphorylation and translocation

BACKGROUND: The 85-kDa cytosolic phospholipase A(2) (cPLA(2)) mediates arachidonic acid (AA) release in MDCK cells. Although calcium and mitogen-activated protein kinases regulate cPLA(2), the correlation of cPLA(2) translocation and phosphorylation with MAPK activation and AA release is unclear. RESULTS: MEK1 inhibition by U0126 inhibited AA release in response to ATP and ionomycin. This directly correlated with inhibition of ERK activation but not with phosphorylation of cPLA(2) on Ser(505), which was only partially inhibited by ERK inhibition. Inhibition of AA release by U0126 was still observed when stoichiometric phosphorylation of cPLA(2) on Ser(505) was maintained by activating p38 with anisomycin. Translocation kinetics of wild-type cPLA(2) and cPLA(2) containing S505A or S727A mutations to Golgi were similar in response to ATP and ionomycin and were not affected by U0126. CONCLUSIONS: These results suggest that the ability of cPLA(2) to hydrolyze membrane phospholipid is reduced by inhibition of the MEK1/ERK pathway and that the reduction in activity is independent of cPLA(2) phosphorylation and translocation to membrane. The results also demonstrate that cPLA(2) mutated at the phosphorylation sites Ser(505) and Ser(727) translocated with similar kinetic as wild-type cPLA(2).