Regulation of intracellular pH by p90Rsk-dependent activation of an Na(+)/H(+) exchanger in starfish oocytes.

摘要: Starfish oocytes arrest at metaphase of the first meiotic division (MI arrest) in ovary and resume meiosis after spawning into seawater. MI is maintained by lower intracellular pH (pHi) release from cellular alkalization. To elucidate pHi regulation oocytes, we cloned starfish (Asterina pectinifera) Na+/H+ exchanger 3 (ApNHE3) expressed plasma membrane oocytes. The cytoplasmic domain ApNHE3 contains p90 ribosomal S6 kinase (p90Rsk) phosphorylation sites, injection a constitutively active p90Rsk upstream regulator Mos to immature stimulated an increase pHi. This was blocked 5-(N-ethyl-N-isopropyl)-amiloride, NHE inhibitor, SL0101, specific Rsk inhibitor. MAPK (MEK) inhibitor U0126 Mos-induced, but not p90Rsk-induced, increase, suggesting that Mos-MEK-MAPK-p90Rsk pathway promotes activation. In cell-free extract, phosphorylates Ser-590, -606, -673. When p90Rsk-dependent dominant-negative C-terminal fragment, or neutralizing antibody, p90Rsk-induced suppressed However, up-regulated via phosphatidylinositol 3-kinase before activation state until spawning, unlikely be primary regulatory mechanism involved exit. After completed, unfertilized eggs maintain their elevated (∼7.4) onset apoptosis. We suggest p90Rsk/ApNHE3-dependent elevation increases fertilization success delaying apoptosis initiation.