The Na⁺/H⁺ Exchanger, NHE1, Differentially Regulates Mitogen-Activated Protein Kinase Subfamilies after Osmotic Shrinkage in Ehrlich Lettre Ascites Cells (original) (raw)

2007, Cellular Physiology and Biochemistry

Osmotic stress modulates mitogen activated protein kinase (MAPK) activities, leading to altered gene transcription and cell death/survival balance, however, the mechanisms involved are incompletely elucidated. Here, we show, using a combination of biochemical and molecular biology approaches, that three MAPKs exhibit unique interrelationships with the Na + /H + exchanger, NHE1, after osmotic cell shrinkage: Extracellular Signal Regulated Kinase (ERK1/2) is inhibited in an NHE1-dependent, pH i -independent manner, c-Jun N-terminal kinase (JNK1/2) is stimulated, in part through NHE1-mediated intracellular alkalinization, and p38 MAPK is activated in an NHE1independent manner, and contributes to NHE1 activation and ERK inhibition. Shrinkage-induced ERK1/2 inhibition was attenuated in Ehrlich Lettre Ascites cells by NHE1 inhibitors (EIPA, cariporide) or removal of extracellular Na + , and mimicked by human (h) NHE1 expression in cells lacking endogenous NHE1 activity. The effect of NHE1 on ERK1/2 was pH i -independent and upstream of MEK1/2. Shrinkageactivation of JNK1/2 was attenuated by EIPA, augmented by hNHE1 expression, and abolished in the presence of HCO 3 -. Basal JNK activity was augmented at alkaline pH i . Shrinkage-activation of p38 MAPK was NHE1-independent, and p38 MAPK inhibition (SB203580) attenuated NHE1 activation and ERK1/2 inhibition. Long-term shrinkage elicited caspase-3 activation and a loss of cell viability, which was augmented by ERK1/2 or JNK1/2 inhibition, and attenuated by p38 MAPK inhibition.