Critical role of protein kinase C α and calcium in growth factor induced activation of the Na+/H+ exchanger NHE1

The ubiquitously expressed Na+/H+ exchanger (NHE1) plays an important role in the regulation of the intracellular pH. Induction of NHE activity by phorbol esters and inhibition of growth factor-mediated stimulation of the NHE by protein kinase C (PKC) inhibitors suggest an implication of PKCs in the regulation of the NHE. Expression of PKC isotype-specific dominant negative and constitutively active mutants or downregulation of PKC by isotype-specific antisense oligonucleotides revealed that stimulation by epidermal growth factor (EGF) or phorbol ester of the NHE in NIH3T3 cells is a PKCα-specific effect. Elevation of cytoplasmic calcium by a Ca2+ ionophore or thapsigargin causes a growth factor-independent stimulation of the NHE predominantly mediated by calcium/calmodulin kinase II. It is concluded that in NIH3T3 cells overexpressing the EGF receptor (EGFR6 cells), EGF requires cPKCα for the activation of the NHE, while calcium/calmodulin-dependent kinases are essential in thapsigargin induced stimulation of the NHE.