Apoptosis-induced alkalinization by the Na(+)/H(+) exchanger isoform 1 is mediated through phosphorylation of amino acids Ser726 and Ser729

    Authors

    A. L. Grenier; K. Abu-Ihweij; G. Zhang; S. M. Ruppert; R. Boohaker; E. R. Slepkov; K. Pridemore; J. J. Ren; L. Fliegel;A. R. Khaled

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    Abbreviated Journal Title

    Am. J. Physiol.-Cell Physiol.

    Keywords

    pH; sodium hydrogen exchanger; mitogen-activated protein kinase; NA-H EXCHANGE; INTRACELLULAR PH; MITOCHONDRIAL-MEMBRANE; DEPENDENT; ACTIVATION; BAX TRANSLOCATION; NHE1; KINASE; PROTEIN; CELLS; INCREASE; Cell Biology; Physiology

    Abstract

    Apoptosis is a complex process essential for normal tissue development and cellular homeostasis. While biochemical events that occur late in the apoptotic process are better characterized, early physiological changes that initiate the progression of cell death remain poorly understood. Previously, we observed that lymphocytes, undergoing apoptosis in response to growth factor withdrawal, experienced a rapid and transient rise in cytosolic pH. We found that the protein responsible was the pH-regulating, plasma membrane protein Na(+)/H(+) exchanger isoform 1 (NHE1), and that its activity was impeded by inhibition of the stress-activated kinase, p38 MAP kinase. In the current study, we examined how NHE1 is activated during apoptosis. We identified the phosphorylation sites on NHE1 that regulate its alkalinizing activity in response to a cell death stimulus. Performing targeted mutagenesis, we observed that substitution of Ser726 and Ser729 for alanines produced a mutant form of NHE1 that did not alkalinize in response to an apoptotic stimulus, and expression of which protected cells from serum withdrawal-induced death. In contrast, substitution of Ser726 and Ser729 for glutamic acids raised the basal pH and induced susceptibility to death. Analysis of serine phosphorylation showed that phosphorylation of NHE1 during apoptosis decreased upon mutation of Ser726 and Ser729. Our findings thus confirm a necessary function for NHE1 during apoptosis and reveal the critical regulatory sites that when phosphorylated mediate the alkalinizing activity of NHE1 in the early stages of a cell death response.

    Journal Title

    American Journal of Physiology-Cell Physiology

    Volume

    295

    Issue/Number

    4

    Publication Date

    1-1-2008

    Document Type

    Article

    Language

    English

    First Page

    C883

    Last Page

    C896

    WOS Identifier

    WOS:000259925800004

    ISSN

    0363-6143

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