Galpha12 differentially regulates Na+-H+ exchanger isoforms.
Activation of several GTPases stimulates Na+-H+ exchange, resulting in an increased efflux of intracellular H+. These GTPases include alpha subunits of the heterotrimeric G proteins Gq and G13, as well as the low molecular weight GTP-binding proteins Ras, Cdc42, and Rho (Hooley, R., Yu, C.-Y., Simon, M., and Barber, D. L. (1996) J. Biol. Chem. 271, 6152-6158). GTPases coupled to the inhibition of Na+-H+ exchange, however, have not been identified. Several neurotransmitters, including somatostatin and dopamine, inhibit Na+-H+ exchange through a guanine-nucleotide-dependent mechanism, suggesting the involvement of a GTPase. In this study we determined that mutational activation of the alpha subunit of G12 inhibits the ubiquitously expressed Na+-H+ exchanger isoform, NHE1. Transient expression of mutationally activated Galpha12 inhibited serum- and Galpha13-stimulated NHE1 activity in HEK293 cells and CCL39 fibroblasts. In addition, in NHE-deficient AP1 cells stably expressing specific NHE isoforms, mutationally activated Galpha12 inhibited NHE1 activity but stimulated activities of the Na+-H+ exchanger (NHE) isoforms NHE2 and NHE3. In contrast, mutationally activated Galpha13, another member of the Galpha12/13 family, stimulated all three NHE isoforms. Although previous studies have identified a parallel action of Galpha12 and Galpha13 in regulating MAP (mitogen-activated protein) kinases and cell growth, these GTPases have opposing effects on NHE1 activity.
Lin
X
X
Department of Stomatology, University of California, San Francisco, California 94143, USA.
Voyno-Yasenetskaya
T A
TA
Hooley
R
R
Lin
C Y
CY
Orlowski
J
J
Barber
D L
DL
D000818:Animals; D019556:COS Cells; D002460:Cell Line; D004247:DNA / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004587:Electrophoresis, Agar Gel; D051960:GTP-Binding Protein alpha Subunit, Gi2; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D019204:GTP-Binding Proteins / Q000502:physiology*; D006146:Guanidines / Q000494:pharmacology; D006801:Humans; D007536:Isomerism; D016133:Polymerase Chain Reaction; D011518:Proto-Oncogene Proteins / Q000502:physiology*; D051381:Rats; D017923:Sodium-Hydrogen Exchangers / Q000096:biosynthesis* / Q000187:drug effects / Q000235:genetics; D013450:Sulfones / Q000494:pharmacology
D006146:Guanidines; D011518:Proto-Oncogene Proteins; D017923:Sodium-Hydrogen Exchangers; D013450:Sulfones; C074107:3-methylsulfonyl-4-piperidinobenzoyl guanidine; D004247:DNA; D019204:GTP-Binding Proteins; C498015:GNAI2 protein, human; D051960:GTP-Binding Protein alpha Subunit, Gi2; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; C498017:Gnai2 protein, rat