The Na+/H+ antiporter cytoplasmic domain mediates growth factor signals and controls "H(+)-sensing".
The amiloride-sensitive Na+/H+ exchanger (NHE1 human isoform) is activated in response to diverse mitogenic and oncogenic signals presumably through phosphorylation. To get insight into the activating mechanism, a set of deletion mutants within the C-terminal cytoplasmic domain of NHE1 has been generated. These mutant forms expressed in antiporter-deficient fibroblasts revealed that deletion of the complete cytoplasmic domain (i) preserves amiloride-sensitive Na+/H+ exchange and activation by intracellular H+, (ii) reduces the affinity of the internal "H(+)-modifier site" in a manner mimicked by cellular ATP depletion, and (iii) abolishes growth factor-induced cytoplasmic alkalinization. We conclude that NHE1 can be separated into two distinct functional domains. One is an N-terminal transporter domain (T) that has all the features required to catalyze amiloride-sensitive Na+/H+ exchange with a built-in H(+)-modifier site. The other is a C-terminal cytoplasmic regulatory domain (R) that (i) determines the set point value of the exchanger and (ii) mediates growth factor signals by interacting with the "H(+)-sensor" in a phosphorylation-dependent manner.
Centre de Biochimie, Centre National de la Recherche Scientifique, Nice, France.
S
S
Wakabayashi
P
P
Fafournoux
C
C
Sardet
J
J
Pouysségur
D000818:Animals; D015152:Blotting, Northern; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D002872:Chromosome Deletion; D006224:Cricetinae; D003593:Cytoplasm / Q000378:metabolism; D004247:DNA / Q000235:genetics / Q000302:isolation & purification; D004988:Ethers, Cyclic / Q000494:pharmacology; D006133:Growth Substances / Q000494:pharmacology*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D019319:Okadaic Acid; D010703:Phorbol Esters / Q000494:pharmacology; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology; D012313:RNA / Q000235:genetics / Q000302:isolation & purification; D015398:Signal Transduction; D012964:Sodium / Q000378:metabolism*; D017923:Sodium-Hydrogen Exchangers; D014162:Transfection
D002352:Carrier Proteins; D004988:Ethers, Cyclic; D006133:Growth Substances; D010703:Phorbol Esters; D010982:Platelet-Derived Growth Factor; D017923:Sodium-Hydrogen Exchangers; D019319:Okadaic Acid; D012313:RNA; D004247:DNA; D012964:Sodium