title: The p42/p44 mitogen-activated protein kinase cascade is determinant in mediating activation of the Na+/H+ exchanger (NHE1 isoform) in response to growth factors.
abstract: The ubiquitously expressed Na+/H+ exchanger NHE1 is the target of multiple signaling pathways, including those activated by tyrosine kinase receptors, G protein-coupled receptors, and integrins. The intracellular pathways leading to activation of NHE1 are poorly understood. To gain more insight into these activation pathways, we examined the role of mitogen-activated protein kinases (MAPKs) as potential mediators of NHE1 activation by extracellular stimuli such as growth factors and hyperosmotic stress. Whereas p44 MAPK does not appear to phosphorylate NHE1 in vitro, we found that inhibition of the p42/p44 MAPK signaling by expression of a dominant negative form of p44 MAPK, by expression of the MAP kinase phosphatase MKP-1, or by inhibition of MAPK kinase 1 (MKK1) with the PD 98059 compound reduced by 50-60% NHE1 activation in response to growth factors. This inhibitory effect also was observed in C-terminal NHE1 deletion mutants in which the major phosphorylation sites have been deleted. Furthermore, the use of a CCL39-derived cell line expressing an estradiol-regulated form of oncogenic Raf-1 (CCL39-deltaRaf-1:ER) revealed that the exclusive activation of the Raf --> MKK1 --> p42/p44 MAPK cascade was capable of inducing NHE1 activation to the same extent as potent growth factors like thrombin. Together, our findings demonstrate that the p42/p44 MAPK cascade plays a predominant role in the regulation of NHE1 by growth factors, an action that is mediated via accessory proteins that remain to be identified. In contrast, we found no evidence in favor of the contribution of any MAPK, p42/p44, p38 MAPKs, and Jun kinase, in NHE1 activation by osmotic stress.
authors.affiliation: Centre de Biochimie, CNRS, Université de Nice, France. Bianchini@unice.fr
authors.forename: L
authors.initials: L
authors.lastname: Bianchini
authors.forename: G
authors.initials: G
authors.lastname: L'Allemain
authors.forename: J
authors.initials: J
authors.lastname: Pouysségur
mesh_terms: D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D002460:Cell Line; D006224:Cricetinae; D003412:Cricetulus; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004958:Estradiol / Q000494:pharmacology; D005419:Flavonoids / Q000494:pharmacology; D006133:Growth Substances / Q000494:pharmacology*; D007328:Insulin / Q000494:pharmacology; D048031:JNK Mitogen-Activated Protein Kinases; D048369:MAP Kinase Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020929:Mitogen-Activated Protein Kinase Kinases; D020928:Mitogen-Activated Protein Kinases; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D019908:Proto-Oncogene Proteins c-raf; D017384:Sequence Deletion; D015398:Signal Transduction; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism*; D013012:Sorbitol / Q000494:pharmacology; D013329:Structure-Activity Relationship; D013917:Thrombin / Q000494:pharmacology; D014882:Water-Electrolyte Balance; D048051:p38 Mitogen-Activated Protein Kinases
chemical_list: D004791:Enzyme Inhibitors; D005419:Flavonoids; D006133:Growth Substances; D007328:Insulin; D011518:Proto-Oncogene Proteins; D017923:Sodium-Hydrogen Exchangers; C069139:growth factor-activatable Na-H exchanger NHE-1; D004958:Estradiol; D013012:Sorbitol; D011505:Protein-Tyrosine Kinases; D017346:Protein Serine-Threonine Kinases; D019908:Proto-Oncogene Proteins c-raf; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D048031:JNK Mitogen-Activated Protein Kinases; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D048369:MAP Kinase Kinase 1; D020929:Mitogen-Activated Protein Kinase Kinases; D013917:Thrombin; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one