Activated mutant of Galpha(12) enhances the hyperosmotic stress response of NIH3T3 cells.
Heterotrimeric G protein G12 stimulates diverse physiological responses including the activities of Na+/H+ exchangers and Jun kinases. We have observed that the expression of the constitutively activated, GTPase-deficient mutant of Galpha(12) (Galpha(12)QL) accelerates the hyperosmotic response of NIH3T3 cells as monitored by the hyperosmotic stress-stimulated activity of JNK1. The accelerated response appears to be partly due to the increased basal activity of JNK since cell lines-such as NIH3T3 cells expressing JNK1-in which JNK activity is elevated, show a similar response. NIH3T3 cells expressing Galpha(12)QL also display heightened sensitivity to hyperosmotic stress. This is in contrast to JNK1-NIH3T3 cells that failed to enhance sensitivity although they do exhibit an accelerated hyperosmotic response. Reasoning that the increased sensitivity seen in Galpha(12)QL cells is due to a signaling component other than JNK, the effect of dimethyamiloride, an inhibitor of Na+/H+ exchanger in this response, was assessed. Treatment of vector control NIH3T3 cells with 50 microM dimethylamiloride potently inhibited their hyperosmotic response whereas the response was only partially inhibited in Galpha(12)QL-NIH3T3 cells. These results, for the first time, identify that NHEs are upstream of the JNK module in the hyperosmotic stress-signaling pathway and that Galpha(12) can enhance this response by modulating either or both of these components namely, JNKs and NHEs in NIH3T3 cells.
Dermott
J M
JM
Fels Institute for Cancer Research and Molecular Biology, Temple University, School of Medicine, Philadelphia, PA 19140, USA.
Wadsworth
S J
SJ
van Rossum
G D
GD
Dhanasekaran
N
N
D016475:3T3 Cells; D000818:Animals; D020962:Heterotrimeric GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D048031:JNK Mitogen-Activated Protein Kinases; D051379:Mice; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D009154:Mutation; D009997:Osmotic Pressure
D048031:JNK Mitogen-Activated Protein Kinases; D020928:Mitogen-Activated Protein Kinases; D020962:Heterotrimeric GTP-Binding Proteins