Submitted on June 26, 2007
Accepted on August 6, 2007
RhoA Required for Acid-Induced Stress Fiber Formation and Trafficking and Activation of NHE3
Xiaojing Yang1, Hai-Chang Huang2, Helen Yin3, Robert J Alpern2, and Patricia Preisig4*
1 Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas, United States
2 Medicine, Yale University, New Haven, Connecticut, United States
3 Physiology, University of Texas Southwestern Medical Center, Dallas, Texas, United States
4 Internal Medicine, Yale University, New Haven, Connecticut, United States
* To whom correspondence should be addressed. E-mail: patricia.preisig{at}yale.edu.
Exposure to an acid load increases apical membrane NHE3 activity, a process that involves exocytic trafficking of the transporter to the apical membrane. We have previously shown that an intact microfilament structure is required for this exocytic process. The present studies demonstrate that acid-induced stress fiber formation is required for stimulation of NHE3 activity. Formation of stress fibers is associated with acid-induced tyrosine phosphorylation and increases in protein abundance of two focal adhesion proteins, p125FAK and paxillin. The Rho kinase inhibitor Y27632 completely blocks acid-induced stress fiber formation, and the increases in apical membrane NHE3 abundance and activity, but has no effect on acid-induced tyrosine phosphorylation of p125FAK or paxillin. Herbimycin A completely blocks acid-induced tyrosine phosphorylation of p125FAK and paxillin, but only partially blocks stress fiber formation and NHE3 activation. These studies demonstrate that Rho kinase mediates acid-induced stress fiber formation, which is required for NHE3 exocytosis, and increases in NHE3 activity. Acid-induced tyrosine phosphorylation of the focal adhesion proteins p125FAK and paxillin is not Rho kinase-dependent. Thus, these two acid-mediated effects are associated, yet independent processes.
