Activation of Na+-H+ Exchange Is Necessary for RhoA-induced Stress Fiber Formation

doi:10.1074/jbc.271.37.22281

Activation of Na⁺-H⁺ Exchange Is Necessary for RhoA-induced Stress Fiber Formation*

From the Departments of ^‡ Stomatology and
^¶ Surgery, University of California, San Francisco, California 94143 and
^§ Onyx Pharmaceuticals, Richmond, California 94806

^∥ Established Investigator for the American Heart Association. To whom correspondence should be addressed:
Box 0512, University of California, San Francisco, CA 94143.
Tel.: 415-476-3764; Fax: 415-502-7338; E-mail: barber{at}itsa.ucsf.edu.

Abstract

The ubiquitously expressed Na⁺-H⁺ exchanger isoform, NHE1, functions in regulating intracellular pH and cell volume. We recently determined that the GTPase Gα13 stimulates NHE1 activity through a RhoA-dependent mechanism (Hooley, R., Yu, C.-Y., Symons, M., and Barber, D. L. (1996) J. Biol. Chem. 271, 6152-6158). RhoA belongs to the Ras superfamily of GTPases and is a key regulator of actin stress fiber formation. We therefore investigated the relationship between RhoA, NHE1 activity, and the regulation of stress fiber assembly. Using two independent approaches, pharmacological inhibition of NHE1 and NHE1-deficient cells, we determined that the induction of stress fibers by lysophosphatidic acid and RhoA is dependent on increased NHE1 activity. These results indicate that stimulation of NHE1 acts downstream of RhoA in a pathway that controls stress fiber formation.

Footnotes

↵* This work was supported in part by National Institutes of Health Grants GM 47413 and DK 40259 (to D. L. B.). The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
↵¹ The abbreviations used are:

PI 5-kinase

phosphatidylinositol 4-phosphate 5-kinase

PBS

phosphate-buffered saline

DME

Dulbecco's modified Eagle's medium

BCECF

2,7-biscarboxyethyl-5(6)-carboxyfluorescein

LPA

lysophosphatidic acid

NHE1

ubiquitous Na⁺-H⁺ exchanger

pH_i

intracellular pH.
- Received May 20, 1996.
- Revision received June 25, 1996.