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A more recent version of this article appeared on March 1, 2003
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Submitted on July 24, 2002
Revised on October 30, 2002
Accepted on November 22, 2002
1 Institute for Cell Dynamics, University of Science and Technology of China, Hefei, CHINA 230027; and Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720, USA
2 Institute for Cell Dynamics, University of Science and Technology of China, Hefei, CHINA 230027
3 Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720, USA
* Corresponding author. E-mail address: xbyao{at}uclink4.berkeley.edu.
Actin cytoskeleton plays an important role in the establishment of epithelial cell polarity. Cdc42, a member of Rho GTPase family, modulates actin dynamics via its regulators, such as IQGAP proteins. Gastric parietal cells are polarized epithelial cells in which regulated acid secretion occurs in the apical membrane upon stimulation. We have previously shown that actin isoforms are polarized to different membrane domains and that the integrity of the actin cytoskeleton is essential for acid secretion. Here we show that Cdc42 is preferentially distributed to the apical membrane of gastric parietal cells. In addition, we revealed that two Cdc42 regulators, IQGAP1 and IQGAP2, are present in gastric parietal cells. Interestingly, IQGAP2 is polarized to the apical membrane of the parietal cells while IQGAP1 is mainly distributed to the basolateral membrane. An IQGAP peptide that competes with full-length IQGAP proteins for Cdc42-binding in vitro also inhibits acid secretion in SLO-permeabilized gastric glands. Furthermore, this peptide disrupts the association of IQGAP and Cdc42 with the apical actin cytoskeleton and prevents the apical membrane remodeling upon stimulation. We propose that IQGAP2 forms a link which associates Cdc42 with the apical cytoskeleton and thus allows for activation of polarized secretion in gastric parietal cells.
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