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Articles in PresS, published online ahead of print July 24, 2002
Am J Physiol Cell Physiol, 10.1152/ajpcell.00473.2001
Submitted on October 4, 2001
Accepted on July 17, 2002
1 Medicine, University of Illinois at Chicago, Chicago, IL, USA
2 Research & Development, Chicago VA: Westside Division, Chicago, IL, USA
3 Medicine, University of Illinois at Chicago, Chicago, IL, USA; Research & Development, Chicago VA: Westside Division, Chicago, IL, USA
* To whom correspondence should be addressed. E-mail: pkdudeja{at}uic.edu.
The present studies were undertaken to examine the possible regulation of apical membrane Cl-/OH- exchanger in Caco2 cells by signal transduction mechanisms involving PKC. Utilizing post-confluent transformed human intestinal epithelial cell line, Caco-2, the effect of phorbol 12-myristate 13-acetate (PMA), an in vitro PKC agonist was assessed on the OH- gradient-driven DIDS-sensitive 36Cl uptake. The results demonstrated that PMA decreased the apical Cl-/OH- exchanger activity, which involved the activation of PKC mediated by PI3-kinase. The data consistent with these conclusions are as follows: i) short term treatment of cells for 1-2 h with PMA (100 nM) significantly decreased (~50%) Cl-/OH- exchange activity compared to control (4
-PMA). No change in Cl-/OH- exchange activity was observed at 15 and 30 min time periods. Down regulation of PKC by PMA (1µM) after 24 h also did not alter Cl-/OH- exchange activity; ii) pretreatment of cells with specific PKC inhibitors chelerytherine chloride (2 µM), calphostin (200 nM) and GF 109203X (50 nM) completely blocked the inhibition by PMA; iii) specific inhibitors for PKC RO 318220 (100 nM) but not for PKC, GO 6976 (5 nM) significantly blocked the PMA-mediated inhibition of Cl-/OH- exchange activity in Caco-2 cells; iv) specific PI3-kinase inhibitors wortmannin (100 nM) and LY 294002 (5 µM) significantly attenuated the inhibitory effect of PMA on Cl-/OH- exchange activity; v) PI3-kinase activators, IRS-1 peptide (0.1-10 µM) or PI (3,4,5)P3 (10 µM) mimicked the effects of PMA on the Cl-/OH- exchange activity in Caco-2 cells; vi) in contrast to the effect of PMA on Cl-/OH- exchange, no effect of PMA (100 nM, 1h) on SO4--/OH- exchange process was observed in Caco-2 cells under similar conditions. These findings provide the first evidence for protein kinase C mediated inhibition of Cl-/OH- exchange activity in Caco-2 cells and indicate the involvement of the PI3-kinase mediated pathways in the regulation of chloride absorption in intestinal epithelial cells.
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