Signaling and growth responses of llc-pk1/cl4 cells transfected with the rabbit at1 angiotensin ii receptor. Burns, Kevin D., and Raymond C. Harris. Departments of Medicine and Physiology, University of Ottawa, and Ottawa General Hospital, Ottawa, Ontario, Canada, K1H 8M5, and the Department of Medicine, Vanderbilt University, Nashville, TN, 37232.
APStracts 2:0027C, 1995.
Angiotensin II receptors of the AT1 subtype are present on the apical and basolateral membranes of renal proximal tubule cells. Cells of the proximal tubule-like cell line, LLC-PK1/Cl4, were transfected with an expression plasmid containing cDNA encoding the rabbit AT1 angiotensin II receptor. In transfected cells, specific binding of [125I]-angiotensin II was detected on both apical and basolateral membranes; wild type LLC-PK1/Cl4 cells did not express angiotensin II receptors. In transfected cells, apical or basolateral angiotensin II increased both S6 kinase activity and incorporation of [3H]-leucine. In cells pretreated with pertussis toxin, the stimulatory effect of apical or basolateral angiotensin II on [3H]-leucine incorporation was abolished. In contrast, angiotensin II did not affect mitogenesis, determined by [3H]-thymidine incorporation. Apical or basolateral angiotensin II (10-6 M) stimulated phosphoinositide turnover, by 13.4 +/- 4.4% (n=8) and 16.3 +/- 4.2% (n=9), respectively. The activity of protein kinase C, determined by phosphorylation of a specific protein kinase C peptide substrate, was also stimulated by angiotensin II in transfected cells. Apical or basolateral angiotensin II had no significant effect on cellular cAMP levels. In permeabilized transfected cells, apical angiotensin II (10-6 M) inhibited the phosphorylation of a specific peptide substrate of protein kinase A; lower apical concentrations or basolateral angiotensin II were without significant effect. These results indicate that AT1 angiotensin II receptors sort to both apical and basolateral membranes in renal epithelial cells, and are coupled to activation of phospholipase C. Angiotensin II stimulates protein synthesis by binding to either apical or basolateral receptors; this effect requires coupling to G proteins and may be mediated by activation of S6 kinase. Since high concentrations of angiotensin II exist in proximal tubule, binding to apical and basolateral receptors may regulate proximal tubule cell growth under physiological conditions. 

Received 21 July 1994; accepted in final form 15 November 1994
APS Manuscript Number C0418-4.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1994 The American Physiological Society.
Published in APStracts on 27 February 1995.