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1 Division of Molecular Cardiology, Cardiovascular Research Institute, The Texas A&M University System Health Science Center, Temple, Texas, United States
* To whom correspondence should be addressed. E-mail: kumar{at}medicine.tamhsc.edu.
We recently reported intracrine effects of angiotensin II (Ang II) on cardiac myocyte growth and hypertrophy that were not inhibited by the AT1 receptor antagonist, losartan. To further determine the role of AT1 for intracrine effects, we studied the effect of intracellular Ang II (iAng II) on cell proliferation in native Chinese hamster ovary (CHO) cells and those stably transfected with AT1 receptor (CHO-AT1). CHO-AT1, but not CHO cells, showed enhanced proliferation following exposure to extracellular Ang II (eAng II). However, when transiently transfected with an iAng II expression vector, both cell types showed significantly enhanced proliferation, compared to those transfected with a scrambled peptide. Losartan blocked eAng II-induced cell proliferation; but, not that induced by iAng II. To further confirm these findings, CHO and CHO-AT1 cells were stably transfected for iAng II expression (CHO-iA and CHO-AT1-iA, respectively). Cells grown in serum-free medium were counted every 24 h, up to 72 h. CHO-iA and CHO-AT1-iA cells showed a steeper growth curve compared to CHO and CHO-AT1, respectively. These observations were confirmed by Wst-1 assay. The AT1 receptor antagonists, losartan, valsartan, telmisartan and candesartan, did not attenuate the faster growth rate of CHO-iA and CHO-AT1-iA cells. eAng II showed an additional growth effect in CHO-AT1-iA cells; which could be selectively blocked by losartan. These data demonstrate that intracrine Ang II can act independent of AT1 receptor and suggest novel intracellular mechanisms of action for Ang II.
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