Visit our Expo - Redox and Inflammation signaling 2012

Session XVII : Cell signaling in health and disease Poster XVII, 61
Intracrine angiotensin II induces intracellular signaling in rabbit kidney convoluted
proximal tubule cells
Jia L. Zhuo, Oscar A. Carretero and Xiao C. Li.
Division of Hypertension and Vascular Research, Henry Ford Hospital, Detroit, MI
48202, USA. E-mail: jzhuo1@hfhs.org
Although the role of extracellular Ang II and the underlying mechanisms mediated by cell
surface AT1 receptors have been well studied in the kidney, whether intracellular Ang II
plays a physiological role in renal proximal tubule cells remains poorly understood. We tested
the hypothesis that extracellular Ang II is taken up by proximal tubule cells through AT1
receptor-mediated endocytosis, and that internalized Ang II induces intracellular calcium
mobilization, activates NF!B, and increases RNA transcription by stimulating cytoplasmic
and nuclear AT1 receptors. When proximal tubule cells were exposed to extracellular Ang II
(1 nM), intracellular Ang II levels were increased by 60% (161 ± 6 vs. 98 ± 5 pg/mg protein;
p < 0.001). The increases in intracellular Ang II were blocked by the endocytotic inhibitors
colchicine (10-6 M) (p < 0.01), phenylarsine oxide (PAO) (10-6 M), which inhibits tyrosine
phosphatase (p < 0.01), and the AT1 receptor blocker losartan (10-5 M) (p < 0.01), but not by
the AT2 receptor antagonist PD 123319 (10-5 M). To determine whether intracellular Ang II
has a physiological role, Ang II was microinjected into single proximal tubule cells (1 nM),
while cell surface AT1 receptors were blocked with extracellular losartan (10-5 M).
Intracellular Ang II induced a robust increase in intracellular calcium, which peaked at 15 to
30 s. When Ang II was microinjected together with losartan, the calcium responses were
blocked while concurrent microinjection of Ang II and PD 123319 had no effect. Moreover,
blockade of AT1 receptor-mediated Ang II internalization by colchicine or losartan inhibited
Ang II-induced activation of NF!B (p < 0.01). Ang II (1 nM) also significantly increased
RNA transcription in freshly isolated proximal tubule cell nuclei (p < 0.01) and the effect was
inhibited by losartan. We conclude that extracellular Ang II is internalized in proximal tubule
cells through AT1 receptor-mediated endocytosis and intracellular Ang II may exert
important intracrine effects by activating cytoplasmic and nuclear AT1 receptors. This work
is supported by grants from National Institutes of Health (RO1DK067299), American Heart
Association Greater Miwest Affiliate (0355551Z), and National Kidney Foundation of
Michigan.
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