Mechanisms of angiotensin II-induced expression of B2kinin receptors

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Abstract
Although the primary roles of the kallikreinkinin system and the renin-angiotensin system are quite divergent, they are often intertwined under pathophysiological conditions. We examined the effect of ANG II on regulation of B2kinin receptors (B2KR) in vascular cells. Vascular smooth muscle cells (VSMC) were treated with ANG II in a concentration (10—9-10—6M)- and time (0–24 h)-dependent manner, and B2KR protein and mRNA levels were measured by Western blots and PCR, respectively. A threefold increase in B2KR protein levels was observed as early as 6 h, with a peak response at 10—7M. ANG II (10—7M) also increased B2KR mRNA levels twofold 4 h after stimulation. Actinomycin D suppressed the increase in B2KR mRNA and protein levels induced by ANG II. To elucidate the receptor subtype involved in mediating this regulation, VSMC were pretreated with losartan (AT1receptor antagonist) and/or PD-123319 (AT2receptor antagonist) at 10 μM for 30 min, followed by ANG II (10—7M) stimulation. Losartan completely blocked the ANG II-induced B2KR increase, whereas PD-123319 had no effect. In addition, expression of B2KR mRNA levels was decreased in AT1Areceptor knockout mice. Finally, to determine whether ANG II stimulates B2KR expression via activation of the MAPK pathway, VSMC were pretreated with an inhibitor of p42/p44mapk(PD-98059) and/or an inhibitor of p38mapk(SB-202190), followed by ANG II (10—7M) for 24 h. Selective inhibition of the p42/p44mapkpathway significantly blocked the ANG II-induced increase in B2KR expression. These findings demonstrate that ANG II regulates expression of B2KR in VSMC and provide a rationale for studying the interaction between ANG II and bradykinin in the pathogenesis of vascular dysfunction.