Angiotensin II Promotes K

Voltage gated Kv7.4 channels have been implicated in vascular smooth muscle cells (VSMCs) activity as they modulate basal arterial contractility, mediate responses to endogenous vasorelaxants, and are down-regulated in several arterial beds in different models of hypertension. Angiotensin II (Ang II) is a key player in hypertension that affects the expression of several classes of ion channels. In this study we evaluated the effects of Ang II on the expression and function of vascular K(v)7.4. Western blot and quantitative PCR revealed that in whole rat mesenteric artery Ang II incubation for 1-7h decreased K(v)7.4 protein expression without reducing transcript levels. Moreover, Ang II decreased XE991 (K(v)7) –sensitive currents, and attenuated membrane potential hyperpolarization and relaxation induced by the K(v)7 activator ML213. Ang II also reduced K(v)7.4 staining at the plasma membrane of VSMCs. Proteasome inhibition with MG132 prevented Ang II-induced decrease of K(v)7.4 levels, and counteracted the functional impairment of ML213-induced relaxation in myography experiments. Proximity Ligation Assays showed that Ang II impaired the interaction of K(v)7.4 with the molecular chaperone HSP90, enhanced the interaction of K(v)7.4 with the E3 ubiquitin ligase CHIP, and increased K(v)7.4 ubiquitination. Similar alterations were found in mesenteric VSMCs isolated from Ang II-infused mice. The effect of Ang II was emulated by 17-AAG that inhibits HSP90 interactions with client proteins. These results show that Ang II downregulates K(v)7.4 by altering protein stability through a decrease of its interaction with HSP90. This leads to the recruitment of CHIP and K(v)7.4 ubiquitination and degradation via the proteasome.