Angiotensin II Promotes K7.4 Channels Degradation Through Reduced Interaction With HSP90 (Heat Shock Protein 90).

Voltage-gated K7.4 channels have been implicated in vascular smooth muscle cells' activity because they modulate basal arterial contractility, mediate responses to endogenous vasorelaxants, and are downregulated 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 K7.4. Western blot and quantitative polymerase chain reaction revealed that in whole rat mesenteric artery, Ang II incubation for 1 to 7 hours decreased K7.4 protein expression without reducing transcript levels. Moreover, Ang II decreased XE991 (K7)-sensitive currents and attenuated membrane potential hyperpolarization and relaxation induced by the K7 activator ML213. Ang II also reduced K7.4 staining at the plasma membrane of vascular smooth muscle cells. Proteasome inhibition with MG132 prevented Ang II-induced decrease of K7.4 levels and counteracted the functional impairment of ML213-induced relaxation in myography experiments. Proximity ligation assays showed that Ang II impaired the interaction of K7.4 with the molecular chaperone HSP90 (heat shock protein 90), enhanced the interaction of K7.4 with the E3 ubiquitin ligase CHIP (C terminus of Hsp70-interacting protein), and increased K7.4 ubiquitination. Similar alterations were found in mesenteric vascular smooth muscle cells isolated from Ang II-infused mice. The effect of Ang II was emulated by 17-AAG (17-demethoxy-17-(2-propenylamino) geldanamycin) that inhibits HSP90 interactions with client proteins. These results show that Ang II downregulates K7.4 by altering protein stability through a decrease of its interaction with HSP90. This leads to the recruitment of CHIP and K7.4 ubiquitination and degradation via the proteasome.