Rapetti-Mauss R, O'Mahony F, Sepulveda FV, Urbach V, Harvey BJ

The cAMP-regulated potassium channel KCNQ1:KCNE3 plays an essential role in transepithelial Cl- secretion. K+ recycling across the basolateral membrane provides the driving force necessary to maintain apical Cl- secretion. The steroid hormone, 17β-estradiol (E2) produces a female specific anti-secretory response in rat distal colon through the inhibition of the KCNQ1:KCNE3 ...

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channel. It has previously been shown that rapid inhibition of the channel conductance resulted from E2-induced uncoupling of the KCNE3 regulatory subunit from the KCNQ1 channel pore complex. The purpose of this study was to determine the mechanism required for sustained inhibition of the channel function. We found that E2 plays a role in regulation of KCNQ1 cell membrane abundance by endocytosis. Ussing chamber experiments have shown that E2 inhibits both Cl- secretion and KCNQ1 current in a colonic cell line HT29cl.19A when cultured as a confluent epithelium. Following E2 treatment, KCNQ1 was retrieved from the plasma membrane by a clathrin mediated endocytosis which involved the association between KCNQ1 and the clathrin adaptor AP-2. Following endocytosis KCNQ1 was accumulated in early endosomes. KCNQ1 was recycled rather than degraded following E2-induced endocytosis by a biphasic mechanism involving Rab4 and Rab11. PKCδ and AMPK were rapidly phosphorylated in response to E2 on their activating phosphorylation sites ser643 and thr172, respectively (as previously shown). Both kinases are necessary for the E2-induced endocytosis since E2 failed to induce KCNQ1 internalisation following pre-treatment with specific inhibitors of both PKCδ and AMPK. The ubiquitin ligase Nedd4.2 binds KCNQ1 in response to E2 to induce channel internalization. This study shows for the first time the regulation of KCNQ1 trafficking by a hormone. In conclusion, we propose that internalisation of KCNQ1 is a sustained estrogen response in modulating intestinal Cl- secretion.

Date: Apr. 22, 2013

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