Molecular mechanism of TMEM16A regulation: role of CaMKII and PP1/PP2A.

This study explored the mechanism by which Ca ²⁺ -activated Cl ^- channels (CaCCs) encoded by the Tmem16a gene are regulated by calmodulin-dependent protein kinase II (CaMKII) and protein phosphatases 1 (PP1) and 2A (PP2A). Ca ²⁺ -activated Cl ^- currents ( I _ClCa ) were recorded from HEK-293 cells expressing mouse TMEM16A. I _ClCa were evoked using a pipette solution in which free Ca ²⁺ concentration was clamped to 500 nM, in the presence (5 mM) or absence of ATP. With 5 mM ATP, I _ClCa decayed to <50% of the initial current magnitude within 10 min after seal rupture. I _ClCa rundown seen with ATP-containing pipette solution was greatly diminished by omitting ATP. I _ClCa recorded after 20 min of cell dialysis with 0 ATP were more than twofold larger than those recorded with 5 mM ATP. Intracellular application of autocamtide-2-related inhibitory peptide (5 µM) or KN-93 (10 µM), two specific CaMKII inhibitors, produced a similar attenuation of TMEM16A rundown. In contrast, internal application of okadaic acid (30 nM) or cantharidin (100 nM), two nonselective PP1 and PP2A blockers, promoted the rundown of TMEM16A in cells dialyzed with 0 ATP. Mutating serine 528 of TMEM16A to an alanine led to a similar inhibition of TMEM16A rundown to that exerted by either one of the two CaMKII inhibitors tested, which was not observed for three putative CaMKII consensus sites for phosphorylation (T273, T622, and S730). Our results suggest that TMEM16A-mediated CaCCs are regulated by CaMKII and PP1/PP2A. Our data also suggest that serine 528 of TMEM16A is an important contributor to the regulation of I _ClCa by CaMKII.