Details

Autor(en) / Beteiligte

• Yang, Tingting
• Hendrickson, Wayne A.
• Colecraft, Henry M.

Titel

Preassociated apocalmodulin mediates Ca²⁺-dependent sensitization of activation and inactivation of TMEM16A/16B Ca²⁺-gated Cl⁻ channels

Ist Teil von

• Proceedings of the National Academy of Sciences - PNAS, 2014-12, Vol.111 (51), p.18213-18218

Ort / Verlag

United States: National Academy of Sciences

Erscheinungsjahr

2014

Quelle

MEDLINE

Beschreibungen/Notizen

• Ca ²⁺-activated chloride currents carried via transmembrane proteins TMEM16A and TMEM16B regulate diverse processes including mucus secretion, neuronal excitability, smooth muscle contraction, olfactory signal transduction, and cell proliferation. Understanding how TMEM16A/16B are regulated by Ca ²⁺ is critical for defining their (patho)/physiological roles and for rationally targeting them therapeutically. Here, using a bioengineering approach—channel inactivation induced by membrane-tethering of an associated protein (ChIMP)—we discovered that Ca ²⁺-free calmodulin (apoCaM) is preassociated with TMEM16A/16B channel complexes. The resident apoCaM mediates two distinct Ca ²⁺-dependent effects on TMEM16A, as revealed by expression of dominant-negative CaM ₁₂₃₄. These effects are Ca ²⁺-dependent sensitization of activation (CDSA) and Ca ²⁺-dependent inactivation (CDI). CDI and CDSA are independently mediated by the N and C lobes of CaM, respectively. TMEM16A alternative splicing provides a mechanism for tuning apoCaM effects. Channels lacking splice segment b selectively lost CDI, and segment a is necessary for apoCaM preassociation with TMEM16A. The results reveal multidimensional regulation of TMEM16A/16B by preassociated apoCaM and introduce ChIMP as a versatile tool to probe the macromolecular complex and function of Ca ²⁺-activated chloride channels. Significance Calcium-activated chloride channels (CaCCs) encoded by transmembrane members 16A and 16B (TMEM16A/16B) are vital for physiological functions ranging from smooth muscle contraction to cell proliferation and are important therapeutic targets. Here, applying a recently developed bioengineering approach referred to as channel inactivation induced by membrane tethering of an associated protein (ChIMP), we found that the Ca ²⁺-sensing protein calmodulin (CaM) is preassociated with TMEM16A/16B channel complexes in its Ca ²⁺-free state (apoCaM). The preassociated apoCaM acts as a resident Ca ²⁺ sensor that increases Ca ²⁺ sensitivity of TMEM16A/16B activation at low intracellular Ca ²⁺ concentrations and also mediates inactivation of TMEM16A channels at high Ca ²⁺ concentrations. The results reveal a previously unidentified role for apoCaM in Ca ²⁺-dependent regulation of TMEM16A/16B channels that is likely physiologically important, and may be a promising site to target for therapy.