Date of Award
Doctor of Philosophy (PhD)
The calcium-activated chloride channel regulator (CLCA) proteins are key signaling molecules, which are implicated in various diseases through their tissue-specific expression. Human CLCA1 protein, overexpressed in airway epithelia under pathophysiological conditions, is centrally involved in the manifestation of IL-13-driven mucus cell metaplasia (MCM), a hallmark feature of asthma and chronic obstructive pulmonary disease (COPD), for which there are currently no available therapeutics. Elucidating the poorly understood molecular basis of CLCA1 function is thus required to design specific inhibitors of CLCA1 activity to treat MCM in asthma and COPD.
Originally misannotated as ion channels, CLCA proteins are secreted soluble proteins that act as regulators of unknown calcium-activated chloride channels (CaCC) in the airways. Additionally, these proteins undergo proteolytic cleavage, adding yet another level of complexity to the mystery of how a secreted protein can regulate chloride currents.
This study focuses on the proteolytic cleavage of CLCA1 and provides mechanistic detail into how secreted CLCA1 protein modulates currents from a CaCC in mammalian cells, which is identified as TMEM16A. For this unique interaction to occur, secreted full-length CLCA1 undergoes a self-cleavage reaction using an N-terminal zincin metalloprotease with a novel fold, which releases the functionally active N-terminal fragment. This cleavage exposes the von Willebrand factor type A (vWA) domain to directly interact with membrane-associated TMEM16A at the C-terminal extracellular loop (loop 9-10). The direct interaction increases TMEM16A surface density by stabilizing the channel on the cell surface and blocking its rapid recycling, thus resulting in increased chloride currents.
Chair and Committee
Tom J. Brett
Gaya K. Amarasinghe, Tom Ellenberger, Colin G. Nichols, Joe H. Steinbach,
Yurtsever, Zeynep, "Mechanism of Calcium-dependent Chloride Channel Activation by the Secreted Regulator CLCA1" (2016). Arts & Sciences Electronic Theses and Dissertations. 789.