期刊
AMERICAN JOURNAL OF PHYSIOLOGY-CELL PHYSIOLOGY
卷 320, 期 5, 页码 C892-C901出版社
AMER PHYSIOLOGICAL SOC
DOI: 10.1152/ajpcell.00481.2020
关键词
adenosine receptor; CFTR; chloride secretion; molecular evolution; shark; structural biology
资金
- Howard Hughes Medical Institute
- University of Alabama
- NIH National Institute of Diabetes and Digestive and Kidney Diseases [R01 DK034208]
- National Institute of Environmental Health Sciences [P30 ES003828]
- National Science Foundation [DBI-0453391]
The study identified a novel adenosine receptor, A(0), in sharks that likely regulates CFTR and represents an ancestral precursor of mammalian adenosine receptors. Experimental results demonstrated that A(0) activates the chloride channel of CFTR.
Adenosine receptors (ADORs) are G protein-coupled purinoceptors that have several functions including regulation of chloride secretion via cystic fibrosis transmembrane conductance regulator (CFTR) in human airway and kidney. We cloned an ADOR from Squalus acanthias (shark) that likely regulates CFTR in the rectal gland. Phylogenic and expression analyses indicate that elasmobranch ADORs are nonolfactory and appear to represent extant predecessors of mammalian ADORs. We therefore designate the shark ADOR as the A(0) receptor. We coexpressed A(0) with CFTR in Xenopus laevis oocytes and characterized the coupling of A(0) to the chloride channel. Two-electrode voltage clamping was performed, and current-voltage (I-V) responses were recorded to monitor CFTR status. Only in A(0)- and CFTR-coinjected oocytes did adenosine analogs produce a significant concentration-dependent activation of CFTR consistent with its electrophysiological signature. A pharmacological profile for A(0) was obtained for ADOR agonists and antagonists that differed markedly from all mammalian ADOR subtypes [agonists: R-phenylisopropyl adenosine (R-PIA) > S-phenyl-isopropyl adenosine (S-PIA) > CGS21680 > N-6-cyclopentyladenosine (CPA) > 2-chloroadenosine (2ClAdo) > CV1808 = N-6-[2-(3,5-dimethoxyphenyl)-2-(2- methylphenyl)ethyl]adenosine (DPMA) > N-ethyl-carboxyl adenosine (NECA); and antagonists: 8-cyclopentyl-1,3- dipropylxanthine (DPCPX) > PD115199 > 1,3-dimethyl-8-phenylxanthine (8PT)> CGS15943]. Structures of human ADORs permitted a high-confidence homology model of the shark A(0) core that revealed unique structural features of ancestral receptors. We conclude that 1) A(0) is a novel and unique adenosine receptor ancestor by functional and structural criteria; 2) A(0) likely activates CFTR in vivo, and this receptor activates CFTR in oocytes, indicating an evolutionary coupling between ADORs and chloride secretion; and 3) A(0) appears to be a nonolfactory evolutionary ancestor of all four mammalian ADOR subtypes.
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