A calcium-sensing receptor mutation causing hypocalcemia disrupts a transmembrane salt bridge to activate beta-arrestin-biased signaling

作者：Gorvin Caroline M; Babinsky Valerie N; Malinauskas Tomas; Nissen Peter H; Schou Anders J; Hanyaloglu Aylin C; Siebold Christian; Jones E Yvonne; Hannan Fadil M^*; Thakker Rajesh V^*

来源：Science Signaling, 2018, 11(518): eaan3714.

DOI：10.1126/scisignal.aan3714

The calcium-sensing receptor (CaSR) is a G protein-coupled receptor (GPCR) that signals through G(q/11) and G(i/o) to stimulate cytosolic calcium (Ca-i(2+)) and mitogen-activated protein kinase (MAPK) signaling to control extracellular calcium homeostasis. Studies of loss- and gain-of-function CASR mutations, which cause familial hypocalciuric hypercalcemia type 1 (FHH1) and autosomal dominant hypocalcemia type 1 (ADH1), respectively, have revealed that the CaSR signals in a biased manner. Thus, some mutations associated with FHH1 lead to signaling predominantly through the MAPK pathway, whereas mutations associated with ADH1 preferentially enhance Ca-i(2+) responses. We report a previously unidentified ADH1-associated R680G CaSR mutation, which led to the identification of a CaSR structural motif that mediates biased signaling. Expressing CaSRR680G in HEK 293 cells showed that this mutation increased MAPK signaling without altering Ca-i(2+) responses. Moreover, this gain of function in MAPK activity occurred independently of G(q/11) and G(i/o) and was mediated instead by a noncanonical pathway involving beta-arrestin proteins. Homology modeling and mutagenesis studies showed that the R680G CaSR mutation selectively enhanced beta-arrestin signaling by disrupting a salt bridge formed between Arg(680) and Glu(767), which are located in CaSR transmembrane domain 3 and extracellular loop 2, respectively. Thus, our results demonstrate CaSR signaling through beta-arrestin and the importance of the Arg(680)-Glu(767) salt bridge in mediating signaling bias.

• 出版日期2018-2-20