Intermolecular interactions between dimeric calcium-sensing receptor monomers are important for its normal function

Intermolecular interactions between dimeric calcium-sensing receptor monomers are important for its normal function

Endocrine-Hypertension Division, Department of Medicine, Brigham and Women’s Hospital, and Harvard Medical School, Boston, MA 02115

Edited by Robert J. Lefkowitz, Duke University Medical Center, Durham, NC, and approved January 14, 1999 (received for review November 13, 1998)

Abstract

We recently demonstrated that the G protein-coupled, extracellular calcium-sensing receptor (CaR) forms disulfide-linked dimers. The functional significance of dimerization of this receptor was suggested by our earlier observations that CaRs carrying certain point mutations exert dominant negative effects on the function of the coexpressed wild-type receptor both in vivo and when cotransfected in human embryonic kidney cells. In this study, we explored the functional consequences of CaR dimerization. Coexpression in human embryonic kidney cells of specific pairs of mutant CaRs, each with reduced or absent activity because of distinct loss-of-function mutations, results in the formation of heterodimers and partially reconstitutes extracellular calcium-dependent signaling. Moreover, our results suggest that the CaR has at least two functionally separable domains. However, the presence of an abnormal domain in each mutant monomer substantially impairs the function of the CaR heterodimer, resulting in the reconstituted CaRs having characteristics distinct from those of the wild-type CaR. Our study suggests that intermolecular interactions within the dimeric CaR are important for the receptor’s function.

Footnotes

↵ * To whom reprint requests should be addressed at: Endocrine Division, 221 Longwood Avenue, Boston, MA 02115. e-mail: MBai{at}bustoff.bwh.harvard.edu.
This paper was submitted directly (Track II) to the Proceedings Office.
ABBREVIATIONS:

[Ca2+]o,

extracellular calcium;

CaR,

[Ca2+]o-sensing receptor;

GPCR,

G protein-coupled receptor;

ECD,

the N-terminal, extracellular domain;

i3,

the third intracellular loop;

C-tail,

the intracellular C-terminal tail;

wt,

the wild type CaR;

[Ca2+]i,

cytosolic calcium;

IP,

inositol phosphate;

HEK cells,

human embryonic kidney cells