Rab1 Small GTP-Binding Protein Regulates Cell Surface Trafficking of the Human Calcium-Sensing Receptor

The human calcium-sensing receptor (hCaR) is a family-3/C G-protein-coupled receptor that regulates Ca2+ homeostasis by controlling parathyroid hormone secretion. Here we investigated the role of Rab1, a small GTP-binding protein that specifically regulates protein transport from the endoplasmic ret...

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Bibliographic Details
Published in:Endocrinology (Philadelphia) 2010-11, Vol.151 (11), p.5114-5123
Main Authors: Zhuang, Xiaolei, Adipietro, Kaylin A, Datta, Shomik, Northup, John K, Ray, Kausik
Format: Article
Language:English
Subjects:
Analysis of Variance
Biological and medical sciences
Blotting, Western
Cell Line
Cell Membrane - metabolism
Cells, Cultured
Endoplasmic Reticulum - metabolism
Enzyme-Linked Immunosorbent Assay
Fundamental and applied biological sciences. Psychology
Golgi Apparatus - metabolism
Humans
Mutation, Missense
Protein Transport
rab1 GTP-Binding Proteins - genetics
rab1 GTP-Binding Proteins - metabolism
Receptors, Calcium-Sensing - genetics
Receptors, Calcium-Sensing - metabolism
RNA, Small Interfering
Transfection
Vertebrates: endocrinology
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Summary:The human calcium-sensing receptor (hCaR) is a family-3/C G-protein-coupled receptor that regulates Ca2+ homeostasis by controlling parathyroid hormone secretion. Here we investigated the role of Rab1, a small GTP-binding protein that specifically regulates protein transport from the endoplasmic reticulum to the Golgi, in cell surface transport of the hCaR. Cell surface expression of hCaR transiently expressed in human embryonic kidney 293 cells was strongly augmented by coexpression of Rab1 and attenuated by disruption of endogenous Rab1 function by expression of the dominant-negative Rab1N124I mutant or depletion of Rab1 with small interfering RNA. Rab1N124I expression also partially attenuated cell surface expression and signaling response to gain-of-function mutants of hCaR with truncated carboxyl-terminal sequences at positions 895 and 903. These carboxyl-tail truncations are similar to a deletion between residues S895 and V1075 found in a patient family causing autosomal dominant hypocalcemia. In addition, coexpression with wild-type Rab1 increased cell surface expression of the loss-of-function missense mutation R185Q, located on the hCaR amino-terminal extracellular ligand-binding domain (ECD), which causes familial hypocalciuric hypercalcemia. Truncated hCaR variants containing either the ECD with the first transmembrane helix or only the ECD also display Rab1-dependent cell surface expression or secretion into the culture medium, respectively. These data reveal a role for Rab1 in hCaR trafficking from the endoplasmic reticulum to the Golgi that regulates receptor cell surface expression and thereby cell signaling responsiveness to extracellular calcium. A Rab1-dependent mechanism regulates intracellular and cell surface delivery of the human calcium-sensing receptor.
ISSN:0013-7227
1945-7170
DOI:10.1210/en.2010-0422