Expression and characterization of inactivating and activating mutations in the human Ca2+o-sensing receptor.
Nearly 30 mutations have been identified to date in the coding region of the extracellular calcium-sensing receptor (CaR) that are associated with inherited human hypo- and hypercalcemic disorders. To understand the mechanisms by which the mutations alter the function of the receptor may help to discern the structure-function relationships in terms of ligand-binding and G protein coupling. In the present studies, we transiently expressed eight known CaR mutations in HEK293 cells. The effects of the mutations on extracellular calcium- and gadolinium-elicited increases in the cytosolic calcium concentration were then examined. Seven inactivating mutations, which cause familial hypocalciuric hypercalcemia and neonatal severe hyperparathyroidism, show a reduced functional activity of the receptor because they may 1) reduce its affinity for agonists; 2) prevent conversion of the receptor from a putatively immature, high mannose form into the fully glycosylated and biologically active form of the CaR, in addition to lowering its affinity for agonists; or 3) fail to couple the receptor to and/or activate its respective G protein(s). Conversely, one activating mutation, which causes a form of autosomal dominant hypocalcemia, appears to increase the affinity of the receptor for its agonists.
Bai
M
M
Endocrine-Hypertension Division, Department of Medicine, Brigham and Women's Hospital, Boston, Massachusetts 02115, USA.
Quinn
S
S
Trivedi
S
S
Kifor
O
O
Pearce
S H
SH
Pollak
M R
MR
Krapcho
K
K
Hebert
S C
SC
Brown
E M
EM
D015153:Blotting, Western; D002118:Calcium / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D002460:Cell Line; D018076:DNA, Complementary; D005682:Gadolinium / Q000378:metabolism; D006031:Glycosylation; D006801:Humans; D006934:Hypercalcemia / Q000235:genetics; D006961:Hyperparathyroidism / Q000235:genetics; D016297:Mutagenesis, Site-Directed; D044169:Receptors, Calcium-Sensing; D011956:Receptors, Cell Surface / Q000235:genetics* / Q000378:metabolism; D015183:Restriction Mapping
C095550:CASR protein, human; D002135:Calcium-Binding Proteins; D018076:DNA, Complementary; D044169:Receptors, Calcium-Sensing; D011956:Receptors, Cell Surface; D005682:Gadolinium; D002118:Calcium