Identification of multiple human calcitonin receptor isoforms: heterologous expression and pharmacological characterization.
The human breast carcinoma cell line T47D is known to express high-affinity calcitonin receptors (CTRs). PCR amplification of the CTR cDNA from T47D mRNA resulted in the identification of two different cDNAs that encode distinct receptor isoforms, h alpha CTR and h beta CTR. The two cDNAs are identical except that the h alpha CTR cDNA contains a 48 bp insert sequence that encodes a 16 amino acid domain in the first cytosolic loop of the receptor. Stable transfection of each receptor cDNA into murine erythroleukaemia (MEL) cells resulted in the expression of receptors with high affinity for radiolabelled salmon calcitonin (h alpha CTR Kd 0.09 nM, h beta CTR Kd 0.12 nM). Ligand competition binding studies did not reveal any significant pharmacological difference between the receptor isoforms. In transfected MEL cells and COS-1 cells the h beta CTR isoform was expressed at tenfold higher levels than the h alpha CTR. A reporter gene assay that monitored the coupling of CTR to adenylate cyclase by increases in beta-galactosidase activity indicated that both receptors were able to stimulate cyclic AMP production in response to ligand binding.
Egerton
M
M
Infection Research Department, ZENECA Pharmaceuticals, Macclesfield, Cheshire, UK.
Needham
M
M
Evans
S
S
Millest
A
A
Cerillo
G
G
McPheat
J
J
Popplewell
M
M
Johnstone
D
D
Hollis
M
M
D000262:Adenylyl Cyclases / Q000378:metabolism; D000595:Amino Acid Sequence; D000682:Amyloid / Q000378:metabolism; D000818:Animals; D001483:Base Sequence; D001667:Binding, Competitive; D001943:Breast Neoplasms / Q000378:metabolism / Q000473:pathology; D002116:Calcitonin / Q000378:metabolism*; D015740:Calcitonin Gene-Related Peptide / Q000378:metabolism; D002277:Carcinoma / Q000378:metabolism / Q000473:pathology; D000242:Cyclic AMP / Q000096:biosynthesis; D018076:DNA, Complementary / Q000235:genetics; D004273:DNA, Neoplasm / Q000235:genetics; D004789:Enzyme Activation / Q000187:drug effects; D005260:Female; D005786:Gene Expression Regulation; D017930:Genes, Reporter; D006801:Humans; D058228:Islet Amyloid Polypeptide; D004915:Leukemia, Erythroblastic, Acute / Q000473:pathology; D051379:Mice; D008969:Molecular Sequence Data; D009363:Neoplasm Proteins / Q000096:biosynthesis / Q000235:genetics; D011487:Protein Conformation; D018003:Receptors, Calcitonin / Q000145:classification* / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D015290:Second Messenger Systems / Q000187:drug effects; D014407:Tumor Cells, Cultured
D000682:Amyloid; D018076:DNA, Complementary; D004273:DNA, Neoplasm; D058228:Islet Amyloid Polypeptide; D009363:Neoplasm Proteins; D018003:Receptors, Calcitonin; C028815:salmon calcitonin; D002116:Calcitonin; D000242:Cyclic AMP; D000262:Adenylyl Cyclases; D015740:Calcitonin Gene-Related Peptide