Expression of two human skeletal calcitonin receptor isoforms cloned from a giant cell tumor of bone. The first intracellular domain modulates ligand binding and signal transduction

J Clin Invest. 1995 Jun;95(6):2680-91. doi: 10.1172/JCI117970.


Two distinct calcitonin (CT) receptor (CTR)-encoding cDNAs (designated GC-2 and GC-10) were cloned and characterized from giant cell tumor of bone (GCT). Both GC-2 and GC-10 differ structurally from the human ovarian cell CTR (o-hCTR) that we cloned previously, but differ from each other only by the presence (GC-10) or absence (GC-2) of a predicted 16-amino acid insert in the putative first intracellular domain. Expression of all three CTR isoforms in COS cells demonstrated that GC-2 has a lower binding affinity for salmon (s) CT (Kd approximately 15 nM) than GC-10 or o-hCTR (Kd approximately 1.5 nM). Maximal stimulatory concentrations of CT resulted in a mean accumulation of cAMP in GC-2 transfected cells that was greater than eight times higher than in cells transfected with GC-10 after normalizing for the number of receptor-expressing cells. The marked difference in maximal cAMP response was also apparent after normalizing for receptor number. GC-2 also demonstrated a more potent ligand-mediated cAMP response compared with GC-10 for both human (h) and sCT (the EC50 values for GC-2 were approximately 0.2 nM for sCT and approximately 2 nM for hCT; EC50 values for GC-10 were approximately 6 nM for sCT and approximately 25 nM for hCT). Reverse transcriptase PCR of GCT RNA indicated that GC-2 transcripts are more abundant than those encoding for GC-10. In situ hybridization on GCT tissue sections demonstrated CTR mRNA expression in osteoclast-like cells. We localized the human CTR gene to chromosome 7 in band q22. The distinct functional characteristics of GC-2 and GC-10, which differ in structure only in the first intracellular domain, indicate that the first intracellular domain of the CTR plays a previously unidentified role in modulating ligand binding and signal transduction via the G protein/adenylate cyclase system.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Base Sequence
  • Bone Neoplasms / genetics
  • Calcitonin / metabolism*
  • Cell Line
  • Chlorocebus aethiops
  • Chromosomes, Human, Pair 7
  • Cloning, Molecular
  • Cyclic AMP / metabolism
  • DNA Primers / chemistry
  • Gene Expression
  • Genes
  • Giant Cell Tumors / genetics
  • Humans
  • In Situ Hybridization
  • In Vitro Techniques
  • Ligands
  • Molecular Sequence Data
  • RNA, Messenger / genetics
  • Receptors, Calcitonin / genetics*
  • Receptors, Calcitonin / metabolism
  • Signal Transduction
  • Structure-Activity Relationship
  • Transfection


  • DNA Primers
  • Ligands
  • RNA, Messenger
  • Receptors, Calcitonin
  • Calcitonin
  • Cyclic AMP