Calcitonin gene-related peptide (CGRP) increases intracellular free Ca2+ concentrations but not cyclic AMP formation in CGRP receptor-positive osteosarcoma cells (OHS-4)

Although calcitonin gene-related peptide (CGRP) ma! act as a local factor in bone, its mechanisms of action an osteoblasts are not well understood. We previously showed the presence of CGRP transcripts and peptide in human OHS-4 osteoblastic cells, The authors investigated the expression of CGRP receptor (CGRP-R) and its intracellular signalling properties in OHS-4 cells. Semi-quantitative RT-PCR analysis showed that OHS-4 cells express much more CC;RP-R than calcitonin (CT)-R transcripts. After amplification of CGRP-R by RT-PCR and cloning of amplified fragments, the predicted CGRP-R sequence in OHS-4 cells was found to share 100% identity with human lung CGRP-R, Biochemical analysis showed that hCGRP did not increase intracellular cAMP levels in synchronized OHS-4 cells whatever was the cell cycle position. However, adenylate cyclase activity nas functional, as human parathyroid hormone increased cAMP levels. In contrast, hCGRP induced a rapid, transient and dose-dependent increase in free cytosolic calcium levels. The data show that CGRP increases intracellular free Ca2+ concentration but is not coupled to adenylate cyclase in CGRP receptor-positive OHS-4 osteosarcoma cells, suggesting that CGRP induces downstream events driven by phospholipase C in these cells. (C) 1999 Academic Press.