Calcitonin (CT) is a peptide hormone that interacts with the cAMP-and phospholipase C-associated CT receptor subtypes. We investigated whether CT modulates the interaction of human tumoral osteoclast-like (GCT23) cells with a protein of the bone matrix, bone sialoprotein-II (BSP-II). Single GCT23 cells loaded with the intracellular Ca2+ indicator fura-2 were treated with the maximal active dose (300 μg/ml) of the 18-mer Arg-Gly-Asp (RGD)- containing BSP-IIA fragment, and the cytosolic free Ca2+ concentration ([Ca2+](i)) Was measured by dual wavelength microfluorometry. BSP-IIA stimulated an elevation in [Ca2+](i) , consisting mainly of a peak, followed by a rapid return toward baseline. Pretreatment with CT induced a modest elevation of [Ca2+](i). However, CT significantly inhibited the response to BSP-IIA in a dose-dependent manner. Maximal inhibition (90% vs. untreated) was observed in the micromolar range. The intracellular mechanisms leading to this effect were investigated by pretreatment of GCT23 cells with the cAMP permeant analog, (Bu2)cAMP, and the protein kinase-C-activating agent, 12-O-tetradecanoylphorbol 13-acetate. Similar to CT, both agents inhibited the response to 300 μg/ml BSP-IIA. The effect induced by CT was specific, because an increase in the extracellular Ca2+ concentration, which is also known to inhibit bone resorption, failed to modify the ability of BSP-IIA to alter [Ca2+ in GCT23 cells. To investigate whether the CT- induced alteration of BSp-IIA-dependent cell signals was due to a modification in the synthesis of cell surface receptors (integrins) for the extracellular matrix macromolecules, 1-h CT-treated [35S]methionine metabolically labeled GCT23 cell lysates were immunoprecipitated with anti- α3-, -α(v)-, -β1-, and -β3-integrin subunit antibodies. Autoradiography demonstrated that 10-7-10-6 M CT did not alter new synthesis of the and the α3β1 receptors. Similarly, CT did not affect surface expression of these receptors, assessed by enzyme-linked immunosorbent assay. Finally, no alteration of the adhesion rate and spreading of GCT23 cells onto BSP-IIA-coated substrates was observed. This indicates that CT-induced down-regulation of immediate cell signals prompted by BSP-IIA in GCT23 cells is a postintegrin receptor event.
|Number of pages||10|
|Publication status||Published - 1995|
ASJC Scopus subject areas
- Endocrinology, Diabetes and Metabolism