Aluminum-induced DNA synthesis in osteoblasts: mediation by a G-protein coupled cation sensing mechanism. J Cell Biochem 1994 Sep;56(1):106-17
Date
09/01/1994Pubmed ID
7806584DOI
10.1002/jcb.240560115Scopus ID
2-s2.0-0028124227 (requires institutional sign-in at Scopus site) 91 CitationsAbstract
Aluminum (Al3+) stimulates de novo bone formation in dogs and is a potent stimulus for DNA synthesis in non-transformed osteoblasts in vitro. The recent identification of a G-protein coupled cation-sensing receptor (BoPCaR), which is activated by polyvalent agonists [e.g., gadolinium (Gd3+) > neomycin > calcium (Ca2+)], suggests that a similar physiologically important cation sensing receptor may be present in osteoblasts and pharmacologically activated by Al3+. To evaluate that possibility, we assessed whether known BoPCaR agonists stimulate DNA synthesis in MC3T3-E1 osteoblasts and examined the additive effects of Al3+ and BoPCaR agonists on DNA synthesis in MC3T3-E1 osteoblast-like cells. We found that Al3+, Gd3+, neomycin, and Ca2+ stimulated DNA synthesis in a dose-dependent fashion, achieving 50% effective extracellular concentrations (EC50) of 10 microM, 30 microM, 60 microM, and 2.5 mM, respectively. Al3+ displayed non-additive effects on DNA synthesis with the BoPCaR agonists as well as an unrelated G-protein coupled receptor agonist, PGF2 alpha, suggesting shared mechanisms of action. In contrast, the receptor tyrosine kinase agonist, IGF-I (10 eta g/ml), displayed additive proliferative effects when combined with AlCl3, indicating distinct signalling pathways. AlCl3 (25 microM) induced DAG levels 2-fold and the phosphorylation of the myristoylated alanine-rich C kinase (MARCKS) substrate 4-fold, but did not increase intracellular calcium concentrations. Down-regulation of PKC by pre-treatment with phorbol 12-myristate 13-acetate as well as PKC inhibition by H-7 and staurosporine blocked Al(3+)-induced DNA synthesis. Finally, Al3+, Gd3+, neomycin, and Ca2+ activated G-proteins in osteoblast membranes as evidenced by increased covalent binding of [32P]-GTP-azidoanilide to putative G alpha subunits. Our findings suggest that Al3+ stimulates DNA synthesis in osteoblasts through a cation sensing mechanism coupled to G-protein activation and signalling cascades involving DAG and PKC-dependent pathways.
Author List
Quarles LD, Hartle JE 2nd, Middleton JP, Zhang J, Arthur JM, Raymond JRAuthor
John R. Raymond MD President, CEO, Professor in the President department at Medical College of WisconsinMESH terms used to index this publication - Major topics in bold
1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine3T3 Cells
Alkaloids
Aluminum
Animals
Biological Transport
Calcium
Clone Cells
Cytosol
DNA
Diacylglycerol Kinase
Dogs
GTP-Binding Proteins
Gadolinium
Growth Substances
Intracellular Signaling Peptides and Proteins
Isoquinolines
Kinetics
Membrane Proteins
Mice
Myristoylated Alanine-Rich C Kinase Substrate
Neomycin
Osteoblasts
Phosphorus Radioisotopes
Phosphorylation
Phosphotransferases (Alcohol Group Acceptor)
Piperazines
Protein Kinase C
Proteins
Receptors, Calcium-Sensing
Receptors, Cell Surface
Staurosporine
Tetradecanoylphorbol Acetate