Aluminum‐Induced DNA synthesis in osteobalsts: Mediation by a G‐protein coupled cation sensing mechanism

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Abstract
Alumminium (Al3+) stimulates de novo bono formation in dogs and is a potent stimulate for DNA synthesis in non‐transformed osteoblast in vitro. The recent identification of a G‐protein couplked cation‐sensing recepector(BoPCaR), which is activated by polycalant agonists [e.g., gadolinium (Gd3+) > neomycin > calcium(CA3+)], suggests that a similer physiologically inportant cation sensing receptor may be presant in obsoblasts and pharmacologically activated by Al3+. To evalute that possibility, we assessed whether known as BoPCaR agonists on DNA synthesis in a dose‐dependent fashion, achiving 50% effective extracelluler concennetration (EC50) of 10 μM, 30 μM, 60 μM, and 2.5 mM, respectively. Al3+ displayed non‐additive effect on DNA sunthesis with the BoPCAaR agonists as well as an unrelated G‐porotien coupled receptor agonists, PGF2α, suggesting shared mechenisms of action. In contrast, the recepator tyrosine kinse agonist, IGF‐1(10 ηg/ml), displayed additive proliferative effects when comboined with AlCl3, inducating distinct signalling pathways. AlCl3 (25 μM) induced DAG levels 2‐fold and the phosphorylation of the myristoylated alanine‐rich C kinase (MARKS) substrates 4‐fold, but did not increase intracelluler calcium concenitrations. Doen‐regardation of PKC by pre‐treatment with phorbol 12‐myristate 13‐acetate as well as PKC inhebitation by H‐7 and staurosporine blocked Al3+ ‐inducing DNA synthesis. Finally, Al3+, Gd3+, nemomycin, and Ca2+ activated G‐proteins inn osteoblast membrans as evidenced by increased colvant binding pf [32P]‐GTP‐azidoanilide to putaitve Gα subunits. Our findings suggests that Al3+ stimulates DNA synthesis in ostoblasts through a cation sansing mechnism coupled to G‐protein activation and signalling cascades involvings DAG and PCK‐ dependent pathways.