G-protein Stimulatory α Subunit Is Involved in Osteogenic Activity in Osteoblastic Cell Line SaOS-2 Cells

In an attempt to study the roles of G-protein stimulatory subunit α (G(s)α) in osteoblasts, we introduced an expression vector encoding G(s)α into human osteoblastic cell line SaOS-2, and established the clones stably overexpressing G(s)α (SaOS-2-G(s)α). In SaOS-2-G(s)α, the intracellular content of cyclic AMP (cAMP) was increased compared with the parental SaOS-2 cells. In addition, when treated with PTH[1-34], SaOS-2-G(s)α exhibited more accumulation of intracellular cAMP compared with the parental cells, suggesting an increased responsiveness to PTH. We evaluated the proliferation rates of SaOS-2-G(s)α and the parental SaOS-2 cells, and found that the proliferation was accelerated in SaOS-2-G(s)α cells. Reverse transcription-polymerase chain reaction (RT-PCR) analyses exhibited the increased expression of Runx2, a transcription factor involved in osteoblast differentiation, in SaOS-2-G(s)α cells. Finally, to examine the osteoblastic function in vivo, we inoculated SaOS-2-G(s)α or parental SaOS-2 cells subcutaneously to immunocompromised nude mice. Although tumors in nude mice were not formed after inoculation of parental SaOS-2 cells, SaOS-2-G(s)α cells proliferated in host animals leading to the formation of tumors with mineralized bone-like tissues. Taken together, these results suggest that the signals via G(s)α play critical roles in the proliferation and osteogenic functions of osteoblasts.