TI - Attenuation of Runx2 by GSK-3beta . AB - A variety of hormones , cytokines and signaling molecules such as 1alpha , 25 ( OH ) 2D3 , tumor necrosis factor alpha , fibroblast growth factor ( FGF ) -2 , glucocorticoids , growth hormone , Akt , Stat1 & 3 , Twist , Src/Yes , Dlx3 , Msx2 , PPARgamma and histone acetylases 3 & 4 have been reported to regulate Runx2 in its expression , subcellular localization , DNA binding and transcriptional activity , although the mechanisms remain largely unknown [28] . The present study showed that GSK-3beta inhibited the DNA binding and transcriptional activity through the S369-S373-S377 PHOSphorylation of the Runx protein . Regulation of Runx2 activity through its phosphorylaTION has been reported by PHOSphorylation-deficient mutagenesis at two conserved serines , Ser104 and Ser451 of the human RUNX2 gene in distinct functional aspects [29] . The Ser104 PHOSphorylation is involved in the heterodimerization with the partner subunit PEBP2beta , which enhances the transcriptional activity of RUNX2 . On the other hand , the PHOSphorylation of Ser451 that resides within the C-terminal transcription inhibition domain of RUNX2 attenuates its transactivity . The consensus site T341 for the PHOSphorylation by PKA in the transactivation domain of mouse Runx2 is shown to be responsible for the induction of Runx2 transcriptional activity by parathyroid hormone ( PTH ) [30] . In addition , FGF-2 induces the Runx2 activity through PHOSphorylation of distinct consensus sites of ERK and PKC pathways [31] -[33] . Meanwhile , the present S369-S373-S377 is located in the negative regulatory region of DNA binding that masks the Runt domain and prevents it from binding to DNA [34] . Hence , the suppression of GSK-3beta may relieve the GSK-3beta -dependent PHOSphorylation of the negative regulatory region of Runx2 , resulting in enhancement of DNA binding ability and transcriptional activity . Insulin and insulin-like growth factor-I function as potent osteoanabolic agents [35] , [36] via the activation of their common signaling molecules insulin receptor SUBstrate ( IRS ) -1 , IRS-2 , and the subsequent PI3K/Akt . In fact , we and others previously reported that the loss-of-function mutation of Irs-1 , Irs-2 , or both Akt1 and Akt2 causes impairment of bone formation in mice [11] , [12] , [37] . As the target of this pathway , a recent study has shown that Akt enhanced transcriptional activity of Runx2 [17] . However , despite the fact that Akt is a serine-threonine kinase , the study failed to show the direct phosphorylaTION of Runx2 by Akt , and there was no consensus site for the PHOSphorylation by Akt in the Runx2 sequence . On the other hand , Akt is known to PHOSphorylate GSK-3beta at Ser9 , causing the inactivation [38] . We therefore speculate that the osteoanabolic action of the insulin/IRS/Akt pathway might also be mediated by the Runx2 PHOSphorylation by GSK-3beta .