CX-4945 stimulates osteoblast differentiation via Smad signaling. (A) The effect of CX-4945 on the viability of C2C12 cells were evaluated using the CCK-8 assay. (B) The effect of CX-4945 on the BMP-2-induced osteoblast differentiation was evaluated by visualized the induction of ALP in C2C12 cells. DMSO was used as a vehicle control. (C) The transcriptional induction of ALP and BMP-2 in C2C12 cells was evaluated. Cells were replenished with BMP-2 (25 ng/ml) or its combination with CX-4945 in media containing 5% FBS every 3 days. After 6 days, the mRNA expression of osteoblast differentiation markers was detected by qRT-PCR. (D) The effect of CX-4945 on the nuclear translocation of Smad1/5/8 was evaluated. C2C12 cells were treated with BMP-2 (25 ng/ml) and CX-4945 (1, 3, or 10 μM) for 6 days. Cells were replenished with BMP-2 (25 ng/ml) or its combination with CX-4945 in media containing 5% FBS every 3 days. After 6 days, the cells were lysed and fractionated, and the phosphorylation levels of nuclear Smad1/5/8 and cytosolic Smad 1/5/8 were determined by Western blot analysis. #p < 0.05; ###p < 0.001 (versus the control); *p < 0.05; **p < 0.01 (versus cells treated with BMP-2 alone).