Transforming growth factor-beta type I receptor/ALK5 contributes to doxazosin-induced apoptosis in H9C2 cells

The mechanism of doxazosin-induced apoptosis through alpha(1)-adrenoceptor-independent pathway has been reported in various types of cell models. However, the molecular events involved in this effect are still not fully discovered. In present study, we proposed that the transforming growth factor-beta type I receptor (TbetaRI/ALK5) may contribute to the doxazosin-induced apoptosis in H9C2 cardiomyoblasts. Via the detection of cell viability, apoptotic nuclei, and caspase-3 activity, we found that doxazosin induced concentration- and time-dependent apoptosis in H9C2 cells. The cell apoptosis induced by 30 muM doxazosin was exacerbated by the addition of 10 ng/ml transforming growth factor-beta1 (TGF-beta1). Doxazosin or TGF-beta1 alone respectively elevated p38 mitogen-activated protein kinases (MAPK) and Smad3 protein phosphorylation in H9C2 cells. However, the cotreatment of doxazosin and TGF-beta1 attenuated the TGF-beta1-induced Smad3 protein phosphorylation and increased doxazosin-induced p38 MAPK protein phosphorylation. Furthermore, inhibitors of TbetaRI/ALK5 (SB431542) and p38 MAPK (SB202190) or TbetaRI/ALK5 knockdown all dramatically reduced the doxazosin-induced apoptosis in H9C2 cells. In conclusion, our results demonstrated that TbetaRI/ALK5-p38 MAPK phosphorylation signaling pathway could contribute to doxazosin-induced cell apoptosis, which could be further enhanced by TGF-beta1 in association with attenuating Smad3 phosphorylation in H9C2 cells.