Vitex rotundifolia Fruit Extract Induces Apoptosis Through the Downregulation of ATF3-Mediated Bcl-2 Expression in Human Colorectal Cancer Cells

Fruit from Vitex rotundifolia L. (VF) has been reported to initiate apoptosis in human colorectal cancer cells through the accumulation of reactive oxygen species. Since various regulatory factors are involved in the apoptotic pathway, further study of the potential mechanisms of VF associated with the induction of apoptosis may be important despite the fact that the molecular target of VF for apoptosis has already been elucidated. In this study, we showed a new potential mechanism for the relationship between VF-mediated ATF3 expression and apoptosis to better understand the apoptotic mechanism of VF in human colorectal cancer cells. VF reduced the cell viability and induced apoptosis in human colorectal cancer cells. VF treatment increased both the protein and mRNA level of ATF3 and upregulated ATF3 promoter activity. The cis-element responsible for ATF3 transcriptional activation by VF was CREB which is located between −147 to −85 of ATF3 promoter. Inhibitions of ERK1/2, p38, JNK and GSK3β blocked VF-mediated ATF3 expression. ATF3 knockdown by ATF3 siRNA attenuated the cleavage of PARP by VF, while ATF3 overexpression increased VF-mediated cleaved PARP. ATF3 knockdown also attenuated VF-mediated cell viability and cell death. In addition, VF downregulated Bcl-2 expression at both protein and mRNA level. ATF3 knockdown by ATF3 siRNA blocked VF-mediated downregulation of Bcl-2. In conclusion, VF may activate ATF3 expression through transcriptional regulation and subsequently suppress Bcl-2 expression as an anti-apoptotic protein, which may result in the induction of apoptosis in human colorectal cancer cells.