Unconjugated
Green tea polyphenol (GTP) is one of the most promising chemopreventive agent for cancer; it can inhibit cancer cell proliferation and induce apoptosis through p53-dependent cell signaling pathways. Unfortunately, many tumor cells lack the functional p53, and little is known about the effect of GTP on the p53-deficient/mutant cancer cells. To understand the p53-independent mechanisms in GTP-treated p53-dificient/mutant cancer cells, we have now examined GTP-induced cytotoxicity in human hepatoma Hep3B cells (p53-deficient). The results showed that GTP could induce Bax and Bak activation, cytochrome c release, caspase activation, and necroptosis of Hep3B cells. Bax and Bak, two key molecules of mitochondrial permeability transition pore (MPTP), were interdependently activated by GTP, with translocation and homo-oligomerization on the mitochondria. Bax and Bak induce cytochrome c release. Importantly, cytochrome c release and necroptosis were diminished in Hep3B cells (Bax(-/-)) and Hep3B cells (Bak(-/-)). Furthermore, overexpression of Bcl-2 could ameliorate GTP-induced cytochrome c release and necroptosis. Together, the findings suggested that GTP-induced necroptosis was modulated by the p53-independent pathway, which was related to the translocation of Bax and Bak to mitochondria, release of cytochrome c, and activation of caspases.
Benzo(a)pyrene-7,8-diol-9,10-epoxide (BPDE) is a highly reactive DNA damage agent and can induce cell death through both p53-independent and -dependent pathways. However, little is known about the molecular mechanisms of p53-independent pathways in BPDE-induced cell death. To understand the p53-independent mechanisms, we have now examined BPDE-induced cytotoxicity in p53-deficient baby mouse kidney (BMK) cells. The results showed that BPDE could induce Bax and Bak activation, cytochrome c release, caspases activation, and necrotic cell death in the BMK cells. Bax and Bak, two key molecules of mitochondrial permeability transition pore, were interdependently activated by BPDE, with Bax and Bak translocation to and Bax/Bak homo-oligomerization in mitochondria, release of cytochrome c was induced. Importantly, cytochrome c release and necrotic cell death were diminished in BMK cells (Bax(-/-)), BMK cells (Bak(-/-)), and BMK cells (Bax(-/-)/Bak(-/-)). Furthermore, overexpression of Bcl-2 could ameliorate BPDE-induced cytochrome c release and necrosis. Together the findings suggested that BPDE-induced necrosis was modulated by the p53-independent pathway, which was related to the translocation of Bax and Bak to mitochondria, release of cytochrome c, and activation of caspases.