The BH3-only protein PUMA is involved in green tea polyphenol induced apoptosis in colorectal cancer cell lines

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The Green tea polyphenol (GTP) has been shown to possess cancer therapeutic effect through induction of apoptosis, while the underlying molecular mechanism of its anticancer effect is not well understood. PUMA (p53-upregulated modulator of apoptosis) plays an important role in the process of apoptosis induction in a variety of human tumor cells in both p53-dependent and -inde- pendent manners. However, whether or not PUMA is involved in the process of GTP-induced ap- optosis in cancer cells has not been well reported. In the present study, we treated HT-29 (mutant p53) and LoVo (wild type p53) human colorectal cancer cells with different concentrations of GTP, which led to repression of cell proliferation and induction of apoptosis in both cell lines. Meanwh- ile, we also observed increased PUMA expression and decreased ERK (extracellular signal-regula- ted kinase) activity in both of GTP-treated tumor cell lines carrying different genotypes of p53. To determine the role of PUMA in GTP-induced apoptosis, we used stable RNA interference (RNAi) to suppress PUMA expression. As a result, apoptosis was abrogated in response to GTP-treatment. We also found that suppression of ERK activity by either RNAi or its specific inhibitor significan- tly enhanced GTP-induced PUMA expression. All these results indicate that PUMA plays a critic- al role in GTP-induced apoptosis pathway in human colorectal cancer cells and can be regulated partly by ERK inactivation. Demonstration of the molecular mechanism involved in the anti-canc- er effect of GTP may be useful in the therapeutic target selection for p53 deficient colorectal canc- er.