Many studies have shown the inhibitory effect of polyphenolic compounds including green tea catechins (-)epigallocatechin 3-gallate (EGCG) against carcinogenesis in rodent models. These include cancers of the colorectal, liver, lung, skin, small intestine, and mammary gland. Our hypothesis is that the cancer chemoprevention effect of tea polyphenolic components such as EGCG, is through induction of apoptotic mechanisms involving the mitogen-activated protein kinases (MAPK) pathway, and the caspases pathway. The overall goal of this project is to identify the molecular mechanisms/targets of apoptotic signaling molecules exhibited by EGCG and other tea polyphenols. Such knowledge will help to develop better chemopreventive agents and to design more effective cancer chemoprevention clinical trials. To test this hypothesis, we will use different cell culture models with the following specific aims: (1) To investigate whether the activation of the MAPK (ERK, JNK, and p38) pathway by EGCG and other tea polyphenols in two human tumor cell line models (cervical squamous carcinoma HeLa, and colon HT29) is involved in apoptosis. Transfection studies with various cDNA constructs encoding for the MAPK cascade as well as structure-activity relationship of the tea polyphenols in MAPK-induced apoptosis will be performed. (2) To determine whether the stimulation of the caspase (the mitochondria-cytochrome c release pathway and the nonmitochondria-cytochrome c release pathway) pathway induced by EGCG and other tea polyphenols in the two human tumor cell lines (HeLa and HT29) is involved in apoptosis. Transfection studies with cDNAs encoding the anti-apoptotic proteins (Bc12 and CrmA) and pro-apoptotic proteins (death receptors -Fas, TNFR, DR4/5, and Bax, Bid) as well as structure-activity relationship of the tea polyphenols in caspase-induced apoptosis will be performed. These studies will complement the studies in Aim 1 and will provide further understanding of the apoptotic signaling mechanisms of tea polyphenolic compounds. Our long-term goal is to identify the molecular targets of the chemopreventive effect exhibited by EGCG and other tea polyphenols. Such knowledge will help to develop better chemopreventive compounds and to design more effective cancer chemoprevention clinical trials.
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