Advanced Centre for Treatment, Research and Education in Cancer, Tata Memorial Centre, Kharghar, Navi Mumbai 410210, India.
Free Radic Biol Med. 2012 Sep 15;53(6):1358-70. doi: 10.1016/j.freeradbiomed.2012.07.017. Epub 2012 Jul 27.
Polymeric black tea polyphenols (PBPs) have been shown to possess anti-tumor-promoting effects in two-stage skin carcinogenesis. However, their mechanisms of action are not fully elucidated. In this study, mechanisms of PBP-mediated antipromoting effects were investigated in a mouse model employing the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA). Compared to controls, a single topical application of TPA to mouse skin increased the translocation of protein kinase C (PKC) from cytosol to membrane. Pretreatment with PBPs 1-3 decreased TPA-induced translocation of PKC isozymes (α, β, η, γ, ε) from cytosol to membrane, whereas PBPs 4 and 5 were less effective. The levels of PKCs δ and ζ in cytosol/membrane were similar in all the treatment groups. Complementary confocal microscopic evaluation showed a decrease in TPA-induced PKCα fluorescence in PBP-3-pretreated membranes, whereas pretreatment with PBP-5 did not show a similar decrease. Based on the experiments with specific enzyme inhibitors and phosphospecific antibodies, both PBP-3 and PBP-5 were observed to decrease TPA-induced level and/or activity of phosphatidylinositol 3-kinase (PI3K) and AKT1 (pS473). An additional ability of PBP-3 to inhibit site-specific phosphorylation of PKCα at all three positions responsible for its activation [PKCα (pT497), PKC PAN (βII pS660), PKCα/βII (pT638/641)] and AKT1 at the Thr308 position, along with a decrease in TPA-induced PDK1 protein level, correlated with the inhibition of translocation of PKC, which may impart relatively stronger chemoprotective activity to PBP-3 than to PBP-5. Altogether, PBP-mediated decrease in TPA-induced PKC phosphorylation correlated well with decreased TPA-induced NF-κB phosphorylation and downstream target proteins associated with proliferation, apoptosis, and inflammation in mouse skin. Results suggest that the antipromoting effects of PBPs are due to modulation of TPA-induced PI3K-mediated signal transduction.
聚合型红茶多酚（PBPs）已被证明在二阶段皮肤致癌作用中具有抗肿瘤促进作用。然而，其作用机制尚未完全阐明。在这项研究中，我们使用肿瘤促进剂 12-O-十四烷酰佛波醇-13-乙酸酯（TPA）在小鼠模型中研究了 PBP 介导的抗促进作用的机制。与对照组相比，TPA 单次局部应用于小鼠皮肤会增加蛋白激酶 C（PKC）从细胞质向膜的易位。用 PBPs 1-3 预处理可降低 TPA 诱导的 PKC 同工酶（α、β、η、γ、ε）从细胞质向膜的易位，而 PBPs 4 和 5 的效果则较差。所有治疗组的细胞质/膜中 PKCs δ 和 ζ 的水平相似。互补的共聚焦显微镜评估显示，在 PBP-3 预处理的膜中，TPA 诱导的 PKCα 荧光减少，而 PBP-5 预处理则没有显示出类似的减少。基于使用特异性酶抑制剂和磷酸特异性抗体的实验，观察到 PBP-3 和 PBP-5 均能降低 TPA 诱导的磷脂酰肌醇 3-激酶（PI3K）和 AKT1（pS473）的水平和/或活性。PBP-3 还具有抑制 PKCα 在负责其激活的三个位置[PKCα（pT497）、PKC PAN（βII pS660）、PKCα/βII（pT638/641）]和 AKT1 在 Thr308 位置的特异性磷酸化的能力，以及降低 TPA 诱导的 PDK1 蛋白水平，这与 PKC 的易位抑制相关，这可能使 PBP-3 比 PBP-5 具有相对更强的化学保护活性。总之，PBP 介导的 TPA 诱导的 PKC 磷酸化减少与 TPA 诱导的 NF-κB 磷酸化以及与小鼠皮肤增殖、凋亡和炎症相关的下游靶蛋白减少密切相关。结果表明，PBPs 的抗促进作用是由于调节 TPA 诱导的 PI3K 介导的信号转导。
