Date Published: January 31, 2017
Publisher: Public Library of Science
Author(s): Tomohiro Matsuo, Yasuyoshi Miyata, Akihiro Asai, Yuji Sagara, Bungo Furusato, Junya Fukuoka, Hideki Sakai, Chih-Pin Chuu.
Green tea polyphenol (GTP) suppresses carcinogenesis and aggressiveness in many types of malignancies including bladder cancer. However, the mechanistic basis of these effects is not well understood. This was investigated in the present study using a mouse model of chemically induced bladder cancer. C3H/He mice (8 weeks old; n = 46) were treated with 0.05% N-butyl-N-(4-hydroxybutyl) nitrosamine (BBN) solution for 14–24 weeks. Mice in the BBN + GTP group (n = 47) were also treated with 0.5% GTP solution over the same period. Tumor cell proliferation and microvessel density were evaluated along with immunohistochemical analysis of human antigen (Hu)R, vascular endothelial growth factor (VEGF)-A, cyclooxygenase (COX)-2, and hemeoxygenase (HO)-1 expression. Cytoplasmic HuR expression in cancer cells was higher at 14 and 24 weeks in the BBN than in the control group and was associated with increased invasion of tumor cells in muscle. However, these effects were not observed in the BBN + GTP group. A multivariate analysis of GTP intake and cytoplasmic HuR expression revealed that GTP was independently associated with COX-2 and HO-1 expression, while cytoplasmic HuR expression was associated with COX-2 and VEGF-A levels. Expression of COX-2 and HO-1 was associated with cell proliferation and that of VEGF-A and HO-1 was associated with angiogenesis. Nuclear HuR expression was not associated with any parameters such as carcinogenesis, muscle invasion, and GTP intake. These results indicate that GTP intake can suppress tumor progression and malignant behavior in an animal model of bladder cancer. We also speculate that GTP directly and indirectly suppresses tumor cell proliferation and angiogenesis via HuR-related pathways in bladder cancer.
Green tea is known to have health-promoting effects that are attributed to catechin polyphenols, which have anti-inflammatory and -oxidative properties [1, 2]. Many studies have demonstrated the anti-cancer effects of green tea polyphenol (GTP) in a variety of malignancies [3, 4, 5], and epidemiologic studies have shown that green tea consumption reduces cancer risk . New cancer treatment strategies in combination with GTP intake have been recommended for several types of cancer [7, 8]. Thus, GTP is thought to be useful not only for cancer prevention but also for treatment.
The present study investigated changes in HuR expression following GTP intake in bladder cancer, based on the findings that HuR expression is positively associated with tumor aggressiveness—including muscle invasion—in bladder cancer patients ; GTP inhibits HuR expression in leukemia cells ; and HuR regulates the expression of various cancer-related molecules in many types of malignancy [22, 23, 30]. Our results in mice showed that cytoplasmic HuR expression was higher in cancer than in non-cancer cells, and higher in invasive as compared to non-invasive cases. These findings are consistent with trends in HuR expression reported in human bladder cancer . We also confirmed for the first time in vivo that cytoplasmic HuR expression was downregulated by GTP intake. Finally, our univariate analysis showed that cytoplasmic HuR expression was associated with tumor volume, angiogenesis, tumor cell proliferation, and expression of COX-2, VEGF-A, and HO-1, which are known to induce malignant transformation of bladder cancer [27, 31]. These results indicate that our animal model is suitable for investigating the pathological roles of HuR in human bladder cancer.
Cytoplasmic HuR expression was upregulated in BBN-induced mouse bladder cancer cells and was associated with increased muscle invasion, effects that were abrogated by GTP intake. Similarly, GTP suppressed tumor cell proliferation, angiogenesis, and expression of the cancer-related factors VEGF-A, COX-2, and HO-1. These findings suggest that GTP inhibits bladder cancer progression by direct and indirect modulation of HuR.