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Hydroquinone (HQ), one of the most important metabolites derived from benzene, is known to be associated with acute myelogenous leukemia risk; however, its carcinogenic mechanism remains unclear. In a previous study, we found that low-level of benzene exposure down-regulated the expression of poly(ADP-ribose)polymerase 1 (PARP1). Here, we employed RNA interference to knock down PARP1 expression in TK6 cells and explored the potential role of PARP1 in HQ-induced cytotoxicity. The results showed that stable PARP1-knockdown cells were successfully constructed and more than 80% inhibition of PARP1 expression was confirmed. We found that HQ treatment of TK6 cells decreased cell viability, increased cell apoptosis, and caspase3/7 activity. Knockdown of PARP1 in HQ-treated TK6 cells prevented caspase3 activation, and increased apoptosis than that in the wild-type TK6 cells, with fully functional PARP1. The results also showed that down-regulation of PARP1 led to a decrease in cell proliferation and an enhanced susceptibility to HQ-induced cytotoxicity with concentration less than 40 μM than that in normal TK6 cells. Moreover, PARP1-knockdown TK6 cells treated with HQ displayed an increased level of DNA double-strand breaks as measured by olive tail moment. No evidence was obtained of an effect of PARP1 depletion on H2AX phosphorylation induction. Under the experimental conditions, PARP1 has a role in HQ-induced DNA damage repair rather than in long-term chromatin modifications signaled by phosphorylated H2AX.

Background: The decoction of Astragalus membranaceus (Huangqi) and Rhizoma curcumae (Ezhu) has been reported as a potential antitumor agent for colorectal cancer (CRC) in experimental and clinical studies, but its underlying mechanism is still unclear. Methods: The current research aims to explore the potential of Astragalus membranaceus (Huangqi) and Rhizoma curcumae (Ezhu) decoction (AR decoction) in the treatment of CRC and explore the underlying mechanism. SW620 cells were transient transfection to overexpress or knock down wnt 5 or β-Catenin. Astragalus membranaceus (Huangqi) and Rhizoma curcumae (Ezhu) -containing serum (AR-CS) was used to interfere with SW620 cells. Additional AR-CS, Wnt5 inhibitor (IWP-4), and β-Catenin inhibitor (JW55) were used to intervene in SW620 cells. Furthermore, subcutaneously injection of SW620 cells into the right flank of nude mice replicated xenograft mice, which were treated with AR decoction for 21 days. Results: AR-CS significantly reduced the mRNA and protein expression levels of Wnt5, β-Catenin, ARF6, and N-Cadherin in SW620 cells, while inhibiting the proliferation and migration of SW620 cells. In cells overexpressing Wnt5 or β-Catenin, these effects of AR-CS were significantly suppressed. On the contrary, the inhibitory effect of AR-CS on the mRNA and protein levels of ARF6 and N-Cadherin and cell proliferation and migration of SW620 was enhanced, when Wnt5 or β-Catenin were knocked down or suppressed by the inhibitors. Moreover, in the mouse model of xenograft tumors, AR decoction not only reduced the tumor volume and inhibited the mRNA levels and protein levels of Wnt5, β-Catenin, ARF6, and N-Cadherin in the tumor, but also inhibit the protein levels of LRP5, LRP6, TCF-4, and LEF1.The histopathology of mice also showed increased apoptosis in tumor tissues, and AR decoction treatment did not cause pathological damage to the kidney and liver. Conclusions: Our results provide evidence that AR decoction inhibits Wnt5/β-catenin signaling and inhibits the development of CRC, which is a promising traditional medicine in the clinical treatment of CRC. [ABSTRACT FROM AUTHOR]