AIM:To evaluate effects of different chemotherapeutic agents on reversing the acquired resistance to TRAIL gene and clarify the involved mechanisms in DLD1-TRAIL/R colon cancer cells.METHODS: Human colon cancer cell line DLD1-TRAIL/R cells that were resistant to TRAIL-expressing adenovector(Ad/gTRAIL) were treated with Ad/gTRAIL combined with different chemotherapeutic agents.Then,the cell viability was measured by MTT method,and apoptotic signaling conditions,including activation of caspase-3 and caspase-8,expression of Bax and Bcl-XL,were measured by Western blotting analysis.RESULTS: In vitro data showed that several chemotherapeutic agents,including 5-fluorouracil(5-FU) and mitomycin c(MMC),overcome the acquired resistance to TRAIL gene in DLD1-TRAIL/R colon cancer cells.The combination of Ad/gTRAIL and 5-FU effectively suppressed tumor growth in vivo in subcutaneous tumors established from DLD1-TRAIL/R cells.Further data showed that treatment with the combination of Ad/gTRAIL and 5-FU or MMC led to enhance the activation of caspase-3.Moreover,MMC but not 5-FU induced overexpression of Bax gene that was sufficient to overcome the resistance to TRAIL gene in DLD1-TRAIL/R cells.CONCLUSION: Chemotherapeutic agents,such as 5-FU and MMC,overcome the acquired resistance to TRAIL gene in DLD1-TRAIL/R cells.The candidate mechanisms for MMC but not 5-FU to overcome this resistance might involve the induction of over-expressed Bax protein in DLD1-TRAIL/R cells.

Background::Ubiquitination plays an essential role in many biological processes, including viral infection, and can be reversed by deubiquitinating enzymes (DUBs). Although some studies discovered that DUBs inhibit or enhance viral infection by various mechanisms, there is lack of information on the role of DUBs in virus regulation, which needs to be further investigated.Methods::Immunoblotting, real-time polymerase chain reaction, in vivo/ in vitro deubiquitination, protein immunoprecipitation, immunofluorescence, and co-localization biological techniques were employed to examine the effect of ubiquitin-specific protease 3 (USP3) on APOBEC3G (A3G) stability and human immunodeficiency virus (HIV) replication. To analyse the relationship between USP3 and HIV disease progression, we recruited 20 HIV-infected patients to detect the levels of USP3 and A3G in peripheral blood and analysed their correlation with CD4 + T-cell counts. Correlation was estimated by Pearson correlation coefficients (for parametric data). Results::The results demonstrated that USP3 specifically inhibits HIV-1 replication in an A3G-dependent manner. Further investigation found that USP3 stabilized 90% to 95% of A3G expression by deubiquitinating Vif-mediated polyubiquitination and blocking its degradation in an enzyme-dependent manner. It also enhances the A3G messenger RNA (mRNA) level by binding to A3G mRNA and stabilizing it in an enzyme-independent manner. Moreover, USP3 expression was positively correlated with A3G expression ( r= 0.5110) and CD4 + T-cell counts ( r= 0.5083) in HIV-1-infected patients. Conclusions::USP3 restricts HIV-1 viral infections by increasing the expression of the antiviral factor A3G. Therefore, USP3 may be an important target for drug development and serve as a novel therapeutic strategy against viral infections.