Background and purpose:miRNA plays important roles in tumorigenesis. It has been reported that many kinds of serum miRNA serve as markers for tumor diagnosis and screening. This study aimed to detect the expression of serum miRNA-31 (miR-31) in colorectal cancer patients and to explore the effect of miR-31 on cell proliferation, apoptosis and cell cycle distribution. Methods: The expressions of miR-31 in 40 cases of colorectal cancer serum and 35 cases of the healthy control were examined by real-time lfuorescent quantitative polymerase chain reaction (RTFQ-PCR). The correlation between miR-31 expression and clinicopathological features of colorectal cancer (including age, gender, depth of inifltration, lymph node metastasis, clinical stage) were further analyzed. The miR-31 mimics, inhibitor and miR-control (negative control) were transfected into HCT116 cells. The effect of miR-31 on cell proliferation was evaluated by CCK-8 method. Flow cytometry was used to examine the change of cell apoptosis and cell cycle. Results:Relative expression of serum miR-31 was signiifcantly increased in cancer patients compared with healthy controls (P<0.01). Expression of serum miR-31 was higher in poorly differentiated carcinoma than that in well or moderately differentiated carcinoma (P<0.05). No correlation was found between serum miR-31 expression and other clinicopathological variables. CCK-8 assay showed that after transfection with miR-31 mimics, the cell proliferation was increased, compared with miR-31 inhibitor and negative control group. Meantime, the apoptotic cell number was signiifcantly decreased, particularly in late apoptosis. The cell number of G1 stage was remarkably increased in miR-31 inhibitor group, compared with miR-31mimics and negative control group. Conclusion:The expression of serum miR-31 is higher in colorectal cancer. miR-31 can promote cell proliferation and inhibit the apoptosis of HCT116 cells. It might be a potential biomarker for colorectal cancer.

Human APOBEC3G (hA3G) is a cytidine deaminase which inhibits HIV-1 replication. The HIV-1 accessory protein viral infectivity factor (Vif) counteracts with hA3G by targeting it for proteasomal degradation. In this work, we constructed and optimized molecular models of the hA3G dimer and the hA3G-Vif complex. The molecular modeling study revealed that the loop7 motif of hA3G appears on the interfaces of both the hA3G-Vif complex and the hA3G dimer. Biochemical analysis provided evidence suggesting that binding of Vif to hA3G results in steric blocking of hA3G dimerization, implying that monomeric hA3G serves as a substrate for Vif-mediated degradation. Furthermore, we presented evidence for the important roles of the loop7 motif, especially the central residues within the region, in hA3G dimerization, hA3G--Vif interaction, Vif-mediated hA3G degradation as well as subcellular localization of hA3G. This work highlights a multiple-task interface formed by loop7 motif, which regulates biological function of hA3G, thus providing the feasibility of the strategy of blocking Vif-mediated A3G degradation by targeting the putative site around loop7.