α-1,3-Fucosyltransferase-VII siRNA inhibits the expression of SLe(x) and hepatocarcinoma cell proliferation

The increased expression of sialyl-Lewisx (SLe(x)) epitope on the surface of tumor cells has been known for decades. However, genetic manipulation of the expression of SLe(x) and the role of SLe(x) in cancer cell proliferation remains to be fully elucidated. The present study suggested that the monoclonal antibody of SLe(x) (KM93) significantly inhibited the proliferation of human hepatocarcinoma (HCC) cells. The expression levels of three sialyl-Lewis oligosaccharide antigens, SLe(x), SLe(a) and dimeric SLe(x) (SDLe(x)), were determined on the cell surface of the MHCC97 human HCC cell line. The expression of SLe(x) was markedly higher in MHCC97 cells than in normal liver cells. The expression of SDLe(x) was also relatively high, however, no significant difference was observed between normal liver cells and HCC cells. The expression of SLe(a) was only detected in trace quantities. Fucosyltransferase (FUT) is the key enzyme of the fucosylation step in the biosynthesis of sialyl-Lewis oligosaccharide antigens. Therefore, the present study investigated the expression of FUTs. It was found that the mRNA and protein expression levels of FUT7 were high in the MHCC97 HCC cell line compared with levels in normal liver cells. FUT6 was also expressed at a high level, although the difference was not statistically significant between MHCC97 cells and normal liver cells. No expression of FUT3 was detected. The results were consistent with the change insialyl-Lewis antigens. The effects of FUT7 small interfering (si)RNA transfection on the expression of FUT7, expression of SLe(x) and MHCC97 cell proliferation were also examined. Following FUT7 siRNA transfection, the expression of FUT7 was markedly downregulated, as determined by western blot and reverse transcription-quantitative polymerase chain reaction methods. The results from flow cytometry showed that the synthesis of SLe(x) was also inhibited, which was consistent with the downregulated expression of FUT7. MHCC97 cell proliferation was also significantly inhibited following FUT7 siRNA transfection, which was correlated with suppression of the S-phase in cell cycle progression. By using inhibitors of various signaling pathways, it was found that the knockdown of FUT7 inhibited the activation of phospholipase Cγ (PLCγ) by inhibiting the translocation and phosphorylation of PLCγ. In conclusion, the results suggested that FUT7 has animportant functional role in human HCC cell proliferation by controlling cell cycle progression via the PLCγ/extracellular signal-regulated kinase signaling pathway. The inhibition of SLe(x) and FUT7 siRNA transfection may provide a novel therapeutic methodology to treat tumors that express SLe(x) glycoconjugates.