| Glycosphingolipids (GSLs) are characteristic components of vertebrate plasma membranes and have the same hydrophobic residue, ceramide, which consists of a sphingosine and a fatty acid. GSLs have been defined as tumor antigens, receptors for microbes and their toxins, and possible modulators of cell proliferation, differentiation, and cell-cell interactions through which GSLs exert its function on cell invasiveness and metastasis. Recently, we found that GM3 regulated cell behaviors including cell shape, cell motility, proliferation and metastasis in B16 cells by transfering cells with B4Gal-T6 sense or antisense cDNA (SM-1 and CSSH-1 are mock and B4Gal-T6 sense cDNA transfectant monoclonal cell lines respectively; CM-1 and CAH-3 are mock and B4Gal-T6 antisense cDNA transfectant monoclonal cell lines respectively).Furthermore, GM3 down-regulation by siRNA targeting St3gal5 (GM3 synthase) resulted in change the cell behaviors including cell shape, cell motility and proliferation. The St3gal5 siRNA transfected cells (one of monoclonal transfectants was B11 cells) were round and refractile and tended to grow distinctly from parental B16 cells. The motility of B11 cells was decreased and cell motlility was possibly mediated by MMP-9. B11 cells proliferated easily in serum free condition or soft agar, possibly because GM3 down regulation enhances its malignancy compared with control cells. Arhgdib was found as a downstream molecule through which GM3 exerts its function on cell behaviors. We further verified that GM3 regulated Arhgdib expression via PI3K/Akt/mTOR pathway. PDK1 in particular was shown to play a critical role in GM3 mediating Arhgdib expression. Moreover, knocking down Arhgdib obviously changed cell shape, modulated cell motility and proliferation just as GM3 expression was suppressed in B16 cells. These results suggested concretely that GM3 modulated cell behaviors via Arhgdib. Finally, TNFαwas screened as a target of Arhgdib.
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