Yuanyan Wei

α2,3-Sialylation regulates the stability of stem cell marker CD133

CD133 is widely used as a marker for the isolation and characterization of normal and cancer stem cells. The dynamic alternation of CD133 glycosylation contributes to the isolation of normal and cancer stem cells, and is supposed to be associated with cell differentiation. Although CD133 has been identified as a N-glycosylated protein, the specific glycosylation status of CD133 remain unclear. Here, we found that CD133 could be sialylated in neural stem cells and glioma-initiating cells, and the sialyl residues attach to CD133 N-glycan terminal via alpha2,3-linkage. Furthermore, desialylation of CD133 by neuraminidase specifically accelerates its degradation in lysosomes-dependent pathway. Taken together, our results characterized CD133 as an alpha2,3-sialylated glycoprotein and revealed that the sialylation modification contributes to the stability of CD133 protein, providing clues to understanding the function of CD133 molecular and to understanding the utility of glycosylated CD133 epitopes in defining neural stem cells and tumour-initiating cells.

Knockdown of BCL2L12 leads to cisplatin resistance in MDA-MB-231 breast cancer cells.

BCL2L12, a newly identified member of Bcl-2 family, contains a BH2 domain and a putative BH3 domain. It was found to be highly expressed in normal breast tissues, and was associated with favorable prognosis in breast cancer patients. Here, we reported that the mRNA levels of BCL2L12 and its transcript variant BCL2L12A could be upregulated upon cisplatin treatment in MDA-MB-231 breast cancer cells. Knockdown of BCL2L12 and BCL2L12A dramatically inhibited cisplatin-induced apoptosis. In contrast, ectopic expressions of each of the proteins promoted cisplatin-induced apoptosis. These results indicated that decreased expressions or loss of BCL2L12 and BCL2L12A may contribute to the cisplatin resistance in breast cancer patients. Furthermore, we found that cisplatin-induced downregulation of beta-catenin was partially suppressed in BCL2L12- and BCL2L12A-knocked down MDA-MB-231 cells, which indicated that knockdown of these two proteins may stabilize beta-catenin in cisplatin-induced apoptosis. In short, we proposed that BCL2L12 and BCL2L12A may play an important role in cisplatin-induced apoptosis in MDA-MB-231 breast cancer cells.

Identification of β-1,4-galactosyltransferase I as a target gene of HBx-induced cell cycle progression of hepatoma cell ☆

BACKGROUND/AIMS The hepatitis B virus-encoded HBx protein contributes to hepatocarcinogenesis with largely unknown mechanisms. It is widely known that N-linked oligosaccharides on glycoproteins are structurally altered during malignant transformation and these alterations are often associated with malignant transformation of cells. beta-1,4-galactosyltransferase I (GalT I) contributes to the biosynthesis of Galbeta-->4GlcNAc structure in the outer chain moieties of N-glycans. METHODS The difference of GalT I expression between normal liver and hepatoma tissues were investigated; the effect of HBx on GalT I expression was investigated; the role of GalT I in hepatoma cell growth and HBx-induced hepatoma cell growth were investigated. RESULTS GalT I was highly expressed in hepatocellular carcinoma and transcriptionally up-regulated by HBx, and functioned as a positive growth regulator in hepatoma cells. Furthermore, decreasing the expression of GalT I in hepatoma cells reduced the ability of tumor formation in vivo and inhibited HBx-induced cell cycle progression. CONCLUSIONS HBx-induced GalT I expression might contribute to HBx-mediated HCC development and progression.

Down-regulation of β1,4GalT V at protein level contributes to arsenic trioxide-induced glioma cell apoptosis

Arsenic trioxide (As2O3) has considerable efficacy in treating solid tumors with induction of apoptosis with largely unknown mechanisms. Posttranslational processing of proteins by glycosylation could have multiple regulating roles in the process of apoptosis. Here, we found that the expression of beta1,6-linked GlcNAc-bearing N-glycans on cell surface protein was gradually decreased after induction of apoptosis by As2O3-treatment. And, As2O3 significantly decreased the protein expression level of beta1,4GalT V, which effectively galactosylates the beta1,6-GlcNAc branch of N-glycans and functions as a positive regulator in glioma development. Furthermore, interfering with the expression of beta1,4GalT V in human glioma cell markedly promoted As2O3-induced cell apoptosis and beta1,4GalT V overexpression significantly reduced As2O3-induced glioma cell apoptosis. Taken together, our results suggested that down-regulation of beta1,4GalT V expression plays an important role in As2O3-induced apoptosis, providing a new mechanism of As2O3-induced cell apoptosis and indicating that inhibitors of beta1,4GalT V may enhance the therapeutic efficiency of As2O3 for malignant glioma.

β1,4-Galactosyltransferase V regulates self-renewal of glioma-initiating cell

Glioma results from unregulated expansion of a self-renewing glioma-initiating cell population. The regulatory pathways which are essential for sustaining the self-renewal of glioma-initiating cells remain largely unknown. Cell surface N-linked oligosaccharides play functional roles in determining cell fate and are associated with glioma malignancy. Previously, we have reported that beta1,4-galactosyltransferase V (beta1,4GalT V) effectively galactosylates the GlcNAcbeta1-->6Man arm of the highly branched N-glycans and positively regulates glioma cell growth. Here, we show that decreasing the expression of beta1,4GalT V by RNA interference in glioma cells attenuated the formation of polylactosamine and inhibited the ability of tumor formation in vivo. Down-regulation of beta1,4GalT V depleted CD133-positive cells in glioma xenograft, and inhibited the self-renewal capacity and the tumorigenic potential of glioma-initiating cells. These data reveal a critical role of beta1,4GalT V in the self-renewal and tumorigenicity of glioma-initiating cells, and indicate that manipulating beta1,4GalT V expression may have therapeutic potential for the treatment of malignant glioma.

Identification of E1AF as a Target Gene of E2F1-induced Apoptosis in Response to DNA Damage

Transcription factor E1AF plays critical roles in neuronal development and tumour metastasis and is regulated by a number of signalling cascades, including the mitogen-activated protein kinase pathways. Accumulated evidence indicted that E1AF might contribute to cell survival in response to environment factors. Here, we provided evidence the cell cycle and apoptosis regulator E2F1 induces E1AF expression at the transcriptional level. DNA damage by etoposide causes E2F1-dependent induction of E1AF expression at transcriptional level. Furthermore, disruption of E1AF expression by E1AF RNAi decreased E2F1-induced apoptosis in response to etoposide. Thus, we conclude that activation of E1AF provides a means for E2F1 to induce cell apoptosis in response to DNA damage.

Regulation of the β1,4-Galactosyltransferase I promoter by E2F1

Cell surface carbohydrate chains are widely known to contribute to cell migration, recognition and proliferation. beta1,4-Galactosyltransferase I (beta1,4GalT I) transfers galactose to the terminal N-acetylglucosamine of complex-type N-glycan, and contributes to cell proliferation, differentiation and migration. Here, we identified beta1,4GalT I as a novel target gene of cell cycle regulator E2F1. E2F1 proteins interact with the promoter of the beta1,4GalT I gene in vivo, and E2F1 over-expression stimulates the activity of beta1,4GalT I promoter and the mRNA and protein expression of beta1,4GalT I, and augments the level of beta1, 4-galactosyltion. Site-specific mutagenesis revealed that this region which contains two E2F1 binding site (nt -215 to -207 and +1 to +6) is necessary for beta1,4GalT I activation by E2F1. Furthermore, down-regulation of beta1,4GalT I expression attenuates E2F1-induced DNA synthesis and cell cycle progression as well as the expression of cell-cycle regulator Cyclin D1. Thus, beta1,4GalT I is an important E2F1 target gene that is required for cell cycle progression in mammalian cells, which elicits a new mechanism of cell growth and a new mechanism of beta1,4GalT I transcription.

E1AF promotes mithramycin A-induced Huh-7 cell apoptosis depending on its DNA-binding domain.

Transcription factor E1AF is widely known to play critical roles in tumor metastasis via directly binding to the promoters of genes involved in tumor migration and invasion. Here, we reported for the first time the pro-apoptotic role of E1AF in tumor cells. The expression of E1AF at protein level was obviously increased during Huh-7 and Hep3B cells apoptosis induced by the anticancer agent mithramycin A. E1AF overexpression markedly enhanced mithramycin A-induced Huh-7 cell apoptosis and the expression of pro-apoptotic protein Bax depending on its DNA-binding domain. And, reduction of E1AF inhibited mithramycin A-induced Huh-7 cell apoptosis. Furthermore, reducing the expression of Bax significantly inhibited E1AF-increased Huh-7 cell apoptosis induced by mithramycin A. Taken together, E1AF increases mithramycin A-induced Huh-7 cells apoptosis and Bax expression depending on its DNA-binding domain, indicating that E1AF might contribute to the therapeutic efficiency of mithramycin A for hepatoma.