Study On The Function And Transcription Regulation Of β1,4-galactosyltransferase Ⅰ And Ⅴ In Tumor

The carbohydrate moieties of cell surface glycoconjugates play important roles in cell adhesion and metastasis. One of the most prominent transformation-associated changes in the sugar chains of glycoproteins is an increase in the large N-glycans of cell surface glycoprotein. β1, 4-galactosyltransferase (GalT) family are the enzymes responsible for the biosynthesis of N-acetyllactosamine on N-glycans by transferring UDP-galactose to the terminal N-acetylglusamine (N-GlcNAc) residues and this family consist of seven members, from GalT I to GalT VII.β1, 4-galactosyltransferas I plays a critical role in neurite extension, cell growth, sperm-egg interaction, cell spreading and migration. The elevated levels of β1,4-galactosyltransferase I (GalT I; EC 2.4.1.38) are detected in highly metastatic lung cancer PGBE1 cells compared with its less metastatic partner PGLH7 cells. Decreasing the GalT I surface expression by small interfering RNA or interfering with the surface of GalT I function by mutation inhibited cell adhesion on laminin, the invasive potential in vitro and tyrosine phosphorylation of focal adhesion kinase. The mechanism by which GalT I activity is up-regulated in highly metastatic cells remains unclear. We identified β1, 4-Galactosyltransferas I as a target gene of E1AF transcription factor. Stable transfection of the E1AF expression plasmid resulted in increased GalT I expression in PGLH7 cells, and stable transfectants migrated faster than control cells. GalT I expression could be induced by epidermal growth factor and dominant active Ras, JNK1, and ERK1.These data suggest an essential role for E1AF in the activation of the human GalT I gene in highly metastatic lung cancer cells.We also investigate the contribution of GalT I in hepatoma. GalT I is highly expressed in hepatoma tissues, compared to the normal tissues. Moreover, GalT I is regulated by AFB1, TPA, p53 and HBX. In this study, decreasing the expression of GalT I in hepatoma cells inhibited the invasion and migration and the ability of tumor formation in vivo and reduced the expression of Cyclin D1/D3. Furthmore, the ectopic expression of GalT I could promote the invasionand growth of hepatoma cells in a galactosylation-dependent manner. We validated for the first time that E2F1 could directly induce the GalT I expression and be involved in GalT I transcription regulation mediated by AFB1, TPA, p53 and HBX. These results provide genetic evidence and cellular mechanisms of liver tumor, identifying a novel target for hepatoma therapy. GalT V can effectively galactosylate the GlcNAc β1→6Man arm of the highly branched N-glycans that are characteristic of glioma. Previously, we have reported that the expression of GalT V is increased in the process of glioma. In this study, the ectopic expression of GalT V could promote the invasion and survival of glioma cells and transformed astrocytes. Consistent with this, decreasing the expression of GalT V in glioma cells promoted apoptosis, inhibited the invasion and migration and the ability of tumor formation in vivo and reduced the activation of AKT. In addition, the activity of GalT V promoter could be induced by epidermal growth factor, dominant active Ras, ERK1, JNK1 and constitutively active AKT.Furthermore, decreasing the expression of GalT V in SHG44 glioma cells markedly promoted etoposide-induced apoptosis and activation of caspases as well as processing of Bid and expression of Bax and Bak. Conversely, the ectopic expression of GalT V attenuated the apoptotic effect of etoposide on SHG44 cells. In addition, both the GalT V transcription and the binding of total or membrane glycoprotein with RCA-I were partially reduced in etoposide-treated SHG44 cells, correlated well with a decreased level of Spl which has been identified as an activator of GalT V transcription. Collectively, our results suggest that down-regulation of GalT V expression plays an important role in etoposide-induced apoptosis and could be mediated by a decreasing level of Spl in SHG44 cells, indicating that inhibitors of GalT V may enhance the therapeutic efficiency of etoposide for malignant glioma. E1AF transcription factor, which is highly expressed in glioma and induced by epidermal growth factor, plays a critical role in glioma invasion via upregulation of GalT V. Decreasing the expression of E1AF in glioma cells reduced GalT V mRNA expression, inhibited the invasion and migration and blocked the positive effect of EGF on glioma invasion. Furthermore, the ectopic expression of E1AF could promote glioma cell invasion in a GalT V-dependent manner. Interestingly, E1AF regulates the GalT V transcription via physicaland functional interactions with Spl, without binding to Ets-binding sites. Taken together, our results suggest that E1AF functions as a novel glioma invasion activator via upregulation of GalT V and might represent a novel target in glioma therapy.In summary, β1, 4-galactosyltransferases play critical roles in apoptosis, tumor growth and invasion and regulates cell signalings involving in tumor behaviors. However, the mechanisms involving the function of 3 1,4-galactosyltransferases should been clearly investigated.