β1,3-N-acetylglucosaminyltransferase 3 在大腸直腸癌中的表現及功能

Abstract

β1,3-N-acetylglucosaminyltransferase 3 (B3GNT3)是屬於β3-GnT family 成員之一。B3GNT3 會表現在high endothelial venule 中並且具有形成core 1 extention structure 的能力而調控lymphocyte homing，除此之外，在KJM-1 pymphoma cells中，B3GNT3 也可以促使poly-N-acetyllactosamine 的生成。T antigen 為一雙醣的結構(Galβ1,3GalNAc)，也稱作core 1 structure，在大腸癌、乳癌、前列腺癌、肝癌以及胃癌中，T antigen 的表現較正常組織來的高，而T antigen 的表現也與tumor progression 和metastasis 有關。雖然B3GNT3 在正常大腸組織中會大量的表現，然而在大腸癌中不論是生理或病理上的功能卻幾乎不了解。我們假設B3GNT3 會經由調控T antigen 或poly-N-acetyllactosamine 而影響大腸癌細胞的行為，在此篇研究中，藉由real-time PCR 發現，在80.46% (70/87)的病人身上，大腸直腸腫瘤中B3GNT3 mRNA 的表現量較正常組織來的低， 而在Western blotting 及immunohistochemistry (IHC)中我們也觀察到B3GNT3 蛋白質的表現在腫瘤組織中較正常組織來的低，除此之外，由IHC 也指出B3GNT3 表現在上皮細胞中，而非基質細胞。為了研究B3GNT3 對於大腸癌細胞的影響，我們建立了能夠大量表現B3GNT3 的HCT116 穩定選殖細胞株。由flow cytometry 的結果顯示，B3GNT3 的大量表現會造成Erythrina cristagalli agglutinin (ECA)與細胞表面的結合變弱，然而能夠辨識細胞表面T antigen 的peanut agglutinin (PNA)卻沒有明顯的變化。大量表現B3GNT3 的HCT116 細胞呈現epithelial-like morphology、細胞proliferation 的能力下降、以及ERK/MAPK 的磷酸化程度減少。由此篇研究發現，B3GNT3 的表現在大部份的大腸直腸癌中有下降的情況發生，而B3GNT3 的過量表現也會抑制了大腸癌細胞的生長。

β1,3-N-acetylglucosaminyltransferase 3 (B3GNT3) is a member of β3-GnT family. It has been found to be expressed in the high endothelial venule and has a core 1 extension enzyme activity to modulate lymphocyte homing. In addition, B3GNT3 can catalyze the biosynthesis of poly-N-acetyllactosamine in KJM-1 lymphoma cells. The disaccharide structure, Galβ1,3GalNAc, is called T antigen or core 1 structure, which is overexpressed in colon, breast, prostate, liver, and stomach tumors. T antigen expression is closely associated with tumor progression and metastasis. Although B3GNT3 is highly expressed in colon tissues, its biological and pathological roles in colorectal cancer are still largely unknown. Here we hypothesized that B3GNT3 could regulate the expression of T antigen and/or poly-N-acetyllactosamine and, in turn, modulate colon cancer cell behavior. In the present study, results from real-time PCR showed that B3GNT3 mRNA expression was down-regulated in 80.46% (70/87) of colorectal tumor tissues compared with their normal counterparts. We also found that B3GNT3 protein was down-regulated in colorectal tumors by Western blotting and immunohistochemistry. Furthermore, immunohistochemistry indicated that B3GNT3 was expressed in the colonic epithelia, but not in stromal cells. To analyze the effects of B3GNT3 on colon cancer cells, HCT116 cells were stably transfected with B3GNT3. Flow cytometry showed that B3GNT3 overexpression decreased ECA lectin binding on the cell surface. However, the binding of PNA lectin, which recognizes T antigen, was not significantly changed. In addition, HCT116 cells overexpressing B3GNT3 showed an epithelial-like morphology and a decreased proliferation compared with control cells, which was associated with a decrease in the phosphorylation of ERK/MAPK. In conclusion, B3GNT3 is frequently downregulated in colorectal cancer and its overexpression suppresses colon cancer cell growth.