Human GalNAc Transferase Isozyme Expression in Cancer Cells

1.用合成肽免疫兔制备了抗人UDP-N-乙酰半乳糖胺两种同工酶：多肽N-乙酰氨基半乳糖转移酶(T1和T2)的多克隆抗体。用免疫组织化学方法研究T1和T2在正常和癌组织中的表达和定位。在13例结肠癌组织中，T1和T2分别有1例(8%)和9例(69%)表达。在6例结肠癌患者的正常结肠组织和20例正常结肠组织中均未见T1和T2的表达。这些结果表明T2蛋白在结肠上皮细胞癌变过程中异质性和上调表达。定量检测了胰腺、结肠、胃和乳腺腺癌细胞系中三种UDP-N-乙酰半乳糖胺：多肽N-乙酰氨基半乳糖转移酶(T1、T2和T3)的mRNA表达水平。T1和T2在所检测的大多数或所有细胞系中呈组成性表达，且低水平表达。三碘甲腺原氨酸差异表达。高分化的腺癌细胞株表达高水平的T3，而中等分化的腺癌细胞株表达低水平的T3。被归类为低分化的细胞株未能在Northern印迹分析中检测到T3mRNA的表达水平。Western blotting证实这些细胞系中存在T3蛋白的差异表达。我们认为肿瘤细胞的糖基化可能部分是通过UDP-N-乙酰半乳糖胺：多肽N-乙酰氨基半乳糖转移酶的差异表达来调节的。

1.Polyclonal antibodies against two isozymes of the human UDP-N-acetylgalactosamine : polypeptide N-acetylgalactosaminyltransferase (T1 and T2) were produced by immunizations of rabbits with synthetic peptides. Histological expression and localization of T1 and T2 in normal and cancer colon tissues were studied by immunohistochmical analysis with these antibodies. In cancer tissuses, T1 and T2 expressions were observed in 1 (8%) and 9 (69%) out of 13 patients with colon cancer, respectively. In normal counterpart of colon tissues in 6 patients with colon cancer and in normal colon tissues in 20 subjects, neither T1 nor T2 expression was observed. These results showed the heterogeneous and up-regulated expression of T2 protein during carcinogenesis of colon epithelial cells.The levels of mRNA expression of three UDP-N-acetylgalactosamine : polypeptide N-acetylgalactosaminyltransferase (T1, T2, and T3) were quantified for human adenocarcinoma cell lines from pancreas, colon, stomach, and breast. T1 and T2 were expressed constitutively and at low levels in most or all cell lines examined. T3 was differentially expressed. Well-differentiated adenocarcinoma cell lines expressed high levels and moderately differetiated cell lines expressed lower levels of T3. Cell lines classified as poorly differentiated failed to express T3 mRNA at levels that could be detected by Northern blot analysis. Differential expression of the T3 protein was confirmed in these cell lines by Western blotting. We propose that glycosylation in tumor cell lines may be regulated in part by differential expression of UDP-N-acetylgalactosamine : polypeptide N-acetylgalactosaminyltransferase.