Mohamad Saharuddin B, Nagasawa Hideko, Uto Yoshihiro, Hori Hitoshi
Department of Biological Science and Technology, Faculty of Engineering, The University of Tokushima, Tokushima 770-8506, Japan.
Comp Biochem Physiol A Mol Integr Physiol. 2002 May;132(1):1-8. doi: 10.1016/s1095-6433(01)00522-0.
Alpha-N-acetyl galactosaminidase (alpha-NaGalase) has been reported to accumulate in serum of cancer patients and be responsible for deglycosylation of Gc protein, which is a precursor of GcMAF-mediated macrophage activation cascade, finally leading to immunosuppression in advanced cancer patients. We studied the biochemical characterization of alpha-NaGalase from several human tumor cell lines. We also examined its effect on the potency of GcMAF to activate mouse peritoneal macrophage to produce superoxide in GcMAF-mediated macrophage activation cascade. The specific activity of alpha-NaGalases from human colon tumor cell line HCT116, human hepatoma cell line HepG2, and normal human liver cells (Chang liver cell line) were evaluated using two types of substrates; GalNAc-alpha-PNP (exo-type substrate) and Gal-beta-GalNAc-alpha-PNP (endo-type substrate). Tumor-derived alpha-NaGalase having higher activity than normal alpha-NaGalase, had higher substrate specificity to the exo-type substrate than to the endo-type substrate, and still maintained its activity at pH 7. GcMAF enhance superoxide production in mouse macrophage, and pre-treatment of GcMAF with tumor cell lysate reduce the activity. We conclude that tumor-derived alpha-NaGalase is different in biochemical characterization compared to normal alpha-NaGalase from normal Chang liver cells. In addition, tumor cell-derived alpha-NaGalase decreases the potency of GcMAF on macrophage activation.
据报道，α-N-乙酰半乳糖胺酶（α-NaGalase）在癌症患者血清中蓄积，并负责Gc蛋白的去糖基化，而Gc蛋白是GcMAF介导的巨噬细胞激活级联反应的前体，最终导致晚期癌症患者出现免疫抑制。我们研究了几种人类肿瘤细胞系中α-NaGalase的生化特性。我们还检测了其对GcMAF在GcMAF介导的巨噬细胞激活级联反应中激活小鼠腹腔巨噬细胞产生超氧化物能力的影响。使用两种类型的底物评估了来自人结肠肿瘤细胞系HCT116、人肝癌细胞系HepG2和正常人肝细胞（Chang肝细胞系）的α-NaGalase的比活性；N-乙酰半乳糖胺-α-对硝基苯磷酸酯（外切型底物）和半乳糖-β-N-乙酰半乳糖胺-α-对硝基苯磷酸酯（内切型底物）。肿瘤来源的α-NaGalase活性高于正常α-NaGalase，对外切型底物的底物特异性高于内切型底物，并且在pH 7时仍保持其活性。GcMAF增强小鼠巨噬细胞中超氧化物的产生，而用肿瘤细胞裂解物预处理GcMAF会降低其活性。我们得出结论，与来自正常Chang肝细胞的正常α-NaGalase相比，肿瘤来源的α-NaGalase在生化特性上有所不同。此外，肿瘤细胞来源的α-NaGalase降低了GcMAF对巨噬细胞激活的能力。
