The Tumor Antigens Tn and SialylTn in Human Colorectal Carcinoma

结肠直肠癌（CRC），包括结肠癌和直肠癌，是西方世界癌症死亡的主要原因，但缺乏可用于该疾病的早期诊断和靶向治疗的可靠生物标志物。肿瘤相关糖抗原（TACA）Tn（GalNAc <$1-Ser/Thr）和sialylTn（STn）（NeuAc <$2 - 6 GalNAc <$1-Ser/Thr）通常出现在结肠癌发生的早期阶段，并且与不良预后和肿瘤转移相关。然而，Tn/STn抗原表达的遗传基础尚不清楚。我们最近发现，Tn/STn抗原的表达可由正常核心10-聚糖生物合成所需的T-合酶的功能丧失引起，这是由于其特异性分子伴侣Cosmc（其由X-连锁（Xq 24）基因编码）的表达受损导致其不正确折叠。我们发现，在人类肿瘤和肿瘤细胞系中，Cosmc的获得性突变，包括编码区的点突变、基因缺失、杂合性缺失和启动子的超甲基化，可导致Cosmc功能障碍，并伴有T合酶活性和Tn/STn表达的丧失。我们的初步研究现在表明，胃肠道（GI）道上皮细胞特异性Cosmc在小鼠中的损失导致Tn/STn抗原在小肠和大肠中的表达。我们假设CRC中的Tn和STn肿瘤抗原是人类结肠癌的新型聚糖生物标志物，并且是由Cosmc的改变或T合酶和/或C3 GnT的表达改变引起的。我们将在四个具体目标中探讨这一假设。目标1：目的2：比较结直肠癌细胞与正常细胞的聚糖和糖肽谱;目的3：通过鉴定Cosmc的改变，以及分析其他糖组学相关基因的转录水平，来确定人原发性结肠肿瘤中Tn/STn表达的分子机制;以及目的4：研制出对Tn或STn抗原具有高度特异性和亲和力的单克隆抗体，可用于结直肠癌的诊断和治疗。该项目将确定Tn和STn在CRC中表达的分子基础及其作为人类结肠癌新型聚糖生物标志物的潜力。

DESCRIPTION (provided by applicant) Colorectal carcinoma (CRC), including colon and rectal cancer, is a leading cause of cancer deaths in the Western world but reliable biomarkers useful for early diagnosis and targeted therapy of this disease are lacking. The tumor-associated carbohydrate antigens (TACAs) termed Tn (GalNAc¿1-Ser/Thr) and sialylTn (STn) (NeuAc¿2-6GalNAc¿1-Ser/Thr) often appear at an early stage of colon carcinogenesis, and are associated with poor prognosis and tumor metastasis. However, the genetic basis for Tn/STn antigen expression is unclear. We recently found that expression of the Tn/STn antigens can arise from loss-of-function of T-synthase, required for normal core 1 O-glycans biosynthesis, due to its incorrect folding as a result of compromised expression of its specific molecular chaperone Cosmc, which is encoded by an X-linked (Xq24) gene. We showed that in human tumors and tumor cell lines, acquired mutations in Cosmc, which include point mutations in the coding region, deletion of the gene, loss-of-heterozygosity, and hypermethylation of its promoter, can result in a dysfunctional Cosmc associated with loss of T-synthase activity and expression of Tn/STn. Our preliminary studies now show that gastrointestinal (GI) tract epithelial cell-specific loss of Cosmc in mice causes Tn/STn antigen expression in the small and large intestine. We hypothesize that Tn and STn tumor antigens in CRC are novel glycan biomarkers for human colon cancer and arise from alterations in Cosmc or altered expression of T-synthase and/or C3GnT. We will explore this hypothesis in 4 specific aims. Aim 1: define the expression of Tn/STn and other TACAs in human primary colon tumors; Aim 2: compare glycan and glycopeptide profiles of colorectal carcinoma cells to normal cells; Aim 3: define the molecular mechanism(s) for Tn/STn expression in human primary colon tumors by identifying the alterations in Cosmc, as well as analyze transcript levels for other glycomics-relevant genes; and Aim 4: develop well- defined monoclonal antibodies that exhibit both high specificity and affinity to Tn or STn antigens, which could be used in both diagnosis and treatment of CRC. This project will define the molecular basis for Tn and STn expression in CRC and their potential as novel glycan biomarkers for human colon cancer.