The Tumor Antigens Tn and SialylTn in Human Colorectal Carcinoma

描述(申请人提供)结直肠癌(CRC)，包括结肠癌和直肠癌，是西方世界癌症死亡的主要原因，但对这种疾病的早期诊断和有针对性的治疗缺乏可靠的生物标志物。肿瘤相关糖类抗原Tn(GalNAc�1-Ser/Thr)和唾液酸Tn(SialylTn)(NeuAc�2-6GalNAc�1-Ser/Thr)常出现在结肠癌发生的早期，与预后不良和肿瘤转移密切相关。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抗原的表达可能是由于T-合成酶功能丧失所致，T-合成酶是正常的核心10-糖聚糖生物合成所必需的，由于其特定的分子伴侣Cosmc的表达受损而导致其不正确的折叠，该分子伴侣由X-连锁(Xq24)基因编码。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、基因的缺失、杂合性丢失及其启动子的高甲基化，可以导致COSMC功能障碍，并与T-合成酶活性和TN/STN的表达丧失相关。我们的初步研究表明，小鼠胃肠道上皮细胞特异性COSMc的丢失导致TN/STN抗原在小肠和大肠中表达。我们假设结直肠癌中的TN和STN肿瘤抗原是人类结肠癌的新的糖链生物标志物，并且起源于COSMC的改变或T-合成酶和/或C3GnT的表达改变。我们将从四个具体目标来探讨这一假说。目的1：确定TN/STN及其他TACA在人原发结肠肿瘤中的表达；目的2：比较结直肠癌细胞与正常细胞的糖链和糖肽谱；目的3：通过鉴定COSMC基因的改变，明确TN/STN在人原发结肠肿瘤中表达的分子机制(S)，并分析其他糖组相关基因的转录水平；目的4：开发对TN或STN抗原具有高度特异性和亲和力的明确的单抗，可用于结直肠癌的诊断和治疗。该项目将确定TN和STN在结直肠癌中表达的分子基础，以及它们作为人类结肠癌新的糖链生物标志物的潜力。

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.