Mucin Glycoproteins in Colon Cancer Metastasis

描述（由申请人提供）：结直肠癌是美国癌症相关死亡的第二大常见原因。结直肠癌相关死亡在很大程度上是由于转移，这是一个复杂的多阶段过程，肿瘤细胞逃离原发肿瘤并在远处建立继发灶。黏液蛋白是结肠的主要分泌糖蛋白，半乳糖凝集素-3是一种内源性黏液蛋白结合蛋白，它们都与人类结肠癌细胞的转移潜力有关。通过鉴定相互作用的配体和结构基序，现在出现了支持粘蛋白和半乳糖凝集素-3特殊功能的直接证据。虽然MUC2粘蛋白基因编码的粘蛋白在转移中的作用已经确定，但MUC2的哪些结构域是促进结肠癌细胞转移所必需的，还有待确定。半乳糖凝集素-3也由不同的结构域组成，这有助于其多效性功能。该蛋白可能定位于细胞核、细胞质、细胞表面或被分泌，因此可能以多种方式促进转移。我们实验室最近的研究表明，半乳糖凝集素-3在转录水平上调节结肠癌细胞中MUC2的表达，并且该蛋白的磷酸化可能是实现这一功能所必需的。本研究的长期目标是确定结肠癌细胞的细胞表面和分泌的糖蛋白如何影响其转移能力，以及半乳糖凝集素-3和MUC2如何相互作用以促进转移。我们假设黏液蛋白载脂蛋白和半乳糖凝集素-3的特定结构域对于它们的转移增强作用是必要的，并且这些分子在转移过程中相互作用促进肿瘤扩散。这一认识可能会导致靶向治疗的发展，以干扰转移。为了实现这些目标，提出了以下具体目标1)“确定分泌黏液蛋白和黏液蛋白异构体在结肠癌转移中的作用”这一目标将研究MUC2结构域和相关的碳水化合物结构与转移有关。2)“确定半乳糖凝集素-3与其碳水化合物配体相互作用的生物学意义”。本研究旨在确定碳水化合物结构，包括黏液蛋白相关结构，这些结构可以作为干扰转移的试剂。3)确定半乳糖凝集素-3调节结肠癌细胞MUC2表达的作用机制。

DESCRIPTION (provided by applicant): Colorectal cancer is the second most common cause of cancer-related death in the United States. Colorectal cancer-related mortality is due in large part to metastasis, a complex multistage process by which tumor cells escape the primary tumor and establish secondary foci at distant sites. Mucins, the major secreted glycoproteins of the colon and galectin-3, an endogenous mucin binding protein have each been associated with the metastatic potential of human colon cancer cells. Direct evidence in support of particular functions for mucin and galectin-3 are now emerging through identification of interacting ligands and structural motifs. While a role for mucins encoded by the MUC2 mucin gene in metastasis has been established, it remains to be determined which structural domains of MUC2 are necessary to promote metastasis of colon cancer cells. Galectin-3 also consists of distinct structural domains which contribute to its pleiotropic functions. The protein may be localized in the nucleus, cytoplasm, cell surface or be secreted and may therefore act in several ways to promote metastasis. Recent work from our laboratory has demonstrated that galectin-3 modulates MUC2 expression in colon cancer cells at the level of transcription, and that phosphorylation of the protein may be necessary for this function. The long-term objective of this proposal is to determine how the cell surface and secreted glycoproteins of colon cancer cells influence their metastatic capacity, and how galecin-3 and MUC2 interact to promote metastasis. We hypothesize that specific structural domains of mucin apoproteins and galectin-3 are necessary for their metastasis-enhancing effects and that these molecules interact to promote tumor spread during metastasis. This knowledge may lead to the development of targeted therapies which interfere with metastasis. To accomplish these goals the following specific aims are proposed 1) "Determine the role of secreted mucins and mucin isoforms in colon cancer metastasis" This aim will examine which MUC2 structural domains and associated carbohydrate structures are responsible for metastasis. 2) "Determine biological significance of the interactions between galectin-3 and its carbohydrate ligands". This aim seeks to identify carbohydrate structures, including mucin- related structures which can be used as reagents to interfere with metastasis. 3) Determine the functional mechanism(s) by which galectin-3 modifies expression of MUC2 in colon cancer cells.