ROLE OF BGP IN BREAST EPITHELIAL CELL POLARIZATION

上皮细胞的特征是它们的极化形态和管腔形成。胆道糖蛋白（biliary glycoprotein， BGP）是一种I型跨膜糖蛋白，存在于胃肠道和乳腺等其他器官中，在上皮细胞的管腔表面呈极化表达。我们已经证明，当在基质（细胞外基质的来源）中生长时，BGP在“正常”乳腺上皮细胞系MCF10F的管腔形成中起重要作用。具体来说，当BGP的表达被BGP反义基因阻断，或者当细胞被抗BGP抗体或重组的可溶性BGP处理时，这些细胞不能形成管腔（腺泡）。乳腺肿瘤细胞系，如MCF7，在基质中不能形成腺泡，不表达BGP，当转染BGP感知基因并在基质中生长时，这些细胞表现出大量细胞死亡和偶尔的腺泡形成。为了描述BGP形成管腔的分子决定因素，我们建议(1)研究MCF7细胞中阻止其向更“正常”表型恢复的缺陷，(2)绘制细胞骨架与BGP细胞质结构域的相互作用，(3)分析负责管腔形成的BGP外结构域的顺反二聚体相互作用，以及(4)确定BGP基因在MCF10F和MCF7细胞中的调控作用。此外，我们发现MCF10F细胞产生肌上皮细胞，这些细胞可以被富集，并显示为BGP阴性，能够诱导CEA（癌胚抗原），这是乳腺癌细胞的标志。我们还将研究CEA和BGP基因在这些细胞中的调控，以深入了解乳腺癌的肿瘤发生过程。

The hallmark of epithelial cells is their polarized morphology and lumen formation. BGP (biliary glycoprotein), a type I transmembrane glycoprotein that is found throughout the gastrointestinal tract and other organs such as the breast, has a polarized expression on the lumenal surface of epithelial cells. We have shown that BGP plays an essential role in the lumen formation of the 'normal" breast epithelial cell line MCF10F when grown in matrigel, a source of extracellular matrix. Specifically, these cells fail to form a lumen (acinus) when BGP expression is blocked with a BGP anti-sense gene, or when the cells are treated with anti-BGP antibody or with recombinant, soluble BGP. In the case of breast tumor cell lines such as MCF7, which fail to form acini in matrigel and do not express BGP, these cells exhibit massive cell death and occasional acinus formation when transfected with the BGP sense gene and grown in matrigel. In order to delineate the molecular determinants of lumen formation by BGP, we propose to (1) study the defects in MCF7 cells which prevent their reversion to a more "normal" phenotype, (2) map cytoskeleton interactions with the cytoplasmic domain of BGP, (3) analyze the cis-trans dimer interactions of the BGP ectodomains responsible for lumen formation, and (4) determine the regulation of the BGP gene in both MCF10F and MCF7 cells. In addition, we have found that MCF10F cells produce myoepithelial cells which can be enriched and shown to be BGP negative and capable of induction of CEA (carcinoembryonic antigen), a hallmark of breast cancer cells. We will also study the regulation of the CEA and BGP genes in these cells in order to gain insight into the process of tumorigenesis in breast cancer.