ROLE OF BGP IN BREAST EPITHELIAL CELL POLARIZATION

上皮细胞的标志是它们的极化形态和管腔形成。 BGP（胆汁糖蛋白）是一种I型跨膜糖蛋白，在整个胃肠道和其他器官如乳腺中发现，在上皮细胞的内腔表面上具有极化表达。我们已经表明，BGP在“正常”乳腺上皮细胞系MCF 10 F的管腔形成中起着至关重要的作用，当生长在matrigel中时，细胞外基质的来源。具体地，当用BGP反义基因阻断BGP表达时，或者当用抗BGP抗体或用重组可溶性BGP处理细胞时，这些细胞不能形成腔（腺泡）。 在乳腺肿瘤细胞系如MCF 7的情况下，其不能在基质胶中形成腺泡并且不表达BGP，当用BGP正义基因转染并在基质胶中生长时，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MCF 7细胞中阻止其恢复到更“正常”表型的缺陷，（2）绘制细胞骨架与BGP胞质结构域的相互作用，（3）分析负责管腔形成的BGP胞外域的顺式-反式二聚体相互作用，（4）确定BGP基因在MCF 10 F和MCF 7细胞中的调控。 此外，我们发现MCF 10 F细胞产生肌上皮细胞，其可以被富集并显示为BGP阴性，并且能够诱导CEA（癌胚抗原），CEA是乳腺癌细胞的标志。 我们还将研究这些细胞中CEA和BGP基因的调控，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.