Analysis of cell adhesion and polarity formation by a novel tumor suppressor protein TSLC1 and its related molecules

形态转化是恶性肿瘤细胞的基本特征。肿瘤抑制因子TSLC 1/IGSF 4参与细胞粘附，并在浸润性癌症中优先失活。我们以前已经表明，TSLC 1协会与肌动蛋白结合蛋白，DAL-1/4.1B，和支架蛋白，膜蛋白棕榈酰化3（MPP 3）。在这里，我们确定MPP 1/p55和MPP 2/DLG 2作为额外的细胞质蛋白结合TSLC 1和研究的作用TSLC 1级联上皮细胞形态和恶性转化。MPP 1、MPP 2和MPP 3直接与DAL-1相互作用，与TSLC 1形成三联复合物。尽管这些复合物在融合的HEK 293细胞中沿着细胞膜定位，但在细胞粘附的早期过程中，只有MPP 2而不是MPP 1或MPP 3被募集到TSLC 1-DAL-1复合物。当TSLC 1功能被RNAi废除时，HEK 293失去上皮样结构，并显示具有未成熟细胞粘附的扁平形态。此外，DAL-1和MPP 2，以及E-钙粘蛋白和ZO-1，从膜上被错误定位。TSLC 1的缺失也与肺癌细胞的转化表型相关。这些发现表明TSLC 1与DAL-1和MPP一起参与上皮样细胞结构的形成，而其功能的丧失可能导致癌细胞的形态转化。

Morphological transformation is a fundamental feature of malignant cancer cells. The tumor suppressor, TSLC1/IGSF4, is involved in cell adhesion and preferentially inactivated in invasive cancer. We have previously shown that TSLC1 associates with an actin-binding protein, DAL-1/4.1B, and a scaffold protein, membrane protein palmitoylated 3(MPP3). Here, we identified MPP1/p55 and MPP2/DLG2 as additional cytoplasmic proteins binding to TSLC1 and investigated the roles of the TSLC1 cascade in epithelial cell morphology and its malignant transformation. MPP1, MPP2, and MPP3 interacted directly with DAL-1, forming a tripartite complex with TSLC1. Whereas these complexes localized along the cell membranes in confluent HEK293 cells, only MPP2, but not MPP1 or MPP3, was recruited to the TSLC1-DAL-1 complex in the early process of cell adhesion. When the TSLC1 function was abrogated by RNAi, HEK293 losed epithelial-like structure and showed flat morphology with immature cell adhesion. Furthermore, DAL-1 and MPP2, as well as E-cadherin and ZO-1, were mislocalized from the membrane. Loss of TSLC1 was also correlated with the transformed phenotype of lung cancer cells. These findings suggest that TSLC1 is involved in the formation of epithelial-like cell structure with DAL-1 and MPPs, while loss of its function could cause morphological transformation of cancer cells.