Department of Surgery, Klinikum rechts der Isar, Technische Universität München, 81675 Munich, Germany.
Int J Biochem Cell Biol. 2011 Nov;43(11):1630-40. doi: 10.1016/j.biocel.2011.07.012. Epub 2011 Jul 28.
SASH1, a member of the SLY-family of signal adapter proteins, is a candidate tumor suppressor in breast and colon cancer. Reduced expression of SASH1 is correlated with aggressive tumor growth, metastasis formation, and inferior prognosis. However, the biological role of SASH1 remains largely unknown. To unravel the function of SASH1, we have analyzed the intracellular localization of endogenous SASH1, and have generated structural SASH1 mutants. SASH1 localized to the nucleus as well as to the cytoplasm in epithelial cells. In addition, SASH1 was enriched in lamellipodia and membrane ruffles, where it co-distributed with the actin cytoskeleton. Moreover, we demonstrate a novel interaction of SASH1 with the oncoprotein cortactin, a known regulator of actin polymerization in lamellipodia. Enhanced SASH1 expression significantly increased the content of filamentous actin, leading to the formation of cell protrusions and elongated cell shape. This activity was mapped to the central, evolutionarily conserved domain of SASH1. Furthermore, expression of SASH1 inhibited cell migration and lead to increased cell adhesion to fibronectin and laminin, whereas knock-down of endogenous SASH1 resulted in significantly reduced cell-matrix adhesion. Taken together, our findings unravel for the first time a mechanistic role for SASH1 in tumor formation by regulating the adhesive and migratory behaviour of cancer cells.
SASH1 是 SLY 家族信号衔接蛋白的成员，是乳腺癌和结肠癌的候选肿瘤抑制因子。SASH1 表达降低与侵袭性肿瘤生长、转移形成和预后不良相关。然而，SASH1 的生物学功能在很大程度上仍是未知的。为了阐明 SASH1 的功能，我们分析了内源性 SASH1 的细胞内定位，并生成了结构 SASH1 突变体。SASH1 在上皮细胞中定位于细胞核和细胞质。此外，SASH1 在片状伪足和膜皱襞中富集，在那里与肌动蛋白细胞骨架共分布。此外，我们证明了 SASH1 与癌蛋白 cortactin 的一种新型相互作用，cortactin 是片状伪足中肌动蛋白聚合的已知调节剂。增强的 SASH1 表达显著增加了丝状肌动蛋白的含量，导致细胞突起的形成和细胞形状的伸长。这种活性被映射到 SASH1 的中央进化保守结构域。此外，SASH1 的表达抑制细胞迁移并导致细胞对纤维连接蛋白和层粘连蛋白的粘附增加，而内源性 SASH1 的敲低则导致细胞-基质粘附显著减少。总之，我们的发现首次揭示了 SASH1 通过调节癌细胞的黏附和迁移行为在肿瘤形成中的机制作用。
