GIT1 (全名為G protein-coupled receptor kinase-interacting protein 1)為一種多功能的蛋白質參與在不同的細胞進展之中。GIT1被標定為ADP ribosylation factor GTPase-activating protein (ARF-GAP) ，其會與G protein-coupled receptor kinases (GRKs) 結合並調控細胞膜運輸。GIT1透過與各種信號分子的互相作用，例如paxillin蛋白、focal adhesion kinase (FAK)、Src 或是 mitogen-activated protein kinase kinase 1 (MEK1)，在正常細胞中可調節focal
adhesion turnover以及移動。由於FAK和Src可以調控癌細胞的移動和生長，故我們想知道GIT1是否也參與癌細胞的移動與生長的過程之中。一開始，我們先確認GIT1在一些癌細胞株(包括HeLa細胞和SW620細胞)中的蛋白表現。 在HeLa細胞其GIT1是充分表達的。當我們將HeLa細胞中以git1 siRNA進行轉染，觀察到GIT1 knockdown時會降低FAK蛋白的表現。進一步發現FAK蛋白下降並非是由於降低FAK的RNA轉錄造成，而是透過降低FAK蛋白的穩定性。在MTT試驗和軟瓊脂實驗中分別指出，GIT1 knockdown會抑制細胞貼附性生長(anchorage-dependent cell growth）以及細胞非貼附性生長(anchorage-independent cell growth)。另一方面，GIT1 knockdown明顯的抑制細胞的移動。由於細胞移動是一個動態的過程，此時focal adhesion的形成和分解是需要協調的。從免疫螢光染色實驗中顯示GIT1 knockdown會降低focal adhesion的形成，因此影響細胞的遷移能力。在本篇研究中，我們證實了GIT1 knockdown會抑制HeLa細胞的生長與移動，這暗示著GIT1可能作為抗癌的標的蛋白。

GIT1 (G protein-coupled receptor kinase-interacting protein 1) is a multidomain protein involved in diverse cellular processes. GIT1 is identified as an ADP
ribosylation factor GTPase-activating protein (ARF-GAP) that binds G protein-coupled receptor kinases (GRKs) and regulates membrane trafficking. By interacting with various signaling molecules, such as paxillin, focal adhesion kinase (FAK), Src and mitogen-activated protein kinase kinase 1 (MEK1), GIT1 modulates focal adhesion turnover and mobility in normal cells. Since FAK and Src could mediate both cell migration and proliferation in cancer cells, we wonder whether GIT1 may also participate in these processes. At first, we confirm the protein expression of GIT1 in several cancer cell lines, including HeLa cells and SW620 cells. HeLa cells express ample GIT1. By transient transfection of git1 siRNA in HeLa cells, we observe that GIT1 knockdown reduces expression of FAK. This FAK reduction is not due to the reduction of RNA transcript, but rather by decreasing FAK protein stability. MTT assay and cell culture in soft agar separately show that GIT1 knockdown inhibits anchorage-dependent and -independent cell growth. In addition, GIT1 knockdown inhibits cell migration. Cell migration is a dynamic process that requires the coordinated formation and disassembly of focal adhesions. Immunofluorescence microscopy shows that GIT1 knockdown reduces focal adhesion formation. This result indicates that GIT1 may affect cell migration via facilitate the formation of focal adhesion. Our results indicate that GIT1 participates in HeLa cell proliferation and migration, suggesting it may be an important anticancer drug target.

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