Grb7參與在細胞移動與腫瘤進程之訊息調控

Abstract

Growth factor receptor bound protein-7 (Grb7) 是一個有數個功能區域 (domain) 的銜接蛋白 (adaptor protein)，能與許多訊息分子產生交互作用並藉此調控細胞功能。我們首先確認了上游激酶 focal adhesion kinase (FAK) 磷酸化Grb7的位置 (Tyr188 和 Tyr 338)。當這些位置被突變，Grb7便無法被磷酸化也不能影響下游如 paxillin 及 ERK1/2 的磷酸化。此外，在 integrin 的訊息傳遞鏈中，FAK和Grb7會結合形成複合物，進而有效影響癌細胞的移動，複製，與不須附著的生長能力。我們進一步發現在 erbB2 及 Grb7 共同大量表現的乳癌細胞株中，當受到表皮生長因子 (EGF) 的刺激，Grb7 會被磷酸化，接著與 Ras-GTPase 產生結合後促進其活性，並影響下游ERK1/2之磷酸化。這條 EGFR-Grb7-Ras- ERK1/2 訊息傳導鏈能提高乳癌細胞的生長能力，進而促進癌化現象。另外，我們在非小細胞肺癌細胞中同樣發現 Grb7會受到 EGF 刺激而磷酸化。在此系統中，Grb7 能透過調控轉錄因子 STAT3 的活性來影響 EphA4 基因表現。EphA4 能和 EGFR 交互作用，產生互相磷酸化與活化的現象，並因此增強 EGFR 的下游訊息傳遞。因此，在 EGFR-Grb7-STAT3-EphA4 的訊息傳遞下，細胞的生長，移動，侵染 (invasion) 與腫瘤進程 (tumor progression) 都受到調控。我們的研究提供了一個對 Grb7參與之訊息傳遞有更多了解的機會。基於眾多證據直指 Grb7 在許多癌症中皆扮演著重要角色，我們的實驗結果也突顯出未來針對 Grb7 發展疾病偵測標誌及標靶治療的可能性。

Growth factor receptor bound protein-7 (Grb7) is a multi-domain adaptor protein which is regulated cell functions by interacting with signaling molecules to transmit signal transduction. We first demonstrate that FAK was capable of phosphorylating the Tyr-188 and Tyr-338 within Grb7, and the tyrosine phosphorylation-deficient mutants evidently altered the phosphorylation of paxillin and ERK1/2 but less on AKT, implying their involvement in the FAK•Grb7-mediated cellular functions. Additionally, the formation of FAK-Grb7 complexes and Grb7 phosphorylation by FAK in an integrin-dependent manner were essential for cell migration, proliferation and anchorage-independent growth in A431 cells, indicating the importance of FAK-Grb7 complexes in tumorigenesis. We further show that Grb7 promotes tumorigenesis through the formation of a novel EGFR-Grb7-Ras signaling complex. Grb7-mediated cell proliferation and growth are essential for the tumorigenesis in erbB2-Grb7-overexpressing SK-Br3 breast cancer cells. EGF-induced de novo Grb7 tyrosine phosphorylation recruits and activates Ras-GTPases and subsequently promotes the phosphorylation of ERK1/2, thereby stimulating tumor growth. We also reveal a novel mechanism by which Grb7 regulates cell migration, proliferation, invasion and tumorigenesis of A549 NSCLC cells through the EGF-triggered EGFR-Grb7-STAT3-EphA4 signaling pathway. Our data provide a better understanding on the signal transduction event for Grb7-mediated cellular functions. Grb7 might have the potential to develop as a prognostic biomarker model and improve the overall sensitivity and specificity of cancer therapies.