Merlin Simone, Pietronave Stefano, Locarno Deborah, Valente Guido, Follenzi Antonia, Prat Maria
Laboratory of Histology, Department of Medical Sciences, Università del Piemonte Orientale A. Avogardro, Novara, Italy.
Cancer Sci. 2009 Apr;100(4):633-8. doi: 10.1111/j.1349-7006.2008.01079.x. Epub 2009 Jan 21.
The c-MET proto-oncogene, encoding the p190 hepatocyte growth factor tyrosine kinase receptor, can acquire oncogenic potential by multiple mechanisms, such as gene rearrangement, amplification and overexpression, point mutation, and ectopic expression, all resulting in its constitutive activation. Hepatocyte growth factor receptor truncated forms are generated by post-translational cleavage: p140 and p130 lack the kinase domain and are inactive. Their C-terminal remnant fragments are generally undetectable in normal cells, but a membrane-associated truncated form is recognized by anti-C-terminus antibodies in some human tumors, suggesting that a hepatocyte growth factor receptor lacking the ectodomain, but retaining the transmembrane and intracellular domains (Met-EC-), could acquire oncogenic properties. Herein we show that NIH-3T3 cells transduced with MET-EC- expressed a membrane-associated constitutively tyrosine-phosphorylated 60-kDa protein and, similarly to NIH-3T3 cells expressing the cytosolic oncoprotein Tpr-Met, showed activated extracellular regulated kinase 1/2 mitogen-activated protein kinase and Akt downstream transducers. Compared to control NIH-3T3 cells, NIH-3T3-Met-EC- cells grew faster and showed anchorage-independent growth and invasive properties in all aspects similar to cells expressing the transforming TPR-MET. Nude female mice injected subcutaneously with NIH-3T3-Met-EC- cells developed visible tumors, displaying the typical morphology of carcinomas with polygonal cells, in contrast to sarcomas with spindle-shaped cells induced by the injection of NIH-3T3-Tpr-Met cells. It is suggested that the different subcellular localization of the oncoproteins, more than differences in signal transduction, could be responsible for the tumor phenotype. All together, these data show that deletion of the ectodomain activates the hepatocyte growth factor receptor and its downstream signaling pathways, unleashing its transforming, invasive, and tumorigenic potential.
编码p190肝细胞生长因子酪氨酸激酶受体的c-MET原癌基因可通过多种机制获得致癌潜能，如基因重排、扩增和过表达、点突变以及异位表达，所有这些都会导致其组成性激活。肝细胞生长因子受体截短形式是通过翻译后切割产生的：p140和p130缺乏激酶结构域且无活性。它们的C末端残余片段在正常细胞中通常无法检测到，但在一些人类肿瘤中，一种膜相关截短形式可被抗C末端抗体识别，这表明缺乏胞外结构域但保留跨膜和胞内结构域的肝细胞生长因子受体（Met-EC-）可能获得致癌特性。在此我们表明，用MET-EC-转导的NIH-3T3细胞表达一种膜相关的组成性酪氨酸磷酸化60 kDa蛋白，并且与表达胞质癌蛋白Tpr-Met的NIH-3T3细胞类似，显示出细胞外调节激酶1/2丝裂原活化蛋白激酶和Akt下游转导分子的激活。与对照NIH-3T3细胞相比，NIH-3T3-Met-EC-细胞生长更快，并且在所有方面都表现出不依赖贴壁生长和侵袭特性，类似于表达转化性TPR-MET的细胞。皮下注射NIH-3T3-Met-EC-细胞的雌性裸鼠长出可见肿瘤，呈现出具有多边形细胞的典型癌形态，这与注射NIH-3T3-Tpr-Met细胞诱导产生的具有梭形细胞的肉瘤形成对比。提示癌蛋白不同的亚细胞定位而非信号转导差异可能是肿瘤表型的原因。总之，这些数据表明胞外结构域的缺失激活了肝细胞生长因子受体及其下游信号通路，释放了其转化、侵袭和致瘤潜能。
