Woods D, Cherwinski H, Venetsanakos E, Bhat A, Gysin S, Humbert M, Bray P F, Saylor V L, McMahon M
Cancer Research Institute and Department of Cellular and Molecular Pharmacology, San Francisco, California 94115, USA.
Mol Cell Biol. 2001 May;21(9):3192-205. doi: 10.1128/MCB.21.9.3192-3205.2001.
Alterations in the expression of integrin receptors for extracellular matrix (ECM) proteins are strongly associated with the acquisition of invasive and/or metastatic properties by human cancer cells. Despite this, comparatively little is known of the biochemical mechanisms that regulate the expression of integrin genes in cells. Here we demonstrate that the Ras-activated Raf-MEK-extracellular signal-regulated kinase (ERK) signaling pathway can specifically control the expression of individual integrin subunits in a variety of human and mouse cell lines. Pharmacological inhibition of MEK1 in a number of human melanoma and pancreatic carcinoma cell lines led to reduced cell surface expression of alpha6- and beta3-integrin. Consistent with this, conditional activation of the Raf-MEK-ERK pathway in NIH 3T3 cells led to a 5 to 20-fold induction of cell surface alpha6- and beta3-integrin expression. Induced beta3-integrin was expressed on the cell surface as a heterodimer with alphav-integrin; however, the overall level of alphav-integrin expression was not altered by Ras or Raf. Raf-induced beta3-integrin was observed in primary and established mouse fibroblast lines and in mouse and human endothelial cells. Consistent with previous reports of the ability of the Raf-MEK-ERK signaling pathway to induce beta3-integrin gene transcription in human K-562 erythroleukemia cells, Raf activation in NIH 3T3 cells led to elevated beta3-integrin mRNA. However, unlike immediate-early Raf targets such as heparin binding epidermal growth factor and Mdm2, beta3-integrin mRNA was induced by Raf in a manner that was cycloheximide sensitive. Surprisingly, activation of the Raf-MEK-ERK signaling pathway by growth factors and mitogens had little or no effect on beta3-integrin expression, suggesting that the expression of this gene requires sustained activation of this signaling pathway. In addition, despite the robust induction of cell surface alphavbeta3-integrin expression by Raf in NIH 3T3 cells, such cells display decreased spreading and adhesion, with a loss of focal adhesions and actin stress fibers. These data suggest that oncogene-induced alterations in integrin gene expression may participate in the changes in cell adhesion and migration that accompany the process of oncogenic transformation.
细胞外基质（ECM）蛋白整合素受体表达的改变与人类癌细胞获得侵袭性和/或转移性密切相关。尽管如此，对于调节细胞中整合素基因表达的生化机制却知之甚少。在此，我们证明Ras激活的Raf-MEK-细胞外信号调节激酶（ERK）信号通路能够特异性地控制多种人类和小鼠细胞系中单个整合素亚基的表达。在多种人类黑色素瘤和胰腺癌细胞系中对MEK1进行药理学抑制，导致α6-和β3-整合素的细胞表面表达降低。与此一致，在NIH 3T3细胞中条件性激活Raf-MEK-ERK通路导致细胞表面α6-和β3-整合素表达诱导5至20倍。诱导的β3-整合素作为与αv-整合素的异二聚体在细胞表面表达；然而，αv-整合素的总体表达水平并未因Ras或Raf而改变。在原代和已建立的小鼠成纤维细胞系以及小鼠和人类内皮细胞中观察到Raf诱导的β3-整合素。与之前关于Raf-MEK-ERK信号通路能够在人类K-562红白血病细胞中诱导β3-整合素基因转录的报道一致，NIH 3T3细胞中的Raf激活导致β3-整合素mRNA升高。然而，与Raf的即时早期靶标如肝素结合表皮生长因子和Mdm2不同，β3-整合素mRNA以对放线菌酮敏感的方式被Raf诱导。令人惊讶的是，生长因子和有丝分裂原对Raf-MEK-ERK信号通路的激活对β3-整合素表达几乎没有影响，这表明该基因的表达需要该信号通路的持续激活。此外，尽管Raf在NIH 3T3细胞中强烈诱导细胞表面αvβ3-整合素表达，但这些细胞的铺展和黏附减少，粘着斑和肌动蛋白应力纤维丧失。这些数据表明，癌基因诱导的整合素基因表达改变可能参与致癌转化过程中伴随的细胞黏附和迁移变化。
