Induction of beta 3-Integrin Gene Expression by Sustained Activation of the Ras-Regulated Raf-MEK-Extracellular Signal-Regulated Kinase Signaling Pathway

• Published in: Molecular and cellular biology 2001-05, Vol.21 (9), p.3192-3205
• Main Authors: Woods, D, Cherwinski, H, Venetsanakos, E, Bhat, A, Gysin, S, Humbert, M, Bray, P F, Saylor, V L, McMahon, M
• Format: Article
• Language: English
• Subjects: ERK protein; MEK protein; Raf protein
• ISSN: 0270-7306
• 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 alpha 6- and beta 3-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 alpha 6- and beta 3-integrin expression. Induced beta 3-integrin was expressed on the cell surface as a heterodimer with alpha v-integrin; however, the overall level of alpha v-integrin expression was not altered by Ras or Raf. Raf-induced beta 3-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 beta 3-integrin gene transcription in human K-562 erythroleukemia cells, Raf activation in NIH 3T3 cells led to elevated beta 3-integrin mRNA. However, unlike immediate-early Raf targets such as heparin binding epidermal growth factor and Mdm2, beta 3-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 beta 3- 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 alpha v beta 3-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.