The tumour suppressor DiRas3 interacts with C‐RAF and downregulates MEK activity to restrict cell migration. (28th December 2012)

• Record Type: Journal Article
• Authors: Klingauf, Mirko; Beck, Matthias; Berge, Ulrich; Turgay, Yagmur; Heinzer, Stephan; Horvath, Peter; Kroschewski, Ruth
• Is Part Of: Biology of the cell. Volume 105:Number 2(2013:Feb.)
• Page Start: 91
• Page End: 107
• Publication Date: 2012-12-28
• Subjects: Cytology -- Periodicals; Electron microscopy -- Periodicals; 571.6
• DOI: 10.1111/boc.201200030
• Languages: English
• ISSNs: 0248-4900

Abstract

<abstract abstract-type="main" xml:lang="en"> <title>Abstract</title> <sec id="abs1-1" sec-type="section"> <title>Background information</title> <p>The mitogenic pathway, composed of RAF kinases, mitogen‐activated protein kinase kinases (MEK) and extracellular signal‐regulated kinases (ERK), promotes cell proliferation and migration and is upregulated in many tumours. DiRas3 (ARHI, Noey2), a mainly GTP‐bound Ras‐like protein with an unusual N‐terminal extension, is predominantly lost in ovarian and breast cancers. Its re‐expression in these tissues impairs cell proliferation, autophagy, apoptosis and cell migration. Further, loss of DiRas3 correlates with an increase in growth factor‐induced ERK phosphorylation. Therefore, <italic>DIRAS3</italic> proves to be a curious gene with remarkable tumour suppressing capabilities. However, how DiRas3 interferes with ERK phosphorylation, has remained unknown.</p> </sec> <sec id="abs1-2" sec-type="section"> <title>Results</title> <p>We demonstrate that DiRas3 associates <italic>in vivo</italic> with C‐RAF and directly binds <italic>in vitro</italic> to C‐RAF, which is upstream of MEK and ERK. Direct binding of DiRas3 to C‐RAF is nucleotide independent, and DiRas3's N‐terminal extension alone is not sufficient for binding C‐RAF. DiRas3 expression inhibits the activating phosphorylations of MEK and ERK. Serum‐induced recruitment of DiRas3 to the plasma membrane depends mainly on its N‐terminal extension and less on its C‐terminus, bound nucleotide or the presence of Ras–GTP. Correspondingly, removal of the N‐terminal extension strongly decreases DiRas3's inhibition of MEK and ERK phosphorylations. Tyrosyl‐phosphatases do not contribute significantly to reduction of ERK‐phosphorylation byDiRas3. Consistently, downregulation of DiRas3 results in a small but significant and persistent increase in MEK and ERK phosphorylation, but does not increase phosphorylation of P38, AKT and c‐Jun NH2‐terminal kinase. Finally, downregulation of DiRas3 causes increased cell migration, through a mechanism that is MEK dependent.</p> </sec> <sec id="abs1-3" sec-type="section"> <title>Conclusions</title> <p>These results support a model in which serum signals induce the recruitment of DiRas3 to the plasma membrane, where it is tethered via its N‐ and C‐termini. At the plasma membrane, DiRas3 interacts with C‐RAF to specifically suppress the activating phosphorylations on MEK and ERK, thus restricting migration of non‐cancer cells. This effect is relatively small, but it is also persistent, suggesting that it contributes to the maintenance of the non‐migratory phenotype of non‐cancerous tissues, in which DiRas3 is expressed.</p> </sec> </abstract>