Epidermal growth factor receptor (EGFR) and Stat3 signal through Kras and have mutually opposite effects on Cten

Abstract

BackgroundCten is a protein located at focal adhesions and has beenreported to be an oncogene in colon, breast, lung andgastric cancer [1-3]. We have previously shown thanCten is a target of K-ras in colorectal and pancreatic can-cer [4]. In this study, we investigated whether two otherproposed mechanisms i.e. EGFR and Stat3 signaling wereinvolved in regulating Cten expression.Materials and methodsEGF was used to stimulate the EGFR while the PD153035to inhibit the EGFR. On the other hand, IL-6 used to sti-mulate the STAT3 and siRNA for STAT3 was used forknockdown. The effect was confirmed using Western blotand QPCR and cell motility was assessed by transwellchambers.ResultsInitially we manipulated EGFR signaling by (i) stimulationwith EGF and (ii) inhibition by the PD153035 in the color-ectal cancer cell lines SW620 and C32. In C32, EGF stimu-lation resulted in up-regulation of Kras and Cten whilstexposure to PD153035 resulted in down-regulation of bothKras and Cten. EGFR activation and inhibition wasreflected by, respectively, increased and decreased cellmotility although the effect of EGFR activation was lost byCten Knockdown. In SW620, which harbours a KRASmutation, modulating EGFR activity in this way had noeffect on either Kras or Cten. Stat3 signaling has also beenreported to positively regulate Cten. We tested this inSW620 by directly knocking down Stat3 and exposing cellsto interleukin-6 (an activator of Stat3). Stat3 knockdownresulted in increased Cten whilst Stat3 activation resultedin downregulation of Cten. Testing for Kras expressionshowed that Stat3 was negatively regulating Kras and thiswas reflected in the Cten expression. Functional analysishowever showed that inhibition of Stat3 resulted in areduction of cell motility in a Kras and Cten-independentmanner.ConclusionsWe conclude that both EGFR signals through Krasto modulate Cten (and consequently ILK/FAK) and stimu-lates cell motility. Stat3 however negatively regulates Krasand consequently Cten although its net effect is tostimulate motility through an alternative mechanism.