Abstract 1078: ErbB/Pi3K signaling contributes to EGFR ligand expression in colorectal cancer cells

Abstract

Abstract Background: Cellular expression of EGFR ligands is tightly regulated and is thought to be maintained by an autocrine signaling component in colorectal cancer cells. More importantly, the expression levels of individual ligands have gained recent interest since their expression of their mRNA was found to be linked to anti-EGFR therapy response. Since the expression of these ligands can be regulated by EGFR signaling elicited by EGF, we decided to investigate the contribution of MAPK as well as the PI3K axis, to EREG expression, in K-Ras wild-type colon cancer cells. Methods Colon cancer cells were used to interrogate EGFR downstream signaling. Several inhibitors targeting the ErbBs and the MAPK and PI3K/Akt pathways were used to dissect the pathways downstream of EGFR maintaining ligand mRNA levels in the lim1215 colon cancer cell line. Additionally, we used ER and AR reporter assays to selectively evaluate involvement of the EGFR pathway in transcriptional regulation of the pathway. Consequently, blockade and activation of EGFR pathway members was assessed by Western Blot. Results We show that Ereg and Areg mRNA levels are specifically maintained by erbb1 signaling. Treatment of lim1215 cells with inhibitors blocking Erbb1 (cetuximab) or ErbB1/Erbb2 (lapatinib) did results in near complete inhibition of Ereg and Areg expression in Kras/pi3K wild-type cells, while blockade of ErbB2 alone (which is activated in these cells) with Trastuzumab did not decrease Ereg nor Areg mRNA levels. Downstream of EGFR, we show that MEK signaling is not required for maintenance of EREG and AREG levels in lim1215 cells. Conversely, blockade of PI3K signaling by Akt inhibitors or PI3K inhibitors abolished EREG mRNA levels in these cells. This was reflected by the ability of overexpressed Akt to induce EREG and AREG reporter activity in 293T cells. In contrast, this activation could be rescued by the addition of Akt and PI3K inhibitors, but not MEK inhibitors in cellular media. Conclusions In this work we show that PI3K signaling is required for the transcription of EGFR ligands in colon cancer cells. In this regard, this provides additional insights to the recent findings that link PI3K/Akt signaling to Receptor Tyrosine Kinase expression and activation in cancer cells. Therefore, a global understanding of the signaling networks that control ligand availability and receptor abundance will be crucial in combining ErbB pathway inhibitors in the treatment of kras wild-type colon cancers. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1078. doi:1538-7445.AM2012-1078