Feedback Effects of p38 MAPK and ERK Pathway Inhibition on EGFR- and IGF-1R-Mediated Signaling and Motility in Human Prostate Cancer Cells

Program: Abstracts - Orals, Featured Poster Presentations, and Posters
Session: MON 389-405-Signaling Originating from Membrane Receptors
Monday, June 17, 2013: 1:45 PM-3:45 PM
Expo Halls ABC (Moscone Center)

Poster Board MON-393
Suzan Marie Semaan*, James Balducci and Yao Huang
St. Joseph's Hospital and Medical Center, Phoenix, AZ
Epidermal growth factor receptor (EGFR) and insulin-like growth factor type 1 receptor (IGF1R) play pivotal roles in tumor growth, progression, and metastasis, and are important therapeutic targets. A better understanding of potential EGFR and IGF1R crosstalk and feedback loops of their signaling pathways is fundamental for development of more effective treatment and prevention strategies. We have previously reported that Akt plays a central role in EGFR-driven cell motility (1) and ERK is critical in modulating EGFR trafficking (1,2). In this study, we investigated the feedback effects of p38 MAPK and ERK inhibition on EGFR and IGF1R-mediated signaling and motility in human prostate cancer DU145 cells. First, immunoblotting with phospho-residue specific antibodies indicated that both EGF and IGF1 promoted EGFR phosphorylation at Thr669. In contrast, tyrosine phosphorylation of EGFR and IGF1R was detected only upon the engagement of their respective cognate ligands, EGF and IGF1. Both ligands activated ERK and Akt with EGF more potent on ERK and IGF1 more potent on Akt. EGF but not IGF1 activated p38 MAPK. Next, using p38 and ERK pathway inhibitors, SB203580 (SB) and PD98059 (PD), respectively, we uncovered that EGF-induced EGFR threonine phosphorylation was ERK dependent but p38 MAPK independent, whereas the IGF1-induced one was p38 and ERK dependent. Interestingly, SB treatment led to enhanced EGF-induced EGFR threonine phosphorylation. PD treatment resulted in elevated tyrosine phosphorylation of EGFR (EGF-induced) and IGF1R (IGF1-induced). Furthermore, SB suppressed EGF-induced Akt activation but rather boosted EGF-induced ERK activation (consistent with enhanced EGFR threonine phosphorylation). In contrast, PD augmented EGF- and IGF1-induced Akt activation. Finally, wound closure assay results showed that both ligands promoted DU145 cell migration. With p38 pathway inhibition, EGF or IGF1-induced motility was decreased. However, only EGF-directed motility correlated with reduced Akt activity. With ERK pathway inhibition, only EGF-directed motility was enhanced, which correlated with increased Akt activity. Collectively, our findings suggest distinct mechanisms underlying EGF- and IGF1-mediated EGFR threonine phosphorylation and differential feedback effects of blockade of p38 MAPK and ERK pathways on EGFR and IGF1R-driven cell motility, i.e. EGF-induced motility is Akt dependent whereas the IGF1-induced one is independent of Akt.

(1)  Gan Y et al., Oncogene 2010; 29: 4947. (2)  Huang Y et al., Oncogene 2006; 25: 7565.

Nothing to Disclose: SMS, JB, YH

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Sources of Research Support: St. Joseph’s Foundation (SJF) Startup Fund