EGFR ligands exhibit functional differences in models of paracrine and autocrine signaling

Abstract

Epidermal growth factor (EGF) family peptides are ligands for the EGF receptor (EGFR). Here, we elucidate functional differences among EGFR ligands and mechanisms underlying these distinctions. In 32D/EGFR myeloid and MCF10A breast cells, soluble amphiregulin (AR), transforming growth factor alpha (TGFα), neuregulin 2 beta, and epigen stimulate greater EGFR coupling to cell proliferation and DNA synthesis than do EGF, betacellulin, heparin-binding EGF-like growth factor, and epiregulin. EGF competitively antagonizes AR, indicating that its functional differences reflect dissimilar intrinsic activity at EGFR. EGF stimulates much greater phosphorylation of EGFR Tyr1045 than does AR. Moreover, the EGFR Y1045F mutation and z-cbl dominant-negative mutant of the c-cbl ubiquitin ligase potentiate the effect of EGF but not of AR. Both EGF and AR stimulate phosphorylation of EGFR Tyr992. However, the EGFR Y992F mutation and phospholipase C gamma inhibitor U73122 reduce the effect of AR much more than that of EGF. Expression of TGFα in 32D/EGFR cells causes greater EGFR coupling to cell proliferation than does expression of EGF. Moreover, expression of EGF in 32D/EGFR cells causes these cells to be largely refractory to stimulation with soluble EGF. Thus, EGFR ligands are functionally distinct in models of paracrine and autocrine signaling and EGFR coupling to biological responses may be specified by competition among functionally distinct EGFR ligands.

Keywords::

• Amphiregulin
• EGF
• TGFα, EGF receptor
• ligand specificity
• autocrine and paracrine growth regulation

Acknowledgement

We thank Allison Lange for minor contributions to the work described here. We acknowledge support from the National Cancer Institute of the National Institutes of Health (R21CA080770 and R01CA114209 to DJR; R01CA115830 to JS; P30CA023168 to the Purdue University Center for Cancer Research), the US Army Medical Research and Materiel Command Breast Cancer Research Program (DAMD17-00-1-0416 to DJR), the Indiana Elks Foundation (to DJR) and the American Cancer Society (IRG-58-006 to the Purdue University Center for Cancer Research). KJW was supported in part by a National Institutes of Health predoctoral training grant to the Purdue University interdisciplinary graduate program in Biochemistry and Molecular Biology and a FIRST post-doctoral fellowship (K12GM000680) through Emory University.

Declaration of Interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.