PT  - JOURNAL ARTICLE
AU  - Daniela A. Eisinger
AU  - Hermann Ammer
TI  - Epidermal Growth Factor Treatment switches δ-Opioid Receptor-stimulated ERK1/2 Signaling from an EGF to an IGF-1 Receptor-dependent Mechanism
AID  - 10.1124/mol.110.064956
DP  - 2010 Nov 15
TA  - Molecular Pharmacology
PG  - mol.110.064956
4099  - http://molpharm.aspetjournals.org/content/early/2010/11/15/mol.110.064956.short
4100  - http://molpharm.aspetjournals.org/content/early/2010/11/15/mol.110.064956.full
AB  - δ-Opioid receptor (DOR)-induced activation of extracellular signal-regulated kinases 1 and 2 (ERK1/2) is mediated by transactivation of epidermal growth factor (EGF) receptors. Here we demonstrate that in stably DOR-expressing HEK293 (HEK/DOR) cells down-regulation of EGF receptors by chronic EGF (0.1 μg; 18 h) treatment, but not siRNA, results in functional desensitization of EGF (10 ng/ml)-stimulated ERK1/2 signaling. In EGF receptor desensitized (HEK/DOR-EGFR) cells, however, DADLE (1 μM) and etorphine (0.1 μM) retained their ability to stimulate ERK1/2 activation. The newly acquired signal transduction mechanism is insensitive to the EGF receptor blockers AG1478 and CL-387-785, does not involve DOR internalization and activation of the focal adhesion kinase pp125 FAK, but requires MMP-dependent release of soluble growth factors. A supernatant transfer assay in which conditioned growth media of opioid-treated HEK/DOR and HEK/DOR-EGFR "donor" cells are used to stimulate ERK1/2 activity in DOR-lacking HEK293 wt and HEK293-EGFR "acceptor" cells revealed that chronic EGF treatment produces a switch in the receptor tyrosine kinase (RTK) system transactivated by opioids. Using microfluidic electrophoresis, chemical inhibitors, phosphorylation-specific antibodies, and EGF receptor-deficient CHO-K1 cells, we identified the release of an IGF-1-like peptide and activation of IGF-1 receptors in HEK/DOR-EGFR cells after DOR activation. A similar switch from a TrkA to an IGF-1 receptor-dependent ERK1/2 signaling was observed for chronically nerve growth factor-treated Neuroblastoma x Glioma (NG108-15) cells. These results indicate that transactivation of the dominant RTK system in a given cellular setting may represent a general feature of opioids to maintain mitogenic signaling.