Ligand-independent phosphorylation of Y869 (Y845) links mutant EGFR signaling to stat-mediated gene expression.

Yang S, Park K, Turkson J, Arteaga CL
Exp Cell Res. 2008 314 (2): 413-9

PMID: 17927978 · PMCID: PMC3221731 · DOI:10.1016/j.yexcr.2007.09.002

Activating mutants of EGFR have been identified in a subset of non-small-cell lung cancers. To investigate mutant-driven signaling, we focused on Y869, a residue in the same activation loop where the L858R and L861Q mutations are located. We observed ligand-independent phosphorylation of Y869 in 32D cells EGFR(L858R) and EGFR(L861Q). The EGFR tyrosine kinase inhibitor (TKI) erlotinib inhibited Y869 P-EGFR in intact cells as well as in a cell-free kinase reaction. Expression of kinase domain of EGFR(L858R) and EGFR(L861Q) exhibited auto-phosphorylation of Y869; this was inhibited by EGFR TKIs but not by Src kinase inhibitor. P-Y859 of EGFR-mediated downstream component, STAT5, was also analyzed. Y694 P-STAT5 was eliminated by erlotinib treatment. Analysis of immune-complexes showed constitutive association of mutant EGFRs with STAT5 and Src which was unaffected by erlotinib or PP1. On the other hand, 32D-EGFR(WT) exhibited constitutive STAT5 phosphorylation and association of EGFR with JAK2. In these cells, a JAK2 inhibitor abrogated P-STAT5 whereas mutant EGFRs did not associate with JAK2. Expression of c-myc was regulated by EGFR/STAT5 signaling in cells expressing EGFR(L858R) and EGFR(L861Q). Our results suggest that ligand-independent and Src activity-independent phosphorylation of Y869 in mutant EGFR regulates STAT5 activation and c-myc expression.

MeSH Terms (12)

ErbB Receptors Erlotinib Hydrochloride Genes, myc Humans Ligands Mutation Phosphorylation Proto-Oncogene Proteins pp60(c-src) Quinazolines Signal Transduction STAT5 Transcription Factor Tumor Cells, Cultured

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