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Signaling and Regulation

Ligand Binding Up-Regulates EphA2 Messenger RNA Through the Mitogen-Activated Protein/Extracellular Signal-Regulated Kinase Pathway¹

¹ Department of Basic Medical Sciences, Purdue University Cancer Center, West Lafayette, IN and ² MedImmune, Inc., Gaithersburg, MD

Requests for reprints: Michael S. Kinch, MedImmune, Inc., 35 West Watkins Mill Road, Gaithersburg, MD 20878. Phone: (240) 632-4639; Fax: (301) 527-4200. E-mail: kinchm{at}medimmune.com

The EphA2 receptor tyrosine kinase is overexpressed in aggressive cancer cells, where it critically influences many aspects of malignant character. Although high levels of EphA2 have been documented in many different cancers, relatively little is known of the mechanisms that govern EphA2 gene expression in normal or malignant cells. Our present studies demonstrate that EphA2 influences the regulation of its own gene expression. Specifically, ligand-mediated phosphorylation of EphA2 transmits signals to the nucleus via extracellular signal-regulated kinase kinases to up-regulate de novo EphA2 gene expression and synthesis. This mechanism governs EphA2 expression in normal and malignant cells. In normal cells, EphA2 protein expression is balanced by ligand-mediated induction of EphA2 gene expression countered by EphA2 protein turnover. These findings suggest that EphA2 expression and ligand binding are intimately linked in epithelial cells. Increased understanding of this mechanism could have important implications for understanding the causes of EphA2 overexpression and for developing new strategies for therapeutic intervention in the many cancers that overexpress EphA2.