EGF receptor signaling inhibits keratinocyte apoptosis: evidence for mediation by Bcl-X_L

Abstract

Signaling through the epidermal growth factor receptor (EGFR) has been primarily implicated in the growth of epithelial cells including keratinocytes. However, the mechanism by which EGFR stimulation promotes keratinocyte cell growth is poorly understood. Here we report that human keratinocytes undergo apoptosis when incubated with the blocking EGFR monoclonal antibody 225 IgG, or PD153035, a highly specific EGFR tyrosine kinase inhibitor. Endogenous mRNA and protein levels of Bcl-X_L, a member the Bcl-2 family which suppresses apoptosis, were specifically inhibited by EGFR blockade. Furthermore, stimulation of EGFR signaling through two natural ligands, transforming growth factor (TGF)-α and epidermal growth factor (EGF), increased the expression of Bcl-X_L in quiescent keratinocytes and HaCaT cells. Finally, ectopic expression of Bcl-X_L in HaCaT cells increased survival after EGFR blockade when compared to untransfected cells or HaCaT keratinocytes transfected with empty vector. These results suggest that the anti-apoptotic protein Bcl-X_L plays an important role in the maintenance of keratinocyte survival in response to EGFR signaling.