Phosphatase-mediated crosstalk control of ERK and p38 MAPK signaling in corneal epithelial cells

PURPOSE. To test the hypothesis that the protein phosphatases PP2A and MKP-1 are involved in controlling epidermal growth factor (EGF)-induced increases in rabbit corneal epithelial cell (RCEC) migration by mediating crosstalk between signaling pathways eliciting EGF receptor control of migration and proliferation. METHODS. Western blot analysis was used to determine the phosphorylation status of Erk1/2, p38, and the mitogen-activated protein kinase (MAPK) kinase (MEK1/2) using inhibitors of Erk1/2 or p38 and dominant- negative (d/n) Erk1 or d/n p38 cell lines. Coimmunoprecipitation was used to evaluate protein phosphatase (PP) 2A and Erk1/2 interaction. Short- interfering RNA (siRNA) transfection was performed to analyze the involvement of MAPK phosphatase (MKP)-1 in crosstalk. Scratchwound assay was used to determine EGF-dependent effects on cell migration. RESULTS. EGF (10 ng/mL) induced changes in activation of Erk1/2 and p38, which were enhanced by inhibition with 10 mu M SB203580 and 10 mu M PD98059, respectively. PP inhibition with sodium orthovanadate (100 mu M), okadaic acid (10 nM), or Ro 31-8220 (10 mu M) resulted in larger and more prolonged increases in the phosphorylation status of Erk1/2 and p38. After 1 hour, EGF induced 14-fold increases in MKP-1 protein expression. After MKP-1 siRNA transfection, EGF had induced a similar pattern of changes in the phosphorylation status in Erk1/2 and p38 following PP inhibition. EGF-induced cell migration was enhanced by Erk1/2 pathway inhibition and was accentuated after PP inhibition. Conversely, p38 pathway inhibition eliminated this response. CONCLUSIONS. EGF-induced changes in Erk1/2 and p38 phosphorylation status are dependent on PP-mediated crosstalk. This control modulates the magnitude of growth factor-induced increases in corneal epithelial cell migration.