ERBB4 PROMOTES CYCLOOXYGENASE-2 EXPRESSION AND CELL SURVIVAL IN

The ErbB4 receptor tyrosine kinase is expressed at high levels in human and mouse colitis, and inhibits colon epithelial cell apoptosis in the presence of pro-inflammatory cytokines. In this study, we investigated the molecular mechanisms responsible for ErbB4-induced cell survival. In cultured mouse colon epithelial cells, ErbB4 overexpression resulted in increased levels of cyclooxygenase-2 (COX-2) mRNA and protein; in contrast, ErbB4 knockdown with siRNA blocked COX-2 accumulation in response to tumor necrosis factor. While ErbB4 is expressed as up to four different isoforms in epithelial tissues, its ability to promote COX-2 expression was isoform-independent. ErbB4-stimulated COX-2 induction was associated with an increase in mRNA half-life and was blocked by inhibition of Src, phosphatidylinositol 3-kinase, or epidermal growth factor (EGF) receptor (R). Furthermore, ErbB4 expression promoted EGFR phosphorylation in the presence of heregulin, implicating ErbB4-EGFR heterodimerization in these responses. With regard to the cellular responses to ErbB4 activation, increased survival of ErbB4-expressing cells in the presence of pro-inflammatory cytokines was sensitive to the COX-2 inhibitor celecoxib. Furthermore, ErbB4-overexpressing cells acquired the ability to form colonie