EGF stimulates cyclooxygenase-2 expression through the STAT5 signaling pathway in human lung adenocarcinoma A549 cells

The epidermal growth factor receptor (EGFR) can be activated by several growth factors within the tumor microenvironment, and it can activate several signaling pathways. For tumor development, these EGFR-related signaling pathways may converge on several common nuclear transcription factors, one such transcription factor being STAT5. STAT5 plays an important role in the oncogenic signal transduction pathway in non-small cell lung cancer. In this study, we examined whether the epidermal growth factor (EGF) can stimulate cyclooxygenase-2 (COX-2) expression in human lung adeno­carcinoma A549 cells transfected with or without STAT5 siRNA or dominant-negative (DN)-STAT5, and identified the pathways involved in this response. We found that STAT5 siRNA significantly reduced EGF-induced COX-2 expression, and STAT5 phosphorylation. STAT5 phosphorylation predominantly mediates EGF-induced COX-2 promoter activity. STAT5 siRNA was found to inhibit COX-2 expression in resting A549 cells despite the absence of detectable activated phosphorylated STAT5. Using an adenoviral system, we expressed DN-STAT5 in human lung adenocarcinoma A549 cells in order to broaden the investigation and to determine the role of STAT5 in EGF-mediated COX-2 gene expression. The overexpression of DN-STAT5 significantly inhibited EGF-induced COX-2 expression, and we found that EGF induced the tyrosine phosphorylation of STAT5 and up- regulated COX-2 expression. DN-STAT5 also blocked COX-2 promoter activity. Our results demonstrate that EGF stimulates COX-2 expression in human lung adenocarcinoma A549 cells via the activation of the STAT5 pathway and that COX-2 expression may be independent of phosphorylated STAT5 in A549 cells in vitro.