COX-2 regulates Snail expression in gastric cancer via the Notch1 signaling pathway

The conversion of arachidonic acid into prostaglandins by cyclooxygenase (COX)-2 contributes to the biological properties of malignant tumours. During the initiation and development of various tumours, the Notch family plays a key role. However, the association between COX2 and the Notch family in gastric cancer (GC) remains unclear. The present study aimed to clarify the mechanisms through which COX2 participates in the pathogenesis of GC. Quantitative PCR and western blot analysis were used to detect the expression of Notch family members and COX2 in human GC and paracancerous tissues, GES1 cells and GC cell lines (AGS, SGC7901, BGC823, and MGC803) treated with or without celecoxib, prostaglandin E2 and small interfering RNA (siRNA). A CCK8 assay was performed to detect the proliferation of GC cells transfected with siRNA against COX2 (siCOX2). A high mRNA expression of Notch1 and a decreased expression of Notch-1 intracellular active domain (N1IC) in GC were found to be related to the depth of invasion and TNM staging. The mRNA levels of Notch2, Notch3, Jagged1 and N2IC were found to be high in GC. A High expression of COX2 was associated with poorly differentiated and deeply invasive GC. COX2 and Notch1 exhibited an inverse expression pattern in the GES1 cells and different GC cell lines; the inhibition of COX2 increased Notch1 expression and activated the GC cells, whereas Notch1 downregulation had the opposite effect. Notch1 exhibited varying effects on Snail in the GC cell lines. The downregulation of COX2 expression significantly inhibited the proliferation of GC cells. On the whole, the expression of Notch signalling molecules differed in GC. COX2 inversely regulated Notch1 in GC and partially depended on the Notch1 signalling pathway in altering the expression of Snail.