Differential Notch1 and Notch2 Expression and Frequent Activation of Notch Signaling in Gastric Cancers

<jats:title>Abstract</jats:title> <jats:p> <jats:italic>Context</jats:italic> .—The biologic effects of Notch1 and Notch2 vary with cancer types and their potential role(s) in gastric cancers (GCs) remains largely unknown. </jats:p> <jats:p> <jats:italic>Objectives</jats:italic> .—This study aimed to address the previously mentioned issue by checking the expression of Notch1, Notch2, and Notch target gene <jats:italic>Hes1</jats:italic> in GCs, premalignant gastric lesions, and noncancerous endoscopic gastric mucosa and by inhibiting Notch signal transduction in GC cells. </jats:p> <jats:p> <jats:italic>Design</jats:italic> .—The status of Notch1, Notch2, and Hes1 expression in 74 GC surgical specimens, 10 endoscopic samples, and 4 human GC cell lines was evaluated by tissue microarray–based immunohistochemical staining, Western blotting, and reverse transcription-polymerase chain reaction, and the importance of Notch signaling was elucidated by treating 2 GC cell lines with 2 γ-secretase inhibitors. </jats:p> <jats:p> <jats:italic>Results</jats:italic> .—Notch1 was undetectable in noncancerous gastric mucosa but was expressed with nuclear translocation in 16.7% (4 of 24) of chronic gastritis, 50.0% (9 of 18) of intestinal metaplasia, 54.2% (26 of 48) of intestinal GC, and 23.1% (6 of 26) of diffuse GC, showing distinct differences of Notch1 detection rates between either intestinal metaplasia and chronic gastritis or intestinal GCs and diffuse GCs ( <jats:italic>P</jats:italic>  =  .03; <jats:italic>P</jats:italic>  =  .005, respectively). Notch2 nuclear translocation frequencies were 10.0% (1 of 10) in noncancerous endoscopic mucosa, 71.4% (30 of 42) in premalignant lesions, and 97.3% (72 of 74) in GC tissues, demonstrating a correlation of Notch2 expression with both intestinal GC and diffuse GC formation ( <jats:italic>P</jats:italic> < .001). The rates of nuclear-Hes1 labeling were 1 of 10 among noncancerous, 42.9% premalignant, and 81.1% cancer tissues, which were closely correlated with Notch2 ( <jats:italic>P</jats:italic> < .001) rather than Notch1 ( <jats:italic>P</jats:italic>  =  .42) nuclear translocation. Only Notch2 was expressed accompanied with Hes1 nuclear labeling in the 4 GC cell lines established from diffuse GC cases. Inhibition of Notch signaling with γ-secretase inhibitors, L-685,458 and DAPT, prevented Hes1 nuclear translocation but neither suppressed growth nor induced cell death. </jats:p> <jats:p> <jats:italic>Conclusions</jats:italic> .—This study demonstrated a close correlation of Notch2 expression with GC formation and the potential link of Notch1 upregulation with intestinal-like phenotypes of gastric lesions. Although inhibition of Notch activity failed to achieve anti-GC effects, the activated Notch signaling may reflect a potential GC risk. </jats:p>