Abstract 913: Wnt signaling promotes mouse and human gastric stem cell proliferation
Authors: Demitrack Elise Susan , Samuelson Linda C. 
Published: July 2017

Abstract
Background: The Wnt signaling pathway is required for proliferation of intestinal stem cells and activating mutations in the Wnt pathway can promote colorectal cancer. The requirement for Wnt to support gastric stem cell function is much less clear, despite recent reports showing that activating Wnt pathway mutations occur in human gastric cancer. Here we tested the role of Wnt to support stem cell proliferation in the mouse stomach and in human stem cells cultured from control or gastric cancer tissues. Methods: Wnt signaling in the mouse stomach was detected using TCF/Lef:H2B-GFP reporter mice, and Wnt+ gastric cells were identified via GFP immunostaining. Wnt function in SOX2+ gastric stem cells was tested with Sox2-CreER; Apcfl/+ mice, 1-month post-Apc deletion. Wnt regulation of human gastric stem cells was tested in organoid cultures derived from paired control (non-cancer) and gastric cancer tissues. Established organoids were treated with the Wnt inhibitor IWR-1-endo and growth was assessed by quantification of organoid size. Results: GFP+ cells were observed in the gastric epithelium of TCF/Lef:H2B-GFP mice, located throughout corpus glands and at the gland base in antral glands. Interestingly, GFP+ epithelial cells were largely post-mitotic although in the antrum, a subset of GFP+ cells at the gland base co-localized with the antral stem cell marker LGR5. In both corpus and antrum, a subset of GFP+ epithelial cells co-stained with the pan-endocrine marker Chromogranin A and in the antrum, a subset also co-stained with the deep mucous cell marker GSII, suggesting Wnt may regulate gastric cell fate. Analysis of Sox2-CreER; Apcfl/+ mice revealed that Wnt pathway activation in SOX2+ gastric stem cells led to increased epithelial cell proliferation in both corpus and antrum. In the antrum, this incease in proliferation was also accompanied by increased expression of the cancer stem cell marker CD44 at the gland base. Wnt activation also perturbed epithelial cell differentiation in the gastric antrum, with expansion of GSII+ deep mucous cells. Wnt inhibition reduced growth of human gastric organoids derived from non-cancer and gastric cancer tissues. Interestingly, organoids derived from gastric cancer tissue were significantly larger than control organoids and required a 5-fold increase in IWR-1-endo to achieve significant growth inhibition, implying that gastric cancer organoids are somewhat resistant to Wnt inhibition to slow growth. Conclusion: Wnt signaling is a critical pathway for regulation of mouse and human gastric stem cell homeostasis, promoting cellular proliferation. Thus, Wnt may represent an effective therapeutic target for gastric cancers with Wnt-activating mutations.
Citation Format: Elise Susan Demitrack, Linda C. Samuelson. Wnt signaling promotes mouse and human gastric stem cell proliferation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 913. doi:10.1158/1538-7445.AM2017-913