Regulation of the Bmp Signaling Inhibitor Smad6 in Gastritis and Gastric Cancer

Abstract

The bone morphogenetic proteins (BMPs) are important regulators of the growth and differentiation of gastrointestinal tissues and potent inhibitors of gastrointestinal inflammation. We previously reported that inhibition of BMP signaling in the mouse stomach leads to enhanced inflammation and to the development of metaplasia and dysplasia. The goal of this study is to investigate the expression of the BMP signaling inhibitor Smad6 in gastritis and gastric cancer. Expression of Smad6, of the pro-inflammatory cytokine IFN-gamma and of CD44, a molecule involved in gastric inflammation, metaplasia and neoplasia, were assessed in the gastric mucosa of Helicobacter Pylori (HP)-infected C57B/6 mice and in fifty four human antral biopsy samples from individuals with HP gastritis using QRT-PCR. Control antral biopsy samples were obtained from thirty seven normal subjects. Cultures of human organoids derived from normal antral biopsies were used to assess the effect of the cytokines IFNgamma (30 ng/ml), Il-1-beta (5 ng/ml) and Tnf-alfa (10ng/ml) on the expression of Smad6. Mining of TCGA was performed to assess the expression of cytokines, BMP inhibitors, BMP signaling molecules and gastric cancer stem cell markers in gastric neoplasms. Expression of the IFN-gamma, Smad6 and CD44 proteins was measured in 22 human tumors of the antrum using western blots and scanning densitometry. Smad6, CD44 and IFN-gamma mRNA expression was increased in gastritis samples. INF-gamma and Il1-beta but not Tnfalfa induced the expression of Smad6 in human organoids. TCGA analysis indicated an increase in the expression of BMP inhibitors (SMAD6 and BAMBI), gastric cancer stem cell markers (CD44 and LGR5), and cytokines (IL-8 and IFN-gamma) in gastric tumors, and a decrease in that of BMP signaling molecules (BMPR1B, ID1 and ID4). Western blot analysis confirmed a significant increase in the expression of Smad6, IFN-gamma and CD44 proteins in 50% of antral tumors. In summary, gastric inflammation leads to enhanced expression of BMP signaling inhibitors. This event might be an important pathophysiological mechanism for the development of inflammation-linked gastric neoplasia.