(The) roles of osteopontin on gastric and hepatic carcinogenesis in mouse model

Abstract

Osteopontin (OPN), coded by secreted phosphoprotein 1 (Spp1) gene, plays a variety of roles in pathophysiological processes, including inflammation and carcinogenesis. Clinically, the elevated OPN levels in plasma or tissue from patients were identified in inflammatory diseases such as Crohns disease and rheumatoid arthritis, and in various cancers. In this study, we demonstrated the role of OPN in Helicobacter pylori (H. pylori)-induced gastritis, gastric cancer and chemically induced hepatocellular carcinoma using C57BL/6-Spp1tm1Blh(-/-) (OPN KO) mice and OPN knockdown human cancer cell lines. In H. pylori-induced gastritis model, the degree of inflammation of OPN KO mice was lower compared to that of WT mice, with a significant reduction in infiltratied macrophages and the expression of IL-1β, TNF-α, and IFN-γ. Similar to these results, mRNA expression of the pro-inflammatory cytokines was reduced in OPN KD gastric cancer cell lines exposed to H. pylori, and the conditioned media (CM) from these cells decreased the migration of monocytic and macrophage-like cell lines. Furthermore, H. pylori-infected OPN KO mice had a lower number of proliferative gastric epithelial cells than WT mice, in association with a reduction in mitogen-activated protein kinase (MAPK) pathway activation. OPN KD gastric cancer cell lines also showed the suppression of the G1/S cell-cycle after H. pylori co-culture and reduced MAPK activation after IL-1β and TNF-α treatment. In H. pylori and chemical-induced gastric cancer model, the overall incidence of gastric tumors was significantly decreased in OPN KO mice compared to WT mice. Apoptotic cell death was significantly enhanced in OPN KO mice, and was accompanied by upregulation of signal transducer and activator of transcription 1 (STAT1) and inducible nitric oxide synthase (iNOS). In AGS and THP-1 cells, OPN suppression also caused STAT1 upregulation and iNOS overexpression, which resulted in apoptosis of AGS cells. In addition, a negative correlation was clearly identified between expression of OPN and iNOS in human gastric cancer tissues. Our data demonstrate that loss of OPN decreases H. pylori-induced gastric carcinogenesis by suppressing pro-inflammatory immune response and augmenting STAT1 and iNOS-mediated apoptosis of gastric epithelial cells. Furthermore, the overall incidence of chemically induced hepatic tumors at 36 weeks was significantly decreased in OPN KO mice compared to WT mice. Consistent with the result of gastric cancer model, apoptosis was significantly enhanced in OPN KO mice and was accompanied by downregulation of epidermal growth factor receptor (EGFR). In Hep3B and Huh7, OPN suppression also caused the decreased mRNA and protein levels of EGFR with the downregulation of c-Jun, which resulted in the increased apoptotic cell death of both cell lines. In addition, a positive correlation was clearly identified between expression of OPN and EGFR in human HCC tissues. Taken together, these data demonstrate that the loss of OPN decreases the degree of H. pylori-associated gastritis, which resulting in the suppression of gastric cancer development. In addition, it can be concluded that loss of OPN inhibits gastric and hepatic carcinogenesis through promotion of apoptotic cell death in cancer cells.