The pathogenesis of gastric cancer is not completely understood. Tumor necrosis factor-α-induced protein-8 like-2 (TIPE2) has recently been identified as a novel negative regulator gene of the immune system, and studies in mice and humans have suggested its inhibitory action in both inflammation and cancer. In this study, we examined the expression levels of TIPE2 in human gastric cancer tissues and also samples of paraneoplastic control tissue, and found that TIPE2 expression was reduced in gastric cancer. To investigate the role of TIPE2 in gastric cell carcinogenesis, a TIPE2 plasmid was introduced into gastric cell lines and TIPE2 function was examined. Colony-forming assays showed that restoration of TIPE2 expression in gastric cells significantly suppressed cell proliferation. Analysis by flow cytometry showed that the number of cells in the S phase of the cell cycle was reduced concomitant with TIPE2 expression, and cell apoptosis was maintained at a low level. Microarray and western blot analyses revealed that TIPE2 selectively up-regulated N-ras and p27 expression. The role of p27 in mediating TIPE2-associated cell growth inhibition was verified by a p27 siRNA interference assay. In this study, we proved that TIPE2 is an inhibitor of gastric cancer cell growth, and suggest that TIPE2 might promote a p27-associated signaling cascade that leads to restored control of the cell cycle and cell division. Our results provide a new molecular mechanism by which TIPE2 may regulate proliferation of gastric cells.

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The expression pattern of HOX transcript antisense RNA (HOTAIR) in the progression of gastric cancer and the regulation of its expression are still unclear. In the current study, HOTAIR expressions in gastric tissues collected from patients with superficial gastritis, atrophic gastritis, atypical hyperplasia, and gastric cancer as well as normal controls was quantitatively examined. The results showed that the expression of HOTAIR was higher in gastric cancer than in normal tissues, but reached the highest level in atrophic gastritis, suggesting that HOTAIR may be involved in the molecular process of nonresolving inflammation. Then tumor necrosis factor-α-induced protein-8 like-2 (TIPE2), a known gene associated with nonresolving inflammation, was overexpressed and the results showed that the promotion in TIPE2 expression triggered HOTAIR reduction, this result was further verified by microarray analysis and TIPE2 knockout mice. Subsequently, the data obtained from HOTAIR knockdown experiment showed that it significantly enhanced colony forming capability and inhibited p27 expression in AGS cells. Furthermore, deletion constructs and luciferase-based activity assays indicated that the −475 to −443bp region of HOTAIR promoter contained a crucial regulatory element. Transcription factor prediction with software TRANSFAC revealed that nuclear factor-κB signaling protein p65 had a binding site in this region and might have roles in HOTAIR expression. The binding of phosphor-p65 to HOTAIR promoter was verified by chromatin immunoprecipitation, and succeeding experiment results demonstrated that p65 reduction by p65 small interfering RNA and TIPE2 overexpression also decreased HOTAIR expression. Conclusively, our results suggest that HOTAIR was associated with nonresolving inflammation, and its expression is regulated by p65.