Down-regulation of STIP1 regulate apoptosis and invasion of glioma cells via TRAP1/AKT signaling pathway

Abstract Background In recent years, many studies have confirmed that STIP1 (phosphorylation-induced protein 1) is involved in the development and progression of various tumors. However, its potential role in glioma progression and the underlying mechanisms of glioma development remain unclear. Methods We analyzed the expression of STIP1 in 35 human glioma tissue specimens of different grades, using 6 normal brain tissues for comparison. We transfected U87 and U251 cell lines with small interfering RNA (siRNA) to downregulate STIP1, and set up a negative control group and a blank group for comparison. The MTT assay was used to detect cell proliferation, and cell cycle progression and apoptosis were analyzed through flow cytometry. Transwell experiments were employed to detect the invasion and migration of STIP1-depleted and control U87 and U251 cells and western blotting was used to detect the expression of TRAP1/Akt pathway proteins. In addition, immunohistochemical analysis was used to reveal differences in expression and localization between transplanted tumor specimens of each group. Results We observed a high expression of STIP1 in glioblastoma, MTT assay revealed a decreased cell proliferation rate in the STIP1-downregulated cells. Cell cycle analysis revealed an increased proportion of cells in G1 phase, as well as an increase in apoptosis, upon STIP1 downregulation. Western blotting showed that TRAP1, pAkt, and MMP2 expression was decreased upon STIP1 downregulation. In addition, TRAP1, ki-67, and MMP2 displayed a decreased expression in vivo. Conclusions STIP1 is highly expressed in glioblastoma compared to normal brain tissues. Downregulation of STIP1 in glioma cells reduces cell proliferation rate and invasion and increases cell apoptosis.