Downregulation Of TUSC4 Activates PDK1-AKT1 And Contributes To The Malignant Growth Of Glioma Cells

Objective: The aim of this work was to explore the levels of TUSC4 in non-tumor brain and glioma tissues. Moreover, the expression of TUSC4 was observed in NHA compared to several glioma cell lines. The effects and molecular mechanisms of TUSC4 on growth inhibition of glioma were also investigated.Methods: 1. Eighty-four paraffin-embedded astrocytoma samples and twelve non-tumor brain tissues were collected from 2006-2013 in department of pathology, Chongqing Medical University, the IHC was used to test the expression of TUSC4 in these specimens. The relationship between TUSC4 expression and survival of patients was analyzed using Kaplan-meier; 2. Eight glioma surgical specimens and the matched adjacent nontumorous brain tissues were also gathered from 2013-2014 in department of neurosurgery, the second affiliated hospital of Chongqing Medical University, WB was used to detect the TUSC4 in these paired samples; 3. The expression of TUSC4 in NHA and different glioma cell line(U373, SHG44, U118,U87, U251, A172) was estimated using WB; 4. The levels of TUSC4 were increased(LV-TUSC4) or decreased(LV-SiRNA-TUSC4) in various glioma cell lines using lentivirus carriers, CCK8 and FCM were used to evaluate the effects of TUSC4 on the inhibition of cell viability and cell cycle; 5. The subcutaneous tumor formation in nude mice and SI in these tumor tissues were measured after change of TUSC4 expression in glioma cells; 6. The regulation of TUSC4 in the expression and activation of signaling pathway PDK1-AKT1 and downstream target gene(p21, p27, CDK2, CDK4) was examined using WB and enzyme activity assay.Results: 1. The levels of TUSC4 in glioma tissues were reduced compared to non-tumor brain and were negatively correlated with tumor malignancy grade, the lower the TUSC4 expression, the shorter the survival time of the patients; 2. TUSC4 in glioma samples were lower than that in corresponding adjacent non-cancerous brain tissues; 3. The down- regulation of TUSC4 was also found in several glioma cells compared to NHA; 4. TUSC4 was able to inhibit cell viability and induce the cell cycle arrest at G1 phase, coupled with reduced percentages at S phase; 5. TUSC4 suppressed the growth of xenotransplanted tumors and SI in tumor tissues; 6. The phosphorylation and activation of PDK1(Tyr9)-AKT1(Thr308) signaling pathway were depressed by TUSC4,contributing to the up-regulation of target genes p21/27 which exerted anti-cancer function via suppressing the activation of CDK2/4.Conclusion: The down-regulation of TUSC4 was negatively correlated with the histologic grade, resulting in decrease in PDK1/AKT1 inhibition and promotion of malignant growth of glioma. Thus, introduction of TUSC4 in glioma will be conducive to novel strategy for target gene therapy.