Recently, mutations of the isocitrate dehydrogenase (IDH) 1 gene, which specifically occur in the majority of low-grade and secondary high-grade gliomas, have drawn particular attention of neuro-oncologists. Mutations of the IDH1 gene have been proposed to have significant roles in the tumorigenesis, progression and prognosis of gliomas. However, the molecular mechanism of the role of IDH1 mutants in gliomagenesis remains to be elucidated. The present study, showed that forced expression of an IDH1 mutant, of which the 132th amino acid residue arginine is substituted by histidine (IDH1R132H), promoted cell proliferation in cultured cells, while wild-type IDH1 overexpression had no effect on cell proliferation. Consistent with previous studies, it was also observed that expression of hypoxia-inducible factor 1-α (HIF1-α) was upregulated in IDH1R132H expressing cells with the induction of vascular endothelial growth factor (VEGF) expression. However, knockdown of VEGF via small RNA interference had no significant influence on the cell proliferation induced by overexpression of IDH1R132H, implying that another signaling pathway may be involved. Next, forced expression of IDH1R132H was found to activate nuclear factor-κB (NF-κB), since the inhibitory IκB protein (IκBα) was highly phosphorylated and the NF-κB p65 subunit was translocated into the nucleus. Notably, knockdown of HIF1-α significantly blocked NF-κB activation, which was induced by the overexpression of IDH1 mutants. In addition, expression of IDH1 mutants markedly induced the NF-κB target gene expression, including cyclin D1 and E and c-myc, which were involved in the regulation of cell proliferation. In conclusion, it was demonstrated that the IDH1 mutant activated NF-κB in a HIF1-α‑dependent manner and was involved in the regulation of cell proliferation.

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Abstract. We previously demonstrated that 14-3-3β is overexpressed in astrocytomas; however, the underlying mechanisms are poorly understood. Based on the reported multiple functions of 14-3-3β, we hypothesized that it interacts with glycogen synthase kinase 3 β (GSK3β), which regulates β-catenin-mediated oncogene expression and contributes to tumorigenesis and astrocytoma progression. To test these hypotheses, we used 14-3-3β overexpression vectors and small interfering RNA (siRNA) transfection in the human normal astrocyte cell line SVGp12 and the glioma cell line U87, respectively. The results showed that overexpression of 14-3-3β promoted the proliferation of SVGp12 cells, while knockdown of 14-3-3β inhibited the proliferation of U87 cells as analyzed by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and bromodeoxyuridine (BrdU) assays. In Flag-tagged 14-3-3β-overexpressing cells, GSK3β was co-immunoprecipitated with 14-3-3β using a Flag antibody. Knockdown of β-catenin by siRNA blocked cell proliferation induced by overexpression of 14-3-3β. Furthermore, overexpression of 14-3-3β suppressed the phosphorylation of β-catenin leading to its accumulation and nuclear translocation as revealed by western blot analysis. In addition, β-catenin nuclear translocation induced by overexpression of 14-3-3β activated the transcription of oncogenes including c-myc and cyclin D1. Collectively, these results revealed that 14-3-3β regulates the proliferation of astrocytes and glioma cells through the GSK3β/β-catenin signaling pathway. The delineated mechanism of 14-3-3β may be responsible for the tumorigenesis and progression of human astrocytomas. Thus, new therapeutic strategies or drugs aimed at 14-3-3β may have potential for the treatment of human astrocytomas. IntroductionThe highly conserved family of 14-3-3 proteins consisting of seven isoforms (β, γ, ε, η, θ, σ and ξ) has been demonstrated to bind to a wide variety of proteins and to play important roles in a variety of biological processes, including cell cycle control, cell survival and cell death through various signal transduction pathways (1-4). In normal or tumor cells and tissues, 14-3-3 proteins have been suggested to participate in a broad spectrum of human diseases such as cancer (5). However, 14-3-3 proteins exhibit isoform-specific expression in different types of cells and tissues, and the function of 14-3-3 proteins is complex and intricate owing to the high sequence homology of its isoforms (6).The role of 14-3-3 proteins in carcinogenesis has been extensively studied. Accumulating evidence has established an association between 14-3-3 proteins and many types of cancers, including lung, breast, neck and head cancers (5,7). However, different isoforms may act as oncogenes or tumor suppressors in different types of cancers. Abundant expression of 14-3-3ξ is found in breast cancers and promotes cancer progression via the PI3K/Akt pathway (8,9). Knockdown of 14-3-3ξ was found to significantly inhibit lung cancer cell proliferation a...

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