2-hydroxyglutarate-(2-HG)-mediated inhibition of TET2 activity influences DNA hypermethylation in cells harboring mutations of isocitrate dehydrogenases 1 and 2 (IDH1/2). Here, we show that 2-HG also regulates DNA methylation mediated by DNA methyltransferase 1 (DNMT1). DNMT1-dependent hypermethylation of the RIP3 promoter occurred in both IDH1 R132Q knockin mutant mouse embryonic fibroblast (MEFs) and 2-HG-treated wild-type (WT) MEFs. We found that 2-HG bound to DNMT1 and stimulated its association with the RIP3 promoter, inducing hypermethylation that reduces RIP3 protein and consequently impaired RIP3-dependent necroptosis. In human glioma samples, RIP3 protein levels correlated negatively with IDH1 R132H levels. Furthermore, ectopic expression of RIP3 in transformed IDH1-mutated MEFs inhibited the growth of tumors derived from these cells following transplantation into nude mice. Thus, our research sheds light on a mechanism of 2-HG-induced DNA hypermethylation and suggests that impaired necroptosis contributes to the tumorigenesis driven by IDH1/2 mutations.

Two hallmarks of cancer cells are their resistance to apoptosis and ability to thrive despite reduced levels of vital serum components. c-jun N-terminal kinase (JNK) activation is crucial for apoptosis triggered by serum starvation (SS), and isocitrate dehydrogenase 1 (IDH1) mutations are tumorigenic, in part, because they produce the abnormal metabolite 2-hydroxyglutarate (2-HG). However, it is unknown whether 2-HG-induced tumorigenesis is partially due to JNK inhibition and thus defective SS-induced apoptosis. We show here, using IDH1-R132Q knockin mutant mouse cells, that 2-HG inhibits JNK activation induced only by SS and not by UV or doxorubicin, and thus can block apoptosis. Upon SS, Cdc42 normally disrupts mixed lineage kinase 3's (MLK3's) auto-inhibition, triggering the MLK3-MKK4/7-JNK-Bim apoptotic cascade. 2-HG binds to Cdc42 and abolishes its association with MLK3, inactivating MLK3 and apoptosis. Allograft tumor assays in mice demonstrate that this mechanism contributes to tumorigenesis driven by mutant IDH1, a result confirmed by detection of JNK inactivation in human gliomas harboring IDH1-R132H mutations.

Resistance to apoptosis and uncontrolled proliferation are two hallmarks of cancer cells. p53 is crucial for apoptosis triggered by a broad range of stresses and a well-known gatekeeper for neoplastic transformation. Here we show that oncogenic IDH1 R132H/R132Q mutants robustly inhibit p53 expression and such an effect is attributed to 2-HG production. Mechanistically, 2-hydroxyglutarate (2-HG) stabilizes hypoxia-inducible factor-2α, which in turn activates the expression of miR-380-5p, a characterized microRNA against p53 expression. Rescue expression of p53 can inhibit the proliferation rate and impair the resistance of apoptosis induced by doxorubicin in IDH1 R132Q mouse embryonic fibroblast cells. Furthermore, p53 protein levels correlates negatively with IDH1 R132H levels in human glioma samples. Our results thus shed a new light on how p53 is down-regulated by 2-HG and suggests that impairment of p53-mediated apoptosis contributes to the tumorigenesis driven by IDH1 mutants.

BACKGROUND Posterior circulation ischemic strokes can have devastating consequences, despite medical therapies. Extracranial–intracranial bypass for the augmentation of flow is a treatment option for selected patients with hemodynamic compromise and recurrent ischemia. However, posterior circulation bypass carries a higher risk and lower patency rate than bypass with anterior circulation. OBJECTIVE To present the occipital artery to the extradural vertebral artery (OA-eVA) bypass for posterior circulation ischemia. METHODS We retrospectively reviewed our experience of the OA-eVA bypass surgery in the treatment of bilateral vertebral steno-occlusive disease. RESULTS Seventeen patients were identified. Thirteen patients had bilateral vertebral artery (VA) occlusion (type I), while 4 patients had VA occlusion with contralateral VA severe stenosis (type II). All patients had cerebellar or pons infarction, for which the postoperative bypass patency rate was 100%, with carotid angiogram demonstrating excellent filling of the rostral basilar system or the posterior inferior cerebellar artery territory. The long-term follow-up outcome was favorable (modified Rankin score of 0-2) in 82% of patients (7 patients had complete resolution and 7 had improvement of symptoms) and unfavorable in 18%. One type II case without previous endovascular therapy developed recurrent ischemic onset associated with bypass occlusion. CONCLUSION OA-eVA bypass is a minimally invasive and effective alternative to posterior circulation ischemia. It provides sufficient blood flow augmentation to the vertebrobasilar territory. The advantages of this novel therapeutic strategy include avoiding performing craniotomy and deep bypass and achieving shorter operative times compared to conventional bypass surgery.