The tumor suppressor prostate apoptosis response-4 (Par-4) is regulated by mutant IDH1 and kills glioma stem cells.

Prostate apoptosis response-4 (Par-4) is an endogenous tumor suppressor that selectively induces apoptosis in a variety of cancers. Although it has been the subject of intensive research in other cancers, less is known about its significance in gliomas, including whether it is regulated by key driver mutations, has therapeutic potential against glioma stem cells (GSCs), and/or is a prognostic marker. We found that patient-derived gliomas with mutant isocitrate dehydrogenase 1 have markedly lower Par-4 expression (P < 0.0001), which was validated by The Cancer Genome Atlas dataset (P = 2.0 E-13). The metabolic product of mutant IDH1, D-2-hydroxyglutarate (2-HG), can suppress Par-4 transcription in vitro via inhibition of promoter activity as well as enhanced mRNA degradation, but interestingly not by direct DNA promoter hypermethylation. The Selective for Apoptosis induction in Cancer cells (SAC) domain within Par-4 is highly active against glioma cells, including orthotopic xenografts of patient-derived primary GSCs (P < 0.0001). Among high-grade gliomas that are IDH1 wild type, those that express more Par-4 have significantly longer median survival (18.4 vs. 8.0 months, P = 0.002), a finding confirmed in two external GBM cohorts. Together, these data suggest that Par-4 is a significant component of the mutant IDH1 phenotype, that the activity of 2-HG is complex and can extend beyond direct DNA hypermethylation, and that Par-4 is a promising therapeutic strategy against GSCs. Furthermore, not every effect of mutant IDH1 necessarily contributes to the overall favorable prognosis seen in such tumors; inhibition of Par-4 may be one such effect.

Autophagy and oxidative stress in gliomas with IDH1 mutations.

IDH1 mutations in gliomas associate with longer survival. Prooxidant and antiproliferative effects of IDH1 mutations and its D-2-hydroxyglutarate (2-HG) product have been described in vitro, but inconsistently observed. It is also unclear whether overexpression of mutant IDH1 in wild-type cells accurately phenocopies the effects of endogenous IDH1-mutations on tumor apoptosis and autophagy. Herein we investigated the effects of 2-HG and mutant IDH1 overexpression on proliferation, apoptosis, oxidative stress, and autophagy in IDH1 wild-type glioma cells, and compared those results with patient-derived tumors. 2-HG reduced viability and proliferation of U87MG and LN18 cells, triggered apoptosis in LN18 cells, and autophagy in U87MG cells. In vitro studies and flank xenografts of U87MG cells overexpressing R132H IDH1 exhibited increased oxidative stress, including increases of both manganese superoxide dismutase (MnSOD) and p62. Patient-derived IDH1-mutant tumors showed no significant differences in apoptosis or autophagy, but showed p62 accumulation and actually trended toward reduced MnSOD expression. These data indicate that mutant IDH1 and 2-HG can induce oxidative stress, autophagy, and apoptosis, but these effects vary greatly according to cell type.

Nocturnin expression is induced by fasting in the white adipose tissue of restricted fed mice.

The relationship between circadian clocks and metabolism is intimate and complex and a number of recent studies have begun to reveal previously unknown effects of food and its temporal availability on the clock and the rhythmic transcriptome of peripheral tissues. Nocturnin, a circadian deadenylase, is expressed rhythmically in a wide variety of tissues, but we report here that Nocturnin expression is arrhythmic in epididymal white adipose tissue (eWAT) of mice housed in 12:12 LD with ad libitum access to food. However, Nocturnin expression becomes rhythmic in eWAT of mice placed on restricted feeding. We show here that Nocturnin's rhythmic expression pattern is not dependent upon feeding, nor is it acutely induced by feeding in the liver or eWAT of ad libitum fed mice. However, Nocturnin is acutely induced by the absence of the expected meal in eWAT of restricted fed mice. A rise in cAMP levels also induces Nocturnin expression, suggesting that Nocturnin's induction in eWAT by fasting is likely mediated through the same pathways that activate lipolysis. Therefore, this suggests that Nocturnin plays a role in linking nutrient sensing by the circadian clock to lipid mobilization in the adipocytes.

A circadian-regulated gene, Nocturnin, promotes adipogenesis by stimulating PPAR-gamma nuclear translocation.

Nocturnin (NOC) is a circadian-regulated protein related to the yeast family of transcription factors involved in the cellular response to nutrient status. In mammals, NOC functions as a deadenylase but lacks a transcriptional activation domain. It is highly expressed in bone-marrow stromal cells (BMSCs), hepatocytes, and adipocytes. In BMSCs exposed to the PPAR-gamma (peroxisome proliferator-activated receptor-gamma) agonist rosiglitazone, Noc expression was enhanced 30-fold. Previously, we reported that Noc(-/-) mice had low body temperature, were protected from diet-induced obesity, and most importantly exhibited absence of Pparg circadian rhythmicity on a high-fat diet. Consistent with its role in influencing BMSCs allocation, Noc(-/-) mice have reduced bone marrow adiposity and high bone mass. In that same vein, NOC overexpression enhances adipogenesis in 3T3-L1 cells but negatively regulates osteogenesis in MC3T3-E1 cells. NOC and a mutated form, which lacks deadenylase activity, bind to PPAR-gamma and markedly enhance PPAR-gamma transcriptional activity. Both WT and mutant NOC facilitate nuclear translocation of PPAR-gamma. Importantly, NOC-mediated nuclear translocation of PPAR-gamma is blocked by a short peptide fragment of NOC that inhibits its physical interaction with PPAR-gamma. The inhibitory effect of this NOC-peptide was partially reversed by rosiglitazone, suggesting that effect of NOC on PPAR-gamma nuclear translocation may be independent of ligand-mediated PPAR-gamma activation. In sum, Noc plays a unique role in the regulation of mesenchymal stem-cell lineage allocation by modulating PPAR-gamma activity through nuclear translocation. These data illustrate a unique mechanism whereby a nutrient-responsive gene influences BMSCs differentiation, adipogenesis, and ultimately body composition.