Dysregulation of chromatin organization in pediatric and adult brain tumors: oncoepigenomic contributions to tumorigenesis and cancer stem cell properties.

The three-dimensional (3D) organization of the genome is a crucial enabler of cell fate, identity, and function. In this review, we will focus on the emerging role of altered 3D genome organization in the etiology of disease, with a special emphasis on brain cancers. We discuss how different genetic alterations can converge to disrupt the epigenome in childhood and adult brain tumors, by causing aberrant DNA methylation and by affecting the amounts and genomic distribution of histone post-translational modifications. We also highlight examples that illustrate how epigenomic alterations have the potential to affect 3D genome architecture in brain tumors. Finally, we will propose the concept of "epigenomic erosion" to explain the transition from stem-like cells to differentiated cells in hierarchically organized brain cancers.

macroH2A2 antagonizes epigenetic programs of stemness in glioblastoma.

Self-renewal is a crucial property of glioblastoma cells that is enabled by the choreographed functions of chromatin regulators and transcription factors. Identifying targetable epigenetic mechanisms of self-renewal could therefore represent an important step toward developing effective treatments for this universally lethal cancer. Here we uncover an epigenetic axis of self-renewal mediated by the histone variant macroH2A2. With omics and functional assays deploying patient-derived in vitro and in vivo models, we show that macroH2A2 shapes chromatin accessibility at enhancer elements to antagonize transcriptional programs of self-renewal. macroH2A2 also sensitizes cells to small molecule-mediated cell death via activation of a viral mimicry response. Consistent with these results, our analyses of clinical cohorts indicate that high transcriptional levels of this histone variant are associated with better prognosis of high-grade glioma patients. Our results reveal a targetable epigenetic mechanism of self-renewal controlled by macroH2A2 and suggest additional treatment approaches for glioblastoma patients.

Somatostatin Ameliorates ß-Amyloid-Induced Cytotoxicity via the Regulation of CRMP2 Phosphorylation and Calcium Homeostasis in SH-SY5Y Cells.

Somatostatin is involved in the regulation of multiple signaling pathways and affords neuroprotection in response to neurotoxins. In the present study, we investigated the role of Somatostatin-14 (SST) in cell viability and the regulation of phosphorylation of Collapsin Response Mediator Protein 2 (CRMP2) (Ser522) via the blockade of Ca2+ accumulation, along with the inhibition of cyclin-dependent kinase 5 (CDK5) and Calpain activation in differentiated SH-SY5Y cells. Cell Viability and Caspase 3/7 assays suggest that the presence of SST ameliorates mitochondrial stability and cell survival pathways while augmenting pro-apoptotic pathways activated by Aß. SST inhibits the phosphorylation of CRMP2 at Ser522 site, which is primarily activated by CDK5. Furthermore, SST effectively regulates Ca2+ influx in the presence of Aß, directly affecting the activity of calpain in differentiated SH-SY5Y cells. We also demonstrated that SSTR2 mediates the protective effects of SST. In conclusion, our results highlight the regulatory role of SST in intracellular Ca2+ homeostasis. The neuroprotective role of SST via axonal regeneration and synaptic integrity is corroborated by regulating changes in CRMP2; however, SST-mediated changes in the blockade of Ca2+ influx, calpain expression, and toxicity did not correlate with CDK5 expression and p35/25 accumulation. To summarize, our findings suggest two independent mechanisms by which SST mediates neuroprotection and confirms the therapeutic implications of SST in AD as well as in other neurodegenerative diseases where the effective regulation of calcium homeostasis is required for a better prognosis.

Microbiome-derived inosine modulates response to checkpoint inhibitor immunotherapy.

Several species of intestinal bacteria have been associated with enhanced efficacy of checkpoint blockade immunotherapy, but the underlying mechanisms by which the microbiome enhances antitumor immunity are unclear. In this study, we isolated three bacterial species-Bifidobacterium pseudolongum, Lactobacillus johnsonii, and Olsenella species-that significantly enhanced efficacy of immune checkpoint inhibitors in four mouse models of cancer. We found that intestinal B. pseudolongum modulated enhanced immunotherapy response through production of the metabolite inosine. Decreased gut barrier function induced by immunotherapy increased systemic translocation of inosine and activated antitumor T cells. The effect of inosine was dependent on T cell expression of the adenosine A2A receptor and required costimulation. Collectively, our study identifies a previously unknown microbial metabolite immune pathway activated by immunotherapy that may be exploited to develop microbial-based adjuvant therapies.

Somatostatin Maintains Permeability and Integrity of Blood-Brain Barrier in ß-Amyloid Induced Toxicity.

In Alzheimer's disease (AD), the impaired clearance of ß-amyloid peptide (Aß) due to disrupted tight junction and transporter proteins is the prominent cause of disease progression. Somatostatin (SST) blocks the aggregation of Aß and inflammation whereas reduction of SST levels in the CSF and brain tissue is associated with impaired cognitive function and memory loss. However, the role of SST in preservation of blood-brain barrier (BBB) integrity and functionality in Aß-induced toxicity is not known. In the present study using human CMEC/D3 cells, we demonstrate that SST prevents Aß-induced BBB permeability by regulating LRP1 and RAGE expression and improving the disrupted tight junction proteins. Furthermore, SST abrogates Aß-induced JNK phosphorylation and expression of MMP2. Taken together, results presented here suggest that SST might serve as a therapeutic intervention in AD via targeting multiple pathways responsible for neurotoxicity, impaired BBB function, and disease progression.

Somatostatin-Mediated Changes in Microtubule-Associated Proteins and Retinoic Acid-Induced Neurite Outgrowth in SH-SY5Y Cells.

Somatostatin (SST) is a growth hormone inhibitory peptide involved in regulation of several physiological responses of cells including neurotransmission, cell migration, maturation, and neurite formation. In the present study, we examined the role of SST in all-trans retinoic acid (RA)-induced progression of neurite outgrowth in SH-SY5Y cells. We also determined the morphological and developmental changes in prominent intracellular markers of neurite growth including microtubule-associated protein 2 (MAP2), neuron-specific III ß-tubulin (TUJ1), and Tau. Here, we present evidence that SST is a molecular determinant in regulating the transition of SH-SY5Y cells from non-neuronal entity to neuronal phenotype in response to RA. The results from present study reveal that SST changes the distributional pattern of MAP2/Tau and TUJ1, and activates extracellular signal-regulated kinase (ERK1/2) signaling pathway through SST receptors (SSTRs). The expression of MAP2 and Tau remains elevated upon treatment with RA and SST alone or in combination. Importantly, we identified that the cells displaying strong co-expression of SST and TUJ1 are more likely to bear elongated neurite formation than cells devoid of such expression. These findings show that the site-specific expression of MAP2 and TUJ1 is an essential determinant of neurite outgrowth in SH-SY5Y cells in RA-mediated differentiation. Taken together, results presented here further substantiates the role of SST in the promotion of neurite formation and elongation in SH-SY5Y cells in combination with RA. Investigating how SST can improve neurite formation in neurodegenerative disease may help to develop new therapeutic approach in improving cognitive function and memory loss.

Colocalization of cannabinoid receptor 1 with somatostatin and neuronal nitric oxide synthase in rat brain hypothalamus.

Despite several overlapping functions of cannabinoid receptor 1 (CB1 receptor), somatostatin (SST), and neuronal nitric oxide synthase (nNOS) in the hypothalamus, nothing is currently known whether CB1 receptor-positive neurons coexpress SST and nNOS. In the present study, we describe the colocalization of CB1 receptor with SST and nNOS in the rat brain hypothalamus. In the hypothalamus, the distributional patterns and colocalization of CB1 receptor with SST and nNOS were selective and region specific. CB1 receptor and SST exhibited comparable colocalization (<60%) in paraventricular nucleus (PVN) and periventricular nucleus (PeVN), followed by 20% colocalization in ventromedial hypothalamic nucleus (VMH). Neurons showing colocalization between CB1 receptor and nNOS in PeVN constituted >80%, followed by 60 and 30% in PVN and VMH, respectively. In contrast, SST- and nNOS-positive neurons displayed comparable colocalization (>55%) in PeVN and VMH, followed by PVN (~20%). In the median eminence, CB1 receptor-, SST-, and nNOS-like immunoreactivity was mostly confined to the nerve fibers. The morphological colocalization of CB1 receptor with SST and nNOS shed new light on the understanding of their roles in regulation of physiological and pharmacological response to certain stimuli in hypothalamic nuclei specifically in food intake and energy balance.

microRNA-495 inhibits chondrogenic differentiation in human mesenchymal stem cells by targeting Sox9.

The chondrogenic differentiation process of human mesenchymal stem cells (hMSCs) passes through multiple stages, which are carried out by various factors and their interactions. Recently, microRNAs that regulate chondrogenic differentiation have been reported. However, microRNA that regulates SRY-related high mobility group-box gene 9 (Sox9), a chondrogenic key factor, has not been identified in hMSC. In this study, we identified that microRNA-495 (miR-495) is an important regulator of hMSC chondrogenic differentiation. In our microarray, miR-495 was downregulated during transforming growth factor (TGF)-ß3-induced chondrogenic differentiation of hMSCs in vitro. We found that there is an miR-495 binding site in the 3' untranslated region (3'UTR) of Sox9. We confirmed opposite expression between miR-495 and Sox9 by using real-time polymerase chain reaction. Further, overexpression of miR-495 inhibited Sox9 expression, and repression of miR-495 increased expression of Sox9 in SW1353 cells and hMSCs. Additionally, luciferase analysis revealed that miR-495 directly binds to the Sox9 3'UTR, and we confirmed a seed sequence of miR-495 on the Sox9 3'UTR. Subsequently, overexpression of miR-495 repressed the expression of the extracellular matrix (ECM) protein, such as type II collagen (Col2A1), aggrecan, and proteoglycan products, whereas inhibition of miR-495 increased their expression. Collectively, this study indicates that miR-495 directly targets Sox9, ultimately leading to the regulation of chondrogenic differentiation in hMSCs.

Peroxisome proliferator-activated receptor gamma/signal transducers and activators of transcription 5A pathway plays a key factor in adipogenesis of human bone marrow-derived stromal cells and 3T3-L1 preadipocytes.

Adipogenesis is largely dependent on the signal transducers and activators of transcription (STAT) pathway. However, the molecular mechanism of the STAT pathway in the adipogenesis of human bone marrow-derived stromal cells (hBMSCs) remains not well understood. The purpose of this research was to characterize the transcriptional regulation involved in expression of STAT5A and STAT5B during adipogenesis in hBMSCs and 3T3-L1 cells. The expression of STAT5A and STAT5B increases with the onset of adipogenesis in hBMSCs and 3T3-L1 cells. The PPAR response elements regulatory element of STAT5A exists at a promoter region ranging from -346 to -101, and the CCAAT/enhancer-binding protein (C/EBP) regulatory element is located at -196 to -118 of the STAT5B promoter. C/EBPß and C/EBPα bound to the STAT5B promoter region, whereas peroxisome proliferator-activated receptor γ (PPARγ) bound to STAT5A. RNA interference of STAT5A completely blocked differentiation, whereas the inhibition of STAT5B only partially blocked differentiation. We propose that C/EBPα, C/EBPß, and PPARγ control adipogenesis by regulating STAT5B and STAT5A and that STAT5A is necessary, whereas STAT5B plays a supplementary role during adipogenesis. Further, the regulation of PPARγ-STAT5 by C/EBPß signaling seems to be the crucial adipogenesis pathway-initiating cascade of the various adipogenic genes.

miR-449a regulates the chondrogenesis of human mesenchymal stem cells through direct targeting of lymphoid enhancer-binding factor-1.

microRNAs are small molecules, about 17-23 nucleotides in length, that act as translational regulators of their target gene. By binding to a target, microRNAs are known to either inhibit translation or induce degradation of the target. Despite the great interest in microRNAs, however, the exact targets of each individual microRNA in different processes remain largely unknown. In this study, we determined that the lymphoid enhancer-binding factor-1 (LEF-1) was expressed during the chondrogenesis of human bone marrow-derived mesenchymal stem cells (hBM-MSCs) and sought to identify a novel microRNA targeting this gene. Through subsequent studies, we have identified, for the first time, one particular microRNA, miR-449a, that recognizes and regulates the expression of LEF-1 in a dose-dependent and sequence-specific manner. In addition, we observed that the inhibition of LEF-1 via miR-449a led to the subsequent repression of Sox 9, which is a well-established regulator of chondrogenesis. Collectively, this study demonstrated that miR-449a directly targets LEF-1, which in turn affects the expression of Sox 9, ultimately leading to the proper regulation of the differentiation and chondrogenesis of human MSCs (hBM-MSCs).

The effects of COX-2 inhibitor during osteogenic differentiation of bone marrow-derived human mesenchymal stem cells.

Cyclooxygenase-2 (COX-2) inhibitors suppress bone repair and bone formation by suppressing angiogenesis as well as potentially interfering with osteoblast and osteoclast functions. In spite of these reports, there is a controversy over the exact effects of COX-2 inhibitors on bone formation processes itself. This work was designed to investigate the effect of COX-2 inhibitor on osteogenesis of human bone marrow-derived mesenchymal stem cells (MSC). MSCs in osteogenesis were treated with COX-2 inhibitor (celecoxib and naproxen) in the absence or presence of interleukin-1ß (IL-1ß), which was used to induce inflammation. Following differentiation, alkaline phosphatase (ALP) and calcium contents of IL-1ß-treated MSC were significantly reduced by high doses of COX-2 inhibitors compared with the low-dose group. However, in non-inflammatory-conditioned MSCs, ALP and calcium contents were not reduced by COX-2 inhibitors. The mRNA expression of Runx2/Cbf alpha 1, Dlx5, and osteocalcin was also decreased by COX-2 inhibitors in inflammatory-conditioned MSCs and showed a significant decrease for the high dose while they remained constant in the non-inflammatory-conditioned MSCs. These data indicate that the osteogenic potential of MSC is inhibited/delayed by the treatment of high-dose NSAIDs under inflammatory conditions.