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Supplementary Figure 3 from OTX2 Is Critical for the Maintenance and Progression of Shh-Independent Medulloblastomas

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Supplementary Figure 1 from OTX2 Is Critical for the Maintenance and Progression of Shh-Independent Medulloblastomas

Supplementary Figure 4 from OTX2 Is Critical for the Maintenance and Progression of Shh-Independent Medulloblastomas

Supplementary Table 1 from OTX2 Is Critical for the Maintenance and Progression of Shh-Independent Medulloblastomas

OTX2 is a developmentally regulated transcription factor involved in early morphogenesis of the central nervous system. This gene is amplified and overexpressed in medulloblastoma cell lines, but the nature and extent of its genetic alterations in primary tumors have not been evaluated. Analysis of a large cohort of primary medulloblastomas revealed frequent focal copy number gain of a region minimally containing OTX2 as a single gene. OTX2 copy number gain was restricted to tumor subtypes that did not express a molecular signature of Wnt or Shh pathway activation. FISH analysis revealed copy number gain in a subset of cells within medulloblastoma samples, suggesting a late event in tumor progression. Gain of OTX2 copy number was associated with the presence of anaplastic histologic features and shorter survival in medulloblastoma patients. In support of a functional role, ectopic OTX2 expression enhanced proliferation and tumorigenicity of immortalized primary cells, whereas OTX2 knockdown in medulloblastoma cells prolonged the survival of animals bearing xenograft tumors. Mechanistic investigations revealed upregulation of MYC as a potential mechanism whereby OTX2 promotes tumor progression. Our findings define OTX2 as an important oncogenic driver in medulloblastoma. Cancer Res; 70(1); 181–91

Insufficient insulin secretion is a hallmark of type 2 diabetes and has been attributed to beta cell identity loss characterized by decreased expression of several key beta cell genes. The pro-inflammatory factor BMP-2 is upregulated in islets of Langerhans from individuals with diabetes and acts as an inhibitor of beta cell function and proliferation. Exposure to BMP-2 induces expression of Id1-4, Hes-1 and Hey-1 which are transcriptional regulators associated with loss of differentiation. The aim of this study was to investigate the mechanism by which BMP-2 induces beta cell dysfunction and loss of cell maturity. Mouse islets exposed to BMP-2 for 10 days showed impaired glucose-stimulated insulin secretion and beta cell proliferation. BMP-2-induced beta cell dysfunction was associated with decreased expression of cell maturity and proliferation markers specific to the beta cell such as Ins1, Ucn3 and Ki67 and increased expression of Id1-4, Hes-1 and Hey-1. Top 30 most regulated proteins significantly correlated with corresponding mRNA expression. BMP-2-induced gene expression changes were associated with a predominant reduction in acetylation of H3K27 and a decrease in NeuroD1 chromatin binding activity. These results show that BMP-2 induces loss of beta cell maturity and suggest that remodeling of H3K27ac and decreased NeuroD1 DNA binding activity participate in the effect of BMP-2 on beta-cell dysfunction.

Pancreatic β-cells secrete insulin commensurate to circulating nutrient levels to maintain normoglycemia. The ability of β-cells to couple insulin secretion to nutrient stimuli is acquired during a postnatal maturation process. In mature β-cells the insulin secretory response adapts to changes in nutrient state. Both β-cell maturation and functional adaptation rely on the interplay between extracellular cues and cell type-specific transcriptional programs. Here we review emerging evidence that developmental and homeostatic regulation of β-cell function involves collaboration between lineage-determining and signal-dependent transcription factors (LDTFs and SDTFs, respectively). A deeper understanding of β-cell SDTFs and their cognate signals would delineate mechanisms of β-cell maturation and functional adaptation, which has direct implications for diabetes therapies and for generating mature β-cells from stem cells.

The transition from lean to obese states involves systemic metabolic remodeling that impacts insulin sensitivity, lipid partitioning, inflammation, and glycemic control. Here, we have taken a pharmacological approach to test the role of a nutrient-regulated chromatin modifier, lysine-specific demethylase (LSD1), in obesity-associated metabolic reprogramming. We show that systemic administration of an LSD1 inhibitor (GSK-LSD1) reduces food intake and body weight, ameliorates non-alcoholic fatty liver disease (NAFLD), and improves insulin sensitivity and glycemic control in mouse models of obesity. GSK-LSD1 has little effect on systemic metabolism of lean mice, suggesting LSD1 has a context-dependent role in promoting maladaptive changes in obesity. Analysis of insulin target tissues identified white adipose tissue as the major site of insulin sensitization by GSK-LSD1, where it reduces adipocyte inflammation and lipolysis. We demonstrate that GSK-LSD1 reverses NAFLD in a non-hepatocyte-autonomous manner, suggesting an indirect mechanism via inhibition of adipocyte lipolysis and subsequent effects on lipid partitioning. Pair-feeding experiments further revealed that effects of GSK-LSD1 on hyperglycemia and NAFLD are not a consequence of reduced food intake and weight loss. These findings suggest that targeting LSD1 could be a strategy for treatment of obesity and its associated complications including type 2 diabetes and NAFLD. O_FIG O_LINKSMALLFIG WIDTH=189 HEIGHT=200 SRC="FIGDIR/small/469928v1_ufig1.gif" ALT="Figure 1"> View larger version (32K): org.highwire.dtl.DTLVardef@64cf24org.highwire.dtl.DTLVardef@5b6aa4org.highwire.dtl.DTLVardef@1b64594org.highwire.dtl.DTLVardef@1922175_HPS_FORMAT_FIGEXP M_FIG C_FIG

Objective The contribution of beta-cell dysfunction to type 2 diabetes (T2D) is not restricted to insulinopenia in the late stages of the disease. Elevated fasting insulinemia in normoglycemic humans is a major factor predicting the onset of insulin resistance and T2D, demonstrating an early alteration of beta-cell function in T2D. Moreover, an early and chronic increase in fasting insulinemia contributes to insulin resistance in high-fat diet (HFD)-fed mice. However, whether there are genetic factors that promote beta-cell-initiated insulin resistance remains undefined. Human variants of the mitochondrial transporter ABCB10, which regulates redox by increasing bilirubin synthesis, have been associated with an elevated risk of T2D. The effects of T2D ABCB10 variants on ABCB10 expression and the actions of ABCB10 in beta-cells are unknown. Methods The expression of beta-cell ABCB10 was analyzed in published transcriptome datasets from human beta-cells carrying the T2D-risk ABCB10 variant. Insulin sensitivity, beta-cell proliferation, and secretory function were measured in beta-cell-specific ABCB10 KO mice (Ins1Cre-Abcb10flox/flox). The short-term role of beta-cell ABCB10 activity on glucose-stimulated insulin secretion (GSIS) was determined in isolated islets. Results Carrying the T2Drisk allele G of ABCB10 rs348330 variant was associated with increased ABCB10 expression in human beta-cells. Constitutive deletion of Abcb10 in beta-cells protected mice from hyperinsulinemia and insulin resistance by limiting HFD-induced beta-cell expansion. An early limitation in GSIS and H2O2-mediated signaling caused by elevated ABCB10 activity can initiate an over-compensatory expansion of beta-cell mass in response to HFD. Accordingly, increasing ABCB10 expression was sufficient to limit GSIS capacity. In health, ABCB10 protein was decreased during islet maturation, with maturation restricting beta-cell proliferation and elevating GSIS. Finally, ex-vivo and short-term deletion of ABCB10 in islets isolated from HFD-fed mice increased H2O2 and GSIS, which was reversed by bilirubin treatments. Conclusions Beta-cell ABCB10 is required for HFD to induce insulin resistance in mice by amplifying beta-cell mass expansion to maladaptive levels that cause fasting hyperinsulinemia., Highlights • ABCB10 deletion in mouse beta-cells protects from HFD-induced insulin resistance. • ABCB10 deletion increases mouse beta-cell function and limits HFD-induced beta cell expansion. • T2D ABCB10 variant rs348330 is associated with increased ABCB0 expression in beta-cells. • ABCB10 gain-of-function decreases glucose stimulated insulin secretion.

Insulin is an essential regulator of blood glucose homeostasis that is produced exclusively by β cells within the pancreatic islets of healthy individuals. In those affected by diabetes, immune inflammation, damage, and destruction of islet β cells leads to insulin deficiency and hyperglycemia. Current efforts to understand the mechanisms underlying β cell damage in diabetes rely on in vitro-cultured cadaveric islets. However, isolation of these islets involves removal of crucial matrix and vasculature that supports islets in the intact pancreas. Unsurprisingly, these islets demonstrate reduced functionality over time in standard culture conditions, thereby limiting their value for understanding native islet biology. Leveraging a novel, vascularized micro-organ (VMO) approach, we have recapitulated elements of the native pancreas by incorporating isolated human islets within a three-dimensional matrix nourished by living, perfusable blood vessels. Importantly, these islets show long-term viability and maintain robust glucose-stimulated insulin responses. Furthermore, vessel-mediated delivery of immune cells to these tissues provides a model to assess islet-immune cell interactions and subsequent islet killing — key steps in type 1 diabetes pathogenesis. Together, these results establish the islet-VMO as a novel, ex vivo platform for studying human islet biology in both health and disease.

Different approaches have investigated the effects of different extracellular matrices (ECMs) and three-dimensional (3D) culture on islet function, showing encouraging results. Ideally, the proper scaffold should mimic the biochemical composition of the native tissue as it drives numerous signaling pathways involved in tissue homeostasis and functionality. Tissue-derived decellularized biomaterials can preserve the ECM composition of the native tissue making it an ideal scaffold for 3D tissue engineering applications. However, the decellularization process may affect the retention of specific components, and the choice of a proper detergent is fundamental in preserving the native ECM composition. In this study, we evaluated the effect of different decellularization protocols on the mechanical properties and biochemical composition of pancreatic ECM (pECM) hydrogels. Fresh porcine pancreas tissue was harvested, cut into small pieces, rinsed in water, and treated with two different detergents (sodium dodecyl sulfate [SDS] or Triton X-100) for 1 day followed by 3 days in water. Effective decellularization was confirmed by PicoGreen assay, Hoescht, and H&E staining, showing no differences among groups. Use of a protease inhibitor (PI) was also evaluated. Effective decellularization was confirmed by PicoGreen assay and hematoxylin and eosin (H&E) staining, showing no differences among groups. Triton-treated samples were able to form a firm hydrogel under appropriate conditions, while the use of SDS had detrimental effects on the gelation properties of the hydrogels. ECM biochemical composition was characterized both in the fresh porcine pancreas and all decellularized pECM hydrogels by quantitative mass spectrometry analysis. Fibrillar collagen was the major ECM component in all groups, with all generated hydrogels having a higher amount compared with fresh pancreas. This effect was more pronounced in the SDS-treated hydrogels when compared with the Triton groups, showing very little retention of other ECM molecules. Conversely, basement membrane and matricellular proteins were better retained when the tissue was pretreated with a PI and decellularized in Triton X-100, making the hydrogel more similar to the native tissue. In conclusion, we showed that all the protocols evaluated in the study showed effective tissue decellularization, but only when the tissue was pretreated with a PI and decellularized in Triton detergent, the biochemical composition of the hydrogel was closer to the native tissue ECM. Impact Statement The article compares different methodologies for the generation of a pancreas-derived hydrogel for tissue engineering applications. The biochemical characterization of the newly generated hydrogel shows that the material retains all the extracellular molecules of the native tissue and is capable of sustaining functionality of the encapsulated beta-cells.

Adaptation of the insulin secretory response to fluctuating insulin demand is critical for blood glucose homeostasis. We postulated that the epigenome could link changes in metabolic state with adaptive insulin secretion. Here we show that perturbations of nutrient state lead to extensive changes to H3K27 acetylation in pancreatic islets. Genomic sites of H3K27ac deposition acutely regulated by feeding were enriched for binding by the histone demethylase Lsd1, a candidate nutrient sensor known to respond to hormonal and metabolic stimuli. Conditional deletion of Lsd1 in mouse β-cells resulted in hypoglycemia and fasting hyperinsulinemia. Lsd1-deficient β-cells exhibited changes in H3K4me1 and H3K27ac deposition at Lsd1-bound sites. These changes at the chromatin level associated with aberrant expression of nutrient signaling and metabolic genes. We further show that Lsd1 controls feeding-stimulated transcription downstream of cAMP, which has been implicated in the control of β-cell metabolism. Accordingly, Lsd1-deficient β-cells failed to attenuate glucose metabolism in the fasted state, resulting in basal insulin hypersecretion. Further supporting a role for Lsd1 in adaptive insulin secretion, islets from hyperinsulinemic db/db mice exhibited increased H3K27ac and H3K4me1 levels at Lsd1-bound sites. Moreover, genomic sites bound by LSD1 in human islets were enriched for genetic variants associated with fasting glucose and type 2 diabetes in genome-wide association studies, suggesting a conserved role of LSD1 in the regulation of insulin secretion. Combined, our findings provide evidence that nutrient state modulates adaptive insulin secretion through Lsd1-dependent changes to the epigenome. Disclosure M. Wortham: None. F. Liu: None. J. Fleischman: None. M. Wallace: None. A.R. Harrington: None. J. Chiou: None. K. Gaulton: None. C. Metallo: Employee; Spouse/Partner; ICON plc. Research Support; Self; Gilead Sciences, Inc., Nimbus Therapeutics. M. Sander: None. Funding National Institutes of Health (R01DK068471); JDRF (3-PDF-2014-193-A-N)

SUMMARY Pancreatic β cell physiology changes substantially throughout life, yet the mechanisms that drive these changes are poorly understood. Here, we performed comprehensive in vivo quantitative proteomic profiling of pancreatic islets from juvenile and 1-year-old mice. The analysis revealed striking differences in abundance of enzymes controlling glucose metabolism. We show that these changes in protein abundance are associated with higher activities of glucose metabolic enzymes involved in coupling factor generation as well as increased activity of the coupling factor-dependent amplifying pathway of insulin secretion. Nutrient tracing and targeted metabolomics demonstrated accelerated accumulation of glucose-derived metabolites and coupling factors in islets from 1-year-old mice, indicating that age-related changes in glucose metabolism contribute to improved glucose-stimulated insulin secretion with age. Together, our study provides an in-depth characterization of age-related changes in the islet proteome and establishes metabolic rewiring as an important mechanism for age-associated changes in β cell function., In Brief Organismal age impacts fundamental aspects of β cell physiology. Wortham et al. apply proteomics and targeted metabolomics to islets from juvenile and adult mice, revealing age-related changes in metabolic enzyme abundance and production of coupling factors that enhance insulin secretion. This work provides insight into age-associated changes to the β cell., Graphical Abstract

Androgen deficiency in men is associated with metabolic syndrome and diabetes, which has been attributed to actions of androgens upon insulin target tissues. In this issue of Cell Metabolism, Navarro et al. (2016) report a role for androgens and their receptor in the regulation of insulin secretion in β cells.

Decreased insulin secretory capacity in Type 2 diabetes mellitus is associated with beta-cell dedifferentiation and inflammation. We hypothesize that prolonged exposure of beta-cells to low concentrations of IL-1β induce beta-cell dedifferentiation characterized by impaired glucose-stimulated insulin secretion, reduced expression of key beta-cell genes and changes in histone modifications at gene loci known to affect beta-cell function. Ten days exposure to IL-1β at non-cytotoxic concentrations reduced insulin secretion and beta-cell proliferation and decreased expression of key beta-cell identity genes, including MafA and Ucn3 and decreased H3K27ac at the gene loci, suggesting that inflammatory cytokines directly affects the epigenome. Following removal of IL-1β, beta-cell function was normalized and mRNA expression of beta-cell identity genes, such as insulin and Ucn3 returned to pre-stimulation levels. Our findings indicate that prolonged exposure to low concentrations of IL-1β induces epigenetic changes associated with loss of beta-cell identity as observed in Type 2 diabetes.

Insulin secretion must be tightly coupled to nutritional state to maintain blood glucose homeostasis. To this end, pancreatic β-cells sense and respond to changes in metabolic conditions, thereby anticipating insulin demands for a given physiological context. This is achieved in part through adjustments of nutrient metabolism, which is controlled at several levels including allosteric regulation, post-translational modifications, and altered expression of metabolic enzymes. In this review, we discuss mechanisms of β-cell metabolic and functional adaptation in the context of two physiological states that alter glucose-stimulated insulin secretion: fasting and insulin resistance. We review current knowledge of metabolic changes that occur in the β-cell during adaptation and specifically discuss transcriptional mechanisms that underlie β-cell adaptation. A more comprehensive understanding of how β-cells adapt to changes in nutrient state could identify mechanisms to be co-opted for therapeutically modulating insulin secretion in metabolic disease.

Myeloid/lymphoid or mixed-lineage leukemia ( MLL )-family genes encode histone lysine methyltransferases that play important roles in epigenetic regulation of gene transcription. MLL genes are frequently mutated in human cancers. Unlike MLL1, MLL2 (also known as ALR/MLL4) and its homolog MLL3 are not well-understood. Specifically, little is known regarding the extent of global MLL2 involvement in the regulation of gene expression and the mechanism underlying its alterations in driving tumorigenesis. Here we profile the global loci targeted by MLL2. A combinatorial analysis of the MLL2 binding profile and gene expression in MLL2 wild-type versus MLL2 -null isogenic cell lines identified direct transcriptional target genes and revealed the connection of MLL2 to multiple cellular signaling pathways, including the p53 pathway, cAMP-mediated signaling, and cholestasis signaling. In particular, we demonstrate that MLL2 participates in retinoic acid receptor signaling by promoting retinoic acid-responsive gene transcription. Our results present a genome-wide integrative analysis of the MLL2 target loci and suggest potential mechanisms underlying tumorigenesis driven by MLL2 alterations.

Nonalcoholic fatty liver disease (NAFLD) is highly prevalent in the Western population. By mechanisms that are not completely understood, this disease may progress to nonalcoholic steatohepatitis (NASH), fibrosis, cirrhosis, and hepatocellular carcinoma (HCC). db/db mice spontaneously develop hepatic steatosis, which progresses to NASH when these mice are fed a methionine choline-deficient (MCD) diet. The goal of our studies was to identify lipid and methionine metabolism pathways affected by MCD feeding to determine potential causal events leading to the development of NASH from benign steatosis. db/db mice fed the MCD diet for 2 weeks exhibited signs of incipient NASH development such as upregulated cytokines and chemokines. At this time point, MCD diet feeding caused S-adenosylmethionine (SAMe) depletion in db/db mice, while wild-type mice on the same diet retained hepatic SAMe levels. SAMe depletion exerts pleiotropic effects upon liver homeostasis and is commonly associated with a variety of liver insults such as thioacetamide, CCL4, and alcohol treatment; thus, SAMe depletion may serve as the second hit in NASH development. It is possible that differences in hepatic lipid and/or methionine metabolism between wild-type and db/db mice underlay the differential maintenance of SAMe levels during methionine and choline restriction. Indeed, db/db mice exhibited inhibited lipid oxidation pathways, which may be a priming factor for NASH development, and db/db mice fed the MCD diet had differential methionine adenosyltransferase (MAT) expression. The occurrence of SAMe depletion at this early, benign stage of NASH development in db/db mice with fatty liver suggests that SAMe supplementation may be (A) targeted to individuals susceptible to NASH (i.e., NAFLD patients) and (B) preventative of NASH before substantial liver injury has occurred.

Despite an emerging understanding of the genetic alterations giving rise to various tumors, the mechanisms whereby most oncogenes are overexpressed remain unclear. Here we have utilized an integrated approach of genomewide regulatory element mapping via DNase-seq followed by conventional reporter assays and transcription factor binding site discovery to characterize the transcriptional regulation of the medulloblastoma oncogene Orthodenticle Homeobox 2 (OTX2). Through these studies we have revealed that OTX2 is differentially regulated in medulloblastoma at the level of chromatin accessibility, which is in part mediated by DNA methylation. In cell lines exhibiting chromatin accessibility of OTX2 regulatory regions, we found that autoregulation maintains OTX2 expression. Comparison of medulloblastoma regulatory elements with those of the developing brain reveals that these tumors engage a developmental regulatory program to drive OTX2 transcription. Finally, we have identified a transcriptional regulatory element mediating retinoid-induced OTX2 repression in these tumors. This work characterizes for the first time the mechanisms of OTX2 overexpression in medulloblastoma. Furthermore, this study establishes proof of principle for applying ENCODE datasets towards the characterization of upstream trans-acting factors mediating expression of individual genes.

The mechanisms whereby medulloblastoma stem cells coordinate tumor propagation are poorly understood. Using microarray analysis, Corno and colleagues draw parallels and distinctions between medulloblastoma stem cells from the Ptch+/− mouse and normal neural stem cells, identifying Ebf3 as a cancer stem cell–specific transcript critical for tumor growth. Cancer Discov; 2(6); 492–4. ©2012 AACR. Commentary on Corno et al., p. 554.

OTX2 is a developmentally regulated transcription factor that plays important roles in early morphogenesis of the central nervous system. We previously identified OTX2 amplification and overexpression in medulloblastoma cell lines. However, the nature and frequency of OTX2 genetic alterations have not been determined in large sample sizes of primary tumors. To refine our understanding of genomic events affecting OTX2, we analyzed genomic copy number and mRNA expression of OTX2 in a large cohort of primary medulloblastomas. We found that the most frequent focal copy number gain in these primary medulloblastomas (gained in 21% of the tumors, n=201) contained the single gene OTX2, indicating that copy number gain of OTX2 is a driver event in this tumor. In this cohort of tumors, we found that the event was restricted to tumor subtypes that do not express a molecular signature of either Wnt or Shh pathway activation. FISH analysis revealed that OTX2 copy number gain is present in a subset of cells within medulloblastoma samples, suggesting that it is a late event contributing to tumor progression. Gain of OTX2 copy number is associated with the presence of anaplastic histological features and shorter survival in medulloblastoma patients. To verify a functional role of the observed genomic events, we demonstrate that ectopic OTX2 expression enhances proliferation and tumorigenicity of immortalized primary cells and that OTX2 knockdown in medulloblastoma xenografts prolongs survival of recipient animals. Finally, we demonstrate that OTX2 transcriptionally upregulates the medulloblastoma oncogene MYC as a potential mechanism whereby OTX2 promotes tumor progression.

Medulloblastoma (MB) therapy—resection, chemotherapy, and radiation—results in admirable survival rates (70–85% 5-year survival of medium- to high-risk cases) but unacceptable chronic toxicities, including endocrine dysfunction and cognitive impairment. The limited efficacy of the current therapeutic regimen may be linked to the recently discovered MB cancer stem cells, which may regenerate tumors after bulk mass reduction. Nonetheless, the discovery of tumor stem cells as a new target has suggested a potential new approach for improving upon conventional cytotoxic chemotherapy. Differentiation agents that would specifically target tumor stem cells without being universally cytotoxic to proliferating cells could reduce systemic toxicity as well as deplete cell populations responsible for tumor maintenance. All-trans retinoic acid (ATRA) is the first and only differentiation agent that has proven effective in the clinical setting, inducing a 90% remission rate of acute promyelocytic leukemia (APL) when used as adjuvant to chemotherapy. Retinoids have also proven effective against a large fraction of MB cell lines and primary tumors. MB is an embryonal tumor that, like APL, relies upon the circumvention of endogenous differentiation pathways for tumorigenesis. Retinoid resistance in some MB cell lines has hindered its development as a universally applicable therapeutic. It has been shown that retinoid-resistant cell lines can be responsive to downstream targets of retinoid activity, suggesting that retinoid resistance occurs via disruption of upstream components of the pathway. Functional intermediates of retinoid activity have been identified; however, the ultimate targets of such intermediates remain elusive. Some studies have shown that retinoids exert their antitumor effect against MB in part by inducing Bmp2 production and subsequent activation of the TGFβ pathway. Other studies have demonstrated that ATRA silences the OTX2 oncogene, whose expression correlates with ATRA responsiveness of MB cell lines. Alternative pathways accounting for the full effect of retinoids against MB (independent of Bmp2 and OTX2) as well as final targets of known pathways have yet to be identified. Delineation of the pathways through which ATRA exerts its pleiotropic effects could reveal potential therapeutic targets that recapitulate differentiation or apoptosis in both retinoid-sensitive and retinoid-resistant cell lines and thus serve as a more broadly applicable therapy.

Identification of genetic variation predictive of clearance rate of a wide variety of prescription drugs could lead to cost-effective personalized medicine. Here we identify regulatory genes whose variable expression level among individuals may have widespread effects upon clearance rate of a variety of drugs. Twenty liver samples with variable CYP3A activity were profiled for expression level and activity of xenobiotic metabolism genes as well as genes involved in the regulation thereof. Regulatory genes whose expression level accounted for the highest degree of collinearity among expression levels of xenobiotic metabolism genes were identified as possible master regulators of drug clearance rate. Significant linear correlations (p0.05) were identified among mRNA levels of CYP2A6, CYP2B6, CYP2C8, CYP2C9, CYP2C19, MRP2, OATP2, P450 oxidoreductase (POR), and UDP-glucuronosyltranferase 1A1, suggesting that these xenobiotic metabolism genes are coregulated at the transcriptional level. Using partial regression analysis, constitutive androstane receptor (CAR) and hepatic nuclear factor 4 alpha (HNF4 alpha) were identified as the nuclear receptors whose expression levels are most strongly associated with expression of coregulated xenobiotic metabolism genes. POR expression level, which is also associated with CAR and HNF4 alpha expression level, was found to be strongly associated with the activity of many cytochromes P450. Thus, interindividual variation in the expression level of CAR, HNF4 alpha, and POR probably determines variation in expression and activity of a broad scope of xenobiotic metabolism genes and, accordingly, clearance rate of a variety of xenobiotics. Identification of polymorphisms in these candidate master regulator genes that account for their variable expression among individuals may yield readily detectable biomarkers that could serve as predictors of xenobiotic clearance rate.

Medulloblastoma is the most common malignant brain tumor in children. Despite a thorough understanding of the genetic underpinnings of this tumor, the pathogenesis of some variants of medulloblastoma, in particular the non-Shh/non-Wnt subtypes, is poorly understood. One of the most common genetic aberrations in non-Shh/non-Wnt medulloblastomas is copy number gain of the homeobox transcription factor OTX2. Here we have characterized mice engineered to ectopically express Otx2 in the hindbrain to identify the functional consequences of this subtype-specific genetic insult. Otx2 expression induced accumulation of proliferative hyperplasias in the cerebellar white matter and dorsal brainstem that were reminiscent of preneoplastic cells identified in other animal models of medulloblastoma. These hyperplasias were comprised of neuronal progenitor cells that had migrated away from their mitogenic niches. As animals reached adulthood, ectopic cells exited the cell cycle and differentiated, indicating that factors limiting proliferative lifespan prevented full transformation by Otx2. Comparison of the effect of Otx2 with activation of the Shh or Wnt pathways, which occur in distinct subtypes of medulloblastoma, revealed overlap of responsive cell types but distinct developmental processes involved. While activation of the Shh or Wnt pathways give rise to sustained proliferation of neuronal progenitor cells at their mitogenic niches, we found that Otx2 permitted or enhanced migration of these cells away from these niches and induced ectopic proliferation. These findings identify a role for Otx2 overexpression in altering spatiotemporal control of neuronal progenitor cell proliferation and implicate a relationship between the cells of origin of non-Shh/non-Wnt medulloblastomas and those of other medulloblastoma subtypes. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3352. doi:1538-7445.AM2012-3352

Medulloblastoma is the most common malignant brain tumor in children. With the exception of the Sonic Hedgehog (Shh) and Wnt pathways, the molecular events contributing to medulloblastoma tumorigenesis are poorly understood. In this study, we performed DNA copy number analysis upon a large cohort (n=201) of primary medulloblastomas to identify recurrent copy number events of these tumors. The most commonly gained region of the medulloblastoma genome (gained in 21% of tumors) contains the single gene OTX2, which encodes a developmental transcription factor involved in regionalization of the neural tube and specification of various CNS lineages. We found that OTX2 is also commonly overexpressed (74%, n=103) in these tumors. Molecular classification of medulloblastomas identified four distinct subtypes based on gene expression signature. OTX2 overexpression and copy number gain was limited to tumors not exhibiting a signature of Shh pathway activation. We found that OTX2 is necessary for intracranial xenograft formation by medulloblastoma cells and that its expression promotes xenograft tumor formation by immortalized primary cells. Finally, we determined that OTX2 regulates the medulloblastoma oncogene MYC. As a transcription factor, targeting OTX2 function with small molecules presents a challenge. However, retinoids can reduce OTX2 expression and inhibit medulloblastoma growth in vitro, and we have demonstrated that OTX2 silencing is required for this effect. In sum, these studies identify OTX2 as a common but targetable oncogene in Shh-independent medulloblastomas. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 233.