Correction to: Comparative multidimensional molecular analyses of pediatric diffuse intrinsic pontine glioma reveals distinct molecular subtypes.

The original version of this article unfortunately contained a mistake.

Multimodal imaging of biological tissues using combined MALDI and NAPA-LDI mass spectrometry for enhanced molecular coverage.

Mass spectrometry imaging (MSI) is a powerful analytical technique that enables detection, discovery, and identification of multiple classes of biomolecules, while simultaneously mapping their spatial distributions within a sample (e.g., a section of biological tissue). The limitation in molecular coverage afforded by any single MSI platform has led to the development of multimodal approaches that incorporate two or more techniques to obtain greater chemical information. Matrix-assisted laser desorption ionization (MALDI) is a preeminent ionization technique for MSI applications because the wide range of available matrices allows some degree of enhancement with respect to the detection of particular molecular classes. Nonetheless, MALDI has a limited ability to detect and image several classes of molecules, e.g., neutral lipids, in complex samples. Laser desorption ionization from silicon nanopost arrays (NAPA-LDI or NAPA) has been shown to offer complementary coverage with respect to MALDI by providing improved detection of neutral lipids and some small metabolites. Here, we present a multimodal imaging method in which a single tissue section is consecutively imaged at low and high laser fluences, generating spectra that are characteristic of MALDI and NAPA ionization, respectively. The method is demonstrated to map the distributions of species amenable to detection by MALDI (e.g., phospholipids and intermediate-mass metabolites) and NAPA (e.g., neutral lipids such as triglycerides and hexosylceramides, and small metabolites) in mouse brain and lung tissue sections.

Medulloblastoma rendered susceptible to NK-cell attack by TGFß neutralization.

BACKGROUND: Medulloblastoma (MB), the most common pediatric brain cancer, presents with a poor prognosis in a subset of patients with high risk disease, or at recurrence, where current therapies are ineffective. Cord blood (CB) natural killer (NK) cells may be promising off-the-shelf effector cells for immunotherapy due to their recognition of malignant cells without the need for a known target, ready availability from multiple banks, and their potential to expand exponentially. However, they are currently limited by immune suppressive cytokines secreted in the MB tumor microenvironment including Transforming Growth Factor ß (TGF-ß). Here, we address this challenge in in vitro models of MB. METHODS: CB-derived NK cells were modified to express a dominant negative TGF-ß receptor II (DNRII) using retroviral transduction. The ability of transduced CB cells to maintain function in the presence of medulloblastoma-conditioned media was then assessed. RESULTS: We observed that the cytotoxic ability of nontransduced CB-NK cells was reduced in the presence of TGF-ß-rich, medulloblastoma-conditioned media (21.21 ± 1.19% killing at E:T 5:1 in the absence vs. 14.98 ± 2.11% in the presence of medulloblastoma-conditioned media, n = 8, p = 0.02), but was unaffected in CB-derived DNRII-transduced NK cells (21.11 ± 1.84% killing at E:T 5:1 in the absence vs. 21.81 ± 3.37 in the presence of medulloblastoma-conditioned media, n = 8, p = 0.85. We also observed decreased expression of CCR2 in untransduced NK cells (mean CCR2 MFI 826 ± 117 in untransduced NK + MB supernatant from mean CCR2 MFI 1639.29 ± 215 in no MB supernatant, n = 7, p = 0.0156), but not in the transduced cells. Finally, we observed that CB-derived DNRII-transduced NK cells may protect surrounding immune cells by providing a cytokine sink for TGF-ß (decreased TGF-ß levels of 610 ± 265 pg/mL in CB-derived DNRII-transduced NK cells vs. 1817 ± 342 pg/mL in untransduced cells; p = 0.008). CONCLUSIONS: CB NK cells expressing a TGF-ß DNRII may have a functional advantage over unmodified NK cells in the presence of TGF-ß-rich MB, warranting further investigation on its potential applications for patients with medulloblastoma.

Molecular Imaging of Biological Samples on Nanophotonic Laser Desorption Ionization Platforms.

Mass spectrometry imaging (MSI) is a comprehensive tool for the analysis of a wide range of biomolecules. The mainstream method for molecular MSI is matrix-assisted laser desorption ionization, however, the presence of a matrix results in spectral interferences and the suppression of some analyte ions. Herein we demonstrate a new matrix-free MSI technique using nanophotonic ionization based on laser desorption ionization (LDI) from a highly uniform silicon nanopost array (NAPA). In mouse brain and kidney tissue sections, the distributions of over 80 putatively annotated molecular species are determined with 40 µm spatial resolution. Furthermore, NAPA-LDI-MS is used to selectively analyze metabolites and lipids from sparsely distributed algal cells and the lamellipodia of human hepatocytes. Our results open the door for matrix-free MSI of tissue sections and small cell populations by nanophotonic ionization.

Comparative multidimensional molecular analyses of pediatric diffuse intrinsic pontine glioma reveals distinct molecular subtypes.

Diffuse intrinsic pontine glioma (DIPG) is a highly morbid form of pediatric brainstem glioma. Here, we present the first comprehensive protein, mRNA, and methylation profiles of fresh-frozen DIPG specimens (n = 14), normal brain tissue (n = 10), and other pediatric brain tumors (n = 17). Protein profiling identified 2,305 unique proteins indicating distinct DIPG protein expression patterns compared to other pediatric brain tumors. Western blot and immunohistochemistry validated upregulation of Clusterin (CLU), Elongation Factor 2 (EF2), and Talin-1 (TLN1) in DIPGs studied. Comparisons to mRNA expression profiles generated from tumor and adjacent normal brain tissue indicated two DIPG subgroups, characterized by upregulation of Myc (N-Myc) or Hedgehog (Hh) signaling. We validated upregulation of PTCH, a membrane receptor in the Hh signaling pathway, in a subgroup of DIPG specimens. DNA methylation analysis indicated global hypomethylation of DIPG compared to adjacent normal tissue specimens, with differential methylation of 24 genes involved in Hh and Myc pathways, correlating with protein and mRNA expression patterns. Sequencing analysis showed c.83A>T mutations in the H3F3A or HIST1H3B gene in 77 % of our DIPG cohort. Supervised analysis revealed a unique methylation pattern in mutated specimens compared to the wild-type DIPG samples. This study presents the first comprehensive multidimensional protein, mRNA, and methylation profiling of pediatric brain tumor specimens, detecting the presence of two subgroups within our DIPG cohort. This multidimensional analysis of DIPG provides increased analytical power to more fully explore molecular signatures of DIPGs, with implications for evaluating potential molecular subtypes and biomarker discovery for assessing response to therapy.

Pan-cancer atlas of somatic core and linker histone mutations.

Recent genomic data points to a growing role for somatic mutations altering core histone and linker histone-encoding genes in cancer. However, the prevalence and the clinical and biological implications of histone gene mutations in malignant tumors remain incompletely defined. To address these knowledge gaps, we analyzed somatic mutations in 88 linker and core histone genes across 12,743 tumors from pediatric, adolescent and young adult (AYA), and adult cancer patients. We established a pan-cancer histone mutation atlas contextualized by patient age, survival outcome, and tumor location. Overall, 11% of tumors harbored somatic histone mutations, with the highest rates observed among chondrosarcoma (67%), pediatric high-grade glioma (pHGG, >60%), and lymphoma (>30%). Previously unreported histone mutations were discovered in pHGG and other pediatric brain tumors, extending the spectrum of histone gene alterations associated with these cancers. Histone mutation status predicted patient survival outcome in tumor entities including adrenocortical carcinoma. Recurrent pan-cancer histone mutation hotspots were defined and shown to converge on evolutionarily conserved and functional residues. Moreover, we studied histone gene mutations in 1700 pan-cancer cell lines to validate the prevalence and spectrum of histone mutations seen in primary tumors and derived histone-associated drug response profiles, revealing candidate drugs targeting histone mutant cancer cells. This study presents the first-of-its-kind atlas of both core and linker histone mutations across pediatric, AYA, and adult cancers, providing a framework by which specific cancers may be redefined in the context of histone and chromatin alterations.

ONC201 in combination with paxalisib for the treatment of H3K27-altered diffuse midline glioma.

Diffuse midline gliomas (DMG), including diffuse intrinsic pontine gliomas (DIPGs), are the most lethal of childhood cancers. Palliative radiotherapy is the only established treatment, with median patient survival of 9-11 months. ONC201 is a DRD2 antagonist and ClpP agonist that has shown preclinical and emerging clinical efficacy in DMG. However, further work is needed to identify the mechanisms of response of DIPGs to ONC201 treatment and to determine whether recurring genomic features influence response. Using a systems-biological approach, we showed that ONC201 elicits potent agonism of the mitochondrial protease ClpP to drive proteolysis of electron transport chain and tricarboxylic acid cycle proteins. DIPGs harboring PIK3CA-mutations showed increased sensitivity to ONC201, while those harboring TP53-mutations were more resistant. Metabolic adaptation and reduced sensitivity to ONC201 was promoted by redox-activated PI3K/Akt signaling, which could be counteracted using the brain penetrant PI3K/Akt inhibitor, paxalisib. Together, these discoveries coupled with the powerful anti-DIPG/DMG pharmacokinetic and pharmacodynamic properties of ONC201 and paxalisib have provided the rationale for the ongoing DIPG/DMG phase II combination clinical trial NCT05009992.

ONC201 in Combination with Paxalisib for the Treatment of H3K27-Altered Diffuse Midline Glioma.

Diffuse midline gliomas (DMG), including diffuse intrinsic pontine gliomas (DIPG), are the most lethal of childhood cancers. Palliative radiotherapy is the only established treatment, with median patient survival of 9 to 11 months. ONC201 is a DRD2 antagonist and ClpP agonist that has shown preclinical and emerging clinical efficacy in DMG. However, further work is needed to identify the mechanisms of response of DIPGs to ONC201 treatment and to determine whether recurring genomic features influence response. Using a systems-biological approach, we showed that ONC201 elicits potent agonism of the mitochondrial protease ClpP to drive proteolysis of electron transport chain and tricarboxylic acid cycle proteins. DIPGs harboring PIK3CA mutations showed increased sensitivity to ONC201, whereas those harboring TP53 mutations were more resistant. Metabolic adaptation and reduced sensitivity to ONC201 was promoted by redox-activated PI3K/Akt signaling, which could be counteracted using the brain penetrant PI3K/Akt inhibitor, paxalisib. Together, these discoveries coupled with the powerful anti-DIPG/DMG pharmacokinetic and pharmacodynamic properties of ONC201 and paxalisib have provided the rationale for the ongoing DIPG/DMG phase II combination clinical trial NCT05009992. SIGNIFICANCE: PI3K/Akt signaling promotes metabolic adaptation to ONC201-mediated disruption of mitochondrial energy homeostasis in diffuse intrinsic pontine glioma, highlighting the utility of a combination treatment strategy using ONC201 and the PI3K/Akt inhibitor paxalisib.

Upfront Biology-Guided Therapy in Diffuse Intrinsic Pontine Glioma: Therapeutic, Molecular, and Biomarker Outcomes from PNOC003.

PURPOSE: PNOC003 is a multicenter precision medicine trial for children and young adults with newly diagnosed diffuse intrinsic pontine glioma (DIPG). PATIENTS AND METHODS: Patients (3-25 years) were enrolled on the basis of imaging consistent with DIPG. Biopsy tissue was collected for whole-exome and mRNA sequencing. After radiotherapy (RT), patients were assigned up to four FDA-approved drugs based on molecular tumor board recommendations. H3K27M-mutant circulating tumor DNA (ctDNA) was longitudinally measured. Tumor tissue and matched primary cell lines were characterized using whole-genome sequencing and DNA methylation profiling. When applicable, results were verified in an independent cohort from the Children's Brain Tumor Network (CBTN). RESULTS: Of 38 patients enrolled, 28 patients (median 6 years, 10 females) were reviewed by the molecular tumor board. Of those, 19 followed treatment recommendations. Median overall survival (OS) was 13.1 months [95% confidence interval (CI), 11.2-18.4] with no difference between patients who followed recommendations and those who did not. H3K27M-mutant ctDNA was detected at baseline in 60% of cases tested and associated with response to RT and survival. Eleven cell lines were established, showing 100% fidelity of key somatic driver gene alterations in the primary tumor. In H3K27-altered DIPGs, TP53 mutations were associated with worse OS (TP53mut 11.1 mo; 95% CI, 8.7-14; TP53wt 13.3 mo; 95% CI, 11.8-NA; P = 3.4e-2), genome instability (P = 3.1e-3), and RT resistance (P = 6.4e-4). The CBTN cohort confirmed an association between TP53 mutation status, genome instability, and clinical outcome. CONCLUSIONS: Upfront treatment-naïve biopsy provides insight into clinically relevant molecular alterations and prognostic biomarkers for H3K27-altered DIPGs.

Imipridones affect tumor bioenergetics and promote cell lineage differentiation in diffuse midline gliomas.

BACKGROUND: Pediatric diffuse midline gliomas (DMGs) are incurable childhood cancers. The imipridone ONC201 has shown early clinical efficacy in a subset of DMGs. However, the anticancer mechanisms of ONC201 and its derivative ONC206 have not been fully described in DMGs. METHODS: DMG models including primary human in vitro (n = 18) and in vivo (murine and zebrafish) models, and patient (n = 20) frozen and FFPE specimens were used. Drug-target engagement was evaluated using in silico ChemPLP and in vitro thermal shift assay. Drug toxicity and neurotoxicity were assessed in zebrafish models. Seahorse XF Cell Mito Stress Test, MitoSOX and TMRM assays, and electron microscopy imaging were used to assess metabolic signatures. Cell lineage differentiation and drug-altered pathways were defined using bulk and single-cell RNA-seq. RESULTS: ONC201 and ONC206 reduce viability of DMG cells in nM concentrations and extend survival of DMG PDX models (ONC201: 117 days, P = .01; ONC206: 113 days, P = .001). ONC206 is 10X more potent than ONC201 in vitro and combination treatment was the most efficacious at prolonging survival in vivo (125 days, P = .02). Thermal shift assay confirmed that both drugs bind to ClpP, with ONC206 exhibiting a higher binding affinity as assessed by in silico ChemPLP. ClpP activation by both drugs results in impaired tumor cell metabolism, mitochondrial damage, ROS production, activation of integrative stress response (ISR), and apoptosis in vitro and in vivo. Strikingly, imipridone treatment triggered a lineage shift from a proliferative, oligodendrocyte precursor-like state to a mature, astrocyte-like state. CONCLUSION: Targeting mitochondrial metabolism and ISR activation effectively impairs DMG tumorigenicity. These results supported the initiation of two pediatric clinical trials (NCT05009992, NCT04732065).

Mass spectrometry imaging of triglycerides in biological tissues by laser desorption ionization from silicon nanopost arrays.

Mass spectrometry imaging (MSI) is used increasingly to simultaneously detect a broad range of biomolecules while mapping their spatial distributions within biological tissue sections. Matrix-assisted laser desorption ionization (MALDI) is recognized as the method-of-choice for MSI applications due in part to its broad molecular coverage. In spite of the remarkable advantages offered by MALDI, imaging of neutral lipids, such as triglycerides (TGs), from tissue has remained a significant challenge due to ion suppression of TGs by phospholipids, e.g. phosphatidylcholines (PCs). To help overcome this limitation, silicon nanopost array (NAPA) substrates were introduced to selectively ionize TGs from biological tissue sections. This matrix-free laser desorption ionization (LDI) platform was previously shown to provide enhanced ionization of certain lipid classes, such as hexosylceramides (HexCers) and phosphatidylethanolamines (PEs) from mouse brain tissue. In this work, we present NAPA as an MSI platform offering enhanced ionization efficiency for TGs from biological tissues relative to MALDI, allowing it to serve as a complement to MALDI-MSI. Analysis of a standard lipid mixture containing PC(18:1/18:1) and TG(16:0/16:0/16:0) by LDI from NAPA provided an ~49 and ~227-fold higher signal for TG(16:0/16:0/16:0) relative to MALDI, when analyzed without and with the addition of a sodium acetate, respectively. In contrast, MALDI provided an ~757 and ~295-fold higher signal for PC(18:1/18:1) compared with NAPA, without and with additional Na+ . Averaged signal intensities for TGs from MSI of mouse lung and human skin tissues exhibited an ~105 and ~49-fold increase, respectively, with LDI from NAPA compared with MALDI. With respect to PCs, MALDI provided an ~2 and ~19-fold increase in signal intensity for mouse lung and human skin tissues, respectively, when compared with NAPA. The complementary coverage obtained by the two platforms demonstrates the utility of using both techniques to maximize the information obtained from lipid MS or MSI experiments.

Pharmacologic inhibition of lysine-specific demethylase 1 as a therapeutic and immune-sensitization strategy in pediatric high-grade glioma.

BACKGROUND: Diffuse midline gliomas (DMG), including brainstem diffuse intrinsic pontine glioma (DIPG), are incurable pediatric high-grade gliomas (pHGG). Mutations in the H3 histone tail (H3.1/3.3-K27M) are a feature of DIPG, rendering them therapeutically sensitive to small-molecule inhibition of chromatin modifiers. Pharmacological inhibition of lysine-specific demethylase 1 (LSD1) is clinically relevant but has not been carefully investigated in pHGG or DIPG. METHODS: Patient-derived DIPG cell lines, orthotopic mouse models, and pHGG datasets were used to evaluate effects of LSD1 inhibitors on cytotoxicity and immune gene expression. Immune cell cytotoxicity was assessed in DIPG cells pretreated with LSD1 inhibitors, and informatics platforms were used to determine immune infiltration of pHGG. RESULTS: Selective cytotoxicity and an immunogenic gene signature were established in DIPG cell lines using clinically relevant LSD1 inhibitors. Pediatric HGG patient sequencing data demonstrated survival benefit of this LSD1-dependent gene signature. Pretreatment of DIPG with these inhibitors increased lysis by natural killer (NK) cells. Catalytic LSD1 inhibitors induced tumor regression and augmented NK cell infusion in vivo to reduce tumor burden. CIBERSORT analysis of patient data confirmed NK infiltration is beneficial to patient survival, while CD8 T cells are negatively prognostic. Catalytic LSD1 inhibitors are nonperturbing to NK cells, while scaffolding LSD1 inhibitors are toxic to NK cells and do not induce the gene signature in DIPG cells. CONCLUSIONS: LSD1 inhibition using catalytic inhibitors is selectively cytotoxic and promotes an immune gene signature that increases NK cell killing in vitro and in vivo, representing a therapeutic opportunity for pHGG. KEY POINTS: 1. LSD1 inhibition using several clinically relevant compounds is selectively cytotoxic in DIPG and shows in vivo efficacy as a single agent.2. An LSD1-controlled gene signature predicts survival in pHGG patients and is seen in neural tissue from LSD1 inhibitor-treated mice.3. LSD1 inhibition enhances NK cell cytotoxicity against DIPG in vivo and in vitro with correlative genetic biomarkers.

Harmonization of postmortem donations for pediatric brain tumors and molecular characterization of diffuse midline gliomas.

Children diagnosed with brain tumors have the lowest overall survival of all pediatric cancers. Recent molecular studies have resulted in the discovery of recurrent driver mutations in many pediatric brain tumors. However, despite these molecular advances, the clinical outcomes of high grade tumors, including H3K27M diffuse midline glioma (H3K27M DMG), remain poor. To address the paucity of tissue for biological studies, we have established a comprehensive protocol for the coordination and processing of donated specimens at postmortem. Since 2010, 60 postmortem pediatric brain tumor donations from 26 institutions were coordinated and collected. Patient derived xenograft models and cell cultures were successfully created (76% and 44% of attempts respectively), irrespective of postmortem processing time. Histological analysis of mid-sagittal whole brain sections revealed evidence of treatment response, immune cell infiltration and the migratory path of infiltrating H3K27M DMG cells into other midline structures and cerebral lobes. Sequencing of primary and disseminated tumors confirmed the presence of oncogenic driver mutations and their obligate partners. Our findings highlight the importance of postmortem tissue donations as an invaluable resource to accelerate research, potentially leading to improved outcomes for children with aggressive brain tumors.

Mechanism of diepoxybutane-induced p53 regulation in human cells.

Diepoxybutane (DEB) is the most potent active metabolite of the environmental chemical 1,3-butadiene (BD). BD is a known mutagen and human carcinogen and possesses multisystems organ toxicity. We previously reported the elevation of p53 in human TK6 lymphoblasts undergoing DEB-induced apoptosis. In this study, we have characterized the DEB-induced p53 accumulation and investigated the mechanisms by which DEB regulates this p53 accumulation. The elevation of p53 levels in DEB-exposed TK6 lymphoblasts and human embryonic lung (HEL) human fibroblasts was found to be largely due to the stabilization of the p53 protein. DEB increased the acetylation of p53 at lys-382, dramatically reduced complex formation between p53 and its regulator protein mdm2 and induced the phosphorylation of p53 at serines 15, 20, 37, 46, and 392 in human lymphoblasts. A dramatic increase in phosphorylation of p53 at serine 15 in correlation to total p53 levels was observed in DEB-exposed Ataxia Telangiectasia Mutated (ATM) proficient human lymphoblasts as compared to DEB-exposed ATM-deficient human lymphoblasts; this implicates the ATM kinase in the elevation of p53 levels in DEB-exposed cells. Collectively, these findings explain for the first time the mechanism by which p53 accumulates in DEB-exposed cells and contributes to the understanding of the molecular toxicity of DEB and BD.

DNA repair efficiency in transgenic mice over expressing ribosomal protein S3.

Human ribosomal protein S3 (RPS3) has previously been shown to have alternative roles beyond its participation in protein synthesis. For example, our in vitro studies have shown that RPS3 has an extraordinarily high binding affinity for 7,8-dihydro-8-oxoguanine (8-oxoG). Notably, in cells exposed to oxidative stress RPS3 translocates to the nucleus where it co-localizes with foci of 8-oxoG. We have engineered transgenic mice over expressing RPS3 in an attempt to determine the outcome of RPS3 translocation in a whole animal. Mouse embryonic fibroblasts (MEFs) isolated from these transgenic mice showed an increased accumulation of DNA damage in cells exposed to oxidative damage when compared to MEFs from wild-type mice. In MEFs exposed to oxidative stress we observed the translocation of RPS3 from the cytoplasm to the nucleus and co-localizing to 8-oxoG foci, an observation that could involve the blocking of the repair of this mutagenic base and thereby explain why transgenic MEFs exposed to oxidative stress have higher levels of DNA damage.

Matrix-free mass spectrometry imaging of mouse brain tissue sections on silicon nanopost arrays.

Mass spectrometry imaging (MSI) is capable of detection and identification of diverse classes of compounds in brain tissue sections, whereas simultaneously mapping their spatial distributions. Given the vast array of chemical components present in neurological systems, as well as the innate diversity within molecular classes, MSI platforms capable of detecting a wide array of species are useful for achieving a more comprehensive understanding of their biological roles and significance. Currently, matrix-assisted laser desorption ionization (MALDI) is the method of choice for the molecular imaging of brain samples by mass spectrometry. However, nanostructured laser desorption ionization platforms, such as silicon nanopost arrays (NAPA), are emerging as alternative MSI techniques that can provide complementary insight into molecular distributions in the central nervous system. In this work, the molecular coverage of mouse brain lipids afforded by NAPA-MSI is compared to that of MALDI-MSI using two common MALDI matrices. In positive ion mode, MALDI spectra were dominated by phosphatidylcholines and phosphatidic acids. NAPA favored the ionization of phosphatidylethanolamines and glycosylated ceramides, which were poorly detected in MALDI-MSI. In negative ion mode, MALDI favored sulfatides and free fatty acids, whereas NAPA spectra were dominated by signal from phosphatidylethanolamines. The complementarity in lipid coverages between the NAPA- and MALDI-MSI platforms presents the possibility of selective lipid analysis and imaging dependent upon which platform is used. Nanofabrication of the NAPA platform offers better uniformity compared to MALDI, and the wider dynamic range offered by NAPA promises improved quantitation in imaging.

Differential Expression of Wilms' Tumor Protein in Diffuse Intrinsic Pontine Glioma.

Diffuse intrinsic pontine gliomas (DIPGs) are deadly tumors comprising 10%-15% of all childhood CNS cancers. Standard treatment is considered palliative and prognosis is near universal mortality. DIPGs have been classified into genomic subtypes based on histone variants with the lysine to methionine mutation on position 27 of histone tails (K27M). Given the increasing promise of immunotherapy, there have been ongoing efforts to identify tumor-specific antigens to serve as immunologic targets. We evaluated a large cohort of CNS specimens for Wilms' tumor protein (WT1) expression. These specimens include primary pediatric CNS tumors (n = 38 midline gliomas and n = 3 non-midline gliomas; n = 23 DIPG, n = 10 low-grade gliomas, n = 8 high-grade gliomas), and DIPG primary cells. Here, we report the validation of WT1 as a tumor-associated antigen in DIPGs. We further report that WT1 expression is significantly correlated with specific oncohistone variants, with the highest expression detected in the H3.3K27M subgroup. WT1 expression was absent in all control specimens (n = 21). Western blot assays using DIPG primary cells (n = 6) showed a trend of higher WT1 expression in H3.3K27M cells when compared with H3.1 K27M cells and H3 wildtype cells. Our data are the first indication of the association between WT1 and DIPG, with specific upregulation in those harboring oncohistone H3.3K27M.

Translocation of human ribosomal protein S3 to sites of DNA damage is dependant on ERK-mediated phosphorylation following genotoxic stress.

Besides its role in translation and ribosome maturation, human ribosomal protein S3 (hS3) is implicated in DNA damage recognition as reflected by its affinity for abasic sites and 7,8-dihydro-8-oxoguanine (8-oxoG) residues in DNA in vitro. Here, we demonstrate that hS3 is capable of carrying out both roles by its ex vivo translocation from the cytoplasm to the nucleus as a consequence of genotoxic stress. The translocation of hS3 is dependent on ERK1/2-mediated phosphorylation of a threonine residue (T42) of hS3. Two different ectopically expressed site-directed mutants of T42 failed to respond to conditions of genotoxic stress, thus providing a link between DNA damage and ERK1/2 dependent phosphorylation of hS3. Lastly, hS3 was traced in exposed cells to its co-localization with 8-oxoG foci, raising the possibility that hS3 is a member of a cellular DNA damage response pathway that results in its interaction with sites of DNA damage.

Knockdown of ribosomal protein S3 protects human cells from genotoxic stress.

Human ribosomal protein S3 (hS3) has a high apparent binding affinity for the oxidative lesion 7,8-dihydro-8-oxoguanine (8-oxoG). The hS3 ribosomal protein has also been found to inhibit the base excision repair (BER) enzyme hOGG1 from liberating 8-oxoG residing in a 5'-end-labeled oligonucleotide. To understand the in vivo involvement of hS3 in BER, we have turned to RNA interference to generate knockdown of hS3 in cells exposed to DNA damaging agents. Here we show that a 40% knockdown of hS3 resulted in as much as a seven-fold increase in the 24h survival-rate of HEK293 cells exposed to hydrogen peroxide. Significant protection to the alkylating agent methyl methanesulfonate (MMS) was also observed. Protection to the chemotherapeutic alkylating agent Thio-TEPA was only revealed at longer exposure times where the agent became more toxic to untransfected human cells. Overall, these results raise the possibility that hS3 interferes with the repair of the DNA lesions produced by genotoxic agents that potentially could play a role in the onset of cancer and other pathological states such as aging.

Diepoxybutane activates the mitochondrial apoptotic pathway and mediates apoptosis in human lymphoblasts through oxidative stress.

Diepoxybutane (DEB) is the most potent metabolite of the environmental chemical 1,3-butadiene (BD), which is prevalent in petrochemical industrial areas. BD is a known mutagen and human carcinogen, and possesses multi-systems organ toxicity. We recently reported that DEB-induced cell death in TK6 lymphoblasts was due to the occurrence of apoptosis, and not necrosis. In this study, we investigated the molecular mechanisms responsible for DEB-induced apoptosis in these cells. Bax and Bak were found to be over-expressed and activated, and the mitochondrial trans-membrane potential was attenuated in cells undergoing DEB-induced apoptosis. Cytochrome c was depleted from the mitochondria of TK6 cells undergoing apoptosis, and was released into the cytosol in Jurkat T-lymphoblasts exposed to the same concentrations of DEB. Executioner caspase 3 was deduced to be activated by initiator caspase 9. DEB-induced reactive oxygen species (ROS) formation, and the ROS scavenger N-acetyl-L-cysteine effectively blocked DEB-induced apoptosis in TK6 cells. Collectively, these results demonstrate that the mitochondrial apoptotic pathway is activated to mediate DEB-induced apoptosis in human TK6 lymphoblasts. These results further demonstrate that DEB-induced apoptosis is also mediated by the DEB-induced generation of ROS. This is the first report to examine the mechanism of DEB-induced apoptosis in human lymphoblasts.