Member Of Polycomb Repressive Complex Research Articles

How CBX proteins regulate normal and leukemic blood cells.

Hematopoietic stem cell (HSC) fate decisions are dictated by epigenetic landscapes. The Polycomb Repressive Complex 1 (PRC1) represses genes that induce differentiation, thereby maintaining HSC self-renewal. Depending on which chromobox (CBX) protein (CBX2, CBX4, CBX6, CBX7, or CBX8) is part of the PRC1 complex, HSC fate decisions differ. Here, we review how this occurs. We describe how CBX proteins dictate age-related changes in HSCs and stimulate oncogenic HSC fate decisions, either as canonical PRC1 members or by alternative interactions, including non-epigenetic regulation. CBX2, CBX7, and CBX8 enhance leukemia progression. To target, reprogram, and kill leukemic cells, we suggest and describe multiple therapeutic strategies to interfere with the epigenetic functions of oncogenic CBX proteins. Future studies should clarify to what extent the non-epigenetic function of cytoplasmic CBX proteins is important for normal, aged, and leukemic blood cells.

Isothiocyanates Potentiate Tazemetostat-Induced Apoptosis by Modulating the Expression of Apoptotic Genes, Members of Polycomb Repressive Complex 2, and Levels of Tri-Methylating Lysine 27 at Histone 3 in Human Malignant Melanoma Cells.

In this study, we utilized an in vitro model consisting of human malignant melanoma as well as non-tumorigenic immortalized keratinocyte cells with the aim of characterizing the therapeutic effectiveness of the clinical epigenetic drug Tazemetostat alone or in combination with various isothiocyanates. In doing so, we assessed markers of cell viability, apoptotic induction, and expression levels of key proteins capable of mediating the therapeutic response. Our data indicated, for the first time, that Tazemetostat caused a significant decrease in viability levels of malignant melanoma cells in a dose- and time-dependent manner via the induction of apoptosis, while non-malignant keratinocytes were more resistant. Moreover, combinatorial treatment protocols caused a further decrease in cell viability, together with higher apoptotic rates. In addition, a significant reduction in the Polycomb Repressive Complex 2 (PRC2) members [e.g., Enhancer of Zeste Homologue 2 (EZH2), Embryonic Ectoderm Development (EED), and suppressor of zeste 12 (SUZ12)] and tri-methylating lysine 27 at Histone 3 (H3K27me3) protein expression levels was observed, at least partially, under specific combinatorial exposure conditions. Reactivation of major apoptotic gene targets was determined at much higher levels in combinatorial treatment protocols than Tazemetostat alone, known to be involved in the induction of intrinsic and extrinsic apoptosis. Overall, we developed an optimized experimental therapeutic platform aiming to ensure the therapeutic effectiveness of Tazemetostat in malignant melanoma while at the same time minimizing toxicity against neighboring non-tumorigenic keratinocyte cells.

BMI1 fine-tunes gene repression and activation to safeguard undifferentiated spermatogonia fate.

Introduction: Spermatogenesis is sustained by the homeostasis of self-renewal and differentiation of undifferentiated spermatogonia throughout life, which is regulated by transcriptional and posttranscriptional mechanisms. B cell-specific Moloney murine leukemia virus integration site 1 (BMI1), one of spermatogonial stem cell markers, is a member of Polycomb repressive complex 1 (PRC1) and important to spermatogenesis. However, the mechanistic underpinnings of how BMI1 regulates spermatogonia fate remain elusive. Methods: We knocked down BMI1 by siRNA to investigate the role of BMI1 in undifferentiated spermatogonia. Differentially expressed genes were identified by RNA-seq and used for KEGG pathway analysis. We performed ChIP-seq analysis in wild type and BMI1 knockdown cells to explore the underlying molecular mechanisms exerted by BMI1. BMI1-associated alterations in repressive histone modifications were detected via Western blotting and ChIP-seq. Furthermore, we performed mass spectrometry and Co-immunoprecipitation assays to investigate BMI1 co-factors. Finally, we demonstrated the genomic regions occupied by both BMI1 and its co-factor. Results: BMI1 is required for undifferentiated spermatogonia maintenance by both repressing and activating target genes. BMI1 preserves PI3K-Akt signaling pathway for spermatogonia proliferation. Decrease of BMI1 affects the deposition of repressive histone modifications H2AK119ub1 and H3K27me3. BMI also positively regulates H3K27ac deposited genes which are associated with proliferation. Moreover, we demonstrate that BMI1 interacts with Sal-like 4 (SALL4), the transcription factor critical for spermatogonia function, to co-regulate gene expression. Discussion: Overall, our study reveals that BMI1 safeguards undifferentiated spermatogonia fate through multi-functional roles in regulating gene expression programs of undifferentiated spermatogonia.

Abstract 5303: Upregulation of the polycomb group protein SCML2 contributes to aggressive prostate cancer

Abstract Advanced prostate cancer (PC) is the leading cause of death in the US because there is no effective treatment due to the poorly understood disease mechanism. Sex comb on midleg-like-2 (SCML2) is a member of Polycomb repressive complex 1 and regulates homeotic gene expression during development. Using proteomic approaches, we have identified SCML2 as a binding partner of the YAP1 protein complexes isolated from PC cell lines. Both SCML2 and YAP1 regulate basic cellular biology, including stem cell maintenance and carcinogenesis; however, whether SCML2 and YAP1 cooperate to contribute to the aggressive PC in humans remains unknown. We showed that AR-positive cell lines express high levels of SCML2 with a significant increase in castration-resistant PC cells compared to its castration-sensitive cell counter, suggesting a possible role of SCML2 in PC progression. We also showed that androgens regulated the protein-protein interaction between SCML2 and YAP1, as evaluated by proximity ligation assay. In addition, the GST-pulldown assay revealed that SCML2 interacted with the WW/SH3 domain of YAP1, where AR also binds. Besides, our RNAi-aided gene silencing experiment demonstrated that YAP1 and SCML2 might be functionally antagonistic. Moreover, gene silencing and growth assays showed that SCML2 might act as a growth suppressor in castration-sensitive PC cells while acting as a growth mediator or survival factor in castration-resistant PC cells. Furthermore, our analysis of the cancer genome atlas PC data set has indicated that amplification of SCML2 is associated with reduced progression-free survival. These observations suggest that SCML2 and YAP1 interaction is biologically functional, and the degree of their interaction may play a critical role in PC progression downstream of dysregulated androgen/AR signaling. Citation Format: Ava M. Boston, Abdulrahman M. Dwead, Marwah M. Al-Mathkour, Kezhan Khazaw, Bekir Cinar. Upregulation of the polycomb group protein SCML2 contributes to aggressive prostate cancer. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5303.

RYBP Sensitizes Cancer Cells to PARP Inhibitors by Regulating ATM Activity.

Ring1 and YY1 Binding Protein (RYBP) is a member of the non-canonical polycomb repressive complex 1 (PRC1), and like other PRC1 members, it is best described as a transcriptional regulator. Previously, we showed that RYBP, along with other PRC1 members, is also involved in the DNA damage response. RYBP inhibits recruitment of breast cancer gene 1(BRCA1) complex to DNA damage sites through its binding to K63-linked ubiquitin chains. In addition, ataxia telangiectasia mutated (ATM) kinase serves as an important sensor kinase in early stages of DNA damage response. Here, we report that overexpression of RYBP results in inhibition in both ATM activity and recruitment to DNA damage sites. Cells expressing RYBP show less phosphorylation of the ATM substrate, Chk2, after DNA damage. Due to its ability to inhibit ATM activity, we find that RYBP sensitizes cancer cells to poly-ADP-ribose polymerase (PARP) inhibitors. Although we find a synergistic effect between PARP inhibitor and ATM inhibitor in cancer cells, this synergy is lost in cells expressing RYBP. We also show that overexpression of RYBP hinders cancer cell migration through, at least in part, ATM inhibition. We provide new mechanism(s) by which RYBP expression may sensitize cancer cells to DNA damaging agents and inhibits cancer metastasis.

Regulatory roles of alternative splicing at Ezh2 gene in mouse oocytes

BackgroundEnhancer of zeste homologue 2 (EZH2), the core member of polycomb repressive complex 2 (PRC2), has multiple splicing modes and performs various physiological functions. However, function and mechanism of alternative splicing at Ezh2 exon 3 in reproduction are unknown.MethodsWe generated Ezh2Long and Ezh2Short mouse models with different point mutations at the Ezh2 exon 3 alternative splicing site, and each mutant mouse model expressed either the long or the short isoform of Ezh2. We examined mutant mouse fertility and oocyte development to assess the function of Ezh2 alternative splicing at exon 3 in the reproductive system.ResultsWe found that Ezh2Long female mice had normal fertility. However, Ezh2Short female mice had significantly decreased fertility and obstructed oogenesis, with compromised mitochondrial function in Ezh2Short oocytes. Interestingly, increased EZH2 protein abundance and accumulated H3K27me3 were observed in Ezh2Short oocytes.ConclusionsOur results demonstrate that correct Ezh2 alternative splicing at exon 3 is important for mouse oogenesis.

Abstract P5-12-05: Novel pEZH2 T367-PRC2 interaction and methyltransferase activity in the nuclear and cytoplasmic fractions of breast cancer cells

Abstract Introduction: EZH2 is the main enzymatic subunit of the Polycomb Repressive Complex 2 (PRC2) that promotes transcriptional repression by trimethylating histone H3 at lysine 27 (H3K27me3). Several reports evidenced EZH2 overexpression in many types of cancers, including breast cancer. In invasive breast carcinoma high levels of EZH2 are associated with triple-negative breast cancer (TNBC) status, presence of metastasis and poor clinical outcome. Despite an oncogenic role of EZH2 as a transcriptional silencer is well known, recent studies showed the association between high levels of EZH2 and low H3K27me3 in TNBC, suggesting that EZH2 may act via non-canonical mechanisms in breast cancer initiation, development, and progression. Interestingly, emerging data highlight that EZH2 can methylate non-histone substrates, regulating numerous cellular functions in a PRC2-dependent or -independent manner. We have established a critical role of p38-mediated EZH2 T367 phosphorylation in the cytoplasmic compartment in promoting cell migration, invasion, and metastasis in TNBC. Here, we tested the hypothesis that EZH2 phosphorylation at T367 induces EZH2 binding to PRC2 in the cytoplasmic compartment of triple-negative breast cancer cells to methylate non-histone proteins. Methods: In vitro and in vivo studies were carried out by using MDA-MB-231 cells. Stable knockdown followed by rescue of EZH2 was attained using lentiviral transduction of EZH2 with pBabe-myc-EZH2 (wild-type), phospho-deficient pBabe-myc-EZH2 (T367A) or HMTase-deficient p-Babe-myc-EZH2 (H694A) in MDA-MB-231 cells. To better evaluate the relevance of cytoplasmic EZH2 in breast cancer progression, we transiently overexpressed EZH2 full length (WT-EZH2) and EZH2 mutant lacking the nuclear localization signaling (ΔNLS-EZH2) adenoviral constructs in MDA-MB-231 shEZH2 cells. The EZH2-catalytic activity inhibition, in vitro and in vivo, was performed through two different drugs, GSK126 and EPZ6438, which exhibit high selectivity for EZH2 lysine N-methyltransferase (KMTase) activity maintaining PRC2 complex integrity. To investigate the interaction between p-EZH2 T367 and PRC2 complex components we carried out Co-immunoprecipitation assay (Co-IP) in the nuclear and cytoplasmic compartments of MDA-MB-231 cells. The interaction was validated by Proximity ligation assays (PLA). We evaluated EZH2 KMTase in the cytoplasmic and nuclear compartments using MTase-Glo Methyltransferase assay in vitro and in vivo. Xenografts obtained from NOD/SCID mice orthotopically injected with MDA-MB-231 cells and treated 5 days/weeks by intraperitoneal injection with 4% DMSO-30% PEG 300-5% Tween 80 (control), or EPZ-6438 (10mg/kg/day) were used to test EZH2 KMTase in vivo. Results: Co-IP and PLA revealed the binding of p-EZH2 T367 to PRC2-complex members in the cytoplasmic compartment of MDA-MB-231 cells expressing WT-EZH2, H694A-EZH2 and ΔNLS-EZH2. In contrast, T367A-EZH2 showed reduced binding to PRC2 members in the cytoplasm. To test the biological relevance of this interaction we measured the KMTase of WT-EZH2 and mutants-EZH2 in the cytoplasmic fraction of MDA-MB-231 cells. Methyltransferase assays using p38 and histone H3 as substrates, showed that WT-EZH2, H694A-EZH2 and ΔNLS-EZH2 are able to methylate p38 protein in the cytoplasmic fraction of MDA-MB-231 cells, and that this requires T367 phosphorylation of EZH2. Similar results were obtained in xenografts of MDA-MB-231 cells in vivo. Conclusion: Our results provide evidence that EZH2 phosphorylation at T376 induces EZH2 binding to PRC2-complex members in the cytoplasm of triple-negative breast cancer cells to methylate non-histone proteins in vitro and in vivo. These data deepen our understanding of the mechanism(s) by which pEZH2 T367 functions in TNBC progression Citation Format: Giuseppina Daniela Naimo, Maria Elena Gonzalez, Shilpa Reddy Tekula, Jessica Camille Gauss, Loredana Mauro, Sebastiano Andò, Celina Graciela Kleer. Novel pEZH2 T367-PRC2 interaction and methyltransferase activity in the nuclear and cytoplasmic fractions of breast cancer cells [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P5-12-05.

Functional divergence of two duplicated Fertilization Independent Endosperm genes in rice with respect to seed development.

Fertilization Independent Endosperm (FIE) is an essential member of Polycomb Repressive Complex 2 (PRC2) that plays important roles in the developmental regulation of plants. OsFIE1 and OsFIE2 are two FIE homologs in the rice genome. Here, we showed that OsFIE1 probably duplicated from OsFIE2 after the origin of the tribe Oryzeae, but has a specific expression pattern and methylation landscape. During evolution, OsFIE1 underwent a less intensive purifying selection than did OsFIE2. The mutant osfie1 produced smaller seeds and displayed reduced dormancy, indicating that OsFIE1 predominantly functions in late seed development. Ectopic expression of OsFIE1, but not OsFIE2, was deleterious to vegetative growth in a dose-dependent manner. The newly evolved N-terminal tail of OsFIE1 was probably not the cause of the adverse effects on vegetative growth. The CRISPR/Cas9-derived mutant osfie2 exhibited impaired cellularization of the endosperm, which suggested that OsFIE2 is indispensable for early seed development as a positive regulator of cellularization. Autonomous endosperm was observed in both OsFIE2+- and osfie1/OsFIE2+- but at a very low frequency. Although OsFIE1-PRC2 exhibited H3K27me3 methyltransferase ability in plants, OsFIE1-PRC2 is likely to be less important for development in rice than is OsFIE2-PRC2. Our findings revealed the functional divergence of OsFIE1 and OsFIE2 and shed light on their distinct evolution following duplication.

Polycomb-like 2 regulates PRC2 components to affect proliferation in glioma cells

IntroductionThe Polycomb group (PcG) is an important family of transcriptional regulators that controls growth and tumorigenesis. The PcG mainly consists of two complexes, PRC1 and Polycomb Repressive Complex 2 (PRC2). Polycomb-like 2 (PCL2) is known to interact with the PRC2 protein. The role of PCL2 in the development and progression of glioma is unclear.MethodsWe use The Cancer Genome Atlas (TCGA) database to detect the expression of PCL2 in various tumors. 117 cases of clinical glioma (WHOI–IV) were collected, and PCL2 expression and localization were detected by immunohistochemical staining. Glioma cells U87/U251 were infected with overexpressed and interfered PCL2. CCK8 assay, colony formation assay, EdU method, cell cycle and apoptosis were used to detect cell proliferation and apoptosis. Western blot was used to detect the expression of PRC2-related core proteins. After DZNeP intervention, PRC2 protein expression was again measured to discuss the mechanism of PCL2 action.ResultsTCGA database results and immunohistochemical staining results suggest that PCL2 is highly expressed in gliomas. We found that the PCL2 gene promoted tumor cell proliferation, enhanced the colony formation ability, and increased S phase in the cell cycle. The overexpression of PCL2 upregulated the expression levels of EZH2 and EED (two core members of PRC2), decreased the expression of SUZ12, increased the level of H3K27 trimethylation (H3K27me3), H3K4 dimethylation (H3K4me2), and decreased H3K9 dimethylation (H3K9me2). The result after interfering with PCL2 was the opposite.ConclusionsAs an important accessory protein of PRC2, PCL2 can not only change the expression of PRC2 components, but also affect the expression level of Histone methylation. Therefore, PCL2 may be an important hub for regulating the synergy among PRC2 members. This study revealed PCL2 as a new target for tumor research and open up a new avenue for future research in glioma.

SAT-LB34 Repressive Epigenetic Programs Reinforce Steroidogenic Differentiation and Wnt/β-Catenin Signaling in Aggressive Adrenocortical Carcinoma

Adrenocortical carcinoma (ACC) is a rare, aggressive cancer. Up to 75% of patients develop incurable metastatic disease, highlighting an urgent need for novel medical therapies. We recently identified a rapidly progressive ACC subtype characterized by CpG island hypermethylation (CIMP-high), sustained Wnt/β-catenin signaling, steroidogenic differentiation, and cell cycle activation. CIMP-high status alone accounts for 40% of ACC, but predicts 70% of recurrences and >50% of deaths. Intriguingly, hypermethylated CpG islands in CIMP-high ACC are unmethylated in fetal and adult adrenal cortex, suggesting DNA methylation is supported by cancer-specific mechanisms. We therefore sought to investigate how aberrant epigenetic programming contributes to ACC biology. In embryonic stem cells, the Polycomb repressive complex 2 (PRC2) represses differentiation programs through EZH2-mediated histone H3 lysine 27 trimethylation (H3K27me3) deposition in promoter CpG islands free of DNA methylation. Gain or loss of EZH2/PRC2 function prevails in a variety of human cancers, enabling proliferation in a tissue-specific manner. Here, we identify that CIMP-high ACC exhibit high expression of EZH2/H3K27me3, but paradoxically bear DNA hypermethylation in annotated PRC2 target regions. To determine if DNA methylation of PRC2 targets disrupts or is controlled by EZH2, we characterized EZH2’s role in CIMP-high ACC cell line NCI-H295R at baseline and in response to EZH2 inhibition (EZH2i). EZH2-directed IP-MS revealed EZH2 interacts with PRC2 members and DNA methylation-sensitive accessory proteins, but no DNA methyltransferase machinery. ChIP-seq revealed EZH2 and H3K27me3 colocalize in repressive domains genome-wide, but DNA methylation and H3K27me3 are mutually exclusive. EZH2i induced H3K27 demethylation and loss of viability, but with no effect on CIMP-high DNA methylation. These data suggest PRC2 target DNA methylation in CIMP-high ACC is maintained independently of EZH2, enabling EZH2/PRC2 to coordinate alternative programs required for cell survival. We then measured the consequences of EZH2i on the NCI-H295R transcriptome (RNA-seq), EZH2/H3K27me3 deposition genome-wide (ChIP-seq), and chromatin accessibility landscape (ATAC-seq). EZH2i led to global downregulation of cell cycle, Wnt/β-catenin transcriptional programming, and steroidogenic differentiation, partially explained by EZH2i-induced offloading of EZH2 from H3K27me3 domains to accessible promoters genome-wide. Taken together, our studies illustrate how aberrant CpG island hypermethylation in CIMP-high ACC participates in a targetable repressive epigenetic cascade that reinforces oncogenic adrenocortical transcriptional programs. Ultimately, we hope to illuminate novel strategies for tissue-specific disruption of the aberrant epigenetic wiring that defines CIMP-high ACC.

Memory of Divisional History Directs the Continuous Process of Primitive Hematopoietic Lineage Commitment.

SummaryHematopoietic stem cells (HSCs) exist in a dormant state and progressively lose regenerative potency as they undergo successive divisions. Why this functional decline occurs and how this information is encoded is unclear. To better understand how this information is stored, we performed RNA sequencing on HSC populations differing only in their divisional history. Comparative analysis revealed that genes upregulated with divisions are enriched for lineage genes and regulated by cell-cycle-associated transcription factors, suggesting that proliferation itself drives lineage priming. Downregulated genes are, however, associated with an HSC signature and targeted by the Polycomb Repressive Complex 2 (PRC2). The PRC2 catalytic subunits Ezh1 and Ezh2 promote and suppress the HSC state, respectively, and successive divisions cause a switch from Ezh1 to Ezh2 dominance. We propose that cell divisions drive lineage priming and Ezh2 accumulation, which represses HSC signature genes to consolidate information on divisional history into memory.

Age-Related Co-Expression of BCOR and BCORL1 mRNA in Acute Myeloid Leukemia.

Acute myeloid leukemia (AML) is an aggressive hematological malignancy caused by a variety of genetic abnormalities and epigenetic dysregulation. The incidence of AML is strongly related to age, with the highest incidence rates being in older adults. The loss of function mutations in BCOR and BCORL1 genes have been identified in AML. BCL6 corepressor (BCOR) and BCL6 corepressor like 1 (BCORL1) are important epigenetic regu-lators as a member of Polycomb repressive complex 1 (PRC1.1), involved in histone modification processes. We analyzed the BCOR and BCORL1 mRNA expression in 74 adult and 22 pediatric patients with AML by Real-Time quantitative PCR in this study. Our results indicated that both BCOR and BCORL1 mRNA expressions decrease with age (p = 0.009 and p = 0.008, respectively) and there is a positive correlation between BCOR and BCORL1 mRNA expression (p < 0.001). BCOR and BCORL1 mRNA expressions were not significantly different in both adult and pediatric patients with AML compared to control (p > 0.05). Our findings indicate that expression of BCOR and BCORL1 mRNA are down-regulated with age. The increase in AML incidence with age suggests that age-associated BCOR and BCORL1 down-regulation might potentially contribute to age-related epigenetic alterations and form a predisposing condition for the development of elderly AML.

Abstract GMM-055: BMI1 AND RING1A ARE INVOLVED IN H2A UBIQUITINATION AT SITES OF PLATINUM-INDUCED DAMAGE

Abstract Ovarian cancer is the 5th leading cause of death among women with the five year survival rate for ovarian cancer patients being only 46%. The standard of care for treatment of ovarian cancer patients is debulking surgery followed by platinum-taxane based chemotherapy. However, the major obstacle in the treatment of these patients with platinum based agents is development of chemoresistance. The platinum agents, cisplatin and carboplatin damage DNA by forming adducts with adjacent guanines, a high density of which are found in the promoter CpG islands of genes. Aberrant promoter DNA hypermethylation of genes and their subsequent transcriptional repression has been associated with development of cisplatin resistance. However, the mechanism of initiation of this aberrant DNA methylation and subsequent transcriptional repression is not known. Our overall hypothesis is that platinum induced DNA damage or repair of the damage leads to recruitment of repressive proteins to sites of damage. These repressive proteins transiently repress transcription in vicinity of damage to promote repair. However, similar to our findings with enzyme induced double strand breaks, repressive proteins may be retained at some key loci causing persistent transcriptional repression and gene silencing contributing to the development of platinum resistance. Our preliminary data demonstrates that BMI1, a member of polycomb repressive complex 1, localizes to sites of damage after cisplatin treatment. We also observe mono-ubiquitination of H2AX after cisplatin treatment and we hypothesize that this ubiquitination is occurring on K119. Mono-ubiquitination of H2A/H2AX at K119 has been associated with transcriptional repression and gene silencing during development and differentiation and also during repair of ionizing radiation and enzyme induced double strand breaks. Our data suggests that knockdown of RING1A reduces the cisplatin induced H2AX ubiquitination. We are currently determining which repair pathways and/or proteins result in recruitment of BMI1, RING1A to sites of damage. Importantly, after acute cisplatin treatment we also observe a reduction in expression of candidate genes which are known to be methylated in cisplatin resistant cells. We plan to determine if RING1A mediated ubiquitination is responsible for reduction in expression of target genes after acute cisplatin treatment and their methylation in cisplatin resistant cells. Understanding the mechanism of platinum induced gene silencing will enable us to design therapies to avert the development of drug resistant ovarian cancers. Citation Format: Shruthi Sriramkumar, Heather M. O'Hagan. BMI1 AND RING1A ARE INVOLVED IN H2A UBIQUITINATION AT SITES OF PLATINUM-INDUCED DAMAGE [abstract]. In: Proceedings of the 12th Biennial Ovarian Cancer Research Symposium; Sep 13-15, 2018; Seattle, WA. Philadelphia (PA): AACR; Clin Cancer Res 2019;25(22 Suppl):Abstract nr GMM-055.

Updating and interaction of polycomb repressive complex 2 components in maize (Zea mays).

The information on core components in maize polycomb repressive complex2 (PRC2) are updated at a genome-wide scale, and the protein-protein interaction networks of PRC2 components are further provided in maize. The evolutionarily conserved polycomb group (PcG) proteins form multi-subunits polycomb repressive complexes (PRCs) that repress gene expression via chromatin condensation. In Arabidopsis, three distinct PRC2s have been identified, each determining a specific developmental program with partly functional redundancy. However, the core components and biological functions of PRC2 in cereals remain obscure. Here, we updated the information on maize PRC2 components at a genome-wide scale. Maize PRC2 subunits are highly duplicated, with five MSI1, three E(z), two ESC and two Su(z)12 homologs. ZmFIE1 is preferentially expressed in the endosperm, whereas the remaining are broadly expressed in many tissues. ZmCLF/MEZ1 and ZmFIE1 are maternally expressed imprinted genes, in contrast to the paternal-dominantly expression of ZmFIE2 in the endosperm. In maize, E(z) members likely provide a scaffold for assembling PRC2 complexes, whereas Su(z)12 and p55/MSI1-like proteins together reinforce the complex; ESC members probably determine its specificity: FIE1-PRC2 regulates endosperm cell development, whereas FIE2-PRC2 controls other cell types. The duplicated Brassicaceae-specific MEA and FIS2 also directly interact with maize PRC2 members. Together, this study establishes a roadmap for protein-protein interactions of maize PRC2 components, providing new insights into their functions in the growth and development of cereals.

Roles of Polycomb group proteins Enhancer of zeste (E(z)) and Polycomb (Pc) during metamorphosis and larval leg regeneration in the flour beetle Tribolium castaneum

Many organisms both undergo dramatic morphological changes during post-embryonic development and also regenerate lost structures, but the roles of epigenetic regulators in such processes are only beginning to be understood. In the present study, the functions of two histone modifiers were examined during metamorphosis and larval limb regeneration in the red flour beetle Tribolium castaneum. Polycomb (Pc), a member of Polycomb repressive complex 1 (PRC1), and Enhancer of zeste (E(z)), a member of Polycomb repressive complex 2 (PRC2), were silenced in larvae using RNA interference. In the absence of Pc, the head appendages of adults transformed into a leg-like morphology, and the legs and wings assumed a metathoracic identity, indicating that Pc acts to specify proper segmental identity. Similarly, silencing of E(z) led to homeotic transformation of legs and wings. Additional defects were also observed in limb patterning as well as eye morphogenesis, indicating that PcG proteins play critical roles in imaginal precursor cells. In addition, larval legs and antennae failed to re-differentiate when either Pc or E(z) was knocked down, indicating that histone modification is necessary for proper blastema growth and differentiation. These findings indicate that PcG proteins play extensive roles in postembryonic plasticity of imaginal precursor cells.

JAK2 regulates mismatch repair protein-mediated epigenetic alterations in response to oxidative damage.

At sites of chronic inflammation epithelial cells undergo aberrant DNA methylation that contributes to tumorigenesis. Inflammation is associated with an increase in reactive oxygen species (ROS) that cause oxidative DNA damage, which has also been linked to epigenetic alterations. We previously demonstrated that in response to ROS, mismatch repair proteins MSH2 and MSH6 recruit epigenetic silencing proteins DNA methyltransferase 1 (DNMT1) and polycomb repressive complex 2 (PRC2) members to sites of DNA damage, resulting in transcriptional repression of tumor suppressor genes (TSGs). However, it was unclear what signal is unique to ROS that results in the chromatin binding of MSH2 and MSH6. Herein, we demonstrate that in response to hydrogen peroxide (H2 O2 ), JAK2 localizes to the nucleus and interacts with MSH2 and MSH6. Inhibition or knockdown of JAK2 reduces the H2 O2 -induced chromatin interaction of MSH2, MSH6, DNMT1, and PRC2 members, reduces H2 O2 -induced global increase in trimethylation of lysine 27 of histone H3 (H3K27me3), and abrogates oxidative damage-induced transcriptional repression of candidate TSGs. Moreover, JAK2 mRNA expression is associated with CpG island methylator phenotype (CIMP) status in human colorectal cancer. Our findings provide novel insight into the connection between kinase activation and epigenetic alterations during oxidative damage and inflammation. Environ. Mol. Mutagen. 60:308-319, 2019. © 2018 Wiley Periodicals, Inc.

Bmi-1 Regulates Ex Vivo Self-Renewal of Human Erythroblasts

About twelve million units of red blood cells (RBCs) are transfused yearly in the United States. Ex vivo cultured RBCs could serve as a supplemental source to treat alloimmunized patients requiring chronic transfusions. The limited proliferative capacity of erythroid precursors is a major obstacle to generating sufficient numbers of RBCs to constitute even one unit of blood. We previously determined that erythroblasts derived from the murine embryo have a unique ability to self-renew extensively ex vivo, and that Bmi-1, a member of the polycomb repressive complex 1 (PRC1), is both necessary and sufficient to drive the extensive self-renewal of murine bone marrow-derived erythroblasts. Here, we tested the hypothesis that Bmi-1 regulates the ex vivo self-renewal of human erythroid cells. Bmi-1 overexpression increased the proliferative capacity of adult human peripheral blood mononuclear cell-derived erythroblasts, which normally have restricted ex vivo self-renewal, more than 10 billion-fold. Bmi-1-induced self-renewing erythroblasts (iSREs) retained an immature erythroid morphology and cell surface phenotype throughout culture. Chemical inhibition of Bmi-1 led to collapse of the culture, with a massive reduction in cycling cells and an increase in apoptosis. Taken together, these data indicate that Bmi-1 in iSREs is both necessary and sufficient to increase the self-renewal capacity of human erythroid precursors. Importantly, Bmi-1 overexpression does not interfere with the ability of the iSREs to mature into reticulocytes in vitro. Serological analysis of multiple blood group antigens demonstrated that iSRE-derived reticulocytes express the same antigens as the donor's RBCs. Bmi-1 can act as part of canonical or non-canonical PRC1 and different complex members have been associated with hematopoietic self-renewal versus differentiation. Expression studies of self-renewing human erythroblasts revealed that the non-canonical PRC1 member, RYBP, was expressed at higher levels than canonical PRC1 members. In addition, maturation of erythroid precursors is associated with down-regulation of Bmi-1 and non-canonical PRC1 members, as well as the upregulation of several canonical members. Knockdown of RYBP reduced the proliferative capacity of the iSREs, suggesting that Bmi-1 regulates erythroid self-renewal through non-canonical PRC1 interactions. Consistent with this hypothesis, preliminary studies inhibiting canonical PRC1 members led to an additional several trillion-fold increase in the ex vivo proliferative capacity of human iSREs compared to vehicle-treated control cultures. These data suggest that Bmi-1 regulates erythroid self-renewal through non-canonical PRC1. Increasing the ex vivo self-renewal capacity of human erythroblasts ultimately paves the way for the generation of sufficient numbers of cultured RBCs for blood typing and transfusion therapy, as well as the establishment of in vitro models of RBC-intrinsic disorders. DisclosuresPalis:Rubies Therapeutics: Consultancy.

Abstract 5317: JAK2 regulates oxidative damage-induced epigenetic alterations

Abstract Elevated levels of reactive oxygen species at sites of chronic inflammation cause oxidative DNA damage in epithelial cells, contributing to carcinogenesis. Aberrant silencing of key genes by promoter CpG island DNA hypermethylation occurs in many cancers that form at sites of chronic inflammation. Yet, it is not completely understood how these aberrant DNA methylation alterations are initiated. We hypothesize that the recruitment of epigenetic silencing proteins to sites of oxidative DNA damage is important for initiating DNA methylation. Here we demonstrate that after hydrogen peroxide (H2O2) treatment, mismatch repair proteins MSH2 and MSH6 become localized to sites of oxidative DNA damage, resulting in the recruitment of DNA methyltransferase 1 (DNMT1) and Polycomb repressive complex 2 (PRC2) members to chromatin. This recruitment results in the formation of repressive chromatin in the promoters of tumor-suppressor genes and the concomitant transient reduction in their expression. We sought to further understand the mechanism that drives H2O2-induced MSH2 and MSH6 chromatin binding. Janus kinase 2 (JAK2) is a kinase that is canonically known to be activated by cytokines and growth hormones and phosphorylate the transcription factor signal transducer and activator of transcription (STATs). Here, we demonstrate that in response to treatment with H2O2, but not interleukin 6 (IL-6), JAK2 translocates to the nucleus and interacts with MSH2 and MSH6. Nuclear JAK2 is important for H2O2-induced chromatin interaction of MSH2, MSH6, DNMT1 and PRC2 members. Interestingly, H2O2-induces a global and site-specific increase in trimethylation of histone H3 at lysine 27 (H3K27me3) that is also dependent on JAK2. Furthermore, by analyzing TCGA datasets, we demonstrate high JAK2 mRNA expression correlates with CpG island methylator phenotype (CIMP) status in gastric and colorectal cancer. All together, these findings suggest JAK2 plays a key role in initiating oxidative damage-induced epigenetic alterations during inflammation-driven tumorigenesis. Ultimately, understanding the mechanism of initiation of cancer-specific promoter DNA hypermethylation may lead to treatment strategies to reduce aberrant epigenetic changes induced by chronic inflammation and therefore reduce tumorigenesis. Citation Format: Ning Ding, Sam Miller, Heather O'Hagan. JAK2 regulates oxidative damage-induced epigenetic alterations [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5317.

B lymphoma Moloney murine leukemia virus insertion region 1: An oncogenic mediator in prostate cancer

B lymphoma Moloney murine leukemia virus insertion region 1 (BMI1), a core member of polycomb repressive complex 1 (PRC1), has been intensely investigated in the field of cancer epigenetics for decades. Widely known as a critical regulator in cellular physiology, BMI1 is essential in self-renewal and differentiation in different lineages of stem cells. BMI1 also plays a significant role in cancer etiology for its involvement in pathological progress such as epithelial–mesenchymal transition (EMT) and cancer stem cell maintenance, propagation, and differentiation. Importantly, overexpression of BMI1 is predictive for drug resistance, tumor recurrence, and eventual therapy failure of various cancer subtypes, which renders the pharmacological targeting at BMI1 as a novel and promising therapeutic approach. The study on prostate cancer, a prevalent hormone-related cancer among men, has promoted enormous research advancements in cancer genetics and epigenetics. This review summarizes the role of BMI1 as an oncogenic and epigenetic regulator in tumor initiation, progression, and relapse of prostate cancer.

Targeting of BMI-1 with PTC-209 inhibits glioblastoma development

ABSTRACT Glioblastoma multiforme (GBM) is the most common and aggressive brain tumor and refractory to existing therapies. The oncogene BMI-1, a member of Polycomb Repressive Complex 1 (PRC1) plays essential roles in various human cancers and becomes an attractive therapeutic target. Here we showed that BMI-1 is highly expressed in GBM and especially enriched in glioblastoma stem cells (GSCs). Then we comprehensively investigated the anti-GBM effects of PTC-209, a novel specific inhibitor of BMI-1. We found that PTC-209 efficiently downregulates BMI-1 expression and the histone H2AK119ub1 levels at microM concentrations. In vitro, PTC-209 effectively inhibits glioblastoma cell proliferation and migration, and GSC self-renewal. Transcriptomic analyses of TCGA datasets of glioblastoma and PTC-209-treated GBM cells demonstrate that PTC-209 reverses the altered transcriptional program associated with BMI-1 overexpression. And Chromatin Immunoprecipitation assay confirms that the derepressed tumor suppressor genes belong to BMI-1 targets and the enrichment levels of H2AK119ub1 at their promoters is decreased upon PTC-209 treatment. Strikingly, the glioblastoma growth is significantly attenuated by PTC-209 in a murine orthotopic xenograft model. Therefore our study provides proof-of-concept for inhibitors targeting BMI-1 in potential applications as an anti-GBM therapy.