The PML1-WDR5 axis regulates H3K4me3 marks and promotes stemness of estrogen receptor-positive breast cancer

The alternative splicing of PML precursor mRNA gives rise to various PML isoforms, yet their expression profile in breast cancer cells remains uncharted. We discovered that PML1 is the most abundant isoform in all breast cancer subtypes, and its expression is associated with unfavorable prognosis in estrogen receptor-positive (ER+) breast cancers. PML depletion reduces cell proliferation, invasion, and stemness, while heterologous PML1 expression augments these processes and fuels tumor growth and resistance to fulvestrant, an FDA-approved drug for ER + breast cancer, in a mouse model. Moreover, PML1, rather than the well-known tumor suppressor isoform PML4, rescues the proliferation of PML knockdown cells. ChIP-seq analysis reveals significant overlap between PML-, ER-, and Myc-bound promoters, suggesting their coordinated regulation of target gene expression, including genes involved in breast cancer stem cells (BCSCs), such as JAG1, KLF4, YAP1, SNAI1, and MYC. Loss of PML reduces BCSC-related gene expression, and exogenous PML1 expression elevates their expression. Consistently, PML1 restores the association of PML with these promoters in PML-depleted cells. We identified a novel association between PML1 and WDR5, a key component of H3K4 methyltransferase (HMTs) complexes that catalyze H3K4me1 and H3K4me3. ChIP-seq analyses showed that the loss of PML1 reduces H3K4me3 in numerous loci, including BCSC-associated gene promoters. Additionally, PML1, not PML4, re-establishes the H3K4me3 mark on these promoters in PML-depleted cells. Significantly, PML1 is essential for recruiting WDR5, MLL1, and MLL2 to these gene promoters. Inactivating WDR5 by knockdown or inhibitors phenocopies the effects of PML1 loss, reducing BCSC-related gene expression and tumorsphere formation and enhancing fulvestrant’s anticancer activity. Our findings challenge the conventional understanding of PML as a tumor suppressor, redefine its role as a promoter of tumor growth in breast cancer and offer new insights into the unique roles of PML isoforms in breast cancer.


Introduction
The PML protein has diverse cellular functions, including regulating cell-cycle progression, DNA damage responses, and transcription; it also plays important roles in governing immunity, metabolism, and tumorigenesis [1][2][3][4][5][6][7].PML protein is primarily localized in the nucleoplasm and DNA-free sub-nuclear compartments known as PML nuclear bodies (NBs) [8][9][10], which may indirectly regulate transcription by sequestering transcription factors or serving as a platform protein for transcription factor modi cation [11,12].Several studies have suggested that PML binds to chromatin, indicating a direct role in transcriptional regulation [6, 13,14].However, a systematic analysis of the global PML-bound promoters is lacking.
The notion that PML is a tumor suppressor gene was mainly based on studies of the PML4 isoform [12,[15][16][17] and earlier clinical investigations [17].Recent studies have revealed a more complex role for PML in cancer.Knockdown of PML inhibits the proliferation of estrogen receptor-positive (ER+) breast cancer [18] and ovarian cancer cells [19] and reduces tumor growth in mouse xenograft models of triple-negative breast cancer (TNBC) [20][21][22] and glioblastoma [23].Interestingly, the PML-reducing agent arsenic trioxide (ATO), an FDA-approved drug for treating acute promyelocytic leukemia, is an effective agent in inhibiting tumor growth of glioblastoma [23,24] and TNBCs [22].These paradoxical ndings underscore the need to revisit our understanding of PML's role in tumorigenesis.
The PML precursor mRNA undergoes alternative splicing, resulting in multiple isoforms, and the expression patterns of different PML isoforms in cancerous tissues and their speci c contribution to tumorigenesis remain unknown.This study examined the expression pro les of PML isoforms in normal and malignant breast cells and tissues.We found that PML1 is the most abundant isoform expressed in ER + breast tumors and cancer cell lines, with the increased PML1 mRNA associated with poor prognosis of luminal breast cancer patients.Signi cantly, a recent clinical study revealed that the PML gene is ampli ed in 14% of ER + metastatic breast cancer (MBC) [25].We also showed that the loss of PML inhibits the stemness of ER + breast cancer cells, with elevated PML1 expression driving breast cancer stemness, tumor growth, and therapy resistance in xenograft mouse models.
To further understand the mechanism by which PML1 promotes breast tumorigenesis and stemness, we analyzed ChIP-seq data.We found that PML, Myc, and ER bind many common gene promoters, including those encoding breast cancer stem cell (BCSC)-related genes, such as JAG1 [26], KLF4 [27], YAP1 [28], SNAI1 [29], and MYC [30].PML1 promotes the expression of both Myc and ER target genes, thereby increasing ER + breast cancer cell stemness.We also discovered that PML1 associates with WDR5 and regulates H3K4 tri-methylation (H3K4me3), and the inactivation of WDR5 reduces breast cancer cell stemness and related gene expression and enhances the anticancer activity of fulvestrant.Mechanistically, PML is essential for recruiting WDR5, MLL1, and MLL2 to the stemness gene promoters, thus regulating the H3K4me3 marks at these loci.Our ndings rede ne the role of PML, shifting its characterization from a tumor suppressor to a promoter, and highlight the pivotal function of the PML1-WDR5 axis in regulating breast cancer cell stemness and drug resistance.

PML1 is the most abundant isoform in estrogen receptorpositive (ER+) breast tumors
To better understand the expression patterns of PML isoforms in breast cancer patients, we interrogated RNA-seq datasets from normal breast tissues (GTEx) and breast tumors (TCGA).Our results demonstrate that the total PML transcript expression is signi cantly elevated across all breast cancer subtypes compared to normal tissues (Fig. S1).PML1 mRNA is the predominant isoform in normal breast tissues and ER + breast tumors.Moreover, PML1 abundance shifts dramatically from ~ 38% in normal tissues (Fig. 1A) to ~ 67% in ER + tumors (Fig. 1B), while that of PML2 mRNA is expressed at a lower level than PML1 in both normal (~ 30%) and malignant breast tissues (~ 20%).PML4, which encodes an extensively studied tumor suppressor, is expressed at a much lower level (~ 7%).Moreover, higher PML1 mRNA levels are associated with poor prognosis of ER + breast cancer patients (Fig. 1C), but there was no correlation between the expression of other PML isoforms and prognosis (Fig. S2A).Furthermore, the total PML protein abundance is elevated in ER + breast tumors (Fig. 1D).We also observed a trend in which higher PML protein abundance correlates with poor prognosis (Fig. S2B).PML1 and PML4 proteins share the rst 620 amino acids, with PML4 containing a 13 a.a.unique C-terminus and PML1 possessing an additional 262 a.a (Fig. 1E).To better understand the role of PML1 in breast cancer, we generated a PML1-speci c antibody.We con rmed that PML1 and PML4 proteins migrate around 130 kDa and 100 kDa, respectively (Fig. 1F) and that PML1 is the predominant isoform in ER+/HER2-breast cancer cell lines, including MCF-7, T47D, and ZR-75-1 cells (Fig. 1G).These ndings suggest that PML1 is the most abundant isoform in breast cancer, and its high expression may be a potential biomarker for poor prognosis for ER + breast cancer.

PML1 promotes cancer phenotypes and fulvestrant resistance
Our previous study demonstrated that the ectopic overexpression of PML4 inhibits the proliferation, migration, and invasion of MCF-7 cells [18].We expand our studies by investigating the effects of PML on another ER + breast cancer cell line, ZR-75-1.Our results showed that the knockdown of PML reduces the proliferation (Fig. 2A), colony formation (Fig. 2D), and invasion (Fig. 2F) of MCF-7 and ZR-75-1 cells, while PML1 overexpression has the opposite effect (Fig. B, E, and G).Furthermore, MCF-7-HA-PML1 cells, which express virally transduced HA-PML1, exhibit a signi cant increase in the IC 50 (4.499e-008M)for fulvestrant, compared to control cells (1.046e-010M) (Fig. 2H), indicating that higher PML1 expression promotes fulvestrant resistance.This result is consistent with a recent clinical study indicating that the PML gene is ampli ed in 14% of ER + MBC [25](Fig.S3).Moreover, exogenous PML1 rescues the proliferation of PML knockdown cells (Fig. 2C), but PML4 does not (Fig. S4A).Additionally, PML2 inhibits the proliferation and breast cancer cell stemness (Fig. S4B), indicating that PML2 and PML1 have the opposite effects on breast cancer cells.These results suggest that PML isoforms play distinct roles in breast cancer development and progression and that PML1 may play a role in fulvestrant resistance.

PML1 binds and positively regulates stemness gene promoters and promotes breast cancer stem-like cell (BCSC) populations
The observations that PML1 promotes fulvestrant resistance and invasion of breast cancer cells prompted us to investigate PML1's role in cancer cell stemness.Gene Set Enrichment Analysis (GSEA) revealed that affected genes in PML knockdown microarray gene expression study are enriched for genes upregulated in the Mammary_Stem_Cell_Up signature [31](Fig.3A), suggesting PML's role in CSC regulation.Analyses of PML ChIP-seq data in MCF-7 cells revealed that PML binds to more than half of the BCSC-associated gene promoters (Table S3).Knockdown of PML1 signi cantly reduced the expression of a subset of BCSC-related genes (Fig. 3B), while overexpression of PML1 increased their expression (Fig. 3C).Moreover, PML1 knockdown reduced the frequency of BCSCs in extreme limiting dilution assays (ELDAs) (Fig. 3D) and tertiary tumorsphere-formation assays (Fig. 3F, S5), while PML1 overexpression had the opposite effect (Fig. 3E, 3G, and S5).FACS analyses further showed that PML knockdown reduced the ALDH high cell population, while overexpression of PML1 increased it (Fig. 3H-I).
These results suggest that PML1 promotes the stemness of breast cancer cells.

PML1 promotes tumor growth and fulvestrant resistance in a xenograft animal model
Next, we determined the effects of PML1 on the tumor growth of MCF-7 cells.Our results showed that animals xenografted with MCF-7-HA-PML1 cells developed signi cantly larger tumors than those with control cells (Fig. 4A-B).These ndings suggest that PML1 plays a crucial role in promoting tumor growth in breast cancer.HA-PML1 protein expression is con rmed by western blots in tumors stably express HA-PML1 (Fig. 4C), and HA-PML1-expressing tumors show elevated BCSC-related gene expression (Fig. 4D.)Lastly, tumors generated with cells expressing MCF-7-HA-PML1 were resistant to fulvestrant (Fig. 4E).These observations are consistent with the fact that 14% of ER + MBC have the PML gene ampli cation.These ndings suggest that PML1 is crucial in promoting tumor growth and fulvestrant resistance in breast cancer.

ChIP-seq analyses reveal crosstalk between PML1, ER, and Myc-bound promoters
Previous reports have shown that the Myc transcription factor regulates the expression of a subset of stemness genes [32] and Myc interacts with PML4 [33].Analyses of ChIP-seq data for PML, Myc, and ER revealed that most PML-binding sites (~ 77%) are in promoter regions, which account for 23% of proteincoding gene promoters (Fig. 5A and 5E).In contrast, less than 14% of the ER-binding sites are in promoter regions, while ~ 80% are in intergenic regions or introns (Fig. 5B).Interestingly, most Myc-binding sites are in intergenic regions or introns (Fig. 5C).Focusing on PML-bound promoters (Fig. 5D), we found that PML and ER bind 1,387 common promoters (Fig. 5D-E), which accounts for ~ 70% of ER-and ~ 18% of PML1bound promoters, respectively (Fig. 5E, S6A).The top-ranked consensus sequence among PML1 and ER commonly bound promoters is an estrogen-response element (ERE) half-site, -AGGTCA-(Fig.S6B).Myc binds ~ 94% of PML-bound promoters in MCF-7 cells (Fig. 5E).In fact, microarray analyses [34] suggest that affected genes in PML knockdown cells are enriched in Myc-targeted genes (Fig. S6C).Furthermore, ChIP-seq analyses suggest that PML1, Myc, and ER bind several BCSC-related gene promoters (Table S3), including JAG1, KLF4, MYC, SNAI1, and YAP1 (Fig. S7).Using ChIP-qPCR, we con rmed that PML binds these promoters but not NANOG (Fig. 5F) and that PML1, not PML4, binds these promoters (Fig. 5G).These analyses suggest that PML, Myc, and ER regulate gene expression in BCSCs by binding to common promoters.Moreover, microarray gene expression analyses [34] indicate that PML target genes are enriched in estradiol-responsive genes [35](Fig.5H).Proximity ligation assays (PLA) showed that endogenous PML and ER interact (Fig. S8).Furthermore, Coimmunoprecipitation demonstrated endogenous and exogenous PML1 and ER interact (Fig. 5I-J), and the recruitment of PML1 to BCSCrelated gene promoters is induced upon E2 treatment (Fig. 5K), indicating a potential role of PML1 in E2induced ER-target gene expression.Furthermore, the knockdown of ESR1 signi cantly reduces the expression of stemness-related genes, phenocopying the effects of PML1 knockdown (Fig. 5L).However, the loss of PML1 had little or no effect on the ER binding to these promoters (Fig. 5M), suggesting PML1 regulates ER target gene expression without affecting ER binding to the promoters.
To interrogate the role of PML1 in regulating global H3K4me3 across gene promoters, we performed PML knockdown followed by ChIP-seq, which showed that PML1 regulates H3K4me3 levels at numerous gene promoters (Fig. 7A), including gene loci associated with BCSCs (Fig. 7B).Additionally, the H3K4me3 patterns we observed on these promoters align well with publicly accessible data (Figure S7).Importantly, ChIP-qPCR con rmed that the loss of PML1 signi cantly reduced the H3K4me3 mark on BCSC-related gene promoters (Fig. 7C).Because PML1 and PML4 contain the WDR5-interacting domain, we examined whether PML1 and PML4 can restore the H3K4me3 mark in PML knockdown cells, and our data demonstrated that PML1, not PML4, re-establishes the H3K4me3 mark in PML knockdown cells (Fig. 7D).Furthermore, the loss of PML1 signi cantly reduced the associations of WDR5 (Fig. 7E), MLL1 (Fig. 7F), and MLL2 (Fig. 7G) with stemness gene promoters.We further investigated whether WDR5 is required for PML associations with these promoters and found that knockdown of WDR5 markedly reduces the expression of the BCSC-related genes (Fig. 7H) and the H3K4me3 mark (Fig. 7I) but has little or no effect on PML1 associations with these promoters (Fig. 7J).These data suggest that PML1 promotes ER and Myc transcriptional activity through its interaction with WDR5 and the subsequent enrichment of the H3K4me3 mark at target gene promoters.

Inactivation of WDR5 enhances the effectiveness of fulvestrant in PML1-overexpressing cells
The data presented above suggests that WDR5 and PML may act together to modulate the expression of stem cell-associated genes and stemness in breast cancer cells.Our results demonstrate that the knockdown of WDR5 leads to a signi cant decrease in BCSCs population (Fig. 8A and S9) and inhibition of MCF-7 cell proliferation (Fig. 8B).We also found that the knockdown of WDR5 signi cantly enhances the anti-proliferation activity of fulvestrant against PML1-overexpressing cells, reducing the IC 50 from µM to nM (Fig. 8C).We next investigated the effects of pharmacological inhibitors of WDR5, OICR-9429 and compound 16 (C16), on stemness-related gene expression, cell proliferation, and the anticancer activity of fulvestrant.Both inhibitors disrupt the interaction between WDR5 and MLL1 by targeting their interacting sites [38,39].Our results demonstrated that both inhibitors effectively reduced the population of BCSCs (Fig. 8D), inhibited the expression of stemness-related genes (Fig. 8E), and suppressed the proliferation of both control and PML1-overexpressing cells (Fig. 8F-G).Furthermore, both inhibitors enhanced the antigrowth activity of fulvestrant (Fig. 8H).These results suggest that the PML1:WDR5 association has functional signi cance in regulating breast cancer stemness and fulvestrant resistance.

Discussion
Our study provides compelling evidence that PML1 promotes the proliferation, migration, and tumor growth of ER + breast cancer cells.We demonstrated that PML1 is the most abundant isoform expressed in ER + breast tumors and plays a critical role in promoting cancer cell stemness and resistance to fulvestrant.In support of our conclusions, a recent clinical study reported that the PML gene is ampli ed in 14% of ER + MBC cases [25], suggesting that elevated PML1 protein promotes metastasis.These observations a rm the notion that rather than functioning as a tumor suppressor, the PML1 isoform promotes breast tumorigenesis and metastasis.Moreover, we showed that PML1, not PML4, rescues the proliferation and restores H3K4me3 of PML knockdown cells.Our ndings ll the knowledge gap and help to explain the con icting data regarding the role of PML's role in tumorigenesis, which we attribute to the limited understanding of the distinct roles and abundance of different PML spliced isoforms.Importantly, our study elucidates the underlying molecular mechanism by which PML1 promotes the proliferation and stemness of ER + breast cancer cells by regulating the stemness gene expression through the recruitment of WDR5 and establishing the H3K4me3 mark.
Contrasting to previous reports that PML4 interacts and inhibits Myc transcription activity [40], our data showed that PML1 positively regulates MYC expression and that Myc protein binds to ~ 94% of PMLbound promoters, underscoring the critical role of Myc in recruiting PML to promoters and promoting cancer cell stemness.A retrospective study of ER + breast tumors also suggested that the MYC gene ampli cation might contribute to endocrine therapy resistance [41][42][43].These observations suggest that PML1 and Myc work together to promote endocrine therapy resistance and highlight the potential of targeting the PML1-Myc axis as a therapeutic strategy for overcoming endocrine therapy resistance in ER + breast cancer.Future research is needed to elucidate additional mechanisms by which PML1 promotes endocrine therapy resistance, including identifying other potential players.
Our study raises several important questions that warrant further investigation.For example, it is unclear how alternative splicing controls the abundance of different PML isoforms and whether this regulation is a general mechanism that operates across different cancer types.Furthermore, our ndings suggest that alternative splicing is a critical mechanism regulating tumorigenesis, highlighting the need for further research and a potential strategy to treat breast cancer by targeting aberrant alternative splicing.These ndings provide important insights into the complex regulation of PML isoforms and their role in breast cancer and lay the groundwork for future investigations into the molecular mechanisms that drive tumorigenesis.
Our study highlights the importance of nucleoplasmic PML, including chromatin-bound PML, in regulating transcription.By interrogating and combining public datasets, we identi ed over 12,000 PMLbinding sites, primarily found in gene promoters.Moreover, PML proteins associate with more than 70% of ER-bound promoters, and loss of PML had little or no effect on ER associations with the promoters, suggesting that PML is recruited to chromatin by sequence-speci c transcription factors, such as Myc and ER.
Our data also demonstrate that PML1 promotes transcriptional activation, as evidenced by its requirement for the enrichment of H3K4me3 (~ 88%) and the recruitment of WDR5, MLL1, and MLL2 on PML-bound promoters.It is worth noting that Myc binds WDR5 [44], and ER interacts with MLL2 [45], implying that WDR5 may have a broader role in regulating transcriptional activation beyond breast tumors.Previous reports suggest that WDR5 expression is a prognostic factor in breast cancer outcomes [46] and a potential therapeutic target [47].Recent investigations have also linked WDR5 to GBM stemness [48], indicating that it may be a potential target for treating this type of cancer.Overall, our study highlights the importance of WDR5 in PML1-mediated gene expression to promote breast tumor growth and stemness and suggests that targeting the PML1-WDR5 axis may be a promising therapeutic strategy for various cancers.

Cell culture
The HEK293T and MCF-7 cell lines were procured from the American Type Culture Collection (ATCC) and cultured on tissue culture plastic, employing Dulbecco's Modi ed Eagle's medium (DMEM) enriched with 10% fetal bovine serum (FBS) and 50 units/ml Penicillin-Streptomycin Solution (P/S).T47D and ZR-75-1 cells (also from ATCC) were nurtured in RPMI-1640 medium supplemented with 10% FBS and 50 units/ml P/S.In the case of T47D cells, an additional 5 µg/ml insulin was introduced into the medium.Mouse embryonic broblast (MEF) cells were generated in-house and cultured in DMEM supplemented with 10% FBS and 50 units/ml P/S.All cell lines were maintained at 37°C in a 5% CO2 incubator.Transient transfections were performed using Lipofectamine 2000 (Thermo Fisher, #11668019) following the manufacturer's instructions.
Flow cytometry MCF-7 and ZR-75-1 cells were dissociated, antibody-labeled (1-2 ug per 10 6 cells x 1h), and resuspended in 1X PBS as previously described [49].The ALDEFLUOR assay was performed following the manufacturer's instructions, followed by ow cytometry using a BD Accuri C6 Plus Flow Cytometer (BD Biosciences) with the electronic gating set according to cells stained with the corresponding Control (DEAB).

Tumorsphere assays
Cells were subjected to limiting dilution in a 96-well Ultra-Low Attachment Microplate (Corning, AZ, USA, # 3474) in MammoCult Human Medium Kit.The presence of tumorspheres was evaluated after ten days, and the data were analyzed and plotted using the ELDA software (http://bioinf.Wehi.edu.au/software/elda/index.html) [50].Experiments were performed in six replicates, and results from three independent experiments were analyzed.

Gene Set Enrichment Analysis (GSEA)
The PML-KD mRNA expression pro le was analyzed by GSEA using GSEAv4.3.2 software.Signatures M2573, M2156, and M6506 were used to enrich breast LIM_MAMMARY_STEM_CELL_UP(33), DUTERTRE_ESTRADIOL_RESPONSE_24HR_UP [35], and DANG_MYC_TARGETS_UP [51], respectively.All signature les for this analysis were obtained from the GSEA website (www.broadinstitute.org/gsea/).Enrichment plots are used to visualize GSEA results.Enrichment scores (ES) and normalized p (NOM p) values were applied to the sorting pathways enriched after 1000 genome permutations above for analysis.

Statistical analysis
The difference in continuous measurements among groups will be determined using a t-test (two groups) assuming unequal variance or ANOVA (more than two groups) followed by Tukey pair-wise comparison procedure.Differences between groups were considered statistically signi cant at values of p ≤ 0.05.Data were depicted as the mean ± SD, using ***p < 0.001 as signi cance criteria.p < 0.05 and p < 0.01 are designated by * and **, respectively.The likelihood ratio test and Chi-square test were used to assess the signi cance.

Declarations
Figure 1 PML1 is the predominant isoform in HR+ BC cells and patients.A-B, Relative abundance of eight PML protein-coding isoforms (UCSC genome browser, hg38) in normal breast (A) and ER+ breast cancer tissues (B).The nomenclatures of each isoform, de ned by a unique exon and may include more than one sub-isoform, are previously described 59 .C, A correlation of PML1 mRNA levels with survival rates in luminal BC.Patients whose PML1 mRNA ratio is at the top 30% (high, N=196) or bottom 30% of all patients were evaluated for outcomes.D, PML protein abundance is elevated in ER+ breast tumors.E, The structure of PML gene (top) and exon-encoded domains (bottom) in PML1 and PML4.Antigens for panPML and PML1-speci c antibodies are indicated.PML1 is the largest isoform.F, MCF-7 cell lysates expressing HA-PML1 or HA-PML4 probed with HA (lanes 1-3), pan-PML (lanes 4-6), or PML1-speci c antibodies (lanes 7-9).G, PML1 is the predominant isoform in ER+ breast cancer cells.A panPML antibody was used to detect all PML protein isoforms.Figure 4 PML1 promotes tumor growth fulvestrant resistance of MCF-7 cells.A. HA-PML1 stably expressing MCF7 cells (left) generated larger tumors (right) following injection of the same number of viable tumor cells.Images representing tumor size from MCF-7 cells expressing PML1 and vector.B,Quanti cation of tumor growth in mice injected with PML1-overexpressing or empty vector control cells was performed with a sample size of N=10 in each group.C, The western blot showing PML1 overexpression in tumors harvested from mice after 12 weeks of growth.D, The effect of PML1 on stemness gene expression in tumors was assessed with a sample size of N=9 in each group.E, Tumor size was quanti ed at weeks 0 and 8 in mice bearing PML1 or empty vector tumors after fulvestrant treatment, with a sample size of N=7-9 for each group.The data were analyzed using Two-way ANOVA.Heatmaps show representative data from triplicate experiments, while meta-plots illustrate outcomes from triplicate experiments.B,ChIP-seq tracks reveal H3K4me3 distribution on JAG1, KLF4, MYC, SNAI1, and YAP1 genes, with and without PML-knockdown, while genomic tracks depict aggregated outcomes from triplicate experiments.C,Loss of PML signi cantly reduces the H3K4me3 mark.D, PML1, not PML4, restores H3K4me3 marks on BCSC-related gene promoters in PMLknockdown cells.E-G, PML1 is required for the associations of WDR5 (E), MLL1 (F), and MLL2 (G) with the stemness gene promoters.H-J, Loss of WDR5 reduces the expression of the stemness genes (H) and the H3K4me3 (I) mark on their promoters but has little or no effect on PML associations with these gene promoters (J).The data were analyzed using Two-way ANOVA.Each experiment was performed with N=3 in each group.

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