Pioneer and PRDM transcription factors coordinate bivalent epigenetic states to safeguard cell fate.

Pioneer transcription factors (TFs) regulate cell fate by establishing transcriptionally primed and active states. However, cell fate control requires the coordination of both lineage-specific gene activation and repression of alternative-lineage programs, a process that is poorly understood. Here, we demonstrate that the pioneer TF FOXA coordinates with PRDM1 TF to recruit nucleosome remodeling and deacetylation (NuRD) complexes and Polycomb repressive complexes (PRCs), which establish highly occupied, accessible nucleosome conformation with bivalent epigenetic states, thereby preventing precocious and alternative-lineage gene expression during human endoderm differentiation. Similarly, the pioneer TF OCT4 coordinates with PRDM14 to form bivalent enhancers and repress cell differentiation programs in human pluripotent stem cells, suggesting that this may be a common and critical function of pioneer TFs. We propose that pioneer and PRDM TFs coordinate to safeguard cell fate through epigenetic repression mechanisms.

A new Prdm1-Cre line is suitable for studying the second heart field development.

The second heart field (SHF) plays a pivotal role in heart development, particularly in outflow tract (OFT) morphogenesis and septation, as well as in the expansion of the right ventricle (RV). Two mouse Cre lines, the Mef2c-AHF-Cre (Mef2c-Cre) and Isl1-Cre, have been widely used to study the SHF development. However, Cre activity is triggered not only in the SHF but also in the RV in the Mef2c-Cre mice, and in the Isl1-Cre mice, Cre activation is not SHF-specific. Therefore, a more suitable SHF-Cre line is desirable for better understanding SHF development. Here, we generated and characterized the Prdm1-Cre knock-in mice. In comparison with Mef2c-Cre mice, the Cre activity is similar in the pharyngeal and splanchnic mesoderm, and in the OFT of the Prdm1-Cre mice. Nonetheless, it was noticed that Cre expression is largely reduced in the RV of Prdm1-Cre mice compared to the Mef2c-Cre mice. Furthermore, we deleted Hand2, Nkx2-5, Pdk1 and Tbx20 using both Mef2c-Cre and Prdm1-Cre mice to study OFT morphogenesis and septation, making a comparison between these two Cre lines. New insights were obtained in understanding SHF development including differentiation into cardiomyocytes in the OFT using Prdm1-Cre mice. In conclusion, we found that Prdm1-Cre mouse line is a more appropriate tool to monitor SHF development, while the Mef2c-Cre mice are excellent in studying the role and function of the SHF in OFT morphogenesis and septation.

Inhibition of USP7 enhances CD8+ T cell activity in liver cancer by suppressing PRDM1-mediated FGL1 upregulation.

Lymphocyte activation gene 3 (LAG3), an immune checkpoint molecule expressed on activated T cells, functions as a negative regulator of immune responses. Persistent antigen exposure in the tumor microenvironment results in sustained LAG3 expression on T cells, contributing to T cell dysfunction. Fibrinogen-like protein 1 (FGL1) has been identified as a major ligand of LAG3, and FGL1/LAG3 interaction forms a novel immune checkpoint pathway that results in tumor immune evasion. In addition, ubiquitin-specific peptidase 7 (USP7) plays a crucial role in cancer development. In this study we investigated the role of USP7 in modulation of FGL1-mediated liver cancer immune evasion. We showed that knockdown of USP7 or treatment with USP7 inhibitor P5091 suppressed liver cancer growth by promoting CD8+ T cell activity in Hepa1-6 xenograft mice and in HepG2 or Huh7 cells co-cultured with T cells, whereas USP7 overexpression produced the opposite effect. We found that USP7 upregulated FGL1 in HepG2 and Huh7 cells by deubiquitination of transcriptional factor PR domain zinc finger protein 1 (PRDM1), which transcriptionally activated FGL1, and attenuated the CD8+ T cell activity, leading to the liver cancer growth. Interestingly, USP7 could be transcriptionally stimulated by PRDM1 as well in a positive feedback loop. P5091, an inhibitor of USP7, was able to downregulate FGL1 expression, thus enhancing CD8+ T cell activity. In an immunocompetent liver cancer mouse model, the dual blockade of USP7 and LAG3 resulted in a superior antitumor activity compared with anti-LAG3 therapy alone. We conclude that USP7 diminishes CD8+ T cell activity by a USP7/PRDM1 positive feedback loop on FGL1 production in liver cancer; USP7 might be a promising target for liver cancer immunotherapy.

PRDM1 promotes the ferroptosis and immune escape of thyroid cancer by regulating USP15-mediated SELENBP1 deubiquitination.

BACKGROUND: The deubiquitinating enzyme Ubiquitin-specific peptidase 15 (USP15) is upregulated in various cancers and promotes tumor progression by increasing the expression of several oncogenes. This project is designed to explore the role and mechanism of USP15 in thyroid cancer (TC) progression. METHODS: Selenium-binding protein 1 (SELENBP1), USP15, CCL2/5, CXCL10/11, IL-4, and TGF-ß1 mRNA levels were detected using real-time quantitative polymerase chain reaction (RT-qPCR). SELENBP1, USP15, GPX4, IL-10, Arg-1, Granzyme B, TNF-α, and PR domain zinc finger protein 1 (PRDM1) protein levels were examined by western blot assay. Fe+ level, malondialdehyde (MDA), and lipid-ROS levels were determined using special kits. The proportion of CD11b+CD206+ positive cells was detected using a flow cytometry assay. The role of SELENBP1 on TC cell growth was examined using a xenograft tumor model in vivo. After GeneMANIA prediction, the interaction between USP15 and SELENBP1 was verified using Co-immunoprecipitation (CoIP) assay. The binding between PRDM1 and USP15 promoter was predicted by JASPAR and validated using Chromatin immunoprecipitation (ChIP) and dual-luciferase reporter assays. RESULTS: SELENBP1 was increased in TC subjects and cell lines, and its knockdown repressed TC cell proliferation, migration, invasion, immune escape, and induced ferroptosis in vitro, as well as blocked tumor growth in vivo. In mechanism, USP15 interacted with SELENBP1 and maintained its stabilization by removing ubiquitin. Meanwhile, the upregulation of USP15 was induced by the transcription factor PRDM1. CONCLUSION: USP15 transcriptionally mediated by PRDM1 might boost TC cell malignant behaviors through deubiquitinating SELENBP1, providing a promising therapeutic target for TC treatment.

Precocious expression of Blimp1 in B cells causes autoimmune disease with increased self-reactive plasma cells.

The transcription factor Blimp1 is not only an essential regulator of plasma cells, but also a risk factor for the development of autoimmune disease in humans. Here, we demonstrate in the mouse that the Prdm1 (Blimp1) gene was partially activated at the chromatin and transcription level in early B cell development, although mature Prdm1 mRNA did not accumulate due to posttranscriptional regulation. By analyzing a mouse model that facilitated ectopic Blimp1 protein expression throughout B lymphopoiesis, we could demonstrate that Blimp1 impaired B cell development by interfering with the B cell gene expression program, while leading to an increased abundance of plasma cells by promoting premature plasmablast differentiation of immature and mature B cells. With progressing age, these mice developed an autoimmune disease characterized by the presence of autoantibodies and glomerulonephritis. Hence, these data identified ectopic Blimp1 expression as a novel mechanism, through which Blimp1 can act as a risk factor in the development of autoimmune disease.

Simultaneous deletion of Prdm1 and Vsx2 enhancers in the retina alters photoreceptor and bipolar cell fate specification, yet differs from deleting both genes.

The transcription factor OTX2 is required for photoreceptor and bipolar cell formation in the retina. It directly activates the transcription factors Prdm1 and Vsx2 through cell type-specific enhancers. PRDM1 and VSX2 work in opposition, such that PRDM1 promotes photoreceptor fate and VSX2 bipolar cell fate. To determine how OTX2+ cell fates are regulated in mice, we deleted Prdm1 and Vsx2 or their cell type-specific enhancers simultaneously using a CRISPR/Cas9 in vivo retina electroporation strategy. Double gene or enhancer targeting effectively removed PRDM1 and VSX2 protein expression. However, double enhancer targeting favored bipolar fate outcomes, whereas double gene targeting favored photoreceptor fate. Both conditions generated excess amacrine cells. Combined, these fate changes suggest that photoreceptors are a default fate outcome in OTX2+ cells and that VSX2 must be present in a narrow temporal window to drive bipolar cell formation. Prdm1 and Vsx2 also appear to redundantly restrict the competence of OTX2+ cells, preventing amacrine cell formation. By taking a combinatorial deletion approach of both coding sequences and enhancers, our work provides new insights into the complex regulatory mechanisms that control cell fate choice.

Exploring the putative role of PRDM1 and PRDM2 transcripts as mediators of T lymphocyte activation.

BACKGROUND: T cell activation and programming from their naïve/resting state, characterized by widespread modifications in chromatin accessibility triggering extensive changes in transcriptional programs, is orchestrated by several cytokines and transcription regulators. PRDM1 and PRDM2 encode for proteins with PR/SET and zinc finger domains that control several biological processes, including cell differentiation, through epigenetic regulation of gene expression. Different transcripts leading to main protein isoforms with (PR +) or without (PR-) the PR/SET domain have been described. Although many studies have established the critical PRDM1 role in hematopoietic cell differentiation, maintenance and/or function, the single transcript contribution has not been investigated before. Otherwise, very few evidence is currently available on PRDM2. Here, we aimed to analyze the role of PRDM1 and PRDM2 different transcripts as mediators of T lymphocyte activation. METHODS: We analyzed the transcription signature of the main variants from PRDM1 (BLIMP1a and BLIMP1b) and PRDM2 (RIZ1 and RIZ2) genes, in human T lymphocytes and Jurkat cells overexpressing PRDM2 cDNAs following activation through different signals. RESULTS: T lymphocyte activation induced an early increase of RIZ2 and RIZ1 followed by BLIMP1b increase and finally by BLIMP1a increase. The "first" and the "second" signals shifted the balance towards the PR- forms for both genes. Interestingly, the PI3K signaling pathway modulated the RIZ1/RIZ2 ratio in favor of RIZ1 while the balance versus RIZ2 was promoted by MAPK pathway. Cytokines mediating different Jak/Stat signaling pathways (third signal) early modulated the expression of PRDM1 and PRDM2 and the relationship of their different transcripts confirming the early increase of the PR- transcripts. Different responses of T cell subpopulations were also observed. Jurkat cells showed that the acute transient RIZ2 increase promoted the balancing of PRDM1 forms towards BLIMP1b. The stable forced expression of RIZ1 or RIZ2 induced a significant variation in the expression of key transcription factors involved in T lymphocyte differentiation. The BLIMP1a/b balance shifted in favor of BLIMP1a in RIZ1-overexpressing cells and of BLIMP1b in RIZ2-overexpressing cells. CONCLUSIONS: This study provides the first characterization of PRDM2 in T-lymphocyte activation/differentiation and novel insights on PRDM1 and PRDM2 transcription regulation during initial activation phases.

The role of PRDM1 gene polymorphism in the progression of hepatocellular carcinoma in Egyptian patients.

In Egypt, hepatocellular carcinoma (HCC) ranks as the second largest cause of cancer mortality. PRDM1 is a tumor suppressor gene essential for the differentiation and regulation activity of plasma cells and T cells. It plays a vital role in T cell exhaustion of chronic viral infection and HCC. We aimed to study the role of PRDM1 gene polymorphism in HCV and HCC-related to hepatitis C virus (HCV) progress in Egyptians. The case-control study included 300 Egyptian patients divided into 100 HCC,100 cirrhosis, and 100 control. Laboratory investigations were done for some clinicopathological biomarkers, including liver function tests, complete blood picture, serum alpha-fetoprotein, and hepatitis markers (HBsAg, anti-HCV-Ab). TaqMan allelic discrimination assay technique was used to genotype PRDM1 gene polymorphism. Multivariant analysis (logistic regression) assessed the association between the polymorphisms with HCC progression and designed the suggested model for HCC prediction. The frequencies of the G allele and GG phenotype in the control group were significantly more than that of the HCC and cirrhosis group. However, GA genotypes and A allele frequencies significantly increased in the HCC patients than in cirrhosis and controls. In addition, by comparing the HCC group and the non-HCC group (controls and cirrhotic patients), the subjects carrying AA or GA have 2 times more risk to develop HCC than those carrying GG genotypes (odd ratio = 2.045% and 95% confidence interval are (1.123-3.722) p = 0.019). Multivariate analysis results suggested a model of Aspartate transaminase (AST), Albumin, and PRDM1 polymorphism to predict the risk of HCC in Egyptians. In addition, PRDM1 polymorphism has an association with HCC prognosis (tumor size). For PRDM1 polymorphism, the A allele and AA might be considered as HCC-related to the HCV risk factor. In addition, AST, Albumin, and PRDM1 polymorphism predict the risk of HCC in Egyptians Therefore, the polymorphism might help in identifying the susceptible Egyptians to HCC. In addition, polymorphism might have a role in HCC prognosis.

PRDM1 controls the sequential activation of neural, neural crest and sensory progenitor determinants.

During early embryogenesis, the ectoderm is rapidly subdivided into neural, neural crest and sensory progenitors. How the onset of lineage determinants and the loss of pluripotency markers are temporally and spatially coordinated in vivo is still debated. Here, we identify a crucial role for the transcription factor PRDM1 in the orderly transition from epiblast to defined neural lineages in chick. PRDM1 is initially expressed broadly in the entire epiblast, but becomes gradually restricted as cell fates are specified. We find that PRDM1 is required for the loss of some pluripotency markers and the onset of neural, neural crest and sensory progenitor specifier genes. PRDM1 directly activates their expression by binding to their promoter regions and recruiting the histone demethylase Kdm4a to remove repressive histone marks. However, once neural lineage determinants become expressed, they in turn repress PRDM1, whereas prolonged PRDM1 expression inhibits neural, neural crest and sensory progenitor genes, suggesting that its downregulation is necessary for cells to maintain their identity. Therefore, PRDM1 plays multiple roles during ectodermal cell fate allocation.

Reprogramming of Chinese hamster ovary cells towards enhanced protein secretion.

The deficient secretory phenotype of Chinese hamster ovary (CHO) cells is a major limitation for high-level production of biopharmaceuticals, particularly for those with complex molecular architectures and post-translational modifications. To improve CHO cell secretory capacity, we recently engineered CHO cell hosts to overexpress BLIMP1 (CHOB), in a cell engineering strategy that transformed the cellular machinery and led to significantly higher product yields and cell-specific productivities for different rproteins. Here, as a follow-up to our previous study, we developed new CHO cell hosts that co-overexpress BLIMP1 and XBP1s ( CHOBX ), two transcription factors that together drive the professional secretory function of antibody-producing plasma cells. We found that the CHOBX cells presented an improved performance over that of CHOB cells, with better product yields and cell-specific productivities for a recombinant IgG1 and a 'difficult-to-express' EPO-Fc fusion protein. These improvements in the CHOBX-derived cell lines resulted from a series of physiological and metabolic changes due to the synergetic co-expression of BLIMP1 and XBP1s. Firstly, cells presented an inhibited cell growth and arrested cell cycle in G1/G0 phase, features that were directly linked to BLIMP1 expression levels. Secondly, cells increased protein translation (both overall and recombinant protein), expanded the endoplasmic reticulum and improved their capacity to secrete protein more effectively. Lastly, cells showed a metabolic profile favouring energy production, with a pronounced lactate switch and increased consumption of amino acids. This study highlights the value of transcription factors for reprogramming CHO cells towards a desired phenotype, offering the potential to engineer cells with new functionalities for enhanced manufacturing of recombinant therapeutic proteins.

Dysregulated MDR1 by PRDM1/Blimp1 Is Involved in the Doxorubicin Resistance of Non-Germinal Center B-Cell-Like Diffuse Large B-Cell Lymphoma.

INTRODUCTION: The chemoresistance mechanism of diffuse large B-cell lymphoma (DLBCL) is still poorly understood, and patient prognosis remains unsatisfactory. This study aimed to investigate drug resistance mechanisms in non-germinal center B-cell-like (non-GCB) DLBCL. METHODS: Doxorubicin (DOX)-resistant OCI-Ly3 cells were generated through long-term incubation of cells in a medium with gradually increasing DOX concentrations. The expression levels of genes related to drug metabolism were determined using a functional gene grouping polymerase chain reaction (PCR) array. Drug-resistant proteins were identified using bioinformatics, and molecular association networks were subsequently generated. The association and mechanism of key genes were determined using a dual-luciferase reporter assay System and chromatin immunoprecipitation (ChIP). The expression of drug-resistant genes and target genes was then measured using Western blotting and immunohistochemistry. The correlation between gene expressions was analyzed using Spearman's rank correlation coefficient. RESULTS: Using the PCR array, MDR1 was identified as the key gene that regulates DOX resistance in OCI-Ly3/DOX-A100, a non-GCB DLBCL cell line. The dual-luciferase reporter assay system demonstrated that MDR1 transcription could be inhibited by PRDM1. ChIP results showed that PRDM1 had the ability to bind to the promoter region (-1,132 to -996) of MDR1. In OCI-Ly3/DOX cells, NF-κB activity and PRDM1 expression decreased with an increase in drug-resistant index, whereas MDR1 expression increased with enhanced drug resistance. Immunohistochemical analysis revealed that relative MDR1 expression was higher than that of PRDM1 in human DLBCL tissue samples. A negative correlation was observed between MDR1 and PRDM1. CONCLUSION: In non-GCB DLBCL cells, NF-κB downregulates PRDM1 and thereby promotes MDR1 transcription by terminating PRDM1-induced transcriptional inhibition of MDR1. Such a mechanism may explain the reason for disease recurrence in non-GCB DLBCL after R-CHOP or combined CHOP with bortezomib treatment. Our findings may provide a potential therapeutic strategy for reducing drug resistance in patients with DLBCL.

Prdm1 overexpression causes a photoreceptor fate-shift in nascent, but not mature, bipolar cells.

The transcription factors Prdm1 (Blimp1) and Vsx2 (Chx10) work downstream of Otx2 to regulate photoreceptor and bipolar cell fates in the developing retina. Mice that lack Vsx2 fail to form bipolar cells while Prdm1 mutants form excess bipolars at the direct expense of photoreceptors. Excess bipolars in Prdm1 mutants appear to derive from rods, suggesting that photoreceptor fate remains mutable for some time after cells become specified. Here we tested whether bipolar cell fate is also plastic during development. To do this, we created a system to conditionally misexpress Prdm1 at different stages of bipolar cell development. We found that Prdm1 blocks bipolar cell formation if expressed before the fate choice decision occurred. When we misexpressed Prdm1 just after the decision to become a bipolar cell was made, some cells were reprogrammed into photoreceptors. In contrast, Prdm1 misexpression in mature bipolar cells did not affect cell fate. We also provide evidence that sustained misexpression of Prdm1 was selectively toxic to photoreceptors. Our data show that bipolar fate is malleable, but only for a short temporal window following fate specification. Prdm1 and Vsx2 act by stabilizing photoreceptor and bipolar fates in developing OTX2+ cells of the retina.

Transcription factor NF-κB promotes acute lung injury via microRNA-99b-mediated PRDM1 down-regulation.

Acute lung injury (ALI), is a rapidly progressing heterogenous pulmonary disorder that possesses a high risk of mortality. Accumulating evidence has implicated the activation of the p65 subunit of NF-κB [NF-κB(p65)] activation in the pathological process of ALI. microRNAs (miRNAs), a group of small RNA molecules, have emerged as major governors due to their post-transcriptional regulation of gene expression in a wide array of pathological processes, including ALI. The dysregulation of miRNAs and NF-κB activation has been implicated in human diseases. In the current study, we set out to decipher the convergence of miR-99b and p65 NF-κB activation in ALI pathology. We measured the release of pro-inflammatory cytokines (IL-1ß, IL-6, and TNFα) in bronchoalveolar lavage fluid using ELISA. MH-S cells were cultured and their viability were detected with cell counting kit 8 (CCK8) assays. The results showed that miR-99b was up-regulated, while PRDM1 was down-regulated in a lipopolysaccharide (LPS)-induced murine model of ALI. Mechanistic investigations showed that NF-κB(p65) was enriched at the miR-99b promoter region, and further promoted its transcriptional activity. Furthermore, miR-99b targeted PRDM1 by binding to its 3'UTR, causing its down-regulation. This in-creased lung injury, as evidenced by increased wet/dry ratio of mouse lung, myeloperoxidase activity and pro-inflammatory cytokine secretion, and enhanced infiltration of inflammatory cells in lung tissues. Together, our findings indicate that NF-κB(p65) promotion of miR-99b can aggravate ALI in mice by down-regulating the expression of PRDM1.

Overexpression of transcription factor BLIMP1/prdm1 leads to growth inhibition and enhanced secretory capacity in Chinese hamster ovary cells.

Chinese hamster ovary (CHO) cells present inherent limitations for processing and secretion of large amounts of recombinant proteins, especially for those requiring complex post-translational processing. To tackle these limitations, we engineered CHO host cells (CHOK1 and CHOS) to overexpress the transcription factor BLIMP1/prdm1 (a master regulator of the highly-secreting phenotype of antibody-producing plasma cells), generating novel CHO cell lines (referred to as CHOB). The CHOB cell lines exhibited decreased cell densities, prolonged stationary phase and arrested cell cycle in G1/G0 phase but simultaneously had significantly greater product titre for recombinant IgG1 (> 2-fold increase) coupled with a significantly greater cell-specific productivities (> 3-fold increase). We demonstrated that the improved productive phenotype of CHOB cells resulted from a series of changes to cell physiology and metabolism. CHOB cells showed a significantly greater ER size and increased protein synthesis and secretion capacity compared to control cells. In addition, CHOB cells presented a metabolic profile that favoured energy production to support increased recombinant protein production. This study indicated that a cell engineering approach based on BLIMP1 expression offers great potential for improving the secretory capacity of CHO cell hosts utilised for manufacture of recombinant biopharmaceuticals. Our findings also provides a greater understanding of the relationship between cell growth and productivity, valuable generic information for improving productive phenotypes for CHO cell lines during industrial cell line development.

PRDM1 silences stem cell-related genes and inhibits proliferation of human colon tumor organoids.

PRDM1 is a tumor suppressor that plays an important role in B and T cell lymphomas. Our previous studies demonstrated that PRDM1ß is a p53-response gene in human colorectal cancer cells. However, the function of PRDM1ß in colorectal cancer cells and colon tumor organoids is not clear. Here we show that PRDM1ß is a p53-response gene in human colon organoids and that low PRDM1 expression predicts poor survival in colon cancer patients. We engineered PRDM1 knockouts and overexpression clones in RKO cells and characterized the PRDM1-dependent transcript landscapes, revealing that both the α and ß transcript isoforms repress MYC-response genes and stem cell-related genes. Finally, we show that forced expression of PRDM1 in human colon cancer organoids prevents the formation and growth of colon tumor organoids in vitro. These results suggest that p53 may exert tumor-suppressive effects in part through a PRDM1-dependent silencing of stem cell genes, depleting the size of the normal intestinal stem cell compartment in response to DNA damage.

Pax5 Negatively Regulates Osteoclastogenesis through Downregulation of Blimp1.

Paired box protein 5 (Pax5) is a crucial transcription factor responsible for B-cell lineage specification and commitment. In this study, we identified a negative role of Pax5 in osteoclastogenesis. The expression of Pax5 was time-dependently downregulated by receptor activator of nuclear factor kappa B (RANK) ligand (RANKL) stimulation in osteoclastogenesis. Osteoclast (OC) differentiation and bone resorption were inhibited (68.9% and 48% reductions, respectively) by forced expression of Pax5 in OC lineage cells. Pax5 led to the induction of antiosteoclastogenic factors through downregulation of B lymphocyte-induced maturation protein 1 (Blimp1). To examine the negative role of Pax5 in vivo, we generated Pax5 transgenic (Pax5Tg) mice expressing the human Pax5 transgene under the control of the tartrate-resistant acid phosphatase (TRAP) promoter, which is expressed mainly in OC lineage cells. OC differentiation and bone resorption were inhibited (54.2-76.9% and 24.0-26.2% reductions, respectively) in Pax5Tg mice, thereby contributing to the osteopetrotic-like bone phenotype characterized by increased bone mineral density (13.0-13.6% higher), trabecular bone volume fraction (32.5-38.1% higher), trabecular thickness (8.4-9.0% higher), and trabecular number (25.5-26.7% higher) and decreased trabecular spacing (9.3-10.4% lower) compared to wild-type control mice. Furthermore, the number of OCs was decreased (48.8-65.3% reduction) in Pax5Tg mice. These findings indicate that Pax5 plays a negative role in OC lineage specification and commitment through Blimp1 downregulation. Thus, our data suggest that the Pax5-Blimp1 axis is crucial for the regulation of RANKL-induced osteoclastogenesis.

Alternative splicing of medaka bcl6aa and its repression by Prdm1a and Prdm1b.

Bcl6 and Prdm1 (Blimp1) are a pair of transcriptional factors that repressing each other in mammals. Prdm1 represses the expression of bcl6 by binding a cis-element of the bcl6 gene in mammals. The homologs of Bcl6 and Prdm1 have been identified in teleost fish. However, whether these two factors regulate each other in the same way in fish like that in mammals is not clear. In this study, the regulation of bcl6aa by Prdm1 was investigated in medaka. The mRNA of bcl6aa has three variants (bcl6aaX1-X3) at the 5'-end by alternative splicing detected by RT-PCR. The three variants can be detected in adult tissues and developing embryos of medaka. Prdm1a and prdm1b are expressed in the tissues and embryos where and when bcl6aa is expressed. The expression of prdm1a was high while the expression of bcl6aa was low, and vice versa, detected in the spleen after stimulation with LPS or polyI:C. In vitro reporter assay indicated that bcl6aa could be directly repressed by both Prdm1a and Prdm1b in a dosage-dependent manner. After mutation of the key base, G, of all predicted binding sites in the core promoter region of bcl6aa, the repression by Prdm1a and/or Prdm1b disappeared. The binding site of Prdm1 in the bcl6aa gene is GAAAA(T/G). These results indicate that both Prdm1a and Prdm1b directly repress the expression of bcl6aa by binding their binding sites where the 5'-G is critical in medaka fish.

Hypomethylation of PRDM1 is associated with recurrent pregnancy loss.

Recurrent pregnancy loss (RPL) rates have continued to rise during the last few decades, yet the underlying mechanisms remain poorly understood. An emerging area of interest is the mediation of gene expression by DNA methylation during early pregnancy. Here, genome-wide DNA methylation from placental villi was profiled in both RPL patients and controls. Subsequently, differentially expressed genes were analysed for changes in gene expression. Many significant differentially methylated regions (DMRs) were identified near genes dysregulated in RPL including PRDM1. Differentially expressed genes were enriched in immune response pathways indicating that abnormal immune regulation contributes to RPL. Integrated analysis of DNA methylome and transcriptome demonstrated that the expression level of PRDM1 is fine-tuned by DNA methylation. Specifically, hypomethylation near the transcription start site of PRDM1 can recruit other transcription factors, like FOXA1 and GATA2, leading to up-regulation of gene expression and resulting in changes to trophoblast cell apoptosis and migration. These phenotypic differences may be involved in RPL. Overall, our study provides new insights into PRDM1-dependent regulatory effects during RPL and suggests both a mechanistic link between changes in PRDM1 expression, as well as a role for PRDM1 methylation as a potential biomarker for RPL diagnosis.

Loss of prdm1a accelerates melanoma onset and progression.

Melanoma is an aggressive, deadly skin cancer derived from melanocytes, a neural crest cell derivative. Melanoma cells mirror the developmental program of neural crest cells in that they exhibit the same gene expression patterns and utilize similar cellular mechanisms, including increased cell proliferation, epithelial-mesenchymal transition, and migration. Here we studied the role of neural crest regulator PRDM1 in melanoma onset and progression. In development, Prdm1a functions to promote neural crest progenitor fate, and in melanoma, we found that PRDM1 has reduced copy number and is recurrently deleted in both zebrafish and humans. When examining expression of neural crest and melanocyte development genes, we show that sox10 progenitor expression is high in prdm1a-/- mutants, while more differentiated melanocyte markers are reduced, suggesting that normally Prdm1a is required for differentiation. Data mining of human melanoma datasets indicates that high PRDM1 expression in human melanoma is correlated with better patient survival and decreased PRDM1 expression is common in metastatic tumors. When one copy of prdm1a is lost in the zebrafish melanoma model Tg(mitfa:BRAFV600E );p53-/- ;prdm1a+/- , melanoma onset occurs more quickly, and the tumors that form have a larger area with increased expression of sox10. These data demonstrate a novel role for PRDM1 as a tumor suppressor in melanoma.

Genetic association of polymorphisms at the intergenic region between PRDM1 and ATG5 with hepatitis B virus infection in Han Chinese patients.

Chronic hepatitis B virus (HBV) infection is related to chronic hepatitis, cirrhosis, and hepatocellular carcinoma (HCC), and the interplay between the virus and host immune response leads to different outcomes of the infection. PR domain zinc finger protein 1 (PRDM1) and autophagy-related protein 5 (ATG5) are involved in immune response and HBV infection. An intergenic region between PRDM1 and ATG5 (PRDM1-ATG5 region) has been identified, and single-nucleotide polymorphisms (SNPs) in this region were shown to be involved in immune regulation. This study investigated the functionally relevant rs548234, rs6937876, and rs6568431 polymorphisms at the PRDM1-ATG5 region in a Han Chinese population (403 patients with chronic HBV infection [171 chronic hepatitis, 119 cirrhosis, and 113 HCC], 70 infection resolvers, and 196 healthy controls). The frequencies of the rs6568431 allele A in HBV patients (P = .005) and genotype CA in infection resolvers (P = .005) were significantly higher than in healthy controls. In the dominant model, HCC patients had significantly higher frequencies of rs548234 genotypes CC + TC than cirrhosis patients (P = .009). Rs548234 was an independent factor for HCC in comparison with either cirrhosis (P = .005) or all chronic HBV infection without HCC (P = .018). Functional annotation showed evidence of the role of the SNPs in gene regulation. In conclusion, through this study it is revealed for the first time that rs6568431 may be associated with susceptibility to HBV infection and that rs548234 may be associated with HCC risk in chronic HBV infection, supporting the presence of HBV-related disease-causing regulatory polymorphisms in the PRDM1-ATG5 intergenic region.