Poly (ADP-ribose) polymerase 1 promotes HuR/ELAVL1 cytoplasmic localization and inflammatory gene expression by regulating p38 MAPK activity.

Post-transcriptional regulation of cytokine/chemokine mRNA turnover is critical for immune processes and contributes to the mammalian cellular response to diverse inflammatory stimuli. The ubiquitous RNA-binding protein human antigen R (HuR) is an integral regulator of inflammation-associated mRNA fate. HuR function is regulated by various post-translational modifications that alter its subcellular localization and ability to stabilize target mRNAs. Both poly (ADP-ribose) polymerase 1 (PARP1) and p38 mitogen-activated protein kinases (MAPKs) have been reported to regulate the biological function of HuR, but their specific regulatory and crosstalk mechanisms remain unclear. In this study, we show that PARP1 acts via p38 to synergistically promote cytoplasmic accumulation of HuR and stabilization of inflammation-associated mRNAs in cells under inflammatory conditions. Specifically, p38 binds to auto-poly ADP-ribosylated (PARylated) PARP1 resulting in the covalent PARylation of p38 by PARP1, thereby promoting the retention and activity of p38 in the nucleus. In addition, PARylation of HuR facilitates the phosphorylation of HuR at the serine 197 site mediated by p38, which then increases the translocation of HuR to the cytoplasm, ultimately stabilizing the inflammation-associated mRNA expression at the post-transcriptional level.

SATB1, senescence and senescence-related diseases.

Aging leads to an accumulation of cellular mutations and damage, increasing the risk of senescence, apoptosis, and malignant transformation. Cellular senescence, which is pivotal in aging, acts as both a guard against cellular transformation and as a check against cancer progression. It is marked by stable cell cycle arrest, widespread macromolecular changes, a pro-inflammatory profile, and altered gene expression. However, it remains to be determined whether these differing subsets of senescent cells result from unique intrinsic programs or are influenced by their environmental contexts. Multiple transcription regulators and chromatin modifiers contribute to these alterations. Special AT-rich sequence-binding protein 1 (SATB1) stands out as a crucial regulator in this process, orchestrating gene expression by structuring chromatin into loop domains and anchoring DNA elements. This review provides an overview of cellular senescence and delves into the role of SATB1 in senescence-related diseases. It highlights SATB1's potential in developing antiaging and anticancer strategies, potentially contributing to improved quality of life and addressing aging-related diseases.

Cell-Penetrating Peptide TAT-HuR-HNS3 Suppresses Proinflammatory Gene Expression via Competitively Blocking Interaction of HuR with Its Partners.

Proinflammatory cytokines/chemokines are commonly regulated by RNA-binding proteins at posttranscriptional levels. Human Ag R (HuR)/embryonic lethal abnormal vision-like 1 (ELAVL1) is one of the well-characterized RNA-binding proteins that increases the stability of short-lived mRNAs, which encode proinflammatory mediators. HuR employs its nucleocytoplasmic shuttling sequence (HNS) domain, interacting with poly(ADP-ribose) polymerase 1 (PARP1), which accounts for the enhanced poly-ADP-ribosylation and cytoplasmic shuttling of HuR. Also by using its HNS domain, HuR undergoes dimerization/oligomerization, underlying the increased binding of HuR with proinflammatory cytokine/chemokine mRNAs and the disassociation of the miRNA-induced silencing complex from the targets. Therefore, competitively blocking the interactions of HuR with its partners may suppress proinflammatory mediator production. In this study, peptides derived from the sequence of the HuR-HNS domain were synthesized, and their effects on interfering HuR interacting with PARP1 and HuR itself were analyzed. Moreover, cell-penetrating TAT-HuR-HNS3 was delivered into human and mouse cells or administered into mouse lungs with or without exposure of TNF-α or LPS. mRNA levels of proinflammatory mediators as well as neutrophil infiltration were evaluated. We showed that TAT-HuR-HNS3 interrupts HuR-PARP1 interaction and therefore results in a lowered poly-ADP-ribosylation level and decreased cytoplasmic distribution of HuR. TAT-HuR-HNS3 also blocks HuR dimerization and promotes Argonaute 2-based miRNA-induced silencing complex binding to the targets. Moreover, TAT-HuR-HNS3 lowers mRNA stability of proinflammatory mediators in TNF-α-treated epithelial cells and macrophages, and it decreases TNF-α-induced inflammatory responses in lungs of experimental animals. Thus, TAT-HuR-HNS3 is a promising lead peptide for the development of inhibitors to treat inflammation-related diseases.

Long-term follow-up of the cognitive function in children after intravitreal ranibizumab for retinopathy of prematurity.

PURPOSE: To evaluate the long-term cognitive function in children treated with intravitreal ranibizumab (IVR) for retinopathy of prematurity(ROP), and the impact of IVR on the growth and ocular development. METHODS: In this retrospective study, the premature children aged 4 to 9 years who received monotherapy of IVR (IVR group, n = 25) or monotherapy of laser photocoagulation (LP) (LP group, n = 33) for ROP, and the same age premature children with no ROP (Control group, n = 26) were enrolled from 2020 to 2022 in the pediatric fundus clinic of Shenzhen Eye Hospital. Main outcome measures were full-scale intelligence quotient (FSIQ) and index score using the Chinese version of the Wechsler intelligence scale for children-fourth edition (WISC-IV) and Wechsler preschool and primary scale of intelligence-fourth edition (WPPSI-IV). All children were examined and analyzed for growth and ocular development by recording the height, weight, head circumference, spherical equivalent (SE), best corrected visual acuity (BCVA) and axial length (AL). RESULTS: There were 17 children in IVR group, 17 in LP group, and 11 in Control group who received the WISC-IV assessment. There were no significant differences in FSIQ, verbal comprehension index, perceptual reasoning index, working memory index, processing speed index, general ability index and cognitive efficiency index among the three groups. There were 8 children in IVR group, 16 in LP group, and 15 in Control group who received the WPPSI-IV assessment. There were no significant differences in FSIQ, verbal comprehension index, visuospatial index, fluid reasoning index, working memory index, non-verbal index, general ability index and cognitive efficiency index among the three groups. There was no significant difference in BCVA among the three groups (P = 0.74), however, there is an increase for AL in IVR group when compared with LP group (22.60 ± 0.58 vs. 22.13 ± 0.84, P = 0.003), and the ROP patients of IVR group have a significant increase in the AL compared to the Control group(22.60 ± 0.58 vs. 22.03 ± 0.71, P < 0.0001). CONCLUSIONS: Children with a history of IVR have a similar cognitive function outcomes compared to those with a history of LP or were premature without ROP. ROP children with a history of IVR has longer AL than those treated with LP.

Sex-Specific Behavioral and Molecular Responses to Maternal Lipopolysaccharide-Induced Immune Activation in a Murine Model: Implications for Neurodevelopmental Disorders.

Maternal immune activation (MIA) during pregnancy has been increasingly recognized as a critical factor in the development of neurodevelopmental disorders, with potential sex-specific impacts that are not yet fully understood. In this study, we utilized a murine model to explore the behavioral and molecular consequences of MIA induced by lipopolysaccharide (LPS) administration on embryonic day 12.5. Our findings indicate that male offspring exposed to LPS exhibited significant increases in anxiety-like and depression-like behaviors, while female offspring did not show comparable changes. Molecular analyses revealed alterations in pro-inflammatory cytokine levels and synaptic gene expression in male offspring, suggesting that these molecular disruptions may underlie the observed behavioral differences. These results emphasize the importance of considering sex as a biological variable in studies of neurodevelopmental disorders and highlight the need for further molecular investigations to understand the mechanisms driving these sex-specific outcomes. Our study contributes to the growing evidence that prenatal immune challenges play a pivotal role in the etiology of neurodevelopmental disorders and underscores the potential for sex-specific preventative approaches of MIA.

CXC chemokine ligand-10 promotes the accumulation of monocyte-like myeloid-derived suppressor cells by activating p38 MAPK signaling under tumor conditions.

CXC chemokine ligand-10 (CXCL10) is a small (10 kDa) secretory protein in the CXC subfamily of cytokines. CXCL10 has been reported to play an important role in antitumor immunity as a chemotactic factor. Tumor development is always accompanied by the formation of an immunosuppressive tumor microenvironment, and the role of CXCL10 in tumor immunosuppression remains unclear. Here, we reported that CXCL10 expression was significantly upregulated in mice with melanoma, and tumor cells secreted large amounts of CXCL10. Myeloid-derived suppressor cells (MDSCs) are an important part of the immunosuppressive tumor microenvironment. Our results showed that CXCL10 promoted the proliferation of monocyte-like (mo)-MDSCs by activating the p38 MAPK signaling pathway through CXCR3, which led to the abnormal accumulation of mo-MDSCs under tumor conditions. This finding provides a new understanding of the mechanism by which a tumor-induced immunosuppressive microenvironment forms and suggests that CXCL10 could be a potential intervention target for slowing tumor progression.

The key players of parthanatos: opportunities for targeting multiple levels in the therapy of parthanatos-based pathogenesis.

Parthanatos is a form of regulated cell death involved in the pathogenesis of many diseases, particularly neurodegenerative disorders, such as Parkinson's disease, Alzheimer's disease, Huntington's disease, and amyotrophic lateral sclerosis. Parthanatos is a multistep cell death pathway cascade that involves poly (ADP-ribose) polymerase 1 (PARP-1) overactivation, PAR accumulation, PAR binding to apoptosis-inducing factor (AIF), AIF release from the mitochondria, nuclear translocation of the AIF/macrophage migration inhibitory factor (MIF) complex, and MIF-mediated large-scale DNA fragmentation. All the key players in the parthanatos pathway are pleiotropic proteins with diverse functions. An in-depth understanding of the structure-based activity of the key factors, and the biochemical mechanisms of parthanatos, is crucial for the development of drugs and therapeutic strategies. In this review, we delve into the key players of the parthanatos pathway and reveal the multiple levels of therapeutic opportunities for treating parthanatos-based pathogenesis.

Poly(ADP-ribosyl)ation enhances HuR oligomerization and contributes to pro-inflammatory gene mRNA stabilization.

Poly(ADP-ribosyl)ation (PARylation) is an important post-translational modification mainly catalyzed by poly-ADP-ribose polymerase 1 (PARP1). In addition to having important roles in DNA damage detection and repair, it functions in gene expression regulation, especially at the posttranscriptional level. Embryonic lethal abnormal vision-like 1/human antigen R (ELAVL/HuR), a canonical 3' untranslated region AU-rich element-binding protein, is a crucial mRNA-stabilizing protein that protects target mRNAs from RNA-destabilizing protein- or microRNA-induced silencing complex (miRISC)-mediated degradation. Additionally, in some cases, HuR itself either promotes or suppresses translation. Here, we demonstrated that in response to inflammatory stimuli, the PARylation of HuR, mostly at the conserved D226 site, by PARP1 increased the formation of the HuR oligomer/multimer, and HuR oligomerization promoted the disassociation of miRISC and stabilized the pro-inflammatory gene mRNAs. The prevention of PARP1 activation or HuR oligomerization attenuated lipopolysaccharide-induced inflammatory gene expression and the airway recruitment of neutrophils in mouse lungs. The present study verified a novel mechanism of PARP1 and HuR PARylation in the RNA stability regulation, increasing our understanding of how PARP1 regulates gene expression.

Refractive and biometrical characteristics of children with retinopathy of prematurity who received laser photocoagulation or intravitreal ranibizumab injection.

PURPOSE: To investigate the refractive and biometrical developments of children with retinopathy of prematurity (ROP) who received laser photocoagulation (LP) or intravitreal ranibizumab injection as treatment. METHODS: This case-control study involved cases with Zone II Stage 3 ROP. Fourteen children (28 eyes) who received single LP were included in the laser group, and 14 children (27 eyes) who received single intravitreal ranibizumab injection were included in the injection group. The mean age at operation was 37.00±1.72 and 36.36±1.66 weeks for the laser and injection groups, respectively (P=0.161), and refraction measurements and biometry were performed at the mean age of 5.00±1.63 and 5.00±0.94 years for the laser and injection groups, respectively (P=1.000). Spherical equivalent (SE) after mydriatic refraction and best corrected visual acuity (BCVA) were measured by refraction test. Central corneal thickness (CCT), anterior corneal surface curvature and curvature radius, anterior chamber depth (ACD), lens thickness (LT) and axial length (AL) were measured by biometry using the IOL Master700 biometric instrument (Carl Zeiss Meditec AG). The biometrical images were reanalysed using a self-developed program in MATLAB (R2016a, MathWorks, Inc.) to obtain additional eye parameters, including the curvatures of the posterior cornea and the anterior and posterior surfaces of the lens. SPSS (V.23.0) was used for statistical analysis. Independent sample t test was used to compare the eyeball biological and refractive state measures of the two groups, and Pearson correlation coefficient was used to evaluate the correlation between SE and the biological parameters. RESULTS: 1. (1) Cornea-related parameters: CCT (0.54±0.04mm vs 0.55±0.02mm, P>0.05), anterior corneal surface curvature radius (7.56±0.26 mm vs 7.67±0.43mm, P>0.05) and posterior corneal surface curvature radius (6.82±0.27mm vs 6.79±0.42mm, P>0.05). (2) ACD (3.21 ± 0.25mm vs 3.22 ± 0.19mm, P>0.05). (3) Lens-related parameters: anterior lens surface curvature radius (10.04±0.89mm vs 9.82±1.08mm, P>0.05), posterior lens surface curvature radius (5.49±0.55mm vs 5.92±0.73mm, P<0.05) and LT (3.80±0.14mm vs 3.59±0.16mm, P<0.05). (4) AL (21.82±1.07 vs 22.68±1.61, P<0.05). (5) Parameters related to refractive state: SE (-2.43±3.56 vs -0.53±3.12, P<0.05) and BCVA (log MAR, 0.17±0.14 vs 0.21±0.18, P>0.05). 2. (1) The SE of children in the laser group was positively correlated with LT (r=0.438, P<0.05), negatively correlated with ACD (r=-0.437, P<0.05) and had no significant correlation with other eyeball biological indicators (P>0.05). (2) The SE of children in the injection group was negatively correlated with AL (r=-0.537, P<0.05), positively correlated with CCT (r=0.455, P<0.05) and had no significant correlation with other eyeball biological indicators (P>0.05). CONCLUSION: LP and intravitreal ranibizumab injection as ROP treatments produce myopic refraction with increased degree of myopia in children who received LP than in children who received ranibizumab injection. The increased myopia after LP is due to the increases in LT and posterior lens curvature and a shallow ACD.

Enzymatically inactive OGG1 binds to DNA and steers base excision repair toward gene transcription.

8-Oxoguanine DNA glycosylase1 (OGG1)-initiated base excision repair (BER) is the primary pathway to remove the pre-mutagenic 8-oxo-7,8-dihydroguanine (8-oxoG) from DNA. Recent studies documented 8-oxoG serves as an epigenetic-like mark and OGG1 modulates gene expression in oxidatively stressed cells. For this new role of OGG1, two distinct mechanisms have been proposed: one is coupled to base excision, while the other only requires substrate binding of OGG1--both resulting in conformational adjustment in the adjacent DNA sequences providing access for transcription factors to their cis-elements. The present study aimed to examine if BER activity of OGG1 is required for pro-inflammatory gene expression. To this end, Ogg1/OGG1 knockout/depleted cells were transfected with constructs expressing wild-type (wt) and repair-deficient mutants of OGG1. OGG1's promoter enrichment, oxidative state, and gene expression were examined. Results showed that TNFα exposure increased levels of oxidatively modified cysteine(s) of wt OGG1 without impairing its association with promoter and facilitated gene expression. The excision deficient K249Q mutant was even a more potent activator of gene expression; whereas, mutant OGG1 with impaired substrate recognition/binding was not. These data suggested the interaction of OGG1 with its substrate at regulatory regions followed by conformational adjustment in the adjacent DNA is the primary mode to modulate inflammatory gene expression.

c-Abl-Mediated Tyrosine Phosphorylation of PARP1 Is Crucial for Expression of Proinflammatory Genes.

Poly(ADP-ribosyl)ation is a rapid and transient posttranslational protein modification mostly catalyzed by poly(ADP-ribose) polymerase-1 (PARP1). Fundamental roles of activated PARP1 in DNA damage repair and cellular response pathways are well established; however, the precise mechanisms by which PARP1 is activated independent of DNA damage, and thereby playing a role in expression of inflammatory genes, remain poorly understood. In this study, we show that, in response to LPS or TNF-α exposure, the nonreceptor tyrosine kinase c-Abl undergoes nuclear translocation and interacts with and phosphorylates PARP1 at the conserved Y829 site. Tyrosine-phosphorylated PARP1 is required for protein poly(ADP-ribosyl)ation of RelA/p65 and NF-κB-dependent expression of proinflammatory genes in murine RAW 264.7 macrophages, human monocytic THP1 cells, or mouse lungs. Furthermore, LPS-induced airway lung inflammation was reduced by inhibition of c-Abl activity. The present study elucidated a novel signaling pathway to activate PARP1 and regulate gene expression, suggesting that blocking the interaction of c-Abl with PARP1 or pharmaceutical inhibition of c-Abl may improve the outcomes of PARP1 activation-mediated inflammatory diseases.

Lung resided monocytic myeloid-derived suppressor cells contribute to premetastatic niche formation by enhancing MMP-9 expression.

In cancer patients, the prevalence of myeloid-derived suppressor cells (MDSCs) is correlated with the degree of malignancy. In the present study, we investigated the role of circulating M-MDSCs in premetastatic niche formation using a mouse syngeneic tumor model and found that there was an increased frequency of M-MDSCs in the peripheral blood of tumor-bearing mice. M-MDSCs tracking and lung tissue histological analyses revealed that the malignant conditions promote the residence of circulating M-MDSCs and increased tumor cell arrest in the lungs. We further found that MMP-9 expression was increased in the circulating M-MDSCs and the administration of an MMP-9 inhibitor suppressed M-MDSCs transplantation-induced tumor cell arrest in the lung. Therefore, our findings suggest that the expansion of circulating M-MDSCs during tumor progression contributes to premetastatic niche formation by increasing MMP-9 expression.

Novel insights into PARPs in gene expression: regulation of RNA metabolism.

Poly(ADP-ribosyl)ation (PARylation) is an important post-translational modification in which an ADP-ribose group is transferred to the target protein by poly(ADP-riboses) polymerases (PARPs). Since the discovery of poly-ADP-ribose (PAR) 50 years ago, its roles in cellular processes have been extensively explored. Although research initially focused on the functions of PAR and PARPs in DNA damage detection and repair, our understanding of the roles of PARPs in various nuclear and cytoplasmic processes, particularly in gene expression, has increased significantly. In this review, we discuss the current advances in understanding the roles of PARylation with a particular emphasis in gene expression through RNA biogenesis and processing. In addition to updating PARP's significance in transcriptional regulation, we specifically focus on how PARPs and PARylation affect gene expression, especially inflammation-related genes, at the post-transcriptional levels by modulating RNA processing and degrading. Increasing evidence suggests that PARP inhibition is a promising treatment for inflammation-related diseases besides conventional chemotherapy for cancer.

CtIP promotes G2/M arrest in etoposide-treated HCT116 cells in a p53-independent manner.

Acquired resistance to cytotoxic antineoplastic agents is a major clinical challenge in tumor therapy; however, the mechanisms involved are still poorly understood. In this study, we show that knockdown of CtIP, a corepressor of CtBP, promotes cell proliferation and alleviates G2/M phase arrest in etoposide (Eto)-treated HCT116 cells. Although the expression of p21 and growth arrest and DNA damage inducible α (GADD45a), which are important targets of p53, was downregulated in CtIP-deficient HCT116 cells, p53 deletion did not affect G2/M arrest after Eto treatment. In addition, the phosphorylation levels of Ser317 and Ser345 in Chk1 and of Ser216 in CDC25C were lower in CtIP-deficient HCT116 cells than in control cells after Eto treatment. Our results indicate that CtIP may enhance cell sensitivity to Eto by promoting G2/M phase arrest, mainly through the ATR-Chk1-CDC25C pathway rather than the p53-p21/GADD45a pathway. The expression of CtIP may be a useful biomarker for predicting the drug sensitivity of colorectal cancer cells.

Chemokine (C-X-C motif) ligand 1 and CXCL2 produced by tumor promote the generation of monocytic myeloid-derived suppressor cells.

Accumulation of myeloid-derived suppressor cells (MDSC) in tumor-bearing hosts is a hallmark of tumor-associated inflammation, which is thought to be a barrier to immunosurveillance. Multiple factors secreted by tumor cells and tumor stromal cells are reported to be involved in promoting the expansion of MDSC. Herein, we showed that s.c. inoculation of tumor cells and i.v. injection of tumor-conditioned medium increased the number of MDSC. Subsequent investigation elucidated that chemokine (C-X-C motif) ligand 1 (CXCL1) and CXCL2, which were originally characterized as the chemokines of neutrophils, specifically promoted the expansion of monocytic MDSC (mo-MDSC), a subtype of MDSC, in the presence of granulocyte-macrophage colony-stimulating factor. Depletion of CXCL1 or CXCL2 in B16F10 cells or in B16F10-bearing mice noticeably decreased the generation of mo-MDSC in bone marrow. Moreover, we found that, in addition to the tumor cells, tumor-infiltrated CD11b+ myeloid cells also expressed CXCL1 and CXCL2. Furthermore, CXCL1- and CXCL2-induced increase of mo-MDSC was not correlated with chemotaxis, proliferation or apoptosis of mo-MDSC. These findings show a novel role of CXCL1 and CXCL2 in promoting mo-MDSC generation by favoring the differentiation of bone marrow cells in tumor-bearing conditions, which suggests that inhibition of CXCL1 and CXCL2 could decrease mo-MDSC generation and improve host immunosurveillance.

The establishment of methods for free PAR generation and PAR reader detection.

Poly (ADP-ribose) polymerase 1 (PARP1) is a DNA damage sensor that catalyzes the poly (ADP-ribose) (PAR) onto a variety of target proteins, such as histones, DSB repair factors and PARP1 itself under consumption of NAD+. Besides, PARP1 can affect a variety of proteins in noncovalent modification manner to carry out specific cellular functions. Here, we established a method to generate non-radiolabeled free PAR by PARG moderately cleaving PAR from autoPARylated PARP1, and utilized dot-blot assay to determine the interaction between free PAR and interested proteins. The methods to generate free PAR and detect the noncovalent interactions between proteins and free PAR are nonradioactive and convenient, which will facilitate the studies to explore the significance of PAR reading in various biological processes.

ANXA2 could act as a moderator of EGFR-directed therapy resistance in triple negative breast cancer.

Triple negative breast cancer (TNBC) patients cannot benefit from EGFR-targeted therapy even though the EGFR is highly expressed, because patients exhibit resistance to these drugs. Unfortunately, the molecular mechanisms remain relatively unknown. ANXA2, highly expressed in invasive breast cancer cells, is closely related with poor prognosis, and acts as a molecular switch to EGFR activation. In this study, MDA-MB-231 cells and MCF7 cells were used. Our results showed that ANXA2 expression is inversely correlated with cell sensitivity to gefitinib. Knockdown of ANXA2 expression in MDA-MB-231 cells increased the gefitinib induced cell death. When ANXA2 was overexpressed in MCF7 cells, the gefitinib induced cell death was decreased. Furthermore, we demonstrated that phosphorylation of ANXA2 at Tyr23 is negatively correlated with the sensitivity of TNBC to gefitinib. Altogether, our results suggest a new role of ANXA2 in regulating sensitivity of TNBC MDA-MB-231 cells to the EGFR inhibitor gefitinib.

Oxidized Guanine Base Lesions Function in 8-Oxoguanine DNA Glycosylase-1-mediated Epigenetic Regulation of Nuclear Factor κB-driven Gene Expression.

A large percentage of redox-responsive gene promoters contain evolutionarily conserved guanine-rich clusters; guanines are the bases most susceptible to oxidative modification(s). Consequently, 7,8-dihydro-8-oxoguanine (8-oxoG) is one of the most abundant base lesions in promoters and is primarily repaired via the 8-oxoguanine DNA glycosylase-1 (OOG1)-initiated base excision repair pathway. In view of a prompt cellular response to oxidative challenge, we hypothesized that the 8-oxoG lesion and the cognate repair protein OGG1 are utilized in transcriptional gene activation. Here, we document TNFα-induced enrichment of both 8-oxoG and OGG1 in promoters of pro-inflammatory genes, which precedes interaction of NF-κB with its DNA-binding motif. OGG1 bound to 8-oxoG upstream from the NF-κB motif increased its DNA occupancy by promoting an on-rate of both homodimeric and heterodimeric forms of NF-κB. OGG1 depletion decreased both NF-κB binding and gene expression, whereas Nei-like glycosylase-1 and -2 had a marginal effect. These results are the first to document a novel paradigm wherein the DNA repair protein OGG1 bound to its substrate is coupled to DNA occupancy of NF-κB and functions in epigenetic regulation of gene expression.

Recruited monocytic myeloid-derived suppressor cells promote the arrest of tumor cells in the premetastatic niche through an IL-1ß-mediated increase in E-selectin expression.

The tumor premetastatic niche initiated by primary tumors is constructed by multiple molecular factors and cellular components and provides permissive condition that allows circulating tumor cells to successfully metastasize. Myeloid-derived suppressor cells (MDSCs), a population of immature cells in pathological conditions, play a critical role in the formation of the premetastatic niche. However, few researches are focused on the function of monocytic MDSCs (mo-MDSCs), a subtype of MDSCs, in the construction of the niche. Here, we show that the number of mo-MDSCs is significantly increased in the premetastatic lungs of tumor-bearing mice, thus promoting tumor cell arrest and metastasis. Before the arrival of tumor cells, the lung-recruited mo-MDSCs produced IL-1ß, thereby increasing E-selectin expression and promoting tumor cell arrest on endothelial cells. Depletion of mo-MDSCs in the premetastatic lungs decreased IL-1ß production, resulting in reduced E-selectin expression. In addition, compared with alveolar macrophages and interstitial macrophages, mo-MDSCs were the major source of IL-1ß expression in the premetastatic lungs. Cytokine array analyses and transwell experiments revealed that CCL12 recruits mo-MDSCs to premetastatic lungs. CCL12 knockdown in tumor-bearing mice significantly decreased mo-MDSC infiltration into the premetastatic lungs, leading to reduced E-selectin expression. Overall, the permissive conditions produced by the infiltrated mo-MDSCs correlated with increased tumor cell arrest and metastasis. These results reveal a novel role of mo-MDSCs in constructing the premetastatic niche. Thus, inhibition of mo-MDSCs infiltration may change the premetastatic niche to normal condition and attenuate tumor metastasis.

BRG1 promotes the repair of DNA double-strand breaks by facilitating the replacement of RPA with RAD51.

DNA double-strand breaks (DSBs) are a type of lethal DNA damage. The repair of DSBs requires tight coordination between the factors modulating chromatin structure and the DNA repair machinery. BRG1, the ATPase subunit of the chromatin remodelling complex Switch/Sucrose non-fermentable (SWI/SNF), is often linked to tumorigenesis and genome instability, and its role in DSB repair remains largely unclear. In the present study, we show that BRG1 is recruited to DSB sites and enhances DSB repair. Using DR-GFP and EJ5-GFP reporter systems, we demonstrate that BRG1 facilitates homologous recombination repair rather than nonhomologous end-joining (NHEJ) repair. Moreover, the BRG1-RAD52 complex mediates the replacement of RPA with RAD51 on single-stranded DNA (ssDNA) to initiate DNA strand invasion. Loss of BRG1 results in a failure of RAD51 loading onto ssDNA, abnormal homologous recombination repair and enhanced DSB-induced lethality. Our present study provides a mechanistic insight into how BRG1, which is known to be involved in chromatin remodelling, plays a substantial role in the homologous recombination repair pathway in mammalian cells.