The intracellular NADH level regulates atrophic nonunion pathogenesis through the CtBP2-p300-Runx2 transcriptional complex

Suppression of DNMT2/3 by proinflammatory cytokines inhibits CtBP1/2-dependent genes to promote the occurrence of atrophic nonunion

Failure of bone healing after fracture often results in nonunion, but the underlying mechanism of nonunion pathogenesis is poorly understood. Herein, we provide evidence to clarify that the inflammatory microenvironment of atrophic nonunion (AN) mice suppresses the expression levels of DNA methyltransferases 2 (DNMT2) and 3A (DNMT3a), preventing the methylation of CpG islands on the promoters of C-terminal binding protein 1/2 (CtBP1/2) and resulting in their overexpression. Increased CtBP1/2 acts as transcriptional corepressors that, along with histone acetyltransferase p300 and Runt-related transcription factor 2 (Runx2), suppress the expression levels of six genes involved in bone healing: BGLAP (bone gamma-carboxyglutamate protein), ALPL (alkaline phosphatase), SPP1 (secreted phosphoprotein 1), COL1A1 (collagen 1a1), IBSP (integrin binding sialoprotein), and MMP13 (matrix metallopeptidase 13). We also observe a similar phenomenon in osteoblast cells treated with proinflammatory cytokines or treated with a DNMT inhibitor (5-azacytidine). Forced expression of DNMT2/3a or blockage of CtBP1/2 with their inhibitors can reverse the expression levels of BGLAP/ALPL/SPP1/COL1A1/IBSP/MMP13 in the presence of proinflammatory cytokines. Administration of CtBP1/2 inhibitors in fractured mice can prevent the incidence of AN. Thus, we demonstrate that the downregulation of bone healing genes dependent on proinflammatory cytokines/DNMT2/3a/CtBP1/2-p300-Runx2 axis signaling plays a critical role in the pathogenesis of AN. Disruption of this signaling may represent a new therapeutic strategy to prevent AN incidence after bone fracture.

Accumulation of advanced glycation end products promotes atrophic nonunion incidence in mice through a CtBP1/2-dependent mechanism

Atrophic nonunion (AN) is a complex and poorly understood pathological condition resulting from impaired fracture healing. Advanced glycation end products (AGEs) have been implicated in the pathogenesis of several bone disorders, including osteoporosis and osteoarthritis. However, the role of AGEs in the development of AN remains unclear. This study found that mice fed a high-AGE diet had a higher incidence of atrophic nonunion (AN) compared to mice fed a normal diet following tibial fractures. AGEs induced two C-terminal binding proteins (CtBPs), CtBP1 and CtBP2, which were necessary for the development of AN in response to AGE accumulation. Feeding a high-AGE diet after fracture surgery in CtBP1/2-/- and RAGE-/- (receptor of AGE) mice did not result in a significant occurrence of AN. Molecular investigation revealed that CtBP1 and CtBP2 formed a heterodimer that was recruited by histone deacetylase 1 (HDAC1) and runt-related transcription factor 2 (Runx2) to assemble a complex. The CtBP1/2-HDAC1-Runx2 complex was responsible for the downregulation of two classes of bone development and differentiation genes, including bone morphogenic proteins (BMPs) and matrix metalloproteinases (MMPs). These findings demonstrate that AGE accumulation promotes the incidence of AN in a CtBP1/2-dependent manner, possibly by modulating genes related to bone development and fracture healing. These results provide new insights into the pathogenesis of AN and suggest new therapeutic targets for its prevention and treatment.

Vitamin D deficiency triggers intrinsic apoptosis by impairing SPP1-dependent antiapoptotic signaling in chronic hematogenous osteomyelitis

Chronic hematogenous osteomyelitis (CHOM) is a common bone disease characterized by the development of sequestra after bacterial infection. Emerging evidence has shown that vitamin D (VD) deficiency raises the risk of osteomyelitis, but the underlying mechanisms remain obscure. Here, we establish a CHOM model in VD diet-deficient mice by intravenous inoculation of Staphylococcus aureus. Whole-genome microarray analyses using osteoblast cells isolated from sequestra reveal significant downregulation of SPP1 (secreted phosphoprotein 1). Molecular basis investigations show that VD sufficiency activates the VDR/RXR (VD receptor/retinoid X receptor) heterodimer to recruit NCOA1 (nuclear receptor coactivator 1) and transactivate SPP1 in healthy osteoblast cells. Secreted SPP1 binds to the cell surface molecule CD40 to activate serine/threonine-protein kinase Akt1, which then phosphorylates forkhead box O3a (FOXO3a), blocking FOXO3a-mediated transcription. By contrast, VD deficiency impairs the NCOA1-VDR/RXR-mediated overexpression of SPP1, leading to the inactivation of Akt1 and the accumulation of FOXO3a. FOXO3a then upregulates the expression of the apoptotic genes BAX (Bcl2-associated X-protein), BID (BH3 interacting death domain), and BIM (Bcl2-interacting mediator of cell death), to induce apoptosis. Administration of the NCOA1 inhibitor gossypol to the CHOM mice also promotes the occurrence of sequestra. VD supplementation can reactivate the SPP1-dependent antiapoptotic signaling and improve the outcomes of CHOM. Collectively, our data reveal that VD deficiency promotes bone destruction in CHOM by the removal of SPP1-dependent antiapoptotic signaling.

The promotive role of USP1 inhibition in coordinating osteogenic differentiation and fracture healing during nonunion

BACKGROUND

Nonunion is a failure of fracture healing and a major complication after fractures. Ubiquitin-specific protease 1 (USP1) is a deubiquitinase that involved in cell differentiation and cell response to DNA damage. Herein we investigated the expression, function and mechanism of USP1 in nonunion.

METHODS AND RESULTS

Clinical samples were used to detect the USP1 expression in nonunion. ML323 was selected to inhibit USP1 expression throughout the study. Rat models and mouse embryonic osteoblasts cells (MC3T3-E1) were used to investigate the effects of USP1 inhibition on fracture healing and osteogenesis in vivo and in vitro, respectively. Histological changes were examined by micro-computerized tomography (Micro-CT), hematoxylin & eosin (H&E) staining and Masson staining. Alkaline phosphatase (ALP) activity detection and alizarin red staining were used for osteogenic differentiation observation. The expression of related factors was detected by quantitative real-time PCR, western blot or immunohistochemistry (IHC). It was shown that USP1 was highly expressed in nonunion patients and nonunion rats. USP1 inhibition by ML323 promoted fracture healing in nonunion rats and facilitated the expression of osteogenesis-related factors and the signaling of PI3K/Akt pathway. In addition, USP1 inhibition accelerated osteogenic differentiation and promoting PI3K/Akt signaling in MC3T3-E1 cells.

CONCLUSIONS

USP1 inhibition plays a promotive role in coordinating osteogenic differentiation and fracture healing during nonunion. PI3K/Akt may be the downstream pathway of USP1.

Circ_CUX1/miR-130b-5p/p300 axis for parathyroid hormone-stimulation of Runx2 activity in rat osteoblasts: A combined bioinformatic and experimental approach

Parathyroid hormone (PTH) regulates the expression of bone remodeling genes by enhancing the activity of Runx2 in osteoblasts. p300, a histone acetyltransferase, acetylated Runx2 to activate the expression of its target genes. PTH stimulated the expression of p300 in rat osteoblastic cells. Increasing studies suggested the potential of non-coding RNAs (ncRNAs), such as microRNAs (miRNAs) and circular RNAs (circRNAs), in regulating gene expression under both physiological and pathological conditions. In this study, we hypothesized that PTH regulates Runx2 activity via ncRNAs-mediated p300 expression in rat osteoblastic cells. Bioinformatics and experimental approaches identified PTH-upregulation of miR-130b-5p and circ_CUX1 that putatively target p300 and miR-130b-5p, respectively. An antisense-mediated knockdown of circ_CUX1 was performed to determine the sponging activity of circ_CUX1. Knockdown of circ_CUX1 promoted miR-130b-5p activity and reduced p300 expression, resulting in decreased Runx2 acetylation in rat osteoblastic cells. Further, bioinformatics analysis identified the possible signaling pathways that regulate Runx2 activity and osteoblast differentiation via circ_CUX1/miR-130b-5p/p300 axis. The predicted circ_CUX1/miR-130b-5p/p300 axis might pave the way for better diagnostic and therapeutic approaches for bone-related diseases.

CtBP proteins transactivate matrix metalloproteinases and proinflammatory cytokines to mediate the pathogenesis of abdominal aortic aneurysm

Abdominal aortic aneurysm (AAA) is a life-threatening disorder that occurs in the aorta. The inflammatory thickness of the aneurysm wall and perianeurysmal fibrosis are two main causes of AAA pathogenesis; however, the molecular mechanisms involved in these two processes are still unclear. We discovered that C-terminal binding protein 1 (CtBP1) and CtBP2 were overexpressed in the aortas of AAA-model mice created by treatment with CaCl₂ and elastase. Molecular analyses revealed that the CtBP heterodimer couples with histone acetyltransferase p300 and transcription factor AP1 (activator protein 1) to transactivate a set of matrix metalloproteinases (MMPs, including MMP1a, 3, 7, 9, and 12) and proinflammatory cytokines, including interleukin-1 β (IL-1β), IL-6, and tumor necrosis factor-alpha (TNF-α). Knockdown of CtBPs or AP1 subunits or blockage of CtBPs with specific small molecule inhibitors significantly suppressed the in vitro expression of MMPs and proinflammatory cytokines. The administration of CtBP inhibitors in AAA-model mice also inhibited MMPs and proinflammatory cytokines, thereby improving the AAA outcome. Taken together, our results revealed a new regulatory mechanism involving MMPs and proinflammatory cytokines in the pathogenesis of AAA. This discovery suggests that targeting CtBPs may be a therapeutic strategy for AAA by attenuating the inflammatory response and matrix destruction.

Identifying novel interactions of the colon-cancer related APC protein with Wnt-pathway nuclear transcription factors

BACKGROUND

Colon cancer is often driven by mutations of the adenomatous polyposis coli (APC) gene, an essential tumor suppressor gene of the Wnt β-catenin signaling pathway. APC and its cytoplasmic interactions have been well studied. However, various groups have also observed its presence in the nucleus. Identifying novel interactions of APC in the Wnt pathway will provide an opportunity to understand APC's nuclear role better and ultimately identify potential cancer treatment targets.

METHODS

We used the all-vs-all sequencing (AVA-Seq) method to interrogate the interactome of protein fragments spanning most of the 60 Wnt β-catenin pathway proteins. Using protein fragments identified the interacting regions between the proteins with more resolution than a full-length protein approach. Pull-down assays were used to validate a subset of these interactions.

RESULTS

74 known and 703 novel Wnt β-catenin pathway protein-protein interactions were recovered in this study. There were 8 known and 31 novel APC protein-protein interactions. Novel interactions of APC and nuclear transcription factors TCF7, JUN, FOSL1, and SOX17 were particularly interesting and confirmed in validation assays.

CONCLUSION

Based on our findings of novel interactions between APC and transcription factors and previous evidence of APC localizing to the nucleus, we suggest APC may compete and repress CTNNB1. This would occur through APC binding to the transcription factors (JUN, FOSL1, TCF7) to regulate the Wnt signaling pathway including through enhanced marking of CTNNB1 for degradation in the nucleus by APC binding with SOX17. Additional novel Wnt β-catenin pathway protein-protein interactions from this study could lead researchers to novel drug designs for cancer.

Inflammation-dependent activation of NCOA2 associates with p300 and c-MYC/Max heterodimer to transactivate RUNX2-AS1 and mediate RUNX2 downstream bone differentiation genes in the pathology of septic nonunion

Septic nonunion (SN) is a common bone disorder caused by the failure of fracture healing. Local inflammation in fracture sites often causes SN; however, little is known about the molecular mechanisms of SN pathology. Herein, we identified a significant upregulation of the long non-coding RNA (lncRNA) RUNX2-AS1 (Runt-related Transcription Factor 2-Antisense 1) in the biopsies of SN patients. Overexpression or knockdown of RUNX2-AS1 in vitro could inhibit or induce, respectively, the expression of RUNX2 and RUNX2-downstream target genes, including ALPL (Alkaline Phosphatase), COL1A1 (Collagen Type I Alpha 1 Chain), IBSP (Integrin Binding Sialoprotein), MMP13 (Matrix Metallopeptidases), and SPP1 (Secreted Phosphoprotein 1), which are involved in bone differentiation. Mechanically, we demonstrated that a transcription factor c-MYC could assemble a transcriptional complex with its partner Max, a histone acetyltransferase p300, and nuclear receptor coactivator 2 (NCOA2), and this complex then bound to the promoter of RUNX2-AS1 to transactivate its expression. The mRNA and protein levels of NCOA2 were dose-dependently increased by treatment with lipopolysaccharide(LPS), a well-known inflammation trigger. LPS exposure increased the enrichment of the NCOA2-p300-c-MYC/Max complex on the RUNX2-AS1 promoter to activate its expression, thereby downregulating the expression of RUNX2 and RUNX2-downstream target genes. Depletion of NCOA2 reversed the expression of RUNX2-AS1, RUNX2, and RUNX2 target genes following LPS exposure. Taken together, our results demonstrate a new signaling pathway that contributes to the pathology of SN and may aid in preventing SN progression.

Biological and molecular profile of fracture non-union tissue: A systematic review and an update on current insights

Fracture non‐union represents a common complication, seen in 5%–10% of all acute fractures. Despite the enhancement in scientific understanding and treatment methods, rates of fracture non‐union remain largely unchanged over the years. This systematic review investigates the biological, molecular and genetic profiles of both (i) non‐union tissue and (ii) non–union‐related tissues, and the genetic predisposition to fracture non‐union. This is crucially important as it could facilitate earlier identification and targeted treatment of high‐risk patients, along with improving our understanding on pathophysiology of fracture non‐union. Since this is an update on our previous systematic review, we searched the literature indexed in PubMed Medline; Ovid Medline; Embase; Scopus; Google Scholar; and the Cochrane Library using Medical Subject Heading (MeSH) or Title/Abstract words (non‐union(s), non‐union(s), human, tissue, bone morphogenic protein(s) (BMPs) and MSCs) from August 2014 (date of our previous publication) to 2 October 2021 for non‐union tissue studies, whereas no date restrictions imposed on non–union‐related tissue studies. Inclusion criteria of this systematic review are human studies investigating the characteristics and properties of non‐union tissue and non–union‐related tissues, available in full‐text English language. Limitations of this systematic review are exclusion of animal studies, the heterogeneity in the definition of non‐union and timing of tissue harvest seen in the included studies, and the search term MSC which may result in the exclusion of studies using historical terms such as ‘osteoprogenitors’ and ‘skeletal stem cells’. A total of 24 studies (non‐union tissue: n = 10; non–union‐related tissues: n = 14) met the inclusion criteria. Soft tissue interposition, bony sclerosis of fracture ends and complete obliteration of medullary canal are commonest macroscopic appearances of non‐unions. Non‐union tissue colour and surrounding fluid are two important characteristics that could be used clinically to distinguish between septic and aseptic non‐unions. Atrophic non‐unions had a predominance of endochondral bone formation and lower cellular density, when compared against hypertrophic non‐unions. Vascular tissues were present in both atrophic and hypertrophic non‐unions, with no difference in vessel density between the two. Studies have found non‐union tissue to contain biologically active MSCs with potential for osteoblastic, chondrogenic and adipogenic differentiation. Proliferative capacity of non‐union tissue MSCs was comparable to that of bone marrow MSCs. Rates of cell senescence of non‐union tissue remain inconclusive and require further investigation. There was a lower BMP expression in non‐union site and absent in the extracellular matrix, with no difference observed between atrophic and hypertrophic non‐unions. The reduced BMP‐7 gene expression and elevated levels of its inhibitors (Chordin, Noggin and Gremlin) could potentially explain impaired bone healing observed in non‐union MSCs. Expression of Dkk‐1 in osteogenic medium was higher in non‐union MSCs. Numerous genetic polymorphisms associated with fracture non‐union have been identified, with some involving the BMP and MMP pathways. Further research is required on determining the sensitivity and specificity of molecular and genetic profiling of relevant tissues as a potential screening biomarker for fracture non‐unions.

Runx Transcription Factors in T Cells-What Is Beyond Thymic Development?

Runx proteins (also known as Runt-domain transcription factors) have been studied for a long time as key regulators of cellular differentiation. RUNX2 has been described as essential for osteogenesis, whereas RUNX1 and RUNX3 are known to control blood cell development during different stages of cell lineage specification. However, recent studies show evidence of complex relationships between RUNX proteins, chromatin-modifying machinery, the cytoskeleton and different transcription factors in various non-embryonic contexts, including mature T cell homeostasis, inflammation and cancer. In this review, we discuss the diversity of Runx functions in mature T helper cells, such as production of cytokines and chemokines by different CD4 T cell populations; apoptosis; and immunologic memory acquisition. We then briefly cover recent findings about the contribution of RUNX1, RUNX2 and RUNX3 to various immunologic diseases. Finally, we discuss areas that require further study to better understand the role that Runx proteins play in inflammation and immunity.

Non-union bone fractures

The human skeleton has remarkable regenerative properties, being one of the few structures in the body that can heal by recreating its normal cellular composition, orientation and mechanical strength. When the healing process of a fractured bone fails owing to inadequate immobilization, failed surgical intervention, insufficient biological response or infection, the outcome after a prolonged period of no healing is defined as non-union. Non-union represents a chronic medical condition not only affecting function but also potentially impacting the individual's psychosocial and economic well-being. This Primer provides the reader with an in-depth understanding of our contemporary knowledge regarding the important features to be considered when faced with non-union. The normal mechanisms involved in bone healing and the factors that disrupt the normal signalling mechanisms are addressed. Epidemiological considerations and advances in the diagnosis and surgical therapy of non-union are highlighted and the need for greater efforts in basic, translational and clinical research are identified.

The transrepression and transactivation roles of CtBPs in the pathogenesis of different diseases

Gene transcription is strictly controlled by transcriptional complexes, which are assemblies of transcription factors, transcriptional regulators, and co-regulators. Mammalian genomes encode two C-terminal-binding proteins (CtBPs), CtBP1 and CtBP2, which are both well-known transcriptional corepressors of oncogenic processes. Their overexpression in tumors is associated with malignant behavior, such as uncontrolled cell proliferation, migration, and invasion, as well as with an increase in the epithelial-mesenchymal transition. CtBPs coordinate with other transcriptional regulators, such as histone deacetylases (HDACs) and histone acetyltransferases (p300 and CBP [CREBP-binding protein]) that contain the PXDLS motif, and with transcription factors to assemble transcriptional complexes that dock onto the promoters of genes to initiate gene transcription. Emerging evidence suggests that CtBPs function as both corepressors and coactivators in different biological processes ranging from apoptosis to inflammation and osteogenesis. Therapeutic targeting of CtBPs or the interactions required to form transcriptional complexes has also shown promising effects in preventing disease progression. This review summarizes the most recent progress in the study of CtBP functions and therapeutic inhibitors in different biological processes. This knowledge may enable a better understanding of the complexity of the roles of CtBPs, while providing new insights into therapeutic strategies that target CtBPs.

A naturally derived small molecule PSM0537 targets the AF1Q-TCF4 interaction to suppress COX2 expression and inhibit cell proliferation and metastasis in osteosarcoma

ALL1 fused gene from chromosome 1q (AF1Q) functions as an oncogene in several types of cancers, but it has not been observed in osteosarcoma. In this study, we revealed that AF1Q was overexpressed in multiple osteosarcoma cell lines, and its expression level increased with the severity of tumor malignancy in osteosarcoma biopsies. AF1Q was coupled with the transcription factor T cell factor 4 (TCF4) to assemble a complex to bind to the promoter of cyclooxygenase 2 (COX2) and activate its expression. The individual knockdown of AF1Q, TCF4, or COX2 in osteosarcoma cell lines significantly decreased cell proliferation and invasion in vitro. The tumor xenograft model also indicated that the individual knockdown of AF1Q, TCF4, or COX2 could inhibit tumor growth and metastasis. On the basis of these promising results, we established an in vitro AlphaScreen method to identify the compounds that disrupted the AF1Q-TCF4 interaction in a naturally derived small molecule pool. We discovered a compound called PSM0537, which showed a strong ability to inhibit the AF1Q-TCF4 interaction at a low dose of half-maximal inhibitory concentration (IC₅₀) (210.3 ± 15.6 nM). The administration of PSM0537 in vitro and in vivo could dramatically inhibit cell proliferation, invasion, and metastasis. Collectively, our findings reveal that the AF1Q-TCF4 transcriptional complex controls the expression of COX2 and that targeting the AF1Q-TCF4 interaction with PSM0537 could inhibit tumor cell growth and metastasis. Our results provide a new path for chemotherapy of osteosarcoma.

RUNX2 promotes malignant progression in gastric cancer by regulating COL1A1

BACKGROUND

Runt-related transcription factor 2 (RUNX2) is an important gene that has been implicated in the progression of human cancer. Aberrant expression of RUNX2 predicts gastric cancer (GC) metastasis. However, the molecular mechanism of RUNX2 remains unknown.

OBJECTIVE

We hypothesize that RUNX2 promotes GC metastasis by regulating the extracellular matrix component collagen type I alpha 1 (COL1A1).

METHODS

The GEPIA database and immunohistochemical staining of 60 GC tissues were used to analyse the correlations between RUNX2 or COL1A1 expression and clinicopathological features, and the Kaplan-Meier method was used to evaluate survival. RT-PCR, western blotting and immunofluorescence were used to detect RUNX2 and COL1A1 expression in GC cells. Migration and invasion assays were performed to assess the influence of RUNX2 and COL1A1 on metastasis.

RESULTS

RUNX2 and COL1A1 were highly expressed at both the gene and protein levels in GC, and patients who were positive for RUNX2 and COL1A1 had shorter survival. RUNX2 and COL1A1 expression linearly correlated with each other (r= 0.15, p< 0.01) and with clinical stage and lymph node metastasis (p< 0.05). Overexpressing RUNX2in vitro enhanced COL1A1 expression and promoted GC cell invasion and migration, whereas COL1A1 knockdown inhibited the increase in cell metastatic capacity promoted by RUNX2. In vivo, GC cells overexpressing RUNX2 promoted lung metastasis, and the downregulation of COL1A1 reduced the metastasis promoted by RUNX2.

CONCLUSIONS

RUNX2 may promote GC metastasis by regulating COL1A1. RUNX2/COL1A1 can be employed as a novel target for therapy in GC.

Long non-coding RNAs: the tentacles of chromatin remodeler complexes

Chromatin remodeler complexes regulate gene transcription, DNA replication and DNA repair by changing both nucleosome position and post-translational modifications. The chromatin remodeler complexes are categorized into four families: the SWI/SNF, INO80/SWR1, ISWI and CHD family. In this review, we describe the subunits of these chromatin remodeler complexes, in particular, the recently identified members of the ISWI family and novelties of the CHD family. Long non-coding (lnc) RNAs regulate gene expression through different epigenetic mechanisms, including interaction with chromatin remodelers. For example, interaction of lncBRM with BRM inhibits the SWI/SNF complex associated with a differentiated phenotype and favors assembly of a stem cell-related SWI/SNF complex. Today, over 50 lncRNAs have been shown to affect chromatin remodeler complexes and we here discuss the mechanisms involved.

Targeting the CtBP1-FOXM1 transcriptional complex with small molecules to overcome MDR1-mediated chemoresistance in osteosarcoma cancer stem cells

Chemoresistance is a major barrier for the chemotherapy of osteosarcoma. The induction of multidrug resistance protein 1 (MDR1), an ATP-dependent transporter, can efflux anti-cancer drugs, thereby decreasing chemosensitivity. However, an actual involvement of MDR1 in the chemoresistance of osteosarcoma cells has not been established. We obtained two cisplatin (CDDP)-resistant osteosarcoma cancer stem cell (CSC) lines using sphere formation medium supplemented with CDDP. These two CDDP-resistant CSC cell lines showed substantial cell proliferation, colony formation, cell invasion, and in vivo tumor growth in the presence of CDDP. Microarray analysis revealed that three genes, MDR1, FOXM1 (forkhead box M1), and CtBP1 (C-Terminal binding protein 1), showed significant overexpression in both cell lines. Mechanistically, CtBP1 assembled with FOXM1 to form a transcriptional complex, which docked onto the MDR1 promoter to activate MDR1 expression. Knockdown or inhibition of the CtBP1-FOXM1 components with specific small molecules, including NSM00158 and NSC95397 for CtBP1 and RCM1 for FOXM1, significantly repressed MDR1 expression. Administration of these three small molecules also significantly inhibited tumor growth in mouse tumor xenograft model. The MDR1-mediated chemoresistance could be reversed by NSM00158 and RCM1. Collectively, our data revealed that the CtBP1-FOXM1 complex activated MDR1 expression and that targeting this complex with their specific inhibitors could reverse MDR1-mediated chemoresistance both in vitro and in vivo. Our results indicate a new therapeutic strategy for overcoming chemoresistance during osteosarcoma treatment.

SWI/SNF complexes act through CBP-1 histone acetyltransferase to regulate acute functional tolerance to alcohol

Background

SWI/SNF chromatin remodeling genes are required for normal acute responses to alcohol in C. elegans and are associated with alcohol use disorder in two human populations. In an effort to discover the downstream genes that are mediating this effect, we identified SWI/SNF-regulated genes in C. elegans.

Results

To identify SWI/SNF-regulated genes in adults, we compared mRNA expression in wild type and swsn-1(os22ts) worms under conditions that produce inactive swsn-1 in mature cells. To identify SWI/SNF-regulated genes in neurons, we compared gene expression in swsn-9(ok1354) null mutant worms that harbor a neuronal rescue or a control construct. RNA sequencing was performed to an average depth of 25 million reads per sample using 50-base, paired-end reads. We found that 6813 transcripts were significantly differentially expressed between swsn-1(os22ts) mutants and wild-type worms and 2412 transcripts were significantly differentially expressed between swsn-9(ok1354) mutants and swsn-9(ok1354) mutants with neuronal rescue. We examined the intersection between these two datasets and identified 603 genes that were differentially expressed in the same direction in both comparisons; we defined these as SWI/SNF-regulated genes in neurons and in adults. Among the differentially expressed genes was cbp-1, a C. elegans homolog of the mammalian CBP/p300 family of histone acetyltransferases. CBP has been implicated in the epigenetic regulation in response to alcohol in animal models and a polymorphism in the human CBP gene, CREBBP, has been associated with alcohol-related phenotypes. We found that cbp-1 is required for the development of acute functional tolerance to alcohol in C. elegans.

Conclusions

We identified 603 transcripts that were regulated by two different SWI/SNF complex subunits in adults and in neurons. The SWI/SNF-regulated genes were highly enriched for genes involved in membrane rafts, suggesting an important role for this membrane microdomain in the acute alcohol response. Among the differentially expressed genes was cbp-1; CBP-1 homologs have been implicated in alcohol responses across phyla and we found that C. elegans cbp-1 was required for the acute alcohol response in worms.

The Monocyte-Derived Exosomal CLMAT3 Activates the CtBP2-p300-NF-κB Transcriptional Complex to Induce Proinflammatory Cytokines in ALI

Monocytes and macrophages are the two major cell types involved in innate immunity. Exosomes act as signaling molecules to regulate cell-to-cell communication by releasing proteins, mRNAs, microRNAs (miRNAs), and long noncoding RNAs (lncRNAs). However, it is still unclear whether monocyte-derived exosomes are involved in the communication between monocytes and macrophages. In this study, we analyzed the differentially expressed lncRNA profiles in monocytes isolated from blood samples of healthy controls and acute lung injury (ALI) patients. We focused our study on investigating the signaling downstream of CLMAT3 (colorectal liver metastasis-associated transcript 3), a lncRNA that regulated proinflammatory cytokine genes. We revealed that CLMAT3 specifically targeted CtBP2 (C-terminal binding protein 2) and repressed its expression. Elevated CtBP2 acted as a coactivator to assemble a transcriptional complex with histone acetyltransferase p300 and NF-κB (nuclear factor κB) subunits. In vitro coculture and in vivo injection of ALI monocyte-derived exosomes increased the production of proinflammatory cytokines. Importantly, the administration of two CtBP2 inhibitors, NSC95397 and MTOB, could significantly reverse CtBP2-mediated transactivation. Collectively, our results support a model in which monocyte-derived exosomal CLMAT3 activates the CtBP2-p300-NF-κB complex to induce proinflammatory cytokines, thus contributing to the pathogenesis of ALI.

NSM00158 Specifically Disrupts the CtBP2-p300 Interaction to Reverse CtBP2-Mediated Transrepression and Prevent the Occurrence of Nonunion

Carboxyl-terminal binding proteins (CtBPs) are transcription regulators that control gene expression in multiple cellular processes. Our recent findings indicated that overexpression of CtBP2 caused the repression of multiple bone development and differentiation genes, resulting in atrophic nonunion. Therefore, disrupting the CtBP2-associated transcriptional complex with small molecules may be an effective strategy to prevent nonunion. In the present study, we developed an in vitro screening system in yeast cells to identify small molecules capable of disrupting the CtBP2-p300 interaction. Herein, we focus our studies on revealing the in vitro and in vivo effects of a small molecule NSM00158, which showed the strongest inhibition of the CtBP2-p300 interaction in vitro. Our results indicated that NSM00158 could specifically disrupt CtBP2 function and cause the disassociation of the CtBP2-p300-Runx2 complex. The impairment of this complex led to failed binding of Runx2 to its downstream targets, causing their upregulation. Using a mouse fracture model, we evaluated the in vivo effect of NSM00158 on preventing nonunion. Consistent with the in vitro results, the NSM00158 treatment resulted in the upregulation of Runx2 downstream targets. Importantly, we found that the administration of NSM00158 could prevent the occurrence of nonunion. Our results suggest that NSM00158 represents a new potential compound to prevent the occurrence of nonunion by disrupting CtBP2 function and impairing the assembly of the CtBP2-p300-Runx2 transcriptional complex.

Twist1 induces chromosomal instability (CIN) in colorectal cancer cells

Twist1 is a basic helix-loop-helix transcription factor, essential during early development in mammals. While Twist1 induces epithelial-to-mesenchymal transition (EMT), here we show that Twist1 overexpression enhances nuclear and mitotic aberrations. This is accompanied by an increase in whole chromosomal copy number gains and losses, underscoring the role of Twist1 in inducing chromosomal instability (CIN) in colorectal cancer cells. Array comparative genomic hybridization (array CGH) analysis further shows sub-chromosomal deletions, consistent with an increased frequency of DNA double strand breaks (DSBs). Remarkably, Twist1 overexpression downmodulates key cell cycle checkpoint factors-Bub1, BubR1, Mad1 and Mad2-that regulate CIN. Mathematical simulations using the RACIPE tool show a negative correlation of Twist1 with E-cadherin and BubR1. Data analyses of gene expression profiles of patient samples from The Cancer Genome Atlas (TCGA) reveal a positive correlation between Twist1 and mesenchymal genes across cancers, whereas the correlation of TWIST1 with CIN and DSB genes is cancer subtype-specific. Taken together, these studies highlight the mechanistic involvement of Twist1 in the deregulation of factors that maintain genome stability during EMT in colorectal cancer cells. Twist1 overexpression enhances genome instability in the context of EMT that further contributes to cellular heterogeneity. In addition, these studies imply that Twist1 downmodulates nuclear lamins that further alter spatiotemporal organization of the cancer genome and epigenome. Notwithstanding their genetic background, colorectal cancer cells nevertheless maintain their overall ploidy, while the downstream effects of Twist1 enhance CIN and DNA damage enriching for sub-populations of aggressive cancer cells.

Inflammation and DNA methylation coregulate the CtBP-PCAF-c-MYC transcriptional complex to activate the expression of a long non-coding RNA CASC2 in acute pancreatitis

Long non-coding RNAs (lncRNAs) are emerging as important regulators involved in the pathogenesis of many diseases. However, it is still unknown if they contribute to the occurrence of acute pancreatitis (AP). Here, we identified a lncRNA CASC2 (Cancer Susceptibility Candidate 2) was significantly upregulated in the pancreatic tissues from AP patients. Knockdown or overexpression of CASC2 in vitro could specifically repress or induce the expression of two proinflammatory cytokines including IL6 (Interleukin 6) and IL17, respectively. Changing the expression levels of several transcription factors that were predicted to bind to the promoter of CASC2, we found c-MYC could specifically regulate the expression of CASC2. Using immunoprecipitation, mass spectrometry, and co-immunoprecipitation assays, we proved that c-MYC assembled a transcriptional complex with PCAF (p300/CBP-associated Factor) and CtBP1/2 (C-terminal Binding Protein 1 and 2), terming as the CtBP-PCAF-c-MYC (CPM) complex. Further investigation revealed that CtBPs were amplified in the pancreatic tissues from AP patients and they functioned as coactivators to induce the expression of CASC2 and thus led to the upregulation of IL6 and IL17. Moreover, we identified that decreased DNA methylation levels in the promoters of CtBPs and inflammatory stimuli coactivated the expression of CtBPs. Collectively, we identified a new signaling pathway in which DNA methylation and inflammatory stimuli coregulate the CPM complex to activate CASC2 expression, whose induction further activates the expression of IL6 and IL17, eventually aggravating inflammation response and causing the pathology of AP.

The role of microglia in neuroprogressive disorders: mechanisms and possible neurotherapeutic effects of induced ketosis

A comprehensive review of molecular mechanisms involved in the promotion and maintenance of distinct microglia phenotypes is provided. The acquisition and perpetuation of predominantly pro-inflammatory microglial phenotypes have been implicated in the pathophysiology of several neuroprogressive diseases and is associated with reduced ATP production via oxidative phosphorylation, increased ATP generation by glycolysis, elevated oxidative and nitrosative stress and other metabolic, inflammatory and hormonal insults. Microglia can also adopt a predominantly anti-inflammatory phenotypes with neuroprotective properties. Strategies that promote and maintain a predominantly anti-inflammatory phenotype may hold promise as novel therapeutic opportunities for neuroprogressive illness. Induced ketosis may promote a transition towards predominantly anti-inflammatory microglial states/phenotypes by several mechanisms, including inhibition of glycolysis and increased NAD⁺ production; engagement of microglial GPR109A receptors; histone deacetylase inhibition; and elevated n-3 polyunsaturated fatty acids levels. Since microglia activation can now be assessed in vivo, these data provide a clear rationale for the design of transdiagnostic randomized controlled trials of the ketogenic diet and other ketosis-inducing strategies for neuroprogressive diseases, which may also provide mechanistic insights through the assessment of "target engagement".

The CARM1-p300-c-Myc-Max (CPCM) transcriptional complex regulates the expression of CUL4A/4B and affects the stability of CRL4 E3 ligases in colorectal cancer

The transcription factor c-Myc and two cullin family members CUL4A/4B function as oncogenes in colorectal cancer. Our recent publication reveals that c-Myc specifically activates the expression of CUL4A/4B through binding to their promoters. However, the underlying mechanism of how c-Myc actions in this process is still unknown. Using mass spectrometry and immunoprecipitation assays, we identified c-Myc formed a transcriptional complex with its partner Max (Myc-associated factor X), a histone acetyltransferase p300 and a coactivator associated arginine methyltransferase 1 (CARM1) in the present study. Knockdown or overexpression of the components of CARM1-p300-c-Myc-Max (CPCM) complex resulted in a decrease or increase of CUL4A/4B levels, respectively. Individual knockdown or inhibition of CPCM components decreased cell proliferation, colony formation, and cell invasion. Biochemically, knockdown or inhibition of CPCM components decreased their occupancies on the promoters of CUL4A/4B and resulted in their downregulation. Importantly, inhibition of CPCM components also caused a decrease of CRL4 E3 ligase activities and eventually led to an accumulation of ST7 (suppression of tumorigenicity 7), the specific substrate of CRL4 E3 ligases in colorectal cancer. Moreover, the in vivo tumor formation results indicated that knockdown or inhibition of CPCM components significantly decreased the tumor volumes. Together, our results suggest that the CPCM complex mediates explicitly the expression of CUL4A/4B, and thus affects the stability of CRL4 E3 ligases and the ubiquitination of ST7. These results provide more options by targeting the CPCM components to inhibit tumor growth in the therapy of colorectal cancer.

DNA methylation is involved in the pathogenesis of osteoarthritis by regulating CtBP expression and CtBP-mediated signaling

Osteoarthritis (OA) is a common type of arthritis. Chronic inflammation is an important contributor to the pathogenesis of OA. The maturation and secretion of proinflammatory cytokines are controlled by inflammasomes, especially NLRP1 (NLR Family Pyrin Domain Containing 1) and NLRP3. In this study, we identified a transactivation mechanism of NLRP3 mediated by CtBPs (C-terminal-binding proteins). We found that both the mRNA and protein levels of CtBPs were significantly increased in OA biopsies. Analyzing the profiles of differentially expressed genes in CtBP-knockdown and overexpression cells, we found that the expression of NLRP3 was dependent on CtBP levels. By the knockdown or overexpression of transcription factors that potentially bind to the promoter of NLRP3, we found that only AP1 could specifically regulate the expression of NLRP3. Using immunoprecipitation (IP) and Co-IP assays, we found that AP1 formed a transcriptional complex with a histone acetyltransferase p300 and CtBPs. The knockdown of any member of this transcriptional complex resulted in a decrease in the expression of NLRP3. To explore the underlying mechanism of CtBP overexpression, we analyzed their promoters and found that they were abundant in CpG islands. Treatment with the DNA methylation inhibitor 5-aza-2′-deoxycytidine (AZA) or knockdown of DNMTs (DNA methyltransferases) resulted in the overexpression of CtBPs, while overexpression of DNMTs caused the reverse effects on CtBP expression. Collectively, our results suggest that the decreased DNA methylation levels in the promoters of CtBPs upregulate their expression. Increased CtBPs associated with p300 and AP1 to form a transcriptional complex and activate the expression of NLRP3 and its downstream signaling, eventually aggravating the inflammatory response and leading to the pathogenesis of OA.

Transforming growth factor beta (TGF-β) is activated by the CtBP2-p300-AP1 transcriptional complex in chronic renal failure

Chronic renal failure (CRF), also known as chronic kidney disease (CKD), is a common renal disorder characterized by gradual kidney dysfunction. Molecular dissection reveals that transforming growth factor beta (TGF-β) plays a central role in the pathogenesis of CRF. However, the mechanism underlying TGF-β upregulation has not been demonstrated. Here, we verified that the elevated level of TGF-β was associated with the severity of CRF stages and the activation of TGF-β-mediated signaling in 120 renal biopsies from CRF patients. By analyzing the promoter region of the TGFB1 gene, we identified one AP-1 (activator protein 1) and four NF-κB (nuclear factor kappa-light-chain-enhancer of activated B cells) binding sites. Knockdown of two AP-1 subunits (c-Jun and c-FOS) or blockage of AP-1 signaling with two inhibitors T-5224 and SR11302 could cause the downregulation of TGFB1, whereas knockdown of two NF-κB subunits (p65 and p50) or blockage of NF-κB signaling with two inhibitors TPCA1 and BOT-64 could not change the expression of TGFB1. Using mass spectrometry and coimmunoprecipitation analyses, we found that both c-Jun and c-FOS formed a complex with CtBP2 (C-terminal binding protein 2) and histone acetyltransferase p300. Our in vitro data demonstrated that induction of CtBP2 by recombinant IL-1β (interleukin-1 beta) led to the upregulation of TGFB1 and the activation of TGF-β downstream signaling, while knockdown of CtBP2 resulted in the reversed effects. Using chromatin immunoprecipitation assays, we revealed that the CtBP2-p300-AP1 complex specifically bound to the promoter of TGFB and that knockdown or blockage of CtBP2 significantly decreased the occupancies of the p300 and AP-1 subunits. Our results support a model in which the CtBP2-p300-AP1 transcriptional complex activates the expression of TGFB1, increasing its production and extracellular secretion. The secreted TGF-β binds to its receptors and initiates downstream signaling.

Downregulation of miR-199a-3p mediated by the CtBP2-HDAC1-FOXP3 transcriptional complex contributes to acute lung injury by targeting NLRP1

Emerging evidence indicates that microRNAs (miRNAs) play fundamental roles in the pathogenesis of multiple diseases, including acute lung injury (ALI). Here, we discovered that miR-199a-3p was significantly downregulated in ALI lung tissues using a microarray analysis. In vitro lipopolysaccharide (LPS) treatment of the human epithelial cell line A549 and the human macrophage cell line U937 caused a decrease of miR-199a-3p. Mechanically, miR-199a-3p specifically bound to the 3'-untranslated region (3'-UTR) of NLRP1 (nucleotide-binding oligomerization domain, leucine-rich repeat and pyrin domain-containing protein 1), a critical member of inflammasomes. Ectopic overexpression or downregulation of miR-199a-3p resulted in the repression or induction of NLRP1, respectively, thereby downregulating or activating its downstream events. Moreover, transcription factor FOXP3 (forkhead box P3) was able to specifically bind to the promoter of miR-199a-3p. Knockdown or overexpression of FOXP3 resulted in a decrease or induction miR-199a-3p expression, respectively. Using immunoprecipitation (IP), mass spectrometry and co-IP assays, we found that FOXP3 formed a transcriptional complex with HDAC1 (histone deacetylase 1) and CtBP2 (C-terminal-binding protein 2). Collectively, our results suggested that the CtBP2-HDAC1-FOXP3 transcriptional complex (CHFTC) could specifically bind to the promoter of miR-199a-3p and repress its expression. Downregulation of miR-199a-3p eliminated its inhibition of NLRP1, causing activation of NLRP1 and cleavage of pro-IL-1β and pro-IL-18 mediated by Caspase-1. The secretion of IL-1β and IL-18 further aggravated the inflammatory response and resulted in the occurrence of ALI.

The CtBP1-p300-FOXO3a transcriptional complex represses the expression of the apoptotic regulators Bax and Bim in human osteosarcoma cells

C-terminal binding protein 1 (CtBP1), a well-known transcriptional corepressor, functions as an oncogene in multiple cancer types, including osteosarcoma, by modulating the transcription of many tumor suppressors, such as cadherin 1 (CDH1), phosphatase and tensin homolog (PTEN), Bcl2-associated X (Bax), Bcl-2-interacting mediator (Bim), and cyclin-dependent kinase inhibitor 1A (CDKN1A). However, it is still unclear how CtBP1 regulates the expression of these downstream targets. Here, we identified that CtBP1 is overexpressed in osteosarcoma cells and found that CtBP1 directly interacts with the transcription factor forkhead box O3 (FOXO3a) and the histone acetyltransferase p300 in vivo and in vitro. Through microarray analysis, we found that CtBP1 negatively regulates FOXO3a levels. In contrast to the CtBP1 level, the FOXO3a expression level was found to be significantly reduced in osteosarcoma cells. Knockdown of CtBP1 or overexpression of FOXO3a in U2OS cells resulted in different gene expression patterns, and the former caused upregulation of CtBP1 downstream target genes such as CDH1, PTEN, Bax, Bim, and CDKN1A, whereas the latter caused upregulation of Bax and Bim, but not CDH1, PTEN, and CDKN1A. Further analysis indicated that the CtBP1-p300-FOXO3a transcriptional complex specifically binds to the promoters of Bax and Bim. Inhibition of CtBP1 by the constitutive expression of Pep1-E1A^WT peptide in U2OS and OSA cells reversed oncogenic phenotypes, including colony formation, cellular proliferation, and migration, and limited tumor growth in vivo. Together our results demonstrated that the CtBP1-p300-FOXO3a transcriptional complex represses the expression of the apoptotic regulators Bax and Bim in human osteosarcoma cells and that targeting CtBP1-mediated transcriptional events might be a potential therapeutic strategy for the osteosarcoma treatment.