Regulation of the G1/S transition phase in mesangial cells by E2F1

ZFP36L1 and ZFP36L2 reduce cyclin D1 expression by decreasing expression of E2F1 and long 3'UTR isoform of CCND1 transcripts

The CCND1 mRNA possesses at least two distinct lengths of the 3'-untranslated region (3'UTR), with the long isoform containing multiple AU-rich elements (AREs). The tandem zinc finger (TZF) domains of human ZFP36 family members have the capacity to bind to AREs and promote mRNA degradation. Our previous study demonstrated that mutations in the TZF domain of ZFP36L1 or ZFP36L2 increased the CCND1 expression. In this study, we investigated whether ZFP36L1 and ZFP36L2 could downregulate the expression of the long 3'UTR isoform of CCND1 mRNA in human colorectal cancer (CRC) cells. Firstly, the Gene Expression Profiling Interactive Analysis 2 database indicated downregulation of ZFP36 and ZFP36L1, while E2F1 and CCND1 were upregulated in human CRC tissues compared to normal colorectal tissues. Overexpression of ZFP36L1 and/or ZFP36L2 in T-REx-293, DLD-1, and HCT116 cells led to a decrease in the total CCND1, long isoform ratio of CCND1 mRNA, and E2F1 expression. Conversely, knockdown of ZFP36L1 and ZFP36L2 in HCT116 cells resulted in an increase in total CCND1, long isoform ratio of CCND1 mRNA, and E2F1 expression. Knockdown of E2F1 decreased CCND1 expression, indicating a potential role for E2F1 in regulating CCND1 expression at the transcriptional level. These findings suggest that ZFP36L1 and ZFP36L2 play a negative role in CCND1 expression. The underlying mechanisms might involve the reduction of E2F1 transactivation at the transcriptional level and the promotion of AREs-mediated decay of the long 3'UTR isoform of CCND1 through posttranscriptional processes.

The Role of the DNA Methyltransferase Family and the Therapeutic Potential of DNMT Inhibitors in Tumor Treatment

Members of the DNA methyltransferase (DNMT) family have been recognized as major epigenetic regulators of altered gene expression during tumor development. They establish and maintain DNA methylation of the CpG island of promoter and non-CpG region of the genome. The abnormal methylation status of tumor suppressor genes (TSGs) has been associated with tumorigenesis, leading to genomic instability, improper gene silence, and immune evasion. DNMT1 helps preserve methylation patterns during DNA replication, whereas the DNMT3 family is responsible for de novo methylation, creating new methylation patterns. Altered DNA methylation significantly supports tumor growth by changing gene expression patterns. FDA-approved DNMT inhibitors reverse hypermethylation-induced gene repression and improve therapeutic outcomes for cancer. Recent studies indicate that combining DNMT inhibitors with chemotherapies and immunotherapies can have synergistic effects, especially in aggressive metastatic tumors. Improving the treatment schedules, increasing isoform specificity, reducing toxicity, and utilizing genome-wide analyses of CRISPR-based editing to create personalized epigenetic therapies tailored to individual patient needs are promising strategies for enhancing therapeutic outcomes. This review discusses the interaction between DNMT regulators and DNMT1, its binding partners, the connection between DNA methylation and tumors, how these processes contribute to tumor development, and DNMT inhibitors' advancements and pharmacological properties.

Calcineurin-mediated dephosphorylation stabilizes E2F1 protein by suppressing binding of the FBXW7 ubiquitin ligase subunit

The transcription factor E2F1 serves as a regulator of the cell cycle and promotes cell proliferation. It is highly expressed in cancer tissues and contributes to their malignant transformation. Degradation by the ubiquitin-proteasome system may help to prevent such overexpression of E2F1 and thereby to suppress carcinogenesis. A detailed understanding of the mechanisms underlying E2F1 degradation may therefore inform the development of new cancer treatments. We here identified SCFFBXW7 as a ubiquitin ligase for E2F1 by comprehensive analysis. We found that phosphorylation of E2F1 at serine-403 promotes its binding to FBXW7 (F-box/WD repeat-containing protein 7) followed by its ubiquitination and degradation. Furthermore, calcineurin, a Ca2+/calmodulin-dependent serine-threonine phosphatase, was shown to stabilize E2F1 by mediating its dephosphorylation at serine-403 and thereby preventing FBXW7 binding. Treatment of cells with Ca2+ channel blockers resulted in downregulation of both E2F1 protein and the expression of E2F1 target genes, whereas treatment with the Ca2+ ionophore ionomycin induced upregulation of E2F1. Finally, the calcineurin inhibitor FK506 attenuated xenograft tumor growth in mice in association with downregulation of E2F1 in the tumor tissue. Impairment of the balance between the opposing actions of FBXW7 and calcineurin in the regulation of E2F1 abundance may therefore play an important role in carcinogenesis.

Developmental exposure to nonylphenol leads to depletion of the neural precursor cell pool in the hippocampal dentate gyrus

Developmental exposure to nonylphenol (NP) results in irreversible impairments of the central nervous system (CNS). The neural precursor cell (NPC) pool located in the subgranular zone (SGZ), a substructure of the hippocampal dentate gyrus, is critical for the development of hippocampal circuits and some hippocampal functions such as learning and memory. However, the effects of developmental exposure to NP on this pool remain unclear. Thus, our aim was to clarify the impacts of developmental exposure to NP on this pool and to explore the potential mechanisms. Animal models of developmental exposure to NP were created by treating Wistar rats with NP during pregnancy and lactation. Our data showed that developmental exposure to NP decreased Sox2-and Ki67-positive cells in the SGZ of offspring. Inhibited activation of Shh signaling and decreased levels of its downstream mediators, E2F1 and cyclins, were also observed in pups developmentally exposed to NP. Moreover, we established the in vitro model in the NE-4C cells, a neural precursor cell line, to further investigate the effect of NP exposure on NPCs and the underlying mechanisms. Purmorphamine, a small purine-derived hedgehog agonist, was used to specifically modulate the Shh signaling. Consistent with the in vivo results, exposure to NP reduced cell proliferation by inhibiting the Shh signaling in NE-4C cells, and purmorphamine alleviated this reduction in cell proliferation by restoring this signaling. Altogether, our findings support the idea that developmental exposure to NP leads to inhibition of the NPC proliferation and the NPC pool depletion in the SGZ located in the dentate gyrus. Furthermore, we also provided the evidence that suppressed activation of Shh signaling may contribute to the effects of developmental exposure to NP on the NPC pool.

Circ_0001495 influences the development of endometriosis through the miRNA-34c-5p/E2F3 axis

Endometriosis is a chronic gynecological condition characterized by the presence of endometrial glands and stroma outside the uterine cavity., accounting for 7% of all female malignant tumors and 20%- 30% of malignant tumors of the female reproductive system. Multiple studies have shown that circular RNA (circRNA) has the potential to become a targeted target and marker for EM. However, the roles of circ_0001495 in EM are still unclear. Our research aims to reveal the molecular mechanism of circ_0001495 in EM. In this study, RT-PCR or western blot were conducted to determine mRNA and protein expression. cell viability, proliferation, migration, invasion, and apoptosis were assessed by CCK-8, EdU, wound healing, transwell, and flow cytometry analyses, respectively. Additionally, the targeting relationship between miR-34c-5p and circ_0001495 or E2F3 was confirmed through dual-luciferase reporter gene assay. We found significant overexpression of circ_0001495 in EM tissues and cells. Knockdown of circ_0001495 inhibited the proliferation, migration and invasion of ectopic endometrial stromal cells (EESCs) and increased cell apoptosis. Moreover, we found that circ_0001495 regulated E2F3 levels by interacting with miR-34c-5p in EESC. Furthermore, in vitro, miR-34c-5p inhibition or E2F3 overexpression could attenuate the effect of circ_0001495 silencing on EM progression. In addition, the vivo experiment demonstrated that inhibition of circ_0001495 could repress the development of endometriosis by regulating the miR-34c-5p/E2F3 axis. In conclusion, our study suggested that circ_0001495 promoted EM progression in vitro and in vivo through the miR-34c-5p/E2F3 axis, which might be a potential therapeutic target for EM.

Microcephaly Gene Mcph1 Deficiency Induces p19ARF-Dependent Cell Cycle Arrest and Senescence

MCPH1 has been identified as the causal gene for primary microcephaly type 1, a neurodevelopmental disorder characterized by reduced brain size and delayed growth. As a multifunction protein, MCPH1 has been reported to repress the expression of TERT and interact with transcriptional regulator E2F1. However, it remains unclear whether MCPH1 regulates brain development through its transcriptional regulation function. This study showed that the knockout of Mcph1 in mice leads to delayed growth as early as the embryo stage E11.5. Transcriptome analysis (RNA-seq) revealed that the deletion of Mcph1 resulted in changes in the expression levels of a limited number of genes. Although the expression of some of E2F1 targets, such as Satb2 and Cdkn1c, was affected, the differentially expressed genes (DEGs) were not significantly enriched as E2F1 target genes. Further investigations showed that primary and immortalized Mcph1 knockout mouse embryonic fibroblasts (MEFs) exhibited cell cycle arrest and cellular senescence phenotype. Interestingly, the upregulation of p19ARF was detected in Mcph1 knockout MEFs, and silencing p19Arf restored the cell cycle and growth arrest to wild-type levels. Our findings suggested it is unlikely that MCPH1 regulates neurodevelopment through E2F1-mediated transcriptional regulation, and p19ARF-dependent cell cycle arrest and cellular senescence may contribute to the developmental abnormalities observed in primary microcephaly.

Polychlorinated biphenyls exposure and type 2 diabetes: Molecular mechanism that causes insulin resistance and islet damage

Polychlorinated biphenyls (PCBs) are typical persistent organic pollutants that have been associated with type 2 diabetes (T2DM) in cohort studies. This review aims to comprehensively assess the molecular mechanisms of PCBs-induced T2DM. Recent progress has been made in the research of PCBs in liver tissue, adipose tissue, and other tissues. By influencing the function of nuclear receptors, such as the aryl hydrocarbon receptor (AhR), pregnancy X receptor (PXR), and peroxisome proliferator activated receptor γ (PPARγ), as well as the inflammatory response, PCBs disrupt the balance of hepatic glucose and lipid metabolism. This is associated with insulin resistance (IR) in the target organ of insulin. Through androgen receptor (AR), estrogen receptor α/β (ERα/β), and pancreato-duodenal-homeobox gene-1 (PDX-1), PCBs affect the secretion of insulin and increase blood glucose. Thus, this review is a discussion on the relationship between PCBs exposure and the pathogenesis of T2DM. It is hoped to provide basic concepts for diabetes research and disease treatment.

Analysis of Transcriptomic Differences in the Ovaries of High- and Low-Laying Ducks

The egg-laying performance of Shan Ma ducks (Anas Platyrhynchos) is a crucial economic trait. Nevertheless, limited research has been conducted on the egg-laying performance of this species. We examined routine blood indicators and observed higher levels of metabolic and immune-related factors in the high-egg-production group compared with the low-egg-production group. Furthermore, we explored the ovarian transcriptome of both high- and low-egg-production groups of Shan Ma ducks using Illumina NovaSeq 6000 sequencing. A total of 1357 differentially expressed genes (DEGs) were identified, with 686 down-regulated and 671 up-regulated in the high-egg-production (HEP) ducks and low-egg-production (LEP) ducks. Several genes involved in the regulation of ovarian development, including neuropeptide Y (NPY), cell cycle protein-dependent kinase 1 (CDK1), and transcription factor 1 (E2F1), exhibited significant differential expressions at varying stages of egg production. Pathway functional analysis revealed that the DEGs were primarily associated with the steroid biosynthesis pathway, and the neuroactive ligand-receptor interaction pathway exhibited higher activity in the HEP group compared to the LEP group. This study offers valuable information about and novel insights into high egg production.

Mathematical Models Including microRNA Levels of Mesenteric Adipose Tissue May Predict Postoperative Relapse in Crohn's Disease Patients

Background and Aims

Recent evidence suggests that the mesenteric adipose tissue (MAT) near the affected intestine may play a role in Crohn's disease (CD) pathophysiology. Modulation of several transcripts has already been identified in the MAT of CD in the literature. Therefore, our aim was to validate the microRNA (miRNA) transcript levels and their target genes in the MAT of active CD patients and correlate them with clinical and epidemiological data.

Methods

Samples from the MAT of surgical specimens from 25 active CD patients were obtained. The control group comprised fifteen patients who underwent surgery for other diseases, except inflammatory bowel diseases. Transcriptional levels of miRNA and their target genes were assessed by quantitative real-time polymerase chain reaction. The correlation between transcripts and clinical characteristics was obtained using multiple linear regression. The mathematical models (M) underwent a statistical filter to ensure robustness and reliability (P value < .05; adjusted R-squared (Rˆ2)> .99; correct predictions of more than 60%).

Results

miRNA-650 and miRNA-29c were upregulated in the MAT of CD compared to the control group (P < .0001 and P = .0032, respectively), besides presenting decreased levels of their target genes. Two were target genes of the miRNA-650: glutamine-fructose-6-phosphate transaminase 2 (P = .012) and aldehyde dehydrogenase 4 family (P = .0035); and 4 were targets of the miRNA-29c: cell death-inducing DFFA-like effector c (P = .001), E2F transcription factor-1 (P = .007), hypoxia-inducible factor 3 subunit alpha (P = .0029), and pyruvate dehydrogenase kinase 4 (P = .0054). We found 2 M with statistical strength and robustness. The performance test identified one model with 100% accuracy for predicting the month of recurrence and determining patients with less risk of early relapse after surgery.

Conclusion

We demonstrate that miRNA-650 and miRNA-29c and some of their target genes, besides clinical and epidemiological variables, may be useful in a model to predict when disease relapse may occur in CD patients who underwent surgery. These findings constitute a potential tool to guide postoperative clinical management.

Small RNA Profiling in an HTLV-1-Infected Patient with Acute Adult T-Cell Leukemia-Lymphoma at Diagnosis and after Maintenance Therapy: A Case Study

Small RNAs (sRNAs) are epigenetic regulators of essential biological processes associated with the development and progression of leukemias, including adult T-cell leukemia/lymphoma (ATLL) caused by human T-cell lymphotropic virus type 1 (HTLV-1), an oncogenic human retrovirus originally discovered in a patient with adult T-cell leukemia/lymphoma. Here, we describe the sRNA profile of a 30-year-old woman with ATLL at the time of diagnosis and after maintenance therapy with the aim of correlating expression levels with response to therapy.

Co-inhibition of ATM and ROCK synergistically improves cell proliferation in replicative senescence by activating FOXM1 and E2F1

The multifaceted nature of senescent cell cycle arrest necessitates the targeting of multiple factors arresting or promoting the cell cycle. We report that co-inhibition of ATM and ROCK by KU-60019 and Y-27632, respectively, synergistically increases the proliferation of human diploid fibroblasts undergoing replicative senescence through activation of the transcription factors E2F1 and FOXM1. Time-course transcriptome analysis identified FOXM1 and E2F1 as crucial factors promoting proliferation. Co-inhibition of the kinases ATM and ROCK first promotes the G2/M transition via FOXM1 activation, leading to accumulation of cells undergoing the G1/S transition via E2F1 activation. The combination of both inhibitors increased this effect more significantly than either inhibitor alone, suggesting synergism. Our results demonstrate a FOXM1- and E2F1-mediated molecular pathway enhancing cell cycle progression in cells with proliferative potential under replicative senescence conditions, and treatment with the inhibitors can be tested for senomorphic effect in vivo.

xCT contributes to colorectal cancer tumorigenesis through upregulation of the MELK oncogene and activation of the AKT/mTOR cascade

Colorectal cancer (CRC) is one of the most commonly diagnosed and deadly malignant tumors globally, and its occurrence and progression are closely related to the poor histological features and complex molecular characteristics among patients. It is urgent to identify specific biomarkers for effective treatment of CRC. In this study, we performed comprehensive experiments to validate the role of xCT expression in CRC tumorigenesis and stemness and confirmed xCT knockdown significantly suppressed the proliferation, migration, and stemness of CRC cells in vitro and effectively inhibited CRC tumorigenesis and metastasis in vivo. In addition, bioinformatic analysis and luciferase assays were used to identify E2F1 as a critical upstream transcription factor of SLC7A11 (the gene encoding for xCT) that facilitated CRC progression and cell stemness. Subsequent RNA sequencing, western blotting, rescue assay, and immunofluorescence assays revealed MELK directly co-expressed with xCT in CRC cells, and its upregulation significantly attenuated E2F1/xCT-mediated tumorigenesis and stemness in CRC. Further molecular mechanism exploration confirmed that xCT knockdown may exert an antitumor effect by controlling the activation of MELK-mediated Akt/mTOR signaling. Erastin, a specific inhibitor of xCT, was also proven to effectively inhibit CRC tumorigenesis and cell stemness. Altogether, our study showed that E2F1/xCT is a promising therapeutic target of CRC that promotes tumorigenesis and cell stemness. Erastin is also an effective antitumoral agent for CRC.

Positive regulation of ataxia-telangiectasia-mutated protein (ATM) by E2F transcription Factor 1 (E2F-1) in cisplatin-resistant nasopharyngeal carcinoma cells

Objective

To explore the mechanism of E2F transcription Factor 1 (E2F-1)-mediated ataxia-telangiectasia-mutated protein (ATM) in cisplatin (DDP)-resistant nasopharyngeal carcinoma (NPC).

Methods

E2F-1 and ATM expression was assessed in DDP-resistant NPC cell lines (CNE2/DDP and HNE1/DDP) and parental cells. Then, DDP-resistant NPC cells were transfected with control shRNA (short hairpin RNA) or E2F-1 shRNAs with or without ATM lentiviral activation particles. The half maximal inhibitory concentration (IC50) was evaluated by 3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide (MTT) assay, and the cell cycle and cell proliferation were measured by flow cytometry and EdU staining, respectively. In addition, the expression of genes and proteins was quantified by quantitative reverse-transcription polymerase chain reaction (qRT–PCR) and western blotting, respectively.

Results

Both E2F-1 and ATM expression in DDP-resistant NPC cells was much higher than that in parental cells. E2F-1 shRNA reduced ATM expression in DDP-resistant NPC cells, but ATM overexpression had no significant effect on E2F-1. ATM overexpression enhanced DDP resistance in DDP-resistant NPC cells with increased IC50 values, which was reversed by E2F-1 inhibition. Meanwhile, ATM overexpression resulted in upregulation of ABCA2 and ABCA5 in DDP-resistant NPC cells, induced elevations in the transition of the cells into S-phase, and increased cell proliferation with enhanced expression of cyclin E1, CDK2, and Ki67, which was reversed by E2F-1 shRNAs.

Conclusion

Downregulation of E2F-1, possibly by regulating ATM, could block the cell cycle in the G1 phase and reduce the proliferation of CNE2/DDP cells, thereby reversing the resistance of human NPC cells to DDP.

Insulin-Like Growth Factor 2 mRNA Binding Protein 3 Promotes Cell Proliferation of Malignant Mesothelioma Cells by Downregulating p27Kip1

Malignant mesothelioma is a tumor with a poor prognosis, mainly caused by asbestos exposure and with no adequate treatment yet. To develop future therapeutic targets, we analyzed the microarray dataset GSE 29370 of malignant mesothelioma and reactive mesothelial hyperplasia, downloaded from the Gene Expression Omnibus (GEO) database. We identified insulin-like growth factor 2 mRNA binding protein 3 (IGF2BP3) as one of the significantly upregulated genes in malignant mesothelioma. IGF2BP3 functions as an oncoprotein in many human cancers; however, to our knowledge, this is the first study on the biological function of IGF2BP3 in malignant mesothelioma cells. The knockdown of IGF2BP3 in malignant mesothelioma cells resulted in the suppression of cell proliferation with an increase in the proportion of cells in the G1 phase of the cell cycle. Furthermore, knockdown of IGF2BP3 inhibited cell migration and invasion. We focused on the cell cycle assay to investigate the role of IGF2BP3 in cell proliferation in malignant mesothelioma. Among the various proteins involved in cell cycle regulation, the expression of p27 Kip1 (p27) increased significantly upon IGF2BP3 knockdown. Next, p27 siRNA was added to suppress the increased expression of p27. The results showed that p27 knockdown attenuated the effects of IGF2BP3 knockdown on cell proliferation and G1 phase arrest. In conclusion, we found that IGF2BP3 promotes cell proliferation, a critical step in tumorigenesis, by suppressing the expression of p27 in malignant mesothelioma.

Fargesin Inhibits EGF-Induced Cell Transformation and Colon Cancer Cell Growth by Suppression of CDK2/Cyclin E Signaling Pathway

Although the lignan compound fargesin is a major ingredient in Shin-Yi, the roles of fargesin in carcinogenesis and cancer cell growth have not been elucidated. In this study, we observed that fargesin inhibited cell proliferation and transformation by suppression of epidermal growth factor (EGF)-stimulated G₁/S-phase cell cycle transition in premalignant JB6 Cl41 and HaCaT cells. Unexpectedly, we found that signaling pathway analyses showed different regulation patterns in which fargesin inhibited phosphatidylinositol 3-kinase/AKT signaling without an alteration of or increase in mitogen activated protein kinase (MAPK) in JB6 Cl41 and HaCaT cells, while both signaling pathways were abrogated by fargesin treatment in colon cancer cells. We further found that fargesin-induced colony growth inhibition of colon cancer cells was mediated by suppression of the cyclin dependent kinase 2 (CDK2)/cyclin E signaling axis by upregulation of p21^WAF1/Cip1, resulting in G₁-phase cell cycle accumulation in a dose-dependent manner. Simultaneously, the suppression of CDK2/cyclin E and induction of p21^WAF1/Cip1 were correlated with Rb phosphorylation and c-Myc suppression. Taken together, we conclude that fargesin-mediated c-Myc suppression inhibits EGF-induced cell transformation and colon cancer cell colony growth by the suppression of retinoblastoma (Rb)-E2F and CDK/cyclin signaling pathways, which are mainly regulated by MAPK and PKB signaling pathways.

E2F1: Cause and Consequence of DNA Replication Stress

In mammalian cells, cell cycle entry occurs in response to the correct stimuli and is promoted by the transcriptional activity of E2F family members. E2F proteins regulate the transcription of S phase cyclins and genes required for DNA replication, DNA repair, and apoptosis. The activity of E2F1, the archetypal and most heavily studied E2F family member, is tightly controlled by the DNA damage checkpoints to modulate cell cycle progression and initiate programmed cell death, when required. Altered tumor suppressor and oncogenic signaling pathways often result in direct or indirect interference with E2F1 regulation to ensure higher rates of cell proliferation independently of external cues. Despite a clear link between dysregulated E2F1 activity and cancer progression, literature on the contribution of E2F1 to DNA replication stress phenotypes is somewhat scarce. This review discusses how dysfunctional tumor suppressor and oncogenic signaling pathways promote the disruption of E2F1 transcription and hence of its transcriptional targets, and how such events have the potential to drive DNA replication stress. In addition to the involvement of E2F1 upstream of DNA replication stress, this manuscript also considers the role of E2F1 as a downstream effector of the response to this type of cellular stress. Lastly, the review introduces some reflections on how E2F1 activity is integrated with checkpoint control through post-translational regulation, and proposes an exploitable tumor weakness based on this axis.

DNMT3A inhibits E2F1-induced arterial marker expression and impairs angiogenesis in human umbilical artery endothelial cells

Arterial marker genes EphrinB2 and HEY2 are essential for cardiovascular development and postnatal neovascularization. Our previous study confirmed that E2F1 could activate the transcription of EphrinB2 and HEY2 in human mesenchymal stem cells; however, the detailed mechanism has not been resolved yet. In this study, we focused on the interaction between E2F1 and DNMT3A, a de novo DNA methyltransferase, on regulating the expression of EphrinB2 and HEY2, and explored the potential mechanisms. Gain- and loss-of-function experiments implicated the positive effect of E2F1 on the expression of EphrinB2 and HEY2 and tube formation in human umbilical artery endothelial cells. Accumulation of DNMT3A decreased the levels of EphrinB2 and HEY2, and impaired tube formation induced by E2F1, while inhibiting DNMT3A by RNA interference augmented their expression and angiogenesis in E2F1-trasfected cells. We then asked whether the low expressions of EphrinB2 and HEY2 induced by DNMT3A are related to the methylation status of their promoters. Surprisingly, the methylation status of the CpG islands in the promoter region was not significantly affected by overexpression of exogenous DNMT3A. Furthermore, the interaction between E2F1 and DNMT3A was confirmed by co-immunoprecipitation. DNMT3A could inhibit the transcription of EphrinB2 and HEY2 promoters by affecting the binding of E2F1 to its recognition sequences as revealed by luciferase reporter assay and chromatin immunoprecipitation. These results identified a novel mechanism underlying the cooperation of DNMT3A with E2F1 on regulating target gene expression, and revealed their roles in the angiogenic process.

Effective inhibition of MYC-amplified group 3 medulloblastoma by FACT-targeted curaxin drug CBL0137

Medulloblastoma (MB) is the most common malignant pediatric brain tumor that can be categorized into four major molecular subgroups. Group 3 MB with MYC amplification (MYCamp-G3-MB) has been shown to be highly aggressive and exhibited worst prognosis, indicating the need for novel effective therapy most urgently. A few epigenetic targeted therapeutic strategies have recently been proven to effectively treat preclinical models of MYCamp-G3-MB, including BET inhibition, HDAC inhibition and SETD8 inhibition, unveiling a promising direction for further investigation. In this study, we carried out systemic bioinformatic analyses of public-available MB datasets as well as functional genomic screening datasets of primary MYCamp-G3-MB lines to search for other potential therapeutic targets within epigenetic modulators. We identified SSRP1, a subunit of histone-chaperone FACT complex, to be the top drug target candidate as it is highly cancer-dependent in whole-genome CRISPR-Cas9 screening across multiple MYCamp-G3-MB lines; significantly upregulated in MYCamp-G3-MB compared to normal cerebellum and most of the rest MB subtypes; its higher expression is correlated with worse prognosis; and it has a blood-brain-barrier penetrable targeted drug that has entered early phase human clinical trials already. Then we utilized RNA-interference approach to verify the cancer-dependency of SSRP1 in multiple MYCamp-G3-MB lines and further confirmed the therapeutic efficacy of FACT-targeted curaxin drug CBL0137 on treating preclinical models of MYCamp-G3-MB in vitro and in vivo, including an orthotopic intracranial xenograft model. Mechanistically, transcriptome analyses showed CBL0137 preferentially suppressed cell-cycle and DNA-repair related biological processes. Moreover, it selectively disrupted transcription of MYC and NEUROD1, two critical oncogenic transcription factors of MYCamp-G3-MB, via depleting FACT complex from their promoter regions. In summary, our study demonstrates FACT-targeted CBL0137 works effectively on treating MYCamp-G3-MB, presenting another promising epigenetic-targeted therapeutic strategy against the most devastating form of MB.

Comprehensive Analysis of Zinc Derivatives Pro-proliferative, Anti-Apoptotic and Antimicrobial Effect on Human Fibroblasts and Keratinocytes in a Simulated, Nutrient-deficient Environment In Vitro

Zinc as therapeutic agent in skin and wound care has been known for centuries, but its role is controversial and comprehensive investigations in nutrient-deficient environments are lacking. We aimed to provide a broad analysis of different zinc derivatives on proliferation, apoptosis and antimicrobial properties in a simulated nutrient-deficient environment in vitro. Human fibroblasts (CRL2522) and keratinocytes (HaCaT) were treated with a broad concentration range (10 – 0.0001 µg/mL) of zinc-sulfate (ZnSO₄), -gluconate (ZnGluc) and -histidine (ZnHis) for 1-6 days under nutrient-deficient media conditions. Cell proliferation was investigated by XTT assay. Targeted analyzes in proliferation (E2F1, PCNA) and apoptosis (TP53) associated genes were performed via qRT-PCR and apoptosis was determined via FACS (annexin V/7-AAD staining). Antimicrobial efficacy was investigated using a quantitative suspension method against S. aureus, P. aeruginosa, E. coli, and C. albicans. The results indicated that 0.1 to 0.001 µg/mL Zn increased cell proliferation in both cell lines. Fibroblasts were more susceptible with significant proliferation peaks on days 2 & 6, and days 1 & 4 for keratinocytes. No relevant changes in gene expression were detected for E2F1 and PCNA nor for TP53. Annexin-V/7-AAD-staining of fibroblasts revealed a small, yet insignificant reduction of apoptosis induction for ZnGluc and ZnSO₄. ZnGluc and ZnSO₄ (0.1%) achieved high microbial reductions (4-5 log₁₀ reductions) against tested pathogens. ZnGluc and ZnSO₄ showed relevant pro-proliferative and antimicrobial, as well as tendential anti-apoptotic features in a simulated nutrient-deficient microenvironment in vitro. This further validates a potential benefit of local zinc treatment in deficient wound microenvironments.

Significance of nuclear cathepsin V in normal thyroid epithelial and carcinoma cells

Altered expression and/or localization of cysteine cathepsins is believed to involve in thyroid diseases including cancer. Here, we examined the localization of cathepsins B and V in human thyroid tissue sections of different pathological conditions by immunolabeling and morphometry. Cathepsin B was mostly found within endo-lysosomes as expected. In contrast, cathepsin V was detected within nuclei, predominantly in cells of cold nodules, follicular and papillary thyroid carcinoma tissue, while it was less often detected in this unusual localization in hot nodules and goiter tissue. To understand the significance of nuclear cathepsin V in thyroid cells, this study aimed to establish a cellular model of stable nuclear cathepsin V expression. As representative of a specific form lacking the signal peptide and part of the propeptide, N-terminally truncated cathepsin V fused to eGFP recapitulated the nuclear localization of endogenous cathepsin V throughout the cell cycle in Nthy-ori 3-1 cells. Interestingly, the N-terminally truncated cathepsin V-eGFP was more abundant in the nuclei during S phase. These findings suggested a possible contribution of nuclear cathepsin V forms to cell cycle progression. Indeed, we found that N-terminally truncated cathepsin V-eGFP expressing cells were more proliferative than those expressing full-length cathepsin V-eGFP or wild type controls. We conclude that a specific molecular form of cathepsin V localizes to the nucleus of thyroid epithelial and carcinoma cells, where it might involve in deregulated pathways leading to hyperproliferation. These findings highlight the necessity to better understand cathepsin trafficking in health and disease. In particular, cell type specificity of mislocalization of cysteine cathepsins, which otherwise act in a functionally redundant manner, seems to be important to understand their non-canonical roles in cell cycle progression.

Pharmacological Stimulation of Nurr1 Promotes Cell Cycle Progression in Adult Hippocampal Neural Stem Cells

Nuclear receptor related-1 (Nurr1) protein performs a crucial role in hippocampal neural stem cell (hNSC) development as well as cognitive functions. We previously demonstrated that the pharmacological stimulation of Nurr1 by amodiaquine (AQ) promotes spatial memory by enhancing adult hippocampal neurogenesis. However, the role of Nurr1 in the cell cycle regulation of the adult hippocampus has not been investigated. This study aimed to examine changes in the cell cycle-related molecules involved in adult hippocampal neurogenesis induced by Nurr1 pharmacological stimulation. Fluorescence-activated cell sorting (FACS) analysis showed that AQ improved the progression of cell cycle from G0/G1 to S phase in a dose-dependent manner, and MEK1 or PI3K inhibitors attenuated this progression. In addition, AQ treatment increased the expression of cell proliferation markers MCM5 and PCNA, and transcription factor E2F1. Furthermore, pharmacological stimulation of Nurr1 by AQ increased the expression levels of positive cell cycle regulators such as cyclin A and cyclin-dependent kinases (CDK) 2. In contrast, levels of CDK inhibitors p27KIP1 and p57KIP2 were reduced upon treatment with AQ. Similar to the in vitro results, RT-qPCR analysis of AQ-administered mice brains revealed an increase in the levels of markers of cell cycle progression, PCNA, MCM5, and Cdc25a. Finally, AQ administration resulted in decreased p27KIP1 and increased CDK2 levels in the dentate gyrus of the mouse hippocampus, as quantified immunohistochemically. Our results demonstrate that the pharmacological stimulation of Nurr1 in adult hNSCs by AQ promotes the cell cycle by modulating cell cycle-related molecules.

Circular Trajectory Reconstruction Uncovers Cell-Cycle Progression and Regulatory Dynamics from Single-Cell Hi-C Maps

Single-cell Hi-C technology is emerging and will provide unprecedented opportunities to elucidate chromosomal dynamics with high resolution. How to characterize pseudo time-series of single cells using single-cell Hi-C maps is an essential and challenging topic. To this end, a powerful circular trajectory reconstruction tool CIRCLET is developed to resolve cell cycle phases of single cells by considering multiscale features of chromosomal architectures without specifying a starting cell. CIRCLET reveals its best superiority based on the combination of one feature set about global information and another two feature sets about local interactional information in terms of designed evaluation indexes and verification strategies from a collection of cell-cycle Hi-C maps of 1171 single cells. Further division of the reconstructed trajectory into 12 stages helps to accurately characterize the dynamics of chromosomal structures and explain the special regulatory events along cell-cycle progression. Last but not the least, the reconstructed trajectory helps to uncover important regulatory genes related with dynamic substructures, providing a novel framework for discovering regulatory regions even cancer markers at single-cell resolution.

D-site binding protein regulates cell proliferation through mediating cell cycle progression in rat mesangial cells

Over proliferation of glomerular mesangial cells (MCs) disturbs mesangial homeostasis and leads to renal damage in mesangioproliferative glomerulonephritis. It is documented that transcriptional factors may be involved in the proliferation of MCs. This study aims to identify the key transcriptional factor that prevents the MCs from over proliferation and to clarify its regulatory mechanism. Microarray analysis of glomeruli isolated from Sprague-Dawley rats (SD rats) with or without anti-Thy1 nephritis (anti-Thy1N) showed that the cell cycle pathway was the most enriched pathway in anti-Thy1N model, and the D-site binding protein (DBP) ranked first in the cluster of transcription factors. Compare with normal rats, DBP is markedly decreased accompanied by an over proliferation of MCs in rats with anti-Thy1N. The cell proliferative capacity was measured by 5-Ethynyl-2'-deoxyuridine (EdU) assay in primary rat MCs with DBP knockdown or overexpression, respectively. The results showed that the knockdown of DBP significantly promoted the proliferation of MCs, whereas the overexpression of DBP inhibited the MCs' proliferation, compared to that of the control cells. Further study indicated that DBP arrested G1/S-phase transition by inhibiting the expression of p21, p27 and inducing the Cyclin D1 expression in MCs. The current data suggest that DBP effectively inhibits the proliferation of MCs through G1 phase arrest, and the decrease of DBP may induce mesangial over proliferation in rats with anti-Thy1N.

miR‑329‑3p regulates neural stem cell proliferation by targeting E2F1

Neural stem cells (NSCs) are a class of self‑renewing and undifferentiated progenitor cells that retain the ability to differentiate to neurons, astrocytes and oligodendrocytes. MicroRNAs (miRNAs) are small noncoding RNAs that serve crucial roles in regulating a number of cellular processes, including cell proliferation, differentiation and apoptosis. Our previous GeneChip data indicated that the expression of miR‑329‑3p was increased in neurons compared with NSCs. However, whether miRNA‑329‑3p participates in regulating NSC function remains to be elucidated. In the present study, it was identified that the expression of miR‑329‑3p was upregulated in NSCs during neuronal differentiation, whereas expression of transcription factor E2F1 (E2F1), a putative target gene of miR‑329‑3p, was downregulated. Using luciferase reporter assays, it was confirmed that miR‑329‑3p regulated E2F1 expression. As differentiation has been demonstrated to limit the proliferative capacity of NSCs, the effects of miR‑329‑3p and E2F1 modulation on NSC proliferation were examined. Forced overexpression of miR‑329‑3p or RNA‑mediated silencing of E2F1 inhibited NSC proliferation, and overexpression of miR‑329‑3p also inhibited E2F1 expression. Notably, ectopic expression of E2F1 reversed the inhibition of NSC proliferation induced by miR‑329‑3p overexpression. These results indicated that miR‑329‑3p may serve crucial roles in regulating the proliferation of NSCs, at least in part via inhibition of E2F1 expression. These data improve the understanding of the microRNA‑mRNA regulatory network that controls NSC proliferation.

A Pathway-Based Strategy to Identify Biomarkers for Lung Cancer Diagnosis and Prognosis

Current research has identified several potential biomarkers for lung cancer diagnosis or prognosis. However, most of these biomarkers are derived from a relatively small number of samples using algorithms at the gene level. Hence, gene expression signatures discovered in these studies have little overlaps. In this study, we proposed a new strategy to identify biomarkers from multiple datasets at the pathway level. We integrated the genome-wide expression data of lung cancer tissues from 13 published studies and applied our strategy to identify lung cancer diagnostic and prognostic biomarkers. We identified a 32-gene signature that differentiates lung adenocarcinomas from other lung cancer subtypes. We also discovered a 43-gene signature that can predict the outcome of human lung cancers. We tested their performance in several independent cohorts, which confirmed their robust prognostic and diagnostic power. Furthermore, we showed that the proposed gene expression signatures were independent of several traditional clinical indicators in lung cancer management. Our results suggest that the pathway-based strategy is useful to identify transcriptomic biomarkers from large-scale gene expression datasets that were collected from multiple sources.

E2F is required for STAT3-mediated upregulation of cyclin B1 and Cdc2 expressions and contributes to G2-M phase transition

Activation of transcription factor STAT3 is involved in cell proliferation, differentiation, and cell survival. Constitutive activation of STAT3 pathway has been associated with the oncogenesis of various types of cancers. It has been reported that STAT3 plays a key role in the G1 to S phase cell cycle transition induced by the cytokine receptor subunit gp130, through the upregulation of cyclins D1, D2, D3, A, and Cdc25A and the concomitant downregulation of p21 and p27. However, its role in mediating G2-M phase transition has not been studied. The cyclin B1/Cdc2 complex is widely accepted as the trigger of mitosis in all organisms and is believed to be necessary for progression through S phase and keep active during the G2-M transition and progression. In the present study, we found that activation of STAT3 stimulates cyclin B1 and Cdc2 expressions. Deletion and site-directed mutations on cyclin B1 and Cdc2 promoters indicated that E2F element mediates the upregulation of these two promoters in a STAT3-dependent manner. The findings reported here demonstrated that STAT3 participates in modulating G2-M phase checkpoint by regulating gene expressions of cyclin B1 and Cdc2 via E2F.

Tumor-Suppressing Effect of Silencing of Annexin A3 Expression in Breast Cancer

INTRODUCTION

Annexin A3 (ANXA3) participates in various tumor-associated biological processes, including tumor initiation, progression, and metastasis. The present study was designed to investigate the expression and function of ANXA3 in breast cancer cells.

MATERIALS AND METHODS

Annexin A3 protein expression in breast cancer cell lines was evaluated using Western blot analysis. ANXA3 expression in MDA-MB 231 breast cancer cells was silenced by RNA interference, and the effects of RNA silencing on cell proliferation, colony forming ability, wound-healing, and invasiveness were evaluated. Levels of ANXA3 expression in 30 primary breast cancers were assayed using immunohistochemistry and correlated with patient survival.

RESULTS

Levels of ANXA3 expression were higher in the basal subtype of breast cancer cells, such as MDA-MB 231, HCC-70, and HCC-1954 cells, than in other subtypes. ANXA3 silencing inhibited the activities of MDA-MB 231 and HCC-1954 cells, including their proliferation, invasion across transwell membranes, and wound-healing and colony forming abilities. ANXA3 small interfering RNA (siRNA) also reduced the expression of cycle-dependent kinase protein and increased the expression of E2F1 and p27 proteins compared with control siRNA. Expression of ANXA3 was closely correlated with tumor size, with higher ANXA3 expression associated with reduced disease-free survival in breast cancer patients.

CONCLUSION

These findings indicate that ANXA3 is associated with the natural progression of breast cancer and might be a potential prognostic marker of patient survival.

Cold Shock Proteins Mediate GN with Mesangioproliferation

DNA binding protein A (DbpA) is a member of the human cold shock domain-containing protein superfamily, with known functions in cell proliferation, differentiation, and stress responses. DbpA mediates tight junction-associated activities in tubular epithelial cells, but the function of DbpA in mesangial cells is unknown. Here, we found DbpA protein expression restricted to vascular smooth muscle cells in healthy human kidney tissue but profound induction of DbpA protein expression within the glomerular mesangial compartment in mesangioproliferative nephritis. In vitro, depletion or overexpression of DbpA using lentiviral constructs led to inhibition or promotion, respectively, of mesangial cell proliferation. Because platelet-derived growth factor B (PDGF-B) signaling has a pivotal role in mesangial cell proliferation, we examined the regulatory effect of PDGF-B on DbpA. In vitro studies of human and rat mesangial cells confirmed a stimulatory effect of PDGF-B on DbpA transcript numbers and protein levels. Additional in vivo investigations showed DbpA upregulation in experimental rat anti-Thy1.1 nephritis and murine mesangioproliferative nephritis models. To interfere with PDGF-B signaling, we injected nephritic rats with PDGF-B neutralizing aptamers or the MEK/ERK inhibitor U0126. Both interventions markedly decreased DbpA protein expression. Conversely, continuous PDGF-B infusion in healthy rats induced DbpA expression predominantly within the mesangial compartment. Taken together, these results indicate that DbpA is a novel target of PDGF-B signaling and a key mediator of mesangial cell proliferation.

Loss of Gsα impairs liver regeneration through a defect in the crosstalk between cAMP and growth factor signaling

BACKGROUND & AIMS

The stimulatory G protein α subunit (Gsα) activates the cAMP-dependent pathway by stimulating the production of cAMP and participates in diverse cell processes. Aberrant expression of Gsα results in various pathophysiological disorders, including tumorigenesis, but little is known about its role in liver regeneration.

METHODS

We generated a hepatocyte-specific Gsα gene knockout mouse to demonstrate the essential role of Gsα in liver regeneration using a mouse model with 70% partial hepatectomy (PH) or an intraperitoneal injection of carbon tetrachloride (CCl4).

RESULTS

Gsα inactivation dramatically impaired liver regeneration and blocked proliferating hepatocytes in G1/S transition due to the simultaneous depression of cyclin-dependent kinase 2 (CDK2) and cyclin E1. Loss of Gsα led to a fundamental alteration in gene profiles. Among the altered signaling cascades, the MAPK/Erk pathway, which is downstream of growth factor signaling, was disrupted secondary to a defect in phosphorylated Raf1 (pRaf1), resulting in a deficiency in phosphorylated CREB (pCREB) and CDK2 ablation. The lack of pRaf1 also resulted in a failure to phosphorylate retinoblastoma, which releases and activates E2F1, and a decrease in cyclin E1. Although these factors could be phosphorylated through both Gsα and growth factor signaling, the unique function of Raf1 in the growth factor cascade collapsed in response to the lack of Gsα.

CONCLUSION

The growth factor signaling pathway that promotes hepatocyte proliferation is dependent on Gsα signaling. Loss of Gsα leads to a breakdown of the crosstalk between cAMP and growth factor signaling and dramatically impairs liver regeneration.

Protease Omi facilitates neurite outgrowth in mouse neuroblastoma N2a cells by cleaving transcription factor E2F1

AIM

Omi is an ATP-independent serine protease that is necessary for neuronal function and survival. The aim of this study was to investigate the role of protease Omi in regulating differentiation of mouse neuroblastoma cells and to identify the substrate of Omi involved in this process.

METHODS

Mouse neuroblastoma N2a cells and Omi protease-deficient mnd2 mice were used in this study. To modulate Omi and E2F1 expression, N2a cells were transfected with expression plasmids, shRNA plasmids or siRNA. Protein levels were detected using immunoblot assays. The interaction between Omi and E2F1 was studied using immunoprecipitation, GST pulldown and in vitro cleavage assays. N2a cells were treated with 20 μmol/L retinoic acid (RA) and 1% fetal bovine serum to induce neurite outgrowth, which was measured using Image J software.

RESULTS

E2F1 was significantly increased in Omi knockdown cells and in brain lysates of mnd2 mice, and was decreased in cells overexpressing wild-type Omi, but not inactive Omi S276C. In brain lysates of mnd2 mice, endogenous E2F1 was co-immunoprecipitated with endogenous Omi. In vitro cleavage assay demonstrated that Omi directly cleaved E2F1. Treatment of N2a cells with RA induced marked differentiation and neurite outgrowth accompanied by significantly increased Omi and decreased E2F1 levels, which were suppressed by pretreatment with the specific Omi inhibitor UCF-101. Knockdown of Omi in N2a cells suppressed RA-induced neurite outgrowth, which was partially restored by knockdown of E2F1.

CONCLUSION

Protease Omi facilitates neurite outgrowth by cleaving the transcription factor E2F1 in differentiated neuroblastoma cells; E2F1 is a substrate of Omi.

Transcriptome profile of human neuroblastoma cells in the hypomagnetic field

Research has shown that the hypomagnetic field (HMF) can affect embryo development, cell proliferation, learning and memory, and in vitro tubulin assembly. In the present study, we aimed to elucidate the molecular mechanism by which the HMF exerts its effect, by comparing the transcriptome profiles of human neuroblastoma cells exposed to either the HMF or the geomagnetic field. A total of 2464 differentially expressed genes (DEGs) were identified, 216 of which were up-regulated and 2248 of which were down-regulated after exposure to the HMF. These DEGs were found to be significantly clustered into several key processes, namely macromolecule localization, protein transport, RNA processing, and brain function. Seventeen DEGs were verified by real-time quantitative PCR, and the expression levels of nine of these DEGs were measured every 6 h. Most notably, MAPK1 and CRY2, showed significant up- and down-regulation, respectively, during the first 6 h of HMF exposure, which suggests involvement of the MAPK pathway and cryptochrome in the early bio-HMF response. Our results provide insights into the molecular mechanisms underlying the observed biological effects of the HMF.

Lysine acetyltransferase GCN5 potentiates the growth of non-small cell lung cancer via promotion of E2F1, cyclin D1, and cyclin E1 expression

The lysine acetyltransferases play crucial but complex roles in cancer development. GCN5 is a lysine acetyltransferase that generally regulates gene expression, but its role in cancer development remains largely unknown. In this study, we report that GCN5 is highly expressed in non-small cell lung cancer tissues and that its expression correlates with tumor size. We found that the expression of GCN5 promotes cell growth and the G1/S phase transition in multiple lung cancer cell lines. Further study revealed that GCN5 regulates the expression of E2F1, cyclin D1, and cyclin E1. Our reporter assays indicated that the expression of GCN5 enhances the activities of the E2F1, cyclin D1, and cyclin E1 promoters. ChIP experiments suggested that GCN5 binds directly to these promoters and increases the extent of histone acetylation within these regions. Mechanistic studies suggested that GCN5 interacts with E2F1 and is recruited by E2F1 to the E2F1, cyclin D1, and cyclin E1 promoters. The function of GCN5 in lung cancer cells is abrogated by the knockdown of E2F1. Finally, we confirmed that GCN5 regulates the expression of E2F1, cyclin D1, and cyclin E1 and potentiates lung cancer cell growth in a mouse tumor model. Taken together, our results demonstrate that GCN5 specifically potentiates lung cancer growth by directly promoting the expression of E2F1, cyclin D1, and cyclin E1 in an E2F1-dependent manner. Our study identifies a specific and novel function of GCN5 in lung cancer development and suggests that the GCN5-E2F1 interaction represents a potential target for lung cancer treatment.

Novel pancreatic endocrine maturation pathways identified by genomic profiling and causal reasoning

We have used a previously unavailable model of pancreatic development, derived in vitro from human embryonic stem cells, to capture a time-course of gene, miRNA and histone modification levels in pancreatic endocrine cells. We investigated whether it is possible to better understand, and hence control, the biological pathways leading to pancreatic endocrine formation by analysing this information and combining it with the available scientific literature to generate models using a casual reasoning approach. We show that the embryonic stem cell differentiation protocol is highly reproducible in producing endocrine precursor cells and generates cells that recapitulate many aspects of human embryonic pancreas development, including maturation into functional endocrine cells when transplanted into recipient animals. The availability of whole genome gene and miRNA expression data from the early stages of human pancreatic development will be of great benefit to those in the fields of developmental biology and diabetes research. Our causal reasoning algorithm suggested the involvement of novel gene networks, such as NEUROG3/E2F1/KDM5B and SOCS3/STAT3/IL-6, in endocrine cell development We experimentally investigated the role of the top-ranked prediction by showing that addition of exogenous IL-6 could affect the expression of the endocrine progenitor genes NEUROG3 and NKX2.2.

Methylation-mediated regulation of E2F1 in DNA damage-induced cell death

E2F1 promotes DNA damage-induced apoptosis and the post-translational modifications of E2F1 play an important role in the regulation of E2F1-mediated cell death. Here, we found that Set9 and LSD1 regulate E2F1-mediated apoptosis upon DNA damage. Set9 methylates E2F1 at lysine 185, a conserved residue in the DNA-binding domain of E2F family proteins. The methylation of E2F1 by Set9 leads to the stabilization of E2F1 and up-regulation of its proapoptotic target genes p73 and Bim, and thereby induces E2F1-mediated apoptosis in response to genotoxic agents. We also found that LSD1 demethylates E2F1 at lysine 185 and reduces E2F1-mediated cell death. The identification of the methylation/demethylation of E2F1 by Set9/LSD1 suggests that E2F1 is dynamically regulated by epigenetic enzymes in response to DNA damage.

Estrogen receptor regulates E2F1 expression to mediate tamoxifen resistance

Antiestrogen resistance often develops with prolonged exposure to hormone therapies, including tamoxifen, and is a major problem in the treatment of breast cancer. Understanding the mechanisms involved in the development of antiestrogen resistance is an important step in the development of new targeted therapies. Two forms of antiestrogen resistance exist: de novo resistance and acquired resistance. To mimic acquired resistance, we have established a tamoxifen-resistant breast cancer cell line (MCF-7TamR) by treating parental MCF-7 cells with tamoxifen over a period of 6 months to select for cells with the resistant phenotype. Characterization of the MCF-7TamR cells under normal, hormone-deprived, and tamoxifen-treated conditions suggests that these cells continue to grow in the presence of tamoxifen. Additionally, a greater percentage of resistant cells enter the S phase under tamoxifen conditions, compared with parental MCF-7 cells. Consistent with these growth results, molecular analysis indicates that tamoxifen-resistant cells express higher levels of cyclin E1, cdk2, ACTR, and E2F1. Faslodex or ICI 182, 780 (ICI)-mediated degradation of estrogen receptor (ER) reduced the proliferation of these cells, as well as the level of E2F1 expression in tamoxifen-resistant cells, suggesting that tamoxifen resistance and E2F1 expression are in part dependent on ER. We further showed that tamoxifen enhances the ERalpha/Sp-1 interaction and promotes the recruitment of ERalpha and Sp-1 to the proximal promoter of E2F1 in resistant cells. Collectively, our findings suggest that tamoxifen resistance is a result of increased ERalpha/Sp-1 interaction, which enhances the expression of E2F1 to promote tamoxifen resistance.

Alien inhibits E2F1 gene expression and cell proliferation

Recently, using a proteomic approach we have identified the corepressor Alien as a novel interacting factor of the cell cycle regulator E2F1. Unclear was whether this interaction influences cell proliferation and endogenous E2F1 target gene expression. Here, we show by chromatin immunoprecipitation (ChIP) that Alien is recruited in vivo to the E2F binding sites present in the E2F1 gene promoter, inhibits the transactivation of E2F1 and represses endogenous E2F1 gene expression. Interestingly, using synchronized cells to assess the expression of Alien profile during cell cycle the levels of endogenous Alien are increased during G1, G1/S and G2 phase. Furthermore, stable transfection of Alien leads to reduction of cell proliferation. Thus, the data suggest that Alien acts as a corepressor for E2F1 and is involved in cell cycle regulation.

Preplaced cell division: a critical mechanism of autoprotection againstS-1,2-dichlorovinyl-l-cysteine-induced acute renal failure and death in mice

Previous studies have shown that renal injury initiated by a lethal dose of S-1,2-dichlorovinyl-l-cysteine (DCVC) progresses due to inhibition of cell division and hence renal repair, leading to acute renal failure (ARF) and death in mice. Renal injury initiated by low to moderate doses of DCVC is repaired by timely and adequate stimulation of renal cell division, tubular repair, restoration of renal structure and function leading to survival of mice. Recent studies have established that mice primed with a low dose of DCVC (15 mg/kg ip) 72 h before administration of a normally lethal dose (75 mg/kg ip) are protected from ARF and death (nephro-autoprotection). We showed that renal cell division and tissue repair stimulated by the low dose are sustained even after the lethal dose administration resulting in survival from ARF and death. If renal cell division induced by the low dose is indeed the critical mechanism of this autoprotection, then its ablation by the antimitotic agent colchicine (1.5 mg CLC/kg ip) should abolish autoprotection. The present interventional experiments were designed to test the hypothesis that DCVC autoprotection is due to stimulated cell division and tissue repair by the priming low dose. CLC intervention at 42 and 66 h after the priming dose resulted in marked progressive elevation of plasma blood urea nitrogen and creatinine resulting in ARF and death of mice. Light microscopic examination of hematoxylin and eosin-stained kidney sections revealed progression of renal necrosis concordant with progressively failing renal function. With CLC intervention, S-phase stimulation (as assessed by BrdU pulse labeling), G1-to-S phase clearance, and cell division were diminished essentially abolishing the promitogenic effect of the priming low dose of DCVC. Phospho-retinoblastoma protein (P-pRB), a crucial protein for S-phase stimulation, and other cellular signaling mechanisms regulating P-pRB were investigated. We report that decreased P-pRB via activation of protein phosphatase-1 by CLC is the critical mechanism of this inhibited S-phase stimulation and ablation of autoprotection with CLC intervention. These findings lend additional support to the notion that stimulated cell division and renal tissue repair by the priming dose of DCVC are the critical mechanisms that allow sustained compensatory tissue repair and survival of mice in nephro-autoprotection.

Deregulation of cyclin-dependent kinase 2 activity correlates with UVC-induced apoptosis in Chinese hamster ovary cells

Progression through the cell cycle relies on the activities of cyclin-dependent kinases (Cdk), which in turn are modulated by inhibitory proteins such as p21(waf1/cip1) that are induced when genomic damage occurs. In this study, we show that exposure of normal mammalian cells, such as NIH3T3 fibroblasts, to UVC (25 J/m2, at 254 nm) induces the expression of p21 without causing significant apoptosis, whereas similar treatment of Chinese hamster ovary (CHO-K1) cells with UVC causes apoptosis without inducing p21. The absence of p21 in UV-irradiated CHO-K1 cells is accompanied by the deregulation of Cdk2 activity. The elevation of Cdk2 activity correlates with the increase of UV-induced apoptosis, which can be suppressed by small-molecule Cdk2 inhibitors such as roscovitine and pyrrolidine dithiocarbamate. The results of this study suggest that the deregulation of Cdk2 activity may be critical to UV-induced apoptosis in CHO-K1 cells.

Molecular mechanisms of enhanced renal cell division in protection againstS-1,2-dichlorovinyl-l-cysteine-induced acute renal failure and death

Sustained activation of ERK 1/2 by a low dose (15 mg/kg ip) of S-1,2-dichlorovinyl-l-cysteine (DCVC) 72 h before administration of a lethal dose of DCVC (75 mg/kg ip) enhances renal cell division and protects mice against acute renal failure (ARF) and death (autoprotection). The objective of this study was to determine correlation among extent of S-phase DNA synthesis, activation of transcription factors, expression of G1/S cyclins, cyclin-dependent kinases (CDKs), and CDK inhibitors downstream of ERK 1/2 following DCVC-induced ARF in autoprotection. Administration of the lethal dose alone caused a general downregulation or an unsustainable increase, in transcriptional and posttranscriptional events thereby preventing G1-S transition of renal cell cycle. Phosphorylation of IκBα was inhibited resulting in limited nuclear translocation of NF-κB. However, cyclin D1 expression was high probably due to transcriptional cooperation of AP-1. Cyclin D1/cyclin-dependent kinase 4 (cdk4)-cdk6 system-mediated phosphorylation of retinoblastoma protein was downregulated due to overexpression of p16 at 24 h after exposure to the lethal dose alone. Inhibition of S-phase stimulation was confirmed by proliferating cell nuclear antigen assay (PCNA). This inhibitory response was prevented if the lethal dose was administered 72 h after the low priming dose of DCVC due to promitogenic effect of the low dose. NF-κB-DNA binding is not limited if mice were pretreated with the priming dose. Cyclin D1/cdk4-cdk6 expression stimulated by the priming dose of DCVC was unaltered even after the lethal dose in the autoprotected group, explaining higher phosphorylated-pRB and S-phase stimulation found in this group. These results were corroborated with PCNA immunohistochemistry. These findings suggest that the priming dose relieves the block on compensatory tissue repair by upregulation of promitogenic mechanisms, normally blocked by the high dose when administered without the prior priming dose.

Role of differential and cell type-specific expression of cell cycle regulatory proteins in mediating progressive glomerular injury in human IgA nephropathy

The activities of cell cycle regulatory proteins have been reported to be associated with the development of pathological lesions in glomerulonephritis. To assess the cellular mechanisms underlying the mesangial cell proliferation and glomerulosclerosis in progressive human IgA nephropathy (IgAN), we examined the expression of E2F1, Rb, c-Myc, proliferating cell nuclear antigen (PCNA), cyclins (D1, E and A), cyclin-dependent kinase 2 (CDK2) and CDK inhibitors (p21(waf1), p27(kip1), 57(kip2) and p16(ink4a)) by immunohistochemistry in renal biopsy specimens. Terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) was also performed to detect the presence of apoptosis. In total, 51 cases of IgAN were categorized into four subgroups according to histological severity. A dramatic upregulation of E2F1 expression in mesangial cells was identified in proliferating glomeruli, which correlated well with the proliferation index. High endogenous expression of p27(kip1) and p57(kip2) by podocytes in normal glomeruli and glomeruli with minor lesions was observed to decrease in proliferating and sclerosing glomeruli; this pattern displayed a strong inverse correlation with the mean glomerulosclerosis score and the index of glomerular lesion. Increased apoptotic activity was identified in progressive glomerular lesions of advanced IgAN, which correlated with the proliferative activity in these lesions as assessed by total expression levels of PCNA and CDK2 in glomeruli, E2F1 expression levels in the mesangium, cyclin D1 expression levels in endothelium and the c-Myc glomerular staining score. Our results suggest that the onset and magnitude of mesangial cell proliferation and glomerulosclerosis is associated with the upregulation of E2F1 by mesangial cells and the downregulation of p27(kip1) and p57(kip2) by glomerular epithelial cells. The cell type-specific and coordinated regulation of proliferative and proapoptotic activities of cell cycle regulatory proteins may play an important role in mediating progressive glomerular injury in human IgAN.

Reduced chondrocyte proliferation and chondrodysplasia in mice lacking the integrin-linked kinase in chondrocytes

Chondrocyte proliferation and differentiation requires their attachment to the collagen type II-rich matrix of developing bone. This interaction is mediated by integrins and their cytoplasmic effectors, such as the integrin-linked kinase (ILK). To elucidate the molecular mechanisms whereby integrins control these processes, we have specifically inactivated the ILK gene in growth plate chondrocytes using the Cre-lox methodology. Mice carrying an ILK allele flanked by loxP sites (ILK-fl) were crossed to transgenic mice expressing the Cre recombinase under the control of the collagen type II promoter. Inactivation of both copies of the ILK-fl allele lead to a chondrodysplasia characterized by a disorganized growth plate and to dwarfism. Expression of chondrocyte differentiation markers such as collagen type II, collagen type X, Indian hedgehog and the PTH-PTHrP receptor was normal in ILK-deficient growth plates. In contrast, chondrocyte proliferation, assessed by BrdU or proliferating cell nuclear antigen labeling, was markedly reduced in the mutant growth plates. Cell-based assays showed that integrin-mediated adhesion of primary cultures of chondrocytes from mutant animals to collagen type II was impaired. ILK inactivation in chondrocytes resulted in reduced cyclin D1 expression, and this most likely explains the defect in chondrocyte proliferation observed when ILK is inactivated in growth plate cells.

Growth factor pathways in proliferative glomerulonephritis

Growth factor production, glomerular cell proliferation and glomerular extracellular matrix expansion are prominent features of mesangioproliferative and crescentic glomerulonephritides. Recent studies have provided additional insights into the mechanisms of mesangial cell proliferation and interaction with extracellular matrix, and have focused on selective interruption of relevant mediators of injury. Studies into mitogenic signalling and cell cycle regulation in glomerular epithelial cells support a pathogenetic role for growth factors and glomerular epithelial cell proliferation in focal segmental glomerulosclerosis, and possibly membranous nephropathy. A better appreciation of growth factor pathways may lead to new treatment strategies for human glomerulopathies.