BET Bromodomain Inhibition Blocks an AR-Repressed, E2F1-Activated Treatment-Emergent Neuroendocrine Prostate Cancer Lineage Plasticity Program.

PURPOSE: Lineage plasticity in prostate cancer-most commonly exemplified by loss of androgen receptor (AR) signaling and a switch from a luminal to alternate differentiation program-is now recognized as a treatment resistance mechanism. Lineage plasticity is a spectrum, but neuroendocrine prostate cancer (NEPC) is the most virulent example. Currently, there are limited treatments for NEPC. Moreover, the incidence of treatment-emergent NEPC (t-NEPC) is increasing in the era of novel AR inhibitors. In contradistinction to de novo NEPC, t-NEPC tumors often express the AR, but AR's functional role in t-NEPC is unknown. Furthermore, targetable factors that promote t-NEPC lineage plasticity are also unclear. EXPERIMENTAL DESIGN: Using an integrative systems biology approach, we investigated enzalutamide-resistant t-NEPC cell lines and their parental, enzalutamide-sensitive adenocarcinoma cell lines. The AR is still expressed in these t-NEPC cells, enabling us to determine the role of the AR and other key factors in regulating t-NEPC lineage plasticity. RESULTS: AR inhibition accentuates lineage plasticity in t-NEPC cells-an effect not observed in parental, enzalutamide-sensitive adenocarcinoma cells. Induction of an AR-repressed, lineage plasticity program is dependent on activation of the transcription factor E2F1 in concert with the BET bromodomain chromatin reader BRD4. BET inhibition (BETi) blocks this E2F1/BRD4-regulated program and decreases growth of t-NEPC tumor models and a subset of t-NEPC patient tumors with high activity of this program in a BETi clinical trial. CONCLUSIONS: E2F1 and BRD4 are critical for activating an AR-repressed, t-NEPC lineage plasticity program. BETi is a promising approach to block this program.

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.

Context-Dependent Functions of E2F1: Cell Cycle, Cell Death, and DNA Damage Repair in Cortical Neurons.

DNA damage has been reported to induce cell cycle-related neuronal death. This is significant as aberrant cell cycle re-entry of mature, post-mitotic neurons contributes to neurodegeneration. In this study, we investigate how DNA damage elicited by exposure to the topoisomerase I inhibitor camptothecin (CPT) leads to cycle-related death of cultured cortical neurons and examine the function of E2F1 in this process. CPT treatment induced cell cycle initiation of cortical neurons and elevated the expression of certain cell cycle components (e.g., cyclin D1, CDK4, E2F1) but failed to drive S phase entry or DNA synthesis. The arrest in the cell cycle is explained by the elevated expression of the CDK inhibitor p21Cip1. Though its level was increased after CPT treatment, E2F1 did not drive treated neurons into the G1-S phase transition. E2F1 overexpression led to cell cycle activation and acute neuronal apoptosis without detectable entry of the neurons into S phase. ChIPseq analysis demonstrated that E2F1 predominantly occupies positions on or near the promoters of cell cycle related genes. Instead, in CPT-treated neurons, E2F1 preferentially regulated DNA repair related genes. Our study reveals that the functions of E2F1 in postmitotic neurons are context-dependent and offers novel insights into the role of E2F1 in DNA damage induced cycle-related neuronal death.

Function and characterization of the promoter region of perilipin 1 (PLIN1): Roles of E2F1, PLAG1, C/EBPß, and SMAD3 in bovine adipocytes.

Perilipin 1 (PLIN1) protein, also known as lipid droplet-associated protein, is encoded by the PLIN1 gene and is able to anchor itself to the membranes of lipid droplets. The phosphorylation of PLIN1 is critical for the mobilization of fat in adipose tissue and plays an important role in regulating lipolysis and lipid storage in adipocytes. However, research on the synthesis and lipid metabolism of lipid droplets by PLIN1 in bovine adipocytes is limited. In the present study, we found that bovine PLIN1 was highly expressed in subcutaneous adipose tissue. The highest level of PLIN1 mRNA expression in bovine adipocytes was observed on day 6 of differentiation. Moreover, the cytoplasmic subcellular localization of PLIN1 was observed in bovine preadipocytes. To elucidate the molecular mechanism of bovine PLIN1 transcriptional regulation, we cloned eight fragments containing the 5' regulatory region of the PLIN1 gene. The results showed that the -209/-17 bp region of the bovine PLIN1 gene was the core promoter region. Based on the transcriptional activities of the promoter vector fragments, the luciferase activity of the mutated fragment, the siRNA interference, and the results of the electrophoretic mobility shift assay (EMSA), we identified the binding sites of E2F transcription factor 1 (E2F1), pleiomorphic adenoma gene 1 (PLAG1), CCAAT enhancer binding protein beta (C/EBPß), and SMAD family member 3 (SMAD3) as the transcriptional activators or repressors of the core promoter region. Further experiments confirmed that the knockdown of the PLIN1 gene affected the ability of these transcription factors to regulate the lipid metabolism in bovine adipocytes. In conclusion, our results reveal a potential mechanism for the transcriptional regulation of PLIN1 in bovine adipocytes.

ZBTB7A Mediates the Transcriptional Repression Activity of the Androgen Receptor in Prostate Cancer.

Loss of expression of context-specific tumor suppressors is a critical event that facilitates the development of prostate cancer. Zinc finger and BTB domain containing transcriptional repressors, such as ZBTB7A and ZBTB16, have been recently identified as tumor suppressors that play important roles in preventing prostate cancer progression. In this study, we used combined ChIP-seq and RNA-seq analyses of prostate cancer cells to identify direct ZBTB7A-repressed genes, which are enriched for transcriptional targets of E2F, and identified that the androgen receptor (AR) played a critical role in the transcriptional suppression of these E2F targets. AR recruitment of the retinoblastoma protein (Rb) was required to strengthen the E2F-Rb transcriptional repression complex. In addition, ZBTB7A was rapidly recruited to the E2F-Rb binding sites by AR and negatively regulated the transcriptional activity of E2F1 on DNA replication genes. Finally, ZBTB7A suppressed the growth of castration-resistant prostate cancer (CRPC) in vitro and in vivo, and overexpression of ZBTB7A acted in synergy with high-dose testosterone treatment to effectively prevent the recurrence of CRPC. Overall, this study provides novel molecular insights of the role of ZBTB7A in CRPC cells and demonstrates globally its critical role in mediating the transcriptional repression activity of AR. SIGNIFICANCE: ZBTB7A is recruited to the E2F-Rb binding sites by AR and negatively regulates the transcriptional activity of E2F1 on DNA replication genes.

LncRNA RGMB-AS1 is activated by E2F1 and promotes cell proliferation and invasion in papillary thyroid carcinoma.

OBJECTIVE: To detect the expression of long non-coding ribonucleic acid (lncRNA) RGMB-AS1 in papillary thyroid carcinoma (PTC) and to investigate its influences on PTC cell biological behaviors and its relevant molecular mechanisms. PATIENTS AND METHODS: The expression levels of lncRNA RGMB-AS1 in human PTC tissues, corresponding normal tissues, normal thyroid epithelial cells Nthyori3-1, human PTC cells TPC-1, BCPAP and K1 were detected by quantitative reverse transcription-polymerase chain reaction (qRT-PCR). Si-RGMB-AS1 and control sequence were transfected into TPC-1 and K1 cells. Changes in cell proliferation were detected via cell counting kit 8 (CCK8) assay, and changes in cell migration and invasion capacities were detected by transwell assay. Bioinformatics software was used to predict that the transcription of lncRNA RGMB-AS1 was regulated by the transcription factor E2F1, and changes in lncRNA RGMB-AS1 expression were detected by qRT-PCR after interference in E2F1 expression. Moreover, changes in cell biological functions were detected by CCK8 and transwell assays. Finally, chromatin immunoprecipitation (CHIP) assay was used to detect whether E2F1 bound to lncRNA RGMB-AS1 promoter region. RESULTS: Results of qRT-PCR showed that the lncRNA RGMB-AS1 expression was up-regulated in 38 out of 48 cases of PTC tissues, and it was also up-regulated in PTC cells. Results of CCK8 assay showed that the proliferation capacity of PTC cells was decreased after interference in the expression of lncRNA RGMB-AS1, and results of transwell assay revealed that cell invasion and migration capacities were inhibited. qRT-PCR showed that after interference in E2F1, the expression of lncRNA RGMB-AS1 was down-regulated. Besides, CCK8 and transwell assays showed that proliferation, migration, and invasion capacities of PTC cells were decreased after interference in E2F1. Results of CHIP assay showed that E2F1 bound to lncRNA RGMB-AS1 promoter region. CONCLUSIONS: E2F1 promotes the transcription of lncRNA RGMB-AS1 in PTC. Highly-expressed lncRNA RGMB-AS1 promotes the proliferation, invasion, and migration of PTC.

Resveratrol suppresses doxorubicin-induced cardiotoxicity by disrupting E2F1 mediated autophagy inhibition and apoptosis promotion.

The clinical use of doxorubicin (DOX) is limited by cardiotoxicity, involving the dysregulation of autophagy and apoptosis in the myocardium, which were partly reversed by resveratrol (RSV) supplement. However, a definitive mechanisms accounting for DOX's cardiotoxicity and the protective role of RSV remain poorly defined. The aim of the present study was to clarify the specific role of E2F transcription factor 1 (E2F1) in regulating autophagy and apoptosis in DOX-induced cardiotoxicity as well as the protective effects of RSV. Autophagy and apoptosis were successfully induced by the serum deprivation strategy in H9c2 cardiomyocytes. DOX inhibited autophagy through activating E2F1/mammalian target of rapamycin complex 1 (mTORC1) pathway and further induced apoptosis by activating E2F1/AMP-activated protein kinase α2 (AMPKα2) pathway in starved H9C2 cells. And RSV supplement showed increased autophagy and decreased apoptosis, accompanied with inhibitory effect on E2F1/mTORC1 as well as E2F1/AMPKα2 pathway. Moreover, the favorable effect of RSV on autophagy and apoptosis was dependent on E2F1. The same result was observed in the mouse model of DOX-induced cardiotoxicity in both non-myocardial ischemia and myocardial ischemia condition. Injection with DOX and RSV in combination, resulted in a reduced apoptotic ratio and activated autophagy process compared with the DOX treatment alone. In conclusions, RSV, which has been suggested to attenuate DOX-induced cytotoxicity, significantly blocks induction of E2F1/mTORC1 and E2F1/AMPKα2 pathway by DOX, leading to acceleratory autophagy and inhibitory apoptosis. And E2F1 plays a key role for the protective effect of RSV.

EZH2 enables germinal centre formation through epigenetic silencing of CDKN1A and an Rb-E2F1 feedback loop.

The EZH2 histone methyltransferase is required for B cells to form germinal centers (GC). Here we show that EZH2 mediates GC formation through repression of cyclin-dependent kinase inhibitor CDKN1A (p21Cip1). Deletion of Cdkn1a rescues the GC reaction in Ezh2 -/- mice. Using a 3D B cell follicular organoid system that mimics the GC reaction, we show that depletion of EZH2 suppresses G1 to S phase transition of GC B cells in a Cdkn1a-dependent manner. GC B cells of Cdkn1a -/- Ezh2 -/- mice have high levels of phospho-Rb, indicating that loss of Cdkn1a enables progression of cell cycle. Moreover, the transcription factor E2F1 induces EZH2 during the GC reaction. E2f1 -/- mice manifest impaired GC responses, which is rescued by restoring EZH2 expression, thus defining a positive feedback loop in which EZH2 controls GC B cell proliferation by suppressing CDKN1A, enabling cell cycle progression with a concomitant phosphorylation of Rb and release of E2F1.The histone methyltransferase EZH2 silences genes by generating H3K27me3 marks. Here the authors use a 3D GC organoid and show EZH2 mediates germinal centre (GC) formation through epigenetic silencing of CDKN1A and release of cell cycle checkpoints.

Neuronal tetraploidization in the cerebral cortex correlates with reduced cognition in mice and precedes and recapitulates Alzheimer's-associated neuropathology.

A controversy exists as to whether de novo-generated neuronal tetraploidy (dnNT) occurs in Alzheimer's disease. In addition, the presence of age-associated dnNT in the normal brain remains unexplored. Here we show that age-associated dnNT occurs in both superficial and deep layers of the cerebral cortex of adult mice, a process that is blocked in the absence of E2F1, a known regulator of cell cycle progression. This blockage correlates with improved cognition despite compromised neurogenesis in the adult hippocampus was confirmed in mice lacking the E2f1 gene. We also show that the human cerebral cortex contains tetraploid neurons. In normal humans, age-associated dnNT specifically occurs in the entorhinal cortex whereas, in Alzheimer, dnNT also affects association cortices prior to neurofibrillary tangle formation. Alzheimer-associated dnNT is likely potentiated by altered amyloid precursor protein (APP) processing as it is enhanced in the cerebral cortex of young APPswe/PS1deltaE9 mice, long before the first amyloid plaques are visible in their brains. In contrast to age-associated dnNT, enhanced dnNT in APPswe/PS1deltaE9 mice mostly affects the superficial cortical layers. The correlation of dnNT with reduced cognition in mice and its spatiotemporal course, preceding and recapitulating Alzheimer-associated neuropathology, makes this process a potential target for intervention in Alzheimer's disease.

E2F1-mediated human POMC expression in ectopic Cushing's syndrome.

Cushing's syndrome is caused by excessive adrenocorticotropic hormone (ACTH) secretion derived from pituitary corticotroph tumors (Cushing disease) or from non-pituitary tumors (ectopic Cushing's syndrome). Hypercortisolemic features of ectopic Cushing's syndrome are severe, and no definitive treatment for paraneoplastic ACTH excess is available. We aimed to identify subcellular therapeutic targets by elucidating transcriptional regulation of the human ACTH precursor POMC (proopiomelanocortin) and ACTH production in non-pituitary tumor cells and in cell lines derived from patients with ectopic Cushing's syndrome. We show that ectopic hPOMC transcription proceeds independently of pituitary-specific Tpit/Pitx1 and demonstrate a novel E2F1-mediated transcriptional mechanism regulating hPOMC We identify an E2F1 cluster binding to the proximal hPOMC promoter region (-42 to +68), with DNA-binding activity determined by the phosphorylation at Ser-337. hPOMC mRNA expression in cancer cells was upregulated (up to 40-fold) by the co-expression of E2F1 and its heterodimer partner DP1. Direct and indirect inhibitors of E2F1 activity suppressed hPOMC gene expression and ACTH by modifying E2F1 DNA-binding activity in ectopic Cushing's cell lines and primary tumor cells, and also suppressed paraneoplastic ACTH and cortisol levels in xenografted mice. E2F1-mediated hPOMC transcription is a potential target for suppressing ACTH production in ectopic Cushing's syndrome.

LncRNA HOXA11-AS Promotes Proliferation and Invasion of Gastric Cancer by Scaffolding the Chromatin Modification Factors PRC2, LSD1, and DNMT1.

Long noncoding RNAs (lncRNA) have been implicated in human cancer but their mechanisms of action are mainly undocumented. In this study, we investigated lncRNA alterations that contribute to gastric cancer through an analysis of The Cancer Genome Atlas RNA sequencing data and other publicly available microarray data. Here we report the gastric cancer-associated lncRNA HOXA11-AS as a key regulator of gastric cancer development and progression. Patients with high HOXA11-AS expression had a shorter survival and poorer prognosis. In vitro and in vivo assays of HOXA11-AS alterations revealed a complex integrated phenotype affecting cell growth, migration, invasion, and apoptosis. Strikingly, high-throughput sequencing analysis after HOXA11-AS silencing highlighted alterations in cell proliferation and cell-cell adhesion pathways. Mechanistically, EZH2 along with the histone demethylase LSD1 or DNMT1 were recruited by HOXA11-AS, which functioned as a scaffold. HOXA11-AS also functioned as a molecular sponge for miR-1297, antagonizing its ability to repress EZH2 protein translation. In addition, we found that E2F1 was involved in HOXA11-AS activation in gastric cancer cells. Taken together, our findings support a model in which the EZH2/HOXA11-AS/LSD1 complex and HOXA11-AS/miR-1297/EZH2 cross-talk serve as critical effectors in gastric cancer tumorigenesis and progression, suggesting new therapeutic directions in gastric cancer. Cancer Res; 76(21); 6299-310. ©2016 AACR.

Identification of prognostic microRNA candidates for head and neck squamous cell carcinoma.

The aim of the present study was to uncover potential prognostic microRNA (miRNA) markers in head and neck squamous cell carcinoma (HNSCC). miRNA expression profile and clinical data were obtained from The Cancer Genome Atlas (TCGA) database. Survival analysis was conducted by Kaplan-Meier method. Then, candidate prognostic miRNAs were screened via Cox proportional hazards regression analysis. Furthermore, target genes of miRNAs were predicted, and their interactions and functions were then analyzed. A total of 15 miRNAs were discovered to be significantly related to overall survival. Among them, miR-1251, miR-618 and miR-328 with p<0.05 were potentially significant prognostic factors of HNSCC. In the protein-protein interaction (PPI) network, the target gene of miR-328, MAX, interacted with multiple genes. The target gene of miR-618, E2F1, interacted with genes such as MAX, SMAD3 and IGF1. Furthermore, the target genes of miR-618 (e.g. E2F1 and SMAD3), and the target genes of miR-328 (e.g. MAX) were significantly enriched in the functions of transcriptional regulation. The target gene of miR-1251, IGF1, was associated with functions such as signal transduction. The above miRNAs (miR-1251, miR-618 and miR-328) may be potential prognostic markers in HNSCC.

Genome-wide profiling of long non-coding RNA expression patterns in the EGFR-TKI resistance of lung adenocarcinoma by microarray.

Mutations in the epidermal growth factor receptor (EGFR) make lung adenocarcinoma cells sensitive to EGFR tyrosine kinase inhibitors (TKIs). Long-term cancer therapy may cause the occurrence of acquired resistance to EGFR TKIs. Long non-coding RNAs (lncRNAs) play important roles in tumor formation, tumor metastasis and the development of EGFR-TKI resistance in lung cancer. To gain insight into the molecular mechanisms of EGFR-TKI resistance, we generated an EGFR-TKI-resistant HCC827-8-1 cell line and analyzed expression patterns by lncRNA microarray and compared it with its parental HCC827 cell line. A total of 1,476 lncRNA transcripts and 1,026 mRNA transcripts were dysregulated in the HCC827­8-1 cells. The expression levels of 7 chosen lncRNAs were validated by real-time quantitative PCR. As indicated by functional analysis, several groups of lncRNAs may be involved in the bio-pathways associated with EGFR-TKI resistance through their cis- and/or trans­regulation of protein-coding genes. Thus, lncRNAs may be used as novel candidate biomarkers and potential targets in EGFR-TKI therapy in the future.

Circadian clock gene Per2 plays an important role in cell proliferation, apoptosis and cell cycle progression in human oral squamous cell carcinoma.

Previous studies have shown that the aberrant expression of period circadian clock 2 (Per2) is closely related to the occurrence and development of cancers, but the specific mechanism remains unclear. In the present study, we used shRNA to downregulate Per2 in oral squamous cell carcinoma (OSCC) Tca8113 cells, and then detected the alterations in cell cycle, cell proliferation and apoptosis by flow cytometric analysis and mRNA expression alterations in all the important genes in the cyclin/cyclin-dependent protein kinase (CDK)/cyclin-dependent kinase inhibitor (CKI) cell cycle network by RT-qPCR. We found that in the Tca8113 cells, after Per2 downregulation, the mRNA expression levels of cyclin A2, B1 and D1, CDK4, CDK6 and E2F1 were significantly increased (P<0.05), the mRNA expression levels of p53, p16 and p21 were significantly decreased (P<0.05), cell proliferation was significantly higher (P<0.05), apoptosis was significantly lower (P<0.05) and the number of cells in the G1/G0 phase was significantly decreased (P<0.05). The present study proves that in OSCC, clock gene Per2 plays an important role in cell cycle progression and the balance of cell proliferation and apoptosis by regulation of the cyclin/CDK/CKI cell cycle network. Further research on Per2 may provide a new effective molecular target for cancer treatments.

E2F1: a promising regulator in ovarian carcinoma.

E2F is a family of transcription factors that recognized to regulate the expression of genes essential for a wide range of cellular functions, including cell cycle progression, DNA repair, DNA replication, differentiation, proliferation, and apoptosis. E2F1, the most classic member of the E2F family, exhibits a complex role in tumor development regulation. In recent years, a growing body of data suggested an intimate relationship between E2F1 and ovarian carcinoma. And E2F1 was well identified to play dual functions and serve as a useful prognostic indicator in ovarian carcinoma. However, the mechanism underlying E2F1 associated with ovarian carcinoma remains elusive. It is necessary to clarify the fundamental role of E2F1 in ovarian carcinoma. In this review, we tried to sum up the knowledge of E2F1, including its structure and related mechanism. We also attempt to absorb the research achievements and collect the mechanism of E2F1 in ovarian carcinoma.

HTLV-1 bZIP factor protein targets the Rb/E2F-1 pathway to promote proliferation and apoptosis of primary CD4(+) T cells.

Human T-cell leukemia virus type 1 (HTLV-1) is an oncogenic retrovirus that induces a fatal T-cell malignancy, adult T-cell leukemia (ATL). Among several regulatory/accessory genes in HTLV-1, HTLV-1 bZIP factor (HBZ) is the only viral gene constitutively expressed in infected cells. Our previous study showed that HBZ functions in two different molecular forms, HBZ protein and HBZ RNA. In this study, we show that HBZ protein targets retinoblastoma protein (Rb), which is a critical tumor suppressor in many types of cancers. HBZ protein interacts with the Rb/E2F-1 complex and activates the transcription of E2F-target genes associated with cell cycle progression and apoptosis. Mouse primary CD4(+) T cells transduced with HBZ show accelerated G1/S transition and apoptosis, and importantly, T cells from HBZ transgenic (HBZ-Tg) mice also demonstrate enhanced cell proliferation and apoptosis. To evaluate the functions of HBZ protein alone in vivo, we generated a new transgenic mouse strain that expresses HBZ mRNA altered by silent mutations but encoding intact protein. In these mice, the numbers of effector/memory and Foxp3(+) T cells were increased, and genes associated with proliferation and apoptosis were upregulated. This study shows that HBZ protein promotes cell proliferation and apoptosis in primary CD4(+) T cells through activation of the Rb/E2F pathway, and that HBZ protein also confers onto CD4(+) T-cell immunophenotype similar to those of ATL cells, suggesting that HBZ protein has important roles in dysregulation of CD4(+) T cells infected with HTLV-1.

Regulation of oncogenic KRAS signaling via a novel KRAS-integrin-linked kinase-hnRNPA1 regulatory loop in human pancreatic cancer cells.

Integrin-linked kinase (ILK) is a mediator of aggressive phenotype in pancreatic cancer. On the basis of our finding that knockdown of either KRAS or ILK has a reciprocal effect on the other's expression, we hypothesized the presence of an ILK-KRAS regulatory loop that enables pancreatic cancer cells to regulate KRAS expression. This study aimed to elucidate the mechanism by which this regulatory circuitry is regulated and to investigate the translational potential of targeting ILK to suppress oncogenic KRAS signaling in pancreatic cancer. Interplay between KRAS and ILK and the roles of E2F1, c-Myc and heterogeneous nuclear ribonucleoprotein as intermediary effectors in this feedback loop was interrogated by genetic manipulations through small interfering RNA/short hairpin RNA knockdown and ectopic expression, western blotting, PCR, promoter-luciferase reporter assays, chromatin immunoprecipitation and pull-down analyses. In vivo efficacy of ILK inhibition was evaluated in two murine xenograft models. Our data show that KRAS regulated the expression of ILK through E2F1-mediated transcriptional activation, which, in turn, controlled KRAS gene expression via hnRNPA1-mediated destabilization of the G-quadruplex on the KRAS promoter. Moreover, ILK inhibition blocked KRAS-driven epithelial-mesenchymal transition and growth factor-stimulated KRAS expression. The knockdown or pharmacological inhibition of ILK suppressed pancreatic tumor growth, in part, by suppressing KRAS signaling. These studies suggest that this KRAS-E2F1-ILK-hnRNPA1 regulatory loop enables pancreatic cancer cells to promote oncogenic KRAS signaling and to interact with the tumor microenvironment to promote aggressive phenotypes. This regulatory loop provides a mechanistic rationale for targeting ILK to suppress oncogenic KRAS signaling, which might foster new therapeutic strategies for pancreatic cancer.

E2F1 mediates sustained lipogenesis and contributes to hepatic steatosis.

E2F transcription factors are known regulators of the cell cycle, proliferation, apoptosis, and differentiation. Here, we reveal that E2F1 plays an essential role in liver physiopathology through the regulation of glycolysis and lipogenesis. We demonstrate that E2F1 deficiency leads to a decrease in glycolysis and de novo synthesis of fatty acids in hepatocytes. We further demonstrate that E2F1 directly binds to the promoters of key lipogenic genes, including Fasn, but does not bind directly to genes encoding glycolysis pathway components, suggesting an indirect effect. In murine models, E2F1 expression and activity increased in response to feeding and upon insulin stimulation through canonical activation of the CDK4/pRB pathway. Moreover, E2F1 expression was increased in liver biopsies from obese, glucose-intolerant humans compared with biopsies from lean subjects. Finally, E2f1 deletion completely abrogated hepatic steatosis in different murine models of nonalcoholic fatty liver disease (NAFLD). In conclusion, our data demonstrate that E2F1 regulates lipid synthesis and glycolysis and thus contributes to the development of liver pathology.

CDK4 is an essential insulin effector in adipocytes.

Insulin resistance is a fundamental pathogenic factor that characterizes various metabolic disorders, including obesity and type 2 diabetes. Adipose tissue contributes to the development of obesity-related insulin resistance through increased release of fatty acids, altered adipokine secretion, and/or macrophage infiltration and cytokine release. Here, we aimed to analyze the participation of the cyclin-dependent kinase 4 (CDK4) in adipose tissue biology. We determined that white adipose tissue (WAT) from CDK4-deficient mice exhibits impaired lipogenesis and increased lipolysis. Conversely, lipolysis was decreased and lipogenesis was increased in mice expressing a mutant hyperactive form of CDK4 (CDK4(R24C)). A global kinome analysis of CDK4-deficient mice following insulin stimulation revealed that insulin signaling is impaired in these animals. We determined that insulin activates the CCND3-CDK4 complex, which in turn phosphorylates insulin receptor substrate 2 (IRS2) at serine 388, thereby creating a positive feedback loop that maintains adipocyte insulin signaling. Furthermore, we found that CCND3 expression and IRS2 serine 388 phosphorylation are increased in human obese subjects. Together, our results demonstrate that CDK4 is a major regulator of insulin signaling in WAT.