C/EBP beta isoforms LIP and LAP modulate progression of the cell cycle in the regenerating mouse liver

Molecular mechanism of nanomaterials induced liver injury: A review

The unique physicochemical properties inherent to nanoscale materials have unveiled numerous potential applications, spanning beyond the pharmaceutical and medical sectors into various consumer industries like food and cosmetics. Consequently, humans encounter nanomaterials through diverse exposure routes, giving rise to potential health considerations. Noteworthy among these materials are silica and specific metallic nanoparticles, extensively utilized in consumer products, which have garnered substantial attention due to their propensity to accumulate and induce adverse effects in the liver. This review paper aims to provide an exhaustive examination of the molecular mechanisms underpinning nanomaterial-induced hepatotoxicity, drawing insights from both in vitro and in vivo studies. Primarily, the most frequently observed manifestations of toxicity following the exposure of cells or animal models to various nanomaterials involve the initiation of oxidative stress and inflammation. Additionally, we delve into the existing in vitro models employed for evaluating the hepatotoxic effects of nanomaterials, emphasizing the persistent endeavors to advance and bolster the reliability of these models for nanotoxicology research.

Anti-obesity effects of chlorogenic acid and caffeine- lipid nanoparticles through PPAR-γ/C/EBP-ɑ pathways

Obesity is considered one of the most crucial health problems of the century. Therefore, reducing obesity is critically important. Caffeine (CF) and chlorogenic acid (CLA), which are substantial components in green bean coffee which maximize thermogenesis in brown adipose tissue. In our study, we have prepared CF, CLA, and CF + CLA loaded-solid lipid nanoparticles (SLN) since the SLNs are cost-effective, tissue-localized, and highly stable. The central composite design model was preferred to select the optimized formulation. UHPLC was used for quantification related to the CF and CLA amounts. The high-pressure homogenization (HPH) method was used while SLN formulations were prepared in the presence of poloxamer® 407 (surfactant) and Compritol® 888 ATO (solid lipid). The nanoparticles were characterized, followed by the utilization of 3T3-F442A cell lines for the evaluation of the adipogenesis activity of the formulations. Then, rt-PCR and ELISA studies of adipogenic markers were conducted. After optimal formulations were selected with an average of 110.2 ± 0.1 nm, CF (1 mM) + CLA (0.5 mM)-loaded SLN formulation has been proven significantly effective by using PPAR-γ/C/EBP-a pathways. In a nutshell, our study has shown that CF + CLA loaded-SLN has been affected 45.8% times more than regular extracted coffee (p < 0.05) on the adipocyte cells.

C/EBP β Mediates the Aberrant Inflammatory Response and Cell Cycle Arrest in Lps-stimulated Human Renal Tubular Epithelial Cells by Regulating NF-κB Pathway

BACKGROUND AND AIMS

The main cause of sepsis-induced Acute kidney injury (AKI) is acute infection after surgery and subsequent progression. However, the mechanism by which AKI is caused and developed from sepsis are not completely known. Herein, we determined the role of CCAAT/enhancer-binding protein β (C/EBP β) in sepsis-induced AKI METHODS: C/EBP β expression was up or down-regulated in LPS-stimulated human renal tubular epithelial cells in vitro by recombinant adenoviruses or siRNA. Subsequent analyses included the test of TNF-α and IL-6 levels by ELISA, cell cycle assay by flow cytometry.

RESULTS

C/EBP β was aberrantly expressed in renal tubular epithelial HK-2 cells exposed to LPS. C/EBP β overexpression significantly enhanced, but C/EBP β silencing obviously decreased the production and secretion of inflammatory cytokines TNF-α and IL-6 induced by LPS stimulus in HK-2 cells. And the cell cycle arrest of HK-2 cells induced by LPS was also enhanced after C/EBP β overexpression while attenuated after C/EBP β silencing. Consistent pattern of changes in Cyclin D1 and p21 expression were observed in LPS-stimulated HK-2 cells after C/EBP β silencing and C/EBP β overexpression. Additionally, the increased p-NF-κB levels induced by LPS were found to be obviously decreased after C/EBP β silencing in HK-2 cells. And the enhanced TNF-α and IL-6 secretion as well as cell cycle arrest by C/EBP β overexpression were blocked by BAY11-7082 inhibitor of NF-κB pathway.

CONCLUSIONS

C/EBP β could mediate the LPS-induced aberrant inflammatory response and cell cycle arrest in tubular epithelial cells by NF-κB pathway.

Protein S-glutathionylation stimulate adipogenesis by stabilizing C/EBPβ in 3T3L1 cells

Reactive oxygen species (ROS) increase during adipogenesis and in obesity. Oxidants react with cysteine residues of proteins to form glutathione (GSH) adducts, S-glutathionylation, that are selectively removed by glutaredoxin-1 (Glrx). We have previously reported that Glrx knockout mice had increased protein S-glutathionylation and developed obesity by an unknown mechanism. In this study, we demonstrated that 3T3L1 adipocytes differentiation increased ROS and protein S-glutathionylation. Glrx ablation elevated protein S-glutathionylation and lipid content in 3T3L1 cells. Glrx replenishment decreased the lipid content of Glrx KO 3T3L1 cells. Glrx KO also increased protein expression and protein S-glutathionylation of the adipogenic transcription factor CCAAT enhancer-binding protein (C/EBP) β. Protein S-glutathionylation decreased the interaction of C/EBPβ and protein inhibitor of activated STAT (PIAS) 1, a small ubiquitin-related modifier E3 ligase that facilitates C/EBPβ degradation. Experiments with truncated mutant C/EBPβ demonstrated that PIAS1 interacted with the liver-enriched inhibitory protein (LIP) region of C/EBPβ. Furthermore, mass spectrometry analysis identified protein S-glutathionylation of Cys201 and Cys296 in the LIP region of C/EBPβ. The C201S, C296S double-mutant C/EBPβ prevented protein S-glutathionylation and preserved the interaction with PIAS1. In summary, Glrx ablation stimulated 3T3L1 cell differentiation and adipogenesis via increased protein S-glutathionylation of C/EBPβ, stabilizing and increasing C/EBPβ protein levels.

Persistence of Drug-Resistant Leukemic Stem Cells and Impaired NK Cell Immunity in CML Patients Depend on MIR300 Antiproliferative and PP2A-Activating Functions

Persistence of drug-resistant quiescent leukemic stem cells (LSC) and impaired natural killer (NK) cell immune response account for relapse of chronic myelogenous leukemia (CML). Inactivation of protein phosphatase 2A (PP2A) is essential for CML-quiescent LSC survival and NK cell antitumor activity. Here we show that MIR300 has antiproliferative and PP2A-activating functions that are dose dependently differentially induced by CCND2/CDK6 and SET inhibition, respectively. MIR300 is upregulated in CML LSCs and NK cells by bone marrow microenvironment (BMM) signals to induce quiescence and impair immune response, respectively. Conversely, BCR-ABL1 downregulates MIR300 in CML progenitors to prevent growth arrest and PP2A-mediated apoptosis. Quiescent LSCs escape apoptosis by upregulating TUG1 long noncoding RNA that uncouples and limits MIR300 function to cytostasis. Genetic and pharmacologic MIR300 modulation and/or PP2A-activating drug treatment restore NK cell activity, inhibit BMM-induced growth arrest, and selectively trigger LSC apoptosis in vitro and in patient-derived xenografts; hence, the importance of MIR300 and PP2A activity for CML development and therapy.

Molecular and Morphological Evidence of Hepatotoxicity after Silver Nanoparticle Exposure: A Systematic Review, In Silico, and Ultrastructure Investigation

Silver nanoparticles (AgNPs) have been widely used in a variety of applications in innovative development; consequently, people are more exposed to this particle. Growing concern about toxicity from AgNP exposure has attracted greater attention, while questions about nanosilver-responsive genes and consequences for human health remain unanswered. By considering early detection and prevention of nanotoxicology at the genetic level, this study aimed to identify 1) changes in gene expression levels that could be potential indicators for AgNP toxicity and 2) morphological phenotypes correlating to toxicity of HepG2 cells. To detect possible nanosilver-responsive genes in xenogenic targeted organs, a comprehensive systematic literature review of changes in gene expression in HepG2 cells after AgNP exposure and in silico method, connection up- and down-regulation expression analysis of microarrays (CU-DREAM), were performed. In addition, cells were extracted and processed for transmission electron microscopy to examine ultrastructural alterations. From the Gene Expression Omnibus (GEO) Series database, we selected genes that were up- and down-regulated in AgNPs, but not up- and down-regulated in silver ion exposed cells, as nanosilver-responsive genes. HepG2 cells in the AgNP-treated group showed distinct ultrastructural alterations. Our results suggested potential representative gene data after AgNPs exposure provide insight into assessment and prediction of toxicity from nanosilver exposure.

Mechanisms involved in the activation of C/EBPα by small activating RNA in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is generally accompanied by high mortality and low cure rate. CCAAT enhancer-binding proteins (CEBPs) are transcriptional regulators that play a key role in maintaining liver function. Altered expression of C/EBPα and C/EBPβ occurs in many tumours including HCC. saRNAs are small double-stranded RNAs that enhance target gene expression at the transcriptional level. In this report, we activate CEPBA with saRNAs and suppress CEBPB with siRNAs in cells that represent three different degrees of HCC. We performed functional assays to investigate the effects of enhancing C/EBPα and its downstream targets, p21 and albumin across these lines. We also used Mass-spectrometry (MS) subsequent to a ChIP pull-down assay to characterise the components of the protein complex involved in regulating saRNA function. Putative saRNA interacting protein candidates that were identified by MS were knocked-down with siRNAs to investigate its impact on saRNA activity. We confirmed CEBPA-saRNA decreased proliferation and migration in the differentiated lines (HepG3/Hep3B). The undifferentiated line (PLCPRF5) showed saRNA-induced increase in CEBPA but with no loss in proliferation. This effect was reversed when CEBPB was suppressed with CEBPB-siRNA. When interrogating saRNA mode of action; three saRNA interacting proteins, CTR9, HnRNPA2/B1 and DDX5 were identified by MS. Targeted knock-down of these two proteins (by siRNA) abrogated saRNA activity. This study provides insight into how different HCC lines are affected by CEBPA-saRNAs and that endogenous abundance of CEBPB and saRNA accessory proteins may dictate efficacy of CEBPA-saRNA when used in a therapeutic context.

Aberrant expression of alternative isoforms of transcription factors in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the most prevalent malignancies worldwide and the second leading cause of death among all cancer types. Deregulation of the networks of tissue-specific transcription factors (TFs) observed in HCC leads to profound changes in the hepatic transcriptional program that facilitates tumor progression. In addition, recent reports suggest that substantial aberrations in the production of TF isoforms occur in HCC. In vitro experiments have identified distinct isoform-specific regulatory functions and related biological effects of liver-specific TFs that are implicated in carcinogenesis, which may be relevant for tumor progression and clinical outcome. This study reviews available data on the expression of isoforms of liver-specific and ubiquitous TFs in the liver and HCC and their effects, including HNF4α, C/EBPs, p73 and TCF7L2, and indicates that assessment of the ratio of isoforms and targeting specific TF variants may be beneficial for the prognosis and treatment of HCC.

C/EBPβ-1 promotes transformation and chemoresistance in Ewing sarcoma cells

CEBPB copy number gain in Ewing sarcoma was previously shown to be associated with worse clinical outcome compared to tumors with normal CEBPB copy number, although the mechanism was not characterized. We employed gene knockdown and rescue assays to explore the consequences of altered CEBPB gene expression in Ewing sarcoma cell lines. Knockdown of EWS-FLI1 expression led to a decrease in expression of all three C/EBPβ isoforms while re-expression of EWS-FLI1 rescued C/EBPβ expression. Overexpression of C/EBPβ-1, the largest of the three C/EBPβ isoforms, led to a significant increase in colony formation when cells were grown in soft agar compared to empty vector transduced cells. In addition, depletion of C/EBPβ decreased colony formation, and re-expression of either C/EBPβ-1 or C/EBPβ-2 rescued the phenotype. We identified the cancer stem cell marker ALDH1A1 as a target of C/EBPβ in Ewing sarcoma. Furthermore, increased expression of C/EBPβ led to resistance to chemotherapeutic agents. In summary, we have identified CEBPB as an oncogene in Ewing sarcoma. Overexpression of C/EBPβ-1 increases transformation, upregulates expression of the cancer stem cell marker ALDH1A1, and leads to chemoresistance.

Stat3 and CCAAT enhancer-binding protein β (C/ebpβ) activate Fanconi C gene transcription during emergency granulopoiesis

Interferon consensus sequence–binding protein (Icsbp) is required for terminating emergency granulopoiesis, an episodic event responsible for granulocyte production in response to infections and a key component of the innate immune response. Icsbp inhibits the expression of Stat3 and C/ebpβ, transcription factors essential for initiating and sustaining granulopoiesis, and activates transcription of Fanconi C (FANCC), a DNA repair protein. In prior studies, we noted accelerated bone marrow failure in Fancc^−/− mice undergoing multiple episodes of emergency granulopoiesis, associated with apoptosis of bone marrow cells with unrepaired DNA damage. Additionally, we found increased expression of Fanconi C and F proteins during emergency granulopoiesis. These findings suggest that Icsbp protects the bone marrow from DNA damage by increasing activity of the Fanconi DNA repair pathway, but the mechanisms for FANCC activation during initiation of emergency granulopoiesis are unclear. In this study, we observed that Stat3 and C/ebpβ activate FANCC transcription and contribute to DNA repair. Our findings indicate that FancC expression is increased during Stat3- and C/ebpβ-induced initiation of emergency granulopoiesis by these transcription factors and is maintained through termination by Icsbp. Our work reveals that Stat3- and C/ebpβ-mediated FancC expression is a critical component for initiating and sustaining key innate immune responses.

Reprint of: Heme oxygenase 1 affects granulopoiesis in mice through control of myelocyte proliferation

Heme oxygenase-1 (HO-1) is stress-inducible, cytoprotective enzyme degrading heme to carbon monoxide (CO), biliverdin and Fe²⁺. We showed that HO-1 knock-out mice (HO-1^-/-) have a twofold higher level of granulocytes than wild type (WT) mice, despite decreased concentration of granulocyte colony-stimulating factor (G-CSF) in the blood and reduced surface expression of G-CSF receptor on the hematopoietic precursors. This suggests the effect of HO-1 on granulopoiesis. Here we aimed to determine the stage of granulopoiesis regulated by HO-1. The earliest stages of hematopoiesis were not biased toward myeloid differentiation in HO-1^-/- mice. Within committed granulocytic compartment, in WT mice, HO-1 was up-regulated starting from myelocyte stage. This was concomitant with up-regulation of miR-155, which targets Bach1, the HO-1 repressor. In HO-1^-/- mice granulopoiesis was accelerated between myelocyte and metamyelocyte stage. There was a higher fraction of proliferating myelocytes, with increased nuclear expression of pro-proliferative C/EBPβ (CCAAT/enhancer binding protein beta) protein, especially its active LAP (liver-enriched activator proteins) isoform. Also our mathematical model confirmed shortening the myelocyte cyclic-time and prolonged mitotic expansion in absence of HO-1. It seems that changes in C/EBPβ expression and activity in HO-1^-/- myelocytes can be associated with reduced level of its direct repressor miR-155 or with decreased concentration of CO, known to reduce nuclear translocation of C/EBPs. Mature HO-1^-/- granulocytes were functionally competent as determined by oxidative burst capacity. In conclusion, HO-1 influences granulopoiesis through regulation of myelocyte proliferation. It is accompanied by changes in expression of transcriptionally active C/EBPβ protein. As HO-1 expression vary in human and is up-regulated in response to chemotherapy, it can potentially influence chemotherapy-induced neutropenia.

Heme oxygenase 1 affects granulopoiesis in mice through control of myelocyte proliferation

Heme oxygenase-1 (HO-1) is stress-inducible, cytoprotective enzyme degrading heme to carbon monoxide (CO), biliverdin and Fe²⁺. We showed that HO-1 knock-out mice (HO-1^-/-) have a twofold higher level of granulocytes than wild type (WT) mice, despite decreased concentration of granulocyte colony-stimulating factor (G-CSF) in the blood and reduced surface expression of G-CSF receptor on the hematopoietic precursors. This suggests the effect of HO-1 on granulopoiesis. Here we aimed to determine the stage of granulopoiesis regulated by HO-1. The earliest stages of hematopoiesis were not biased toward myeloid differentiation in HO-1^-/- mice. Within committed granulocytic compartment, in WT mice, HO-1 was up-regulated starting from myelocyte stage. This was concomitant with up-regulation of miR-155, which targets Bach1, the HO-1 repressor. In HO-1^-/- mice granulopoiesis was accelerated between myelocyte and metamyelocyte stage. There was a higher fraction of proliferating myelocytes, with increased nuclear expression of pro-proliferative C/EBPβ (CCAAT/enhancer binding protein beta) protein, especially its active LAP (liver-enriched activator proteins) isoform. Also our mathematical model confirmed shortening the myelocyte cyclic-time and prolonged mitotic expansion in absence of HO-1. It seems that changes in C/EBPβ expression and activity in HO-1^-/- myelocytes can be associated with reduced level of its direct repressor miR-155 or with decreased concentration of CO, known to reduce nuclear translocation of C/EBPs. Mature HO-1^-/- granulocytes were functionally competent as determined by oxidative burst capacity. In conclusion, HO-1 influences granulopoiesis through regulation of myelocyte proliferation. It is accompanied by changes in expression of transcriptionally active C/EBPβ protein. As HO-1 expression vary in human and is up-regulated in response to chemotherapy, it can potentially influence chemotherapy-induced neutropenia.

EGFR and C/EBP-β oncogenic signaling is bidirectional in human glioma and varies with the C/EBP-β isoform

We investigated the intersection of epidermal growth factor receptor (EGFR) and CCAAT enhancer binding protein (C/EBP)-β signaling in glioblastoma (GBM), given that both gene products strongly influence neoplastic behavior. C/EBP-β is known to drive the mesenchymal transcriptional signature in GBM, likely through strong microenvironmental influences, whereas the genetic contributions to its up-regulation in this disease are not well described. We demonstrated that stable overexpression and activation of WT EGFR (U87MG-WT) led to elevated C/EBP-β expression, as well as enhanced nuclear translocation and DNA-binding activity, leading to up-regulation of C/EBP-β transcription and translation. Deeper investigation identified bidirectional regulation, with C/EBP-β also causing up-regulation of EGFR that was at least partially dependent on the STAT3. Based on ChIP-based studies, we also found that that the translational isoforms of C/EBP-β [liver-enriched transcription-activating protein (LAP)-1/2 and liver inhibitory protein (LIP)] have differential occupancy on STAT3 promoter and opposing roles in transcriptional regulation of STAT3 and EGFR. We further demonstrated that the shorter C/EBP-β isoform, LIP, promoted proliferation and migration of U87MG glioma cells, potentially via induction of cytokine IL-6. Our molecular dissection of EGFR and C/EBP-β pathway interactions uncovered a complex signaling network in which increased activity of either EGFR or C/EBP-β leads to the up-regulation of the other, enhancing oncogenic signaling. Disrupting the EGFR-C/EBP-β signaling axis could attenuate malignant behavior of glioblastoma.-Selagea, L., Mishra, A., Anand, M., Ross, J., Tucker-Burden, C., Kong, J., Brat, D. J. EGFR and C/EBP-β oncogenic signaling is bidirectional in human glioma and varies with the C/EBP-β isoform.

miR-191 promotes tumorigenesis of human colorectal cancer through targeting C/EBPβ

MicroRNA-191 (miR-191), a small non-coding RNA, is involved in disease development and cancer diagnosis and prognosis. However, how miR-191 functions in colorectal cancer remains largely unclear. In this study, we show that miR-191 is highly expressed in colon tumor tissues, and that inhibition of miR-191 leads to decreased cell growth, proliferation and tumorigenicity in a xenograft model. Overexpression of miR-191 in colorectal cancer cell lines alters cell cycle progression and cell resistance to 5-Fu induced cell apoptosis. Mechanistic studies demonstrated that miR-191 directly binds to the 3′UTR of the C/EBPβ mRNA and mediates a decrease in the mRNA and protein expression of C/EBPβ. We further showed that C/EBPβ induces growth arrest in a colorectal cancer cell line and that its expression is negatively correlated with the miR-191 level in patient samples. Our findings suggest that miR-191 may be a potential gene therapy target for the treatment of colorectal cancer.

p300 Regulates Liver Functions by Controlling p53 and C/EBP Family Proteins through Multiple Signaling Pathways

The histone acetyltransferase p300 has been implicated in the regulation of liver biology; however, molecular mechanisms of this regulation are not known. In this paper, we examined these mechanisms using transgenic mice expressing a dominant negative p300 molecule (dnp300). While dnp300 mice did not show abnormal growth within 1 year, these mice have many alterations in liver biology and liver functions. We found that the inhibition of p300 leads to the accumulation of heterochromatin foci in the liver of 2-month-old mice. Transcriptome sequencing (RNA-Seq) analysis showed that this inhibition of p300 also causes alterations of gene expression in many signaling pathways, including chromatin remodeling, apoptosis, DNA damage, translation, and activation of the cell cycle. Livers of dnp300 mice have a high rate of proliferation and a much higher rate of proliferation after partial hepatectomy. We found that livers of dnp300 mice are resistant to CCl4-mediated injury and have reduced apoptosis but have increased proliferation after injury. Underlying mechanisms of resistance to liver injury and increased proliferation in dnp300 mice include ubiquitin-proteasome-mediated degradation of C/EBPα and translational repression of the p53 protein by the CUGBP1-eukaryotic initiation factor 2 (eIF2) repressor complex. Our data demonstrate that p300 regulates a number of critical signaling pathways that control liver functions.

TSC1 controls IL-1β expression in macrophages via mTORC1-dependent C/EBPβ pathway

The tuberous sclerosis complex 1 (TSC1) is a tumor suppressor that inhibits the mammalian target of rapamycin (mTOR), which serves as a key regulator of inflammatory responses after bacterial stimulation in monocytes, macrophages, and primary dendritic cells. Previous studies have shown that TSC1 knockout (KO) macrophages produced increased inflammatory responses including tumor necrosis factor-α (TNF-α) and IL-12 to pro-inflammatory stimuli, but whether and how TSC1 regulates pro-IL-1β expression remains unclear. Here using a mouse model in which myeloid lineage-specific deletion of TSC1 leads to constitutive mTORC1 activation, we found that TSC1 deficiency resulted in impaired expression of pro-IL-1β in macrophages following lipopolysaccharide stimulation. Such decreased pro-IL-1β expression in TSC1 KO macrophages was rescued by reducing mTORC1 activity with rapamycin or deletion of mTOR. Rictor deficiency has no detectable effect on pro-IL-1β synthesis, suggesting that TSC1 positively controls pro-IL-1β expression through mTORC1 pathway. Moreover, mechanism studies suggest that mTORC1-mediated downregulation of the CCAAT enhancer-binding protein (C/EBPβ) critically contributes to the defective pro-IL-1β expression. Overall, these findings highlight a critical role of TSC1 in regulating innate immunity by control of the mTOR1-C/EBPβ pathway.

C/EBPβ Isoforms Expression in the Rat Brain during the Estrous Cycle

The CCAAT/enhancer-binding protein beta (C/EBPβ) is a transcription factor expressed in different areas of the brain that regulates the expression of several genes involved in cell differentiation and proliferation. This protein has three isoforms (LAP1, LAP2, and LIP) with different transcription activation potential. The role of female sex hormones in the expression pattern of C/EBPβ isoforms in the rat brain has not yet been described. In this study we demonstrate by western blot that the expression of the three C/EBPβ isoforms changes in different brain areas during the estrous cycle. In the cerebellum, LAP2 content diminished on diestrus and proestrus and LIP content diminished on proestrus and estrus days. In the prefrontal cortex, LIP content was higher on proestrus and estrus days. In the hippocampus, LAP isoforms presented a switch on diestrus day, since LAP1 content was the highest while that of LAP2 was the lowest. The LAP2 isoform was the most abundant one in all the three brain areas. The LAP/LIP ratio changed throughout the cycle and was tissue specific. These results suggest that C/EBPβ isoforms expression changes in a tissue-specific manner in the rat brain due to the changes in sex steroid hormone levels presented during the estrous cycle.

Mdm2 promotes myogenesis through the ubiquitination and degradation of CCAAT/enhancer-binding protein β

Myogenesis is a tightly regulated differentiation process during which precursor cells express in a coordinated fashion the myogenic regulatory factors, while down-regulating the satellite cell marker Pax7. CCAAT/Enhancer-binding protein β (C/EBPβ) is also expressed in satellite cells and acts to maintain the undifferentiated state by stimulating Pax7 expression and by triggering a decrease in MyoD protein expression. Herein, we show that C/EBPβ protein is rapidly down-regulated upon induction of myogenesis and this is not due to changes in Cebpb mRNA expression. Rather, loss of C/EBPβ protein is accompanied by an increase in Mdm2 expression, an E3 ubiquitin ligase. We demonstrate that Mdm2 interacts with, ubiquitinates and targets C/EBPβ for degradation by the 26 S proteasome, leading to increased MyoD expression. Knockdown of Mdm2 expression in myoblasts using a shRNA resulted in high C/EBPβ levels and a blockade of myogenesis, indicating that Mdm2 is necessary for myogenic differentiation. Primary myoblasts expressing the shMdm2 construct were unable to contribute to muscle regeneration when grafted into cardiotoxin-injured muscle. The differentiation defect imposed by loss of Mdm2 could be partially rescued by loss of C/EBPβ, suggesting that the regulation of C/EBPβ turnover is a major role for Mdm2 in myoblasts. Taken together, we provide evidence that Mdm2 regulates entry into myogenesis by targeting C/EBPβ for degradation by the 26 S proteasome.

TGR5 reduces macrophage migration through mTOR-induced C/EBPβ differential translation

The bile acid-responsive G protein-coupled receptor TGR5 is involved in several metabolic processes, and recent studies suggest that TGR5 activation may promote pathways that are protective against diet-induced diabetes. Here, we investigated the role of macrophage-specific TGR5 signaling in protecting adipose tissue from inflammation and associated insulin resistance. Examination of adipose tissue from obese mice lacking macrophage Tgr5 revealed enhanced inflammation, increased chemokine expression, and higher macrophage numbers compared with control obese animals. Moreover, macrophage-specific deletion of Tgr5 exacerbated insulin resistance in obese animals. Conversely, pharmacological activation of TGR5 markedly decreased LPS-induced chemokine expression in primary macrophages. This reduction was mediated by AKT-dependent activation of mTOR complex 1, which in turn induced the differential translation of the dominant-negative C/EBPβ isoform, liver inhibitory protein (LIP). Overall, these studies reveal a signaling pathway downstream of TGR5 that modulates chemokine expression in response to high-fat diet and suggest that targeting this pathway has the potential to be therapeutically exploited for prevention of chronic inflammatory diseases and type 2 diabetes mellitus.

Dendritic cell-mediated survival signals in Eμ-Myc B-cell lymphoma depend on the transcription factor C/EBPβ

The capacity of dendritic cells (DCs) to regulate tumour-specific adaptive immune responses depends on their proper differentiation and homing status. Whereas DC-associated tumour-promoting functions are linked to T-cell tolerance and formation of an inflammatory milieu, DC-mediated direct effects on tumour growth have remained unexplored. Here we show that deletion of DCs substantially delays progression of Myc-driven lymphomas. Lymphoma-exposed DCs upregulate immunomodulatory cytokines, growth factors and the CCAAT/enhancer-binding protein β (C/EBPβ). Moreover, Eμ-Myc lymphomas induce the preferential translation of the LAP/LAP* isoforms of C/EBPβ. C/EBPβ(-/-) DCs are unresponsive to lymphoma-associated cytokine changes and in contrast to wild-type DCs, they are unable to mediate enhanced Eμ-Myc lymphoma cell survival. Antigen-specific T-cell proliferation in lymphoma-bearing mice is impaired; however, this immune suppression is reverted by the DC-restricted deletion of C/EBPβ. Thus, we show that C/EBPβ-controlled DC functions are critical steps for the creation of a lymphoma growth-promoting and -immunosuppressive niche.

Transcription factor C/EBP-β mediates downregulation of dipeptidyl-peptidase III expression by interleukin-6 in human glioblastoma cells

Dipeptidyl-peptidase III (DPP III) is a cytosolic metallo-aminopeptidase implicated in various physiological and pathological processes. A previous study from our laboratory indicated an elevated expression of DPP III in glioblastoma (U87MG) cells. In the present study we investigated the role of interleukin-6 (IL-6), a pleiotropic cytokine produced by glial tumors, in the regulation of DPP III expression. Immunohistochemistry, western blotting and quantitative RT-PCR were used for quantitation of DPP III and IL-6 in human glioblastoma cells and tumors. Cell transfections and DPP III promoter reporter assays were performed to study the transcriptional regulation of DPP III by IL-6. Promoter deletion analysis, site directed mutagenesis, chromatin immunoprecipitation assays and small interfering RNA (siRNA) technology was employed to elucidate the molecular mechanism of IL-6 mediated regulation of DPP III expression in glioblastoma cells. Our results for the first time demonstrate a negative correlation (r = 0.632, P = 0.01) between DPP III and IL-6 in both human tumors and cultured glioblastoma cells. Treatment of U87MG cells with IL-6 significantly decreased DPP III expression with a concomitant increase in the levels of transcription factor CCAAT/enhancer binding protein beta (C/EBP-β). Deletion/mutagenesis of C/EBP-β binding motif of DPP III promoter significantly increased its activity and abolished its responsiveness to IL-6. This effect could also be mimicked by C/EBP-β siRNA. In conclusion our study for the first time demonstrates C/EBP-β mediated transcriptional downregulation of DPP III by IL-6. Our results demonstrating a negative correlation between IL-6 and DPP III taken together with the previously reported prognostic significance of this cytokine in glioblastoma suggests that DPP III may prove useful as a prognostic marker.

Principles of liver regeneration and growth homeostasis

Liver regeneration is perhaps the most studied example of compensatory growth aimed to replace loss of tissue in an organ. Hepatocytes, the main functional cells of the liver, manage to proliferate to restore mass and to simultaneously deliver all functions hepatic functions necessary to maintain body homeostasis. They are the first cells to respond to regenerative stimuli triggered by mitogenic growth factor receptors MET (the hepatocyte growth factor receptor] and epidermal growth factor receptor and complemented by auxiliary mitogenic signals induced by other cytokines. Termination of liver regeneration is a complex process affected by integrin mediated signaling and it restores the organ to its original mass as determined by the needs of the body (hepatostat function). When hepatocytes cannot proliferate, progenitor cells derived from the biliary epithelium transdifferentiate to restore the hepatocyte compartment. In a reverse situation, hepatocytes can also transdifferentiate to restore the biliary compartment. Several hormones and xenobiotics alter the hepatostat directly and induce an increase in liver to body weight ratio (augmentative hepatomegaly). The complex challenges of the liver toward body homeostasis are thus always preserved by complex but unfailing responses involving orchestrated signaling and affecting growth and differentiation of all hepatic cell types.

miR-142-3p prevents macrophage differentiation during cancer-induced myelopoiesis

Tumor progression is accompanied by an altered myelopoiesis causing the accumulation of immunosuppressive cells. Here, we showed that miR-142-3p downregulation promoted macrophage differentiation and determined the acquisition of their immunosuppressive function in tumor. Tumor-released cytokines signaling through gp130, the common subunit of the interleukin-6 cytokine receptor family, induced the LAP∗ isoform of C/EBPβ transcription factor, promoting macrophage generation. miR-142-3p downregulated gp130 by canonical binding to its messenger RNA (mRNA) 3' UTR and repressed C/EBPβ LAP∗ by noncanonical binding to its 5' mRNA coding sequence. Enforced miR expression impaired macrophage differentiation both in vitro and in vivo. Mice constitutively expressing miR-142-3p in the bone marrow showed a marked increase in survival following immunotherapy with tumor-specific T lymphocytes. By modulating a specific miR in bone marrow precursors, we thus demonstrated the feasibility of altering tumor-induced macrophage differentiation as a potent tool to improve the efficacy of cancer immunotherapy.

GeneFriends: an online co-expression analysis tool to identify novel gene targets for aging and complex diseases

BACKGROUND

Although many diseases have been well characterized at the molecular level, the underlying mechanisms are often unknown. Nearly half of all human genes remain poorly studied, yet these genes may contribute to a number of disease processes. Genes involved in common biological processes and diseases are often co-expressed. Using known disease-associated genes in a co-expression analysis may help identify and prioritize novel candidate genes for further study.

RESULTS

We have created an online tool, called GeneFriends, which identifies co-expressed genes in over 1,000 mouse microarray datasets. GeneFriends can be used to assign putative functions to poorly studied genes. Using a seed list of disease-associated genes and a guilt-by-association method, GeneFriends allows users to quickly identify novel genes and transcription factors associated with a disease or process. We tested GeneFriends using seed lists for aging, cancer, and mitochondrial complex I disease. We identified several candidate genes that have previously been predicted as relevant targets. Some of the genes identified are already being tested in clinical trials, indicating the effectiveness of this approach. Co-expressed transcription factors were investigated, identifying C/ebp genes as candidate regulators of aging. Furthermore, several novel candidate genes, that may be suitable for experimental or clinical follow-up, were identified. Two of the novel candidates of unknown function that were co-expressed with cancer-associated genes were selected for experimental validation. Knock-down of their human homologs (C1ORF112 and C12ORF48) in HeLa cells slowed growth, indicating that these genes of unknown function, identified by GeneFriends, may be involved in cancer.

CONCLUSIONS

GeneFriends is a resource for biologists to identify and prioritize novel candidate genes involved in biological processes and complex diseases. It is an intuitive online resource that will help drive experimentation. GeneFriends is available online at: http://genefriends.org/.

The transcription factor C/EBP delta has anti-apoptotic and anti-inflammatory roles in pancreatic beta cells

In the course of Type 1 diabetes pro-inflammatory cytokines (e.g., IL-1β, IFN-γ and TNF-α) produced by islet-infiltrating immune cells modify expression of key gene networks in β-cells, leading to local inflammation and β-cell apoptosis. Most known cytokine-induced transcription factors have pro-apoptotic effects, and little is known regarding “protective” transcription factors. To this end, we presently evaluated the role of the transcription factor CCAAT/enhancer binding protein delta (C/EBPδ) on β-cell apoptosis and production of inflammatory mediators in the rat insulinoma INS-1E cells, in purified primary rat β-cells and in human islets. C/EBPδ is expressed and up-regulated in response to the cytokines IL-1β and IFN-γ in rat β-cells and human islets. Small interfering RNA-mediated C/EBPδ silencing exacerbated IL-1β+IFN-γ-induced caspase 9 and 3 cleavage and apoptosis in these cells. C/EBPδ deficiency increased the up-regulation of the transcription factor CHOP in response to cytokines, enhancing expression of the pro-apoptotic Bcl-2 family member BIM. Interfering with C/EBPδ and CHOP or C/EBPδ and BIM in double knockdown approaches abrogated the exacerbating effects of C/EBPδ deficiency on cytokine-induced β-cell apoptosis, while C/EBPδ overexpression inhibited BIM expression and partially protected β-cells against IL-1β+IFN-γ-induced apoptosis. Furthermore, C/EBPδ silencing boosted cytokine-induced production of the chemokines CXCL1, 9, 10 and CCL20 in β-cells by hampering IRF-1 up-regulation and increasing STAT1 activation in response to cytokines. These observations identify a novel function of C/EBPδ as a modulatory transcription factor that inhibits the pro-apoptotic and pro-inflammatory gene networks activated by cytokines in pancreatic β-cells.

Human CCAAT/enhancer-binding protein β interacts with chromatin remodeling complexes of the imitation switch subfamily

Transcription factor C/EBPβ is involved in several cellular processes, such as proliferation, differentiation, and energy metabolism. This factor exerts its activity through recruitment of different proteins or protein complexes, including the ATP-dependent chromatin remodeling complex SWI/SNF. The C/EBPβ protein is found as three major isoforms, C/EBPβ1, -2, and -3. They are generated by translation at alternative AUG initiation codons of a unique mRNA, C/EBPβ1 being the full-length isoform. It has been found that C/EBPβ1 participates in terminal differentiation processes. Conversely, C/EBPβ2 and -3 promote cell proliferation and are involved in malignant progression in a number of tissues. The mechanisms by which C/EBPβ2 and -3 promote cell proliferation and tumor progression are not fully understood. In this work, we sought to identify proteins interacting with hC/EBPβ using a proteomics approach. We found that all three isoforms interact with hSNF2H and hACF, components of ACF and CHRAC chromatin remodeling complexes, which belong to the imitation switch subfamily. Additional protein-protein interaction studies confirmed this finding and also showed that hC/EBPβ directly interacts with hACF1. By overexpressing hC/EBPβ, hSNF2H, and hACF1 in HepG2 cells and analyzing variations in expression of cyclin D1 and other C/EBPβ target genes, we observed a functional interaction between C/EBPβ and SNF2H/ACF1, characterized mainly by suppression of C/EBPβ transactivation activity in the presence of SNF2H and ACF1. Consistent with these findings, induction of differentiation of HepG2 cells by 1% DMSO was accompanied by a reduction in the level of cyclin D1 expression and the appearance of hC/EBPβ, hSNF2H, and hACF1 on the promoter region of this gene.

LIP expression is regulated by IGF-1R signaling and participates in suppression of anoikis

Background

The transcription factor, CCAAT enhancer binding protein-β (C/EBPβ), is expressed as several distinct protein isoforms (LAP1, LAP2 and LIP) that have opposing actions in cellular proliferation and differentiation. Increases in the ratio of LIP/LAP are associated with aggressive, metastatic breast cancer; however, little is known regarding the molecular mechanisms that regulate LIP expression or the biological actions of an increase in the LIP/LAP ratio. Metastasis is highly dependent upon the suppression of anoikis and the role of C/EBPβ and LIP in this anchorage-independent, survival process is currently not known in mammary epithelial cells. IGF-1R signaling is important for the survival of breast cancer cells and crosstalk between IGF-1R and EGFR signaling pathways have been implicated in the development of more aggressive disease. We therefore evaluated in mammary epithelial cells whether IGF-1R signaling regulates the LIP/LAP ratio, analyzed the potential interplay between EGFR and IGF-1R signaling and addressed the biological significance of increased LIP expression in cellular survival and suppression of anoikis.

Results

Our data provide the first evidence that IGF-1R signaling regulates LIP expression in an EGFR independent manner to increase the LIP/LAP ratio in mammary epithelial cells. Although crosstalk between IGF-1R signaling and EGFR signaling is detectable in MCF10A cells, this crosstalk is not required for the IGF-1 mediated regulation of LIP expression. Rather, the critical regulator of IGF-1 induced LIP expression appears to be EGFR-independent, Akt activity. Our data also demonstrate that increases in LIP expression promote cell survival via suppression of anoikis. Likewise, knockdown of total C/EBPβ leads to increased cell death and suggest that C/EBPβ expression is important for survival and resistance to anoikis. IGF-1 treatment can partially rescue vector control cells from anoikis; however, cells with reduced C/EBPβ expression do not survive anoikis.

Conclusions

Taken together, our data demonstrate that IGF-1R signaling regulates LIP expression in an EGFR independent manner to increase the LIP/LAP ratio in mammary epithelial cells. C/EBPβ expression and elevations in LIP play an important role in regulating cellular survival via suppression of anoikis, in an IGF-1R mediated context or in a manner independent of IGF-1R signaling.

Characterization of the transcriptional signature of C/EBPbeta isoforms (LAP/LIP) in Hep3B cells: implication of LIP in pro-survival functions

BACKGROUND & AIMS

C/EBPbeta is an important mediator of several cellular processes, such as differentiation, proliferation, and survival of hepatic cells. However, a complete catalog of the targets of C/EBPbeta or the mechanism by which this transcription factor regulates certain liver-dependent pathways has not been clearly determined. Two major natural isoforms of this transcription factor exist: the liver-enriched activating protein (LAP) and the liver-enriched inhibitory protein (LIP), a functional LAP antagonist. In this study, we used the opposing transcriptional effects driven by LAP and LIP to determine the genuine C/EBPbeta molecular signature in the Hep3B human hepatoma cell line. We subsequently investigated the role of each of the LAP and LIP isoforms in drug-induced Hep3B cell death.

METHODS

We engineered Hep3B cells with regulated LAP or LIP expression using the Tet-off expression system. The genes that showed inverse regulation by LAP and LIP were identified by cDNA array analysis. The cohort of direct-C/EBPbeta-targets was distinguished from indirect-targets by ChIP-on-chip analysis.

RESULTS

We characterized 676 genes by this approach. Among these genes, 39 are novel direct targets of C/EBPbeta. Eleven of these new direct targets are involved in cell survival, suggesting critical roles for LAP/LIP isoforms in this cellular process. Therefore, we examined the effects of LAP and LIP over-expression on cell survival. We show that LIP promotes survival in staurosporine- or taxol-induced Hep3B cell death.

CONCLUSIONS

Our study provides new molecular and cellular insights into the role of C/EBPbeta in cells of hepatic origin.

Farnesoid X receptor activation by chenodeoxycholic acid induces detoxifying enzymes through AMP-activated protein kinase and extracellular signal-regulated kinase 1/2-mediated phosphorylation of CCAAT/enhancer binding protein β

Farnesoid X receptor (FXR) regulates redox homeostasis and elicits a cytoprotective effect. CCAAT/enhancer binding protein-β (C/EBPβ) plays a role in regulating the expression of hepatocyte-specific genes and contributes to hepatocyte protection and liver regeneration. In view of the role of FXR in xenobiotic metabolism and hepatocyte survival, this study investigated the potential of FXR to activate C/EBPβ for the induction of detoxifying enzymes and the responsible regulatory pathway. Chenodeoxycholic acid (CDCA), a major component in bile acids, activates FXR. In HepG2 cells, CDCA treatment activated C/EBPβ, as shown by increases in its phosphorylation, nuclear accumulation, and expression. 3-(2,6-Dichlorophenyl)-4-(3'-carboxy-2-chlorostilben-4-yl-)oxymethyl-5-isopropyl-isoxazole (GW4064), a synthetic FXR ligand, had similar effects. In addition, CDCA enhanced luciferase gene transcription from the construct containing -1.65-kb GSTA2 promoter, which contained C/EBP response element (pGL-1651). Moreover, CDCA treatment activated AMP-activated protein kinase (AMPK), which led to extracellular signal-regulated kinase 1/2 (ERK1/2) activation, as evidenced by the results of experiments using a dominant-negative mutant of AMPKα and chemical inhibitor. The activation of ERK1/2 was responsible for the activating phosphorylation of C/EBPβ. FXR knockdown attenuated the ability of CDCA to activate AMPK and ERK1/2 and phosphorylate C/EBPβ. Consistently, enforced expression of FXR promoted the phosphorylation of AMPKα, ERK1/2, and C/EBPβ, verifying that C/EBPβ phosphorylation elicited by CDCA results from the activation of AMPK and ERK1/2 by FXR. In mice, CDCA treatment activated C/EBPβ with the induction of detoxifying enzymes in the liver. Our results demonstrate that CDCA induces antioxidant and xenobiotic-metabolizing enzymes by activating C/EBPβ through AMPK-dependent ERK1/2 pathway downstream of FXR.

Intracellular signaling and hepatocellular carcinoma

Liver cancer is the fifth most common cancer and the third most common cause of cancer related death in the world. The recent development of new techniques for the investigations of global change in the gene expression, signaling pathways and wide genome binding has provided novel information for the mechanisms underlying liver cancer progression. Although these studies identified gene expression signatures in hepatocellular carcinoma, the early steps of the development of hepatocellular carcinomas (HCC) are not well understood. The development of HCC is a multistep process which includes the progressive alterations of gene expression leading to the increased proliferation and to liver cancer. This review summarizes recent progress in the identification of the key steps of the development of HCC with the focus on early events of carcinogenesis and on the role of translational and epigenetic alterations in the development of HCC. Quiescent stage of the liver is supported by several tumor suppressor proteins including p53, Rb and C/EBPα. Studies with chemical models of liver carcinogenesis and with human HCC have shown that the elevation of gankyrin is responsible for the elimination of these three proteins at early steps of carcinogenesis. Later stages of progression of the liver cancer are associated with alterations in many signaling pathways including translation which leads to epigenetic silencing/activation of many genes. Particularly, recent reports suggest a critical role of histone deacetylase 1, HDAC1, in the development of HCC through the interactions with transcription factors such as C/EBP family proteins.

Calmodulin controls liver proliferation via interactions with C/EBPbeta-LAP and C/EBPbeta-LIP

A truncated isoform of C/EBPbeta, C/EBPbeta-LIP, is required for liver proliferation. This isoform is expressed at high levels in proliferating liver and in liver tumors. However, high levels of C/EBPbeta-LIP are also observed in non-proliferating livers during acute phase response (APR). In this paper we present mechanisms by which liver regulates activities of C/EBPbeta-LIP. We found that calmodulin (CaM) inhibits the ability of C/EBPbeta-LIP to promote liver proliferation during APR through direct interactions. This activity of CaM is under negative control of Ca(2+), which is reduced in nuclei of livers with APR, whereas it is increased in nuclei of proliferating livers. A mutant CaM, which does not interact with C/EBPbeta-LIP, also fails to inhibit the growth promotion activity of C/EBPbeta-LIP. Down-regulation of CaM in livers of LPS-treated mice causes liver proliferation via activation of C/EBPbeta-LIP. Overexpression of C/EBPbeta-LIP above levels of CaM also initiates liver proliferation in LPS-treated mice. In addition, CaM regulates transcriptional activity of another isoform of C/EBPbeta, C/EBPbeta-LAP, and might control liver biology through the regulation of both isoforms of C/EBPbeta. In searching for molecular mechanisms by which C/EBPbeta-LIP promotes cell proliferation, we found that C/EBPbeta-LIP releases E2F.Rb-dependent repression of cell cycle genes by a disruption of E2F1.Rb complexes and by a direct interaction with E2F-dependent promoters. CaM inhibits these growth promotion activities of C/EBPbeta-LIP and, therefore, supports liver quiescence. Thus, our findings discover a new pathway of the regulation of liver proliferation that involves calcium-CaM signaling.

Transcription factor Smad3 is required for the inhibition of adipogenesis by retinoic acid

The process of adipocyte differentiation is driven by a highly coordinated cascade of transcriptional events that results in the development of the mature adipocyte and in lipid accumulation. One of the early events of differentiation is the up-regulation of CCAAT/enhancer-binding protein beta (C/EBPbeta) expression. C/EBPbeta then acts to up-regulate the expression of adipogenic factors such as C/EBPalpha, which control the late stage of adipogenesis. Retinoic acid (RA) is a potent inhibitor of adipogenesis, and its action appears to block C/EBPbeta transcriptional potential early during differentiation. Using preadipocytes and mesenchymal stem cell models, we show that RA specifically blocks the occupancy of C/EBPbeta of the Cebpa promoter, thereby abrogating the differentiation process. RA does not act directly on C/EBPbeta but rather stimulates the expression of the transforming growth factor beta-effector protein Smad3, which can interact with C/EBPbeta via its Mad homology 1 domain and can interfere with C/EBPbeta DNA binding. The RA-induced increase in Smad3 expression results in increased cytoplasmic and nuclear Smad3, an important event as ectopic expression of Smad3 in preadipocytes in the absence of RA treatment only modestly inhibits adipogenesis and C/EBPbeta DNA binding, suggesting that Smad3 alone is not sufficient to completely recapitulate the effects of retinoic acid treatment during differentiation. However, in the absence of Smad3, RA is not able to inhibit adipocyte differentiation or to elicit a decrease in C/EBPbeta DNA occupancy suggesting that Smad3 is necessary to convey the inhibitory effects of retinoic acid during adipogenesis.

Crosstalk between C/EBPbeta phosphorylation, arginine methylation, and SWI/SNF/Mediator implies an indexing transcription factor code

Cellular signalling cascades regulate the activity of transcription factors that convert extracellular information into gene regulation. C/EBPbeta is a ras/MAPkinase signal-sensitive transcription factor that regulates genes involved in metabolism, proliferation, differentiation, immunity, senescence, and tumourigenesis. The protein arginine methyltransferase 4 PRMT4/CARM1 interacts with C/EBPbeta and dimethylates a conserved arginine residue (R3) in the C/EBPbeta N-terminal transactivation domain, as identified by mass spectrometry of cell-derived C/EBPbeta. Phosphorylation of the C/EBPbeta regulatory domain by ras/MAPkinase signalling abrogates the interaction between C/EBPbeta and PRMT4/CARM1. Differential proteomic screening, protein interaction studies, and mutational analysis revealed that methylation of R3 constraines interaction with SWI/SNF and Mediator complexes. Mutation of the R3 methylation site alters endogenous myeloid gene expression and adipogenic differentiation. Thus, phosphorylation of the transcription factor C/EBPbeta couples ras signalling to arginine methylation and regulates the interaction of C/EBPbeta with epigenetic gene regulatory protein complexes during cell differentiation.

C/EBPbetaDeltauORF mice--a genetic model for uORF-mediated translational control in mammals

Upstream ORFs (uORFs) are translational control elements found predominantly in transcripts of key regulatory genes. No mammalian genetic model exists to experimentally validate the physiological relevance of uORF-regulated translation initiation. We report that mice deficient for the CCAAT/enhancer-binding protein beta (C/EBPbeta) uORF initiation codon fail to initiate translation of the autoantagonistic LIP (liver inhibitory protein) C/EBPbeta isoform. C/EBPbeta(DeltauORF) mice show hyperactivation of acute-phase response genes, persistent repression of E2F-regulated genes, delayed and blunted S-phase entry of hepatocytes after partial hepatectomy, and impaired osteoclast differentiation. These data and the widespread prevalence of uORFs in mammalian transcriptomes suggest a comprehensive role of uORF-regulated translation in (patho)physiology.

p21 is required for dextrose-mediated inhibition of mouse liver regeneration

The inhibitory effect of dextrose supplementation on liver regeneration was first described more than 4 decades ago. Nevertheless, the molecular mechanisms responsible for this observation have not been elucidated. We investigated these mechanisms using the partial hepatectomy model in mice given standard or 10% dextrose (D10)-supplemented drinking water. The results showed that D10-treated mice exhibited significantly reduced hepatic regeneration compared with controls, as assessed by hepatocellular bromodeoxyuridine (BrdU) incorporation and mitotic frequency. D10 supplementation did not suppress activation of hepatocyte growth factor (HGF), induction of transforming growth factor alpha (TGF-alpha) expression, or tumor necrosis factor alpha-interleukin-6 cytokine signaling, p42/44 extracellular signal-regulated kinase (ERK) activation, immediate early gene expression, or expression of CCAAT/enhancer binding protein beta (C/EBPbeta), but did augment expression of the mito-inhibitory factors C/EBPalpha, p21(Waf1/Cip1), and p27(Kip1). In addition, forkhead box M1 (FoxM1) expression, which is required for normal liver regeneration, was suppressed by D10 treatment. Finally, D10 did not suppress either FoxM1 expression or hepatocellular proliferation in p21 null mice subjected to partial hepatectomy, establishing the functional significance of these events in mediating the effects of D10 on liver regeneration.

CONCLUSION

These data show that the inhibitory effect of dextrose supplementation on liver regeneration is associated with increased expression of C/EBPalpha, p21, and p27, and decreased expression of FoxM1, and that D10-mediated inhibition of liver regeneration is abrogated in p21-deficient animals. Our observations are consistent with a model in which hepatic sufficiency is defined by homeostasis between the energy-generating capacity of the liver and the energy demands of the body mass, with liver regeneration initiated when the functional liver mass is no longer sufficient to meet such demand.

Oltipraz promotion of liver regeneration after partial hepatectomy: The role of PI3-kinase-dependent C/EBPbeta and cyclin E regulation

Oltipraz, a representative cancer chemopreventive agent, regenerates cirrhotic liver via CCAAT/enhancer binding protein beta (C/EBPbeta). This study examined the effect of oltipraz on liver regeneration after partial hepatectomy (PH) and explored the role of phosphatidylinositol 3-kinase (PI3K) pathway responsible in liver regeneration. Oltipraz treatment (30 mg/kg/day, for 3 days) promoted liver regeneration in PH rats, but did not increase hepatocyte growth factor production. Subcellular fractionation and electrophoretic mobility shift assays showed that oltipraz treatment increased C/EBPbeta-DNA binding activity in the liver of sham control rats and further enhanced PH-mediated nuclear translocation of C/EBPbeta. The expression of cyclin E and the activity of cyclin E-dependent kinase were both enhanced by oltipraz treatment of PH rats. The signaling pathway that controls C/EBPbeta and cyclin E were studied in H4IIE cells, a rat-derived hepatocyte cell line. Oltipraz potentiated the nuclear accumulation of C/ EBPbeta and C/EBPbeta-DNA binding activity in cells incubated in a medium containing serum. PI3K and its downstream kinase, p70S6 kinase, were both required for C/EBPbeta-dependent induction of cyclin E by oltipraz, as shown by chemical inhibition and plasmid transfection experiments. The results of this study demonstrate that oltipraz treatment enhances liver regeneration after PH, which involves activation of C/EBPbeta and C/EBPbeta-dependent cyclin E expression via the PI3K-p70S6 kinase pathway.

Variations in Interferon Gamma Receptor Gene Expression during Liver Regeneration after Partial Hepatectomy in Rats

Cell-mediated immunity, which includes interferon gamma (IFN-γ) expression, is activated during the process of liver regeneration; however, the genetic pathway of this activation is still unclear. The present study evaluated variations in the interferon gamma receptor (IFN-γR) gene and its mRNA expression during liver regeneration after partial hepatectomy (PH). Male Wistar rats weighing approximately 200 g were subjected to PH (70 or 40%). IFN-γR gene expression in the remnant liver was measured by cDNA microarray, and mRNA expression was verified by real-time quantitative reverse transcription-polymerase chain reaction (Q-PCR) preoperatively and at 2, 4, 6,12, 24, and 72 hours and 7 days postoperatively. The ratio of remnant liver weight to body weight increased markedly after 70 per cent PH and more gradually after 40 per cent PH. It reached near 90 per cent of the preoperative level at 72 hours after PH in both groups. The scanned spots of the genomic survey on the cDNA microarray chips were uneven and increased irregularly in number and density after PH. IFN-γR gene expression increased markedly in a single peak pattern, up to more than double the preoperative level, at 6 hours after 70 per cent PH. The curve in the 40 per cent PH group was flat and peaked at only 1.6 times the preoperative level. The variations in IFN-γR-related mRNA expression were verified by Q-PCR. Elevations in IFN-γR gene and mRNA expression were shown during the early stage of liver regeneration after PH. The genetic pathway of IFN-γ/IFN-γR expression is activated during liver regeneration.

Temporal and functional profile of the transcriptional regulatory network in the early regenerative response to partial hepatectomy in the rat

Background

The goal of these studies was to characterize the transcriptional network regulating changes in gene expression in the remnant liver of the rat after 70% partial hepatectomy (PHx) during the early phase response including the transition of hepatocytes from the quiescent (G₀) state and the onset of the G₁ phase of the cell cycle.

Results

The transcriptome of remnant livers was monitored at 1, 2, 4, and 6 hours after PHx using cDNA microarrays. Differentially regulated genes were grouped into six clusters according their temporal expression profiles. Promoter regions of genes in these clusters were examined for shared transcription factor binding sites (TFBS) by comparing enrichment of each TFBS relative to a reference set using the Promoter Analysis and Interaction Network Toolset (PAINT).

Analysis of the gene expression time series data using ANOVA resulted in a total of 309 genes significantly up- or down-regulated at any of the four time points at a 20% FDR threshold. Sham-operated animals showed no significant differential expression. A subset of the differentially expressed genes was validated using quantitative RT-PCR. Distinct sets of TFBS could be identified that were significantly enriched in each one of the different temporal gene expression clusters. These included binding sites for transcription factors that had previously been recognized as contributing to the onset of regeneration, including NF-κB, C/EBP, HNF-1, CREB, as well as factors, such as ATF, AP-2, LEF-1, GATA and PAX-6, that had not yet been recognized to be involved in this process. A subset of these candidate TFBS was validated by measuring activation of corresponding transcription factors (HNF-1, NK-κB, CREB, C/EBP-α and C/EBP-β, GATA-1, AP-2, PAX-6) in nuclear extracts from the remnant livers.

Conclusion

This analysis revealed multiple candidate transcription factors activated in the remnant livers, some known to be involved in the early phase of liver regeneration, and several not previously identified. The study describes the predominant temporal and functional elements to which these factors contribute and demonstrates the potential of this novel approach to define the functional correlates of the transcriptional regulatory network driving the early response to partial hepatectomy.

Differences in regulation of type I collagen synthesis in primary and passaged hepatic stellate cell cultures: the role of alpha5beta1-integrin

Hepatic stellate cells (HSC) differ in their phenotype depending on the initiation and progression of their activation. Our hypothesis was that different mechanisms govern type I collagen synthesis depending on stage of HSC activation. We investigated the role of alpha(5)beta(1)-integrin as a regulator of type I collagen gene COL1A1 expression in primary and passaged HSC cultures using transgenic mouse containing type I collagen gene COL1A1 promoter linked to the chloramphenicol acetyltransferase (CAT) reporter gene. The alpha(5)beta(1) protein levels increased during the activation and were highest in day 6 primary cultures but decreased in passaged HSC. CAT activity, reflecting COL1A1 expression, was upregulated by alpha(5)beta(1)-integrin. Inhibition of alpha(5)beta(1)-integrin by echistatin and blocking antibody resulted in reduced transgene activity only in early primary cultures (compared with the control, 53.3 +/- 12% echistatin and 58.8 +/- 7% blocking antibody, respectively, P < 0.05). Treatment of passaged HSC with either echistatin or blocking antibody had no effect. Fibronectin, an alpha(5)beta(1)-integrin ligand, increased transgene activity in primary (210 +/- 33%, P < 0.05) but not in passaged HSC cultures (119 +/- 8%). This alpha(5)beta(1)-integrin effect appears to be at least in part mediated by CCAAT enhancer binding protein-beta (C/EBPbeta), because fibronectin increased and alpha(5)-gene silencing by small interfering RNA decreased C/EBPbeta levels. In addition, C/EBPbeta knockout mice showed reduced type I collagen synthesis compared with wild-type littermates. Therefore alpha(5)beta(1)-integrin is an important regulator of type I collagen production in early primary HSC cultures but appears to have no direct role once the HSC are fully activated.

Adipogenic signaling in rat white adipose tissue: modulation by aging and calorie restriction

Alterations in adipogenesis could have significant impact on several aging processes. We previously reported that calorie restriction (CR) in rats significantly increases the level of circulating adiponectin, a distinctive marker of differentiated adipocytes, leading to a concerted modulation in the expression of key transcription target genes and, as a result, to increased fatty acid oxidation and reduced deleterious lipid accumulation in other tissues. These findings led us to investigate further the effects of aging on adipocytes and to determine how CR modulates adipogenic signaling in vivo. CR for 2 and 25 months, significantly increased the expression of PPARgamma, C/EBPbeta and Cdk-4, and partially attenuated age-related decline in C/EBPalpha expression relative to rats fed ad libitum (AL). As a result, adiponectin was upregulated at both mRNA and protein levels, resulting in activation of target genes involved in fatty acid oxidation and fatty acid synthesis, and greater responsiveness of adipose tissue to insulin. Moreover, CR significantly decreased the ratio of C/EBPbeta isoforms LAP/LIP, suggesting the suppression of gene transcription associated with terminal differentiation while facilitating preadipocytes proliferation. Morphometric analysis revealed a greater number of small adipocytes in CR relative to AL feeding. Immunostaining confirmed that small adipocytes were more strongly positive for adiponectin than the large ones. Overall these results suggest that CR increased the expression of adipogenic factors, and maintained the differentiated state of adipocytes, which is critically important for adiponectin biosynthesis and insulin sensitivity.

Portal blood flow regulates volume recovery of the rat liver after partial hepatectomy: molecular evaluation

BACKGROUND/AIM

Liver regeneration is a finely tuned process that is closely regulated by multiple cell cycle steps. Although the portal blood flow affects liver regeneration, the molecular mechanism by which the blood flow regulates gene expression and liver function is largely unknown. The aim of this study was to investigate the molecular effect of portal blood flow on hepatocyte proliferation and gene regulation during liver regeneration.

MATERIALS AND METHODS

We developed a simple surgical rat model to investigate the relation between portal blood flow and liver regeneration by partially ligating the portal trunk with 8-0 Proline sutures under microscopy to reduce the blood flow by 40%. We investigated recovery of liver volume, DNA synthesis, and gene expression associated with cell cycle regulators, comparing partially hepatectomized (PH) rats without (PH group; n = 30) and with partial portal ligation (PHPL group; n = 30) for 7 days after the operation.

RESULTS

The hepatic tissue blood flow and the recovery ratio between liver weight and body weight in the PHPL group were significantly lower than in the PH group after hepatectomy. The peak 5-bromo-2'-deoxyuridine labeling index in the PHPL group was delayed and weak compared with the PH group. The expression of CT-1 and cyclin D, E, and B mRNAs indicated that the liver regeneration in the PHPL group was delayed and weak. In addition, there was reciprocal expression of C/EBPalpha and C/EBPbeta mRNAs, an observation supported by their nuclear protein levels. Furthermore, the cytochrome P-450 protein level in the PHPL group was higher than that in the PH group 1 day after hepatectomy.

CONCLUSION

The portal blood flow regulates the activity of liver regeneration and the gene expression associated with cell cycle regulators, while the functions are maintained.

Age-specific CUGBP1-eIF2 complex increases translation of CCAAT/enhancer-binding protein beta in old liver

The RNA-binding protein CUGBP1 regulates translation of proteins in a variety of biological processes. In this study, we show that aging liver increases CUGBP1 translational activities by induction of a high molecular weight protein-protein complex of CUGBP1. The complex contains CUGBP1, subunits alpha, beta, and gamma of the initiation translation factor eIF2, and four proteins of the endoplasmic reticulum, eR90, CRT, eR60, and Grp78. The induction of the CUGBP1-eIF2 complex in old livers is associated with the elevation of protein levels of CUGBP1 and with the hyper-phosphorylation of CUGBP1 by a cyclin D3-cdk4 kinase, activity of which is increased with age. We have examined the role of the elevation of CUGBP1 and the role of cyclin D3-cdk4-mediated phosphorylation of CUGBP1 in the formation of the CUGBP1-eIF2 complex by using CUGBP1 transgenic mice and young animals expressing high levels of cyclin D3 after injection with cyclin D3 plasmid. These studies showed that both the increased levels of CUGBP1 and cdk4-mediated hyper-phosphorylation of CUGBP1 are involved in the age-associated induction of the CUGBP1-eIF2 complex. The CUGBP1-eIF2 complex is bound to C/EBPbeta mRNA in the liver of old animals, and this binding correlates with the increased amounts of liver-enriched activator protein and liver-enriched inhibitory protein. Consistent with these observations, the purified CUGBP1-eIF2 complex binds to the 5' region of C/EBPbeta mRNA and significantly increases translation of the three isoforms of C/EBPbeta in a cell-free translation system, in cultured cells, and in the liver. Thus, these studies demonstrated that age-mediated induction of the CUGBP1-eIF2 complex changes translation of C/EBPbeta in old livers.

Inducible activation of CEBPB, a gene negatively regulated by BCR/ABL, inhibits proliferation and promotes differentiation of BCR/ABL-expressing cells

Translational regulation by oncogenic proteins may be a rapid and efficient mechanism to modulate gene expression. We report here the identification of the CEBPB gene as a target of translational regulation in myeloid precursor cells transformed by the BCR/ABL oncogene. Expression of CEBPB was repressed in 32D-BCR/ABL cells and reinduced by imatinib (STI571) via a mechanism that appears to depend on expression of the CUG-repeat RNA-binding protein CUGBP1 and the integrity of the CUG-rich intercistronic region of c/ebpbeta mRNA. Constitutive expression or conditional activation of wild-type CEBPB induced differentiation and inhibited proliferation of 32D-BCR/ABL cells in vitro and in mice, but a DNA binding-deficient CEBPB mutant had no effect. The proliferation-inhibitory effect of CEBPB was, in part, mediated by the CEBPB-induced GADD45A gene. Because expression of CEBPB (and CEBPA) is low in the blast crisis (BC) stage of chronic myelogenous leukemia (CML) and is inversely correlated with BCR/ABL tyrosine kinase levels, these findings point to the therapeutic potential of restoring C/EBP activity in CML-BC and, perhaps, other types of acute leukemia.