Identification of the C/EBPα C-terminal tail residues involved in the protein interaction with GABP and their potency in myeloid differentiation of K562 cells

Identification of key modules and driving genes in nonalcoholic fatty liver disease by weighted gene co-expression network analysis

BACKGROUND

Nonalcoholic fatty liver disease (NAFLD) is characterized by excessive liver fat deposition, and progresses to liver cirrhosis, and even hepatocellular carcinoma. However, the invasive diagnosis of NAFLD with histopathological evaluation remains risky. This study investigated potential genes correlated with NAFLD, which may serve as diagnostic biomarkers and even potential treatment targets.

METHODS

The weighted gene co-expression network analysis (WGCNA) was constructed based on dataset E-MEXP-3291. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses were performed to evaluate the function of genes.

RESULTS

Blue module was positively correlated, and turquoise module negatively correlated with the severity of NAFLD. Furthermore, 8 driving genes (ANXA9, FBXO2, ORAI3, NAGS, C/EBPα, CRYAA, GOLM1, TRIM14) were identified from the overlap of genes in blue module and GSE89632. And another 8 driving genes were identified from the overlap of turquoise module and GSE89632. Among these driving genes, C/EBPα (CCAAT/enhancer binding protein α) was the most notable. By validating the expression of C/EBPα in the liver of NAFLD mice using immunohistochemistry, we discovered a significant upregulation of C/EBPα protein in NAFLD.

CONCLUSION

we identified two modules and 16 driving genes associated with the progression of NAFLD, and confirmed the protein expression of C/EBPα, which had been paid little attention to in the context of NAFLD, in the present study. Our study will advance the understanding of NAFLD. Moreover, these driving genes may serve as biomarkers and therapeutic targets of NAFLD.

Host factors associated with either VP16 or VP16-induced complex differentially affect HSV-1 lytic infection

Herpes simplex virus type 1 (HSV-1) is an important human pathogen with neurotropism. Following lytic infection in mucosal or skin epithelium, life-long latency is established mainly in sensory neurons, which can periodically reactivate by stress, leading to recurrent disease and virus transmission. During the virus's productive infection, the tegument protein VP16, a component of HSV-1 virion, is physically associated with two cellular factors, host cell factor-1 (HCF-1), and POU domain protein Oct-1, to construct the VP16-induced complex, which is essential to stimulate immediate early (IE)-gene transcription as well as initiate the lytic programme. Apart from HCF-1 and Oct-1, VP16 also associates with a series of other host factors, making a VP16-induced regulatory switch to either activate or inactivate virus gene transcription. In addition, VP16 has effects on distinct signalling pathways via binding to various host molecules that are essentially related to innate immune responses, RNA polymerases, molecular chaperones, and virus infection-induced host shutoff. VP16 also functionally compensates for given host factors, such as PPAR-γ and ß-catenin. In this review, we provide an overview of the updated insights on the interplay between VP16 and the host factors that coordinate virus infection.

nNOS induction and NOSIP interaction impact granulopoiesis and neutrophil differentiation by modulating nitric oxide generation

Nitric oxide (NO), a versatile free radical and a signalling molecule, plays an important role in the haematopoiesis, inflammation and infection. Impaired proliferation and differentiation of myeloid cells lead to malignancies and Hematopoietic deficiencies. This study was aimed to define the role of nNOS derived NO in neutrophil differentiation (in-vitro) and granulopoiesis (in-vivo) using multipronged approaches. The results obtained from nNOS over-expressing K562 cells revealed induction in C/EBPα derived neutrophil differentiation as evident by an increase in the expression of neutrophil specific cell surface markers, genes, transcription factors and functionality. nNOS mediated response also involved G-CSFR-STAT-3 axis during differentiation. Consistent increase in NO generation was observed during neutrophil differentiation of mice and human CD34⁺ HSPCs. Furthermore, granulopoiesis was abrogated in the nNOS inhibitor treated mice, depicting a decrease in the numbers of BM mature and progenitor neutrophils. Likewise, in vitro inhibition of nNOS in human CD34⁺ HSPCs indicated an indispensable role of nNOS in neutrophil differentiation. Expression of nNOS inhibitory protein, NOSIP was significantly and consistently decreased during the final stage of differentiation and was linked with the augmentation in NO release. Moreover, neutrophils from CML patients had more NOSIP and less NO generation as compared to the PMNs from healthy individuals. The present study thus indicates a critical role of nNOS, and its interaction with NOSIP during neutrophil differentiation. The study also highlights the importance of nNOS in the neutrophil progenitor proliferation and differentiation warranting investigations to assess its role in the haematopoiesis-related disorders.

A combined computational and experimental approach reveals the structure of a C/EBPβ-Spi1 interaction required for IL1B gene transcription

We previously reported that transcription of the human IL1B gene, encoding the proinflammatory cytokine interleukin 1β, depends on long-distance chromatin looping that is stabilized by a mutual interaction between the DNA-binding domains (DBDs) of two transcription factors: Spi1 proto-oncogene at the promoter and CCAAT enhancer-binding protein (C/EBPβ) at a far-upstream enhancer. We have also reported that the C-terminal tail sequence beyond the C/EBPβ leucine zipper is critical for its association with Spi1 via an exposed residue (Arg-232) located within a pocket at one end of the Spi1 DNA-recognition helix. Here, combining in vitro interaction studies with computational docking and molecular dynamics of existing X-ray structures for the Spi1 and C/EBPβ DBDs, along with the C/EBPβ C-terminal tail sequence, we found that the tail sequence is intimately associated with Arg-232 of Spi1. The Arg-232 pocket was computationally screened for small-molecule binding aimed at IL1B transcription inhibition, yielding l-arginine, a known anti-inflammatory amino acid, revealing a potential for disrupting the C/EBPβ-Spi1 interaction. As evaluated by ChIP, cultured lipopolysaccharide (LPS)-activated THP-1 cells incubated with l-arginine had significantly decreased IL1B transcription and reduced C/EBPβ's association with Spi1 on the IL1B promoter. No significant change was observed in direct binding of either Spi1 or C/EBPβ to cognate DNA and in transcription of the C/EBPβ-dependent IL6 gene in the same cells. These results support the notion that disordered sequences extending from a leucine zipper can mediate protein-protein interactions and can serve as druggable targets for regulating gene promoter activity.

The VEGFA -1154G/A polymorphism is associated with reduced risk of rheumatoid arthritis but not with systemic lupus erythematosus in Mexican women

BACKGROUND

Levels of circulating vascular endothelial growth factor (VEGF) (a potent endothelial-cell-specific angiogenic factor) have been correlated with disease activity in patients with rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE). In addition, several single nucleotide polymorphisms (SNPs), including the VEGFA -2578C/A, have been associated with RA in some populations. By contrast, the role of different VEGFA SNPs in the susceptibility to SLE has received little attention. Thus, the present study aimed to determine whether the VEGFA -2578C/A, -1154G/A and -634G/C polymorphisms confer risk or were associated with reduced risk of RA or SLE in a Mexican population.

METHODS

The present study included 903 women from Mexico: 405 were patients with RA, 282 had SLE and 216 were healthy individuals. The genotypes were obtained with TaqMan probes.

RESULTS

The data obtained in the present study suggest that the VEGFA -2578C/A and -634G/C polymorphisms are not risk factors for RA or SLE; however, VEGFA -1154G/A was associated with reduced risk in women with RA (odds ratio = 0.6, p_c  = 0.0051) but not with SLE (odds ratio = 0.7, p_c  = 0.13).

CONCLUSIONS

The present study is the first to document an association between VEGFA -1154G/A and reduced risk in women with RA but not with SLE.

Overexpression of CCAAT Enhancer-Binding Protein α Inhibits the Growth of K562 Cells via the Foxo3a-Bim Pathway

We aimed to investigate the role of CCAAT enhancer-binding protein α (C/EBPα) in the pathogenesis of chronic myeloid leukemia (CML) and the mechanism underlying its effect. Bone marrow specimens from 50 patients with CML and peripheral blood specimens from 20 healthy individuals were collected. K562 cells were treated with imatinib. Subsequently, a stable cell line, K562-C/EBPα, was constructed. Cell proliferation was assayed with cell counting kit-8, and mRNA levels of C/EBPα, forkhead transcription factor FKHRL1 (Foxo3a) and Bim were detected by semiquantitative PCR. The correlation of C/EBPα and BCR-ABL was assessed by Spearman's correlation analysis. The results showed that C/EBPα mRNA levels were significantly reduced in CML patients compared with healthy subjects (p < 0.001) and were negatively correlated with BCR-ABL1 (r = -0.5046, p < 0.01). Additionally, imatinib enhanced the expression of C/EBPα in K562 cells compared with untreated cells (p < 0.05). Overexpression of C/EBPα significantly decreased cell proliferation and upregulated the expressions of the apoptosis-related genes Foxo3a (p < 0.01) and Bim (p < 0.05) in K562 cells. In conclusion, C/EBPα expression was decreased in patients with CML. Imatinib enhances the expression of C/EBPα in K562 cells, and the overexpression of C/EBPα inhibits cell proliferation and increases apoptosis via the Foxo3a-Bim pathway.

[The expression and role of the transcription factor C/EBPα in chronic myeloid leukemia]

OBJECTIVE

To investigate the expression and the possible mechanism of the transcription factor C/EBPα in chronic myeloid leukemia（CML).

METHODS

Bone marrow samples from 50 CML patients（including 33 patients in chronic phase, 7 in accelerated phase and 10 in blast crisis）and peripheral blood specimens of 20 healthy donors were collected. The expression of C/EBPα gene and the effect of Imatinib on its expression was detected by RT- PCR. C/EBPα gene was inserted into lentivirus expression vector pLVX- EGFP- 3FLAG- Puro by recombinant DNA technology to construct C/EBPα stable expression in K562 cells. Cell proliferation was assayed by CCK-8. The expressions of Foxo3a and Bim genes were detected by RT-PCR.

RESULTS

The level of C/EBPα expression was significantly declined in CML patients compared with that of normal control group（P<0.01）and had negative correlation with bcr- abl expression（Spearman r=－ 0.505, P<0.01). The stable K562- C/EBPα cell line was successfully established and confirmed by RT-PCR and Western blot. Cell proliferation ability was lower in the K562- C/EBPα group than that in the non- transfection and mock-vehicle groups. The expressions of Foxo3a and Bim genes were 1.06 ± 0.06 and 0.53 ± 0.07, respectively, which was higher than that of nontransfection and mock-vehicle groups（P<0.01, P<0.05).

CONCLUSION

C/EBPα expression was decreased in CML patients, overexpression of C/EBPα could inhibit K562 cell growth.

Regulation of the C/EBPα signaling pathway in acute myeloid leukemia (Review)

The transcription factor CCAAT/enhancer binding protein α (C/EBPα), as a critical regulator of myeloid development, directs granulocyte and monocyte differentiation. Various mechanisms have been identified to explain how C/EBPα functions in patients with acute myeloid leukemia (AML). C/EBPα expression is suppressed as a result of common leukemia-associated genetic and epigenetic alterations such as AML1-ETO, RARα-PLZF or gene promoter methylation. Recent data have shown that ubiquitination modification also contributes to its downregulation. In addition, 10-15% of patients with AML in an intermediate cytogenetic risk subgroup were characterized by mutations of the C/EBPα gene. As a transcription factor, C/EBPα can translocate into the nucleus and further regulate a variety of genes directly or indirectly, which are all key factors for cell differentiation. This review summarizes recent reports concerning the dysregulation of C/EBPα expression at various levels in human AML. The currently available data are persuasive evidence suggesting that impaired abnormal C/EBPα expression contributes to the development of AML, and restoration of C/EBPα expression as well as its function represents a promising target for novel therapeutic strategies in AML.

The genome-wide molecular signature of transcription factors in leukemia

Transcription factors control expression of genes essential for the normal functioning of the hematopoietic system and regulate development of distinct blood cell types. During leukemogenesis, aberrant regulation of transcription factors such as RUNX1, CBFβ, MLL, C/EBPα, SPI1, GATA, and TAL1 is central to the disease. Here, we will discuss the mechanisms of transcription factor deregulation in leukemia and how in recent years next-generation sequencing approaches have helped to elucidate the molecular role of many of these aberrantly expressed transcription factors. We will focus on the complexes in which these factors reside, the role of posttranslational modification of these factors, their involvement in setting up higher order chromatin structures, and their influence on the local epigenetic environment. We suggest that only comprehensive knowledge on all these aspects will increase our understanding of aberrant gene expression in leukemia as well as open new entry points for therapeutic intervention.