CCAAT/Enhancer binding protein delta (c/EBPdelta) regulation and expression in human mammary epithelial cells: II. Analysis of activating signal transduction pathways, transcriptional, post-transcriptional, and post-translational control

The effects of blunt snout bream (Megalobrama amblycephala) IL-6 trans-signaling on immunity and iron metabolism via JAK/STAT3 pathway

Interleukin-6 (IL-6) is a pleiotropic inflammatory cytokine, which plays a dual role in mammalian inflammation through both classical signaling (IL-6 binds to IL-6 receptor/IL-6R) and trans-signaling (IL-6 binds to soluble IL-6R). However, the function of IL-6, especially the regulatory mechanism of IL-6 trans-signaling in immunity and iron metabolism remains largely unclear in teleost. Here, L8824 cells (Ctenopharyngodon idella hepatic cells) were stimulated with blunt snout bream (Megalobrama amblycephala) IL-6 combination with sIL-6R protein (rmaIL-6+rmasIL-6R/maIL-6 trans-signaling) or STAT3 inhibitor (c188-9), and RNA-sequencing, global transcriptional analyses. The enrichment analysis of GO and KEGG showed that maIL-6 trans-signaling is mainly involved in stress and inflammation response, and the activation of STAT3 is mainly related to cell proliferation, apoptosis and immune regulation. Furthermore, after treated L8824 cells with JAK2 inhibitors, it was found that the induction of IL-6 trans-signaling on the selected immune-related genes could be inhibited. These results implied that in early stage after rmaIL-6+rmasIL-6R treatment, the maIL-6 trans-signaling played an important role in the immune regulation through the JAK2/STAT3 pathway. By extending the rmaIL-6+rmasIL-6R treatment time, it was found that maIL-6 trans-signaling could promote the expression of iron metabolism related genes (ft, tf, tfr1, hamp and fpn1) in L8824 cells, indicating that maIL-6 trans-signaling may be involved in iron metabolism in the non-acute immune phase. Finally, after treated L8824 cells with JAK2 and STAT3 inhibitors, it was found that only tf and fpn1 were regulated by maIL-6 trans-signaling through the JAK2/STAT3 pathway. These findings provided novel insights into IL-6 trans-signaling regulatory mechanism in teleost, enriching our knowledge of fish immunity and iron metabolism.

Macrophage C/EBPδ Drives Gemcitabine, but Not 5-FU or Paclitaxel, Resistance of Pancreatic Cancer Cells in a Deoxycytidine-Dependent Manner

Treatment of pancreatic ductal adenocarcinoma (PDAC), a dismal disease with poor survival rates, is hampered by the high prevalence of chemotherapy resistance. Resistance is accompanied by macrophage infiltration into the tumor microenvironment, and infiltrated macrophages are key players in chemotherapy resistance. In the current manuscript, we identify CCAAT/enhancer-binding protein delta (C/EBPδ) as an important transcription factor driving macrophage-dependent gemcitabine resistance. We show that conditioned medium obtained from wild type macrophages largely diminishes gemcitabine-induced cytotoxicity of PDAC cells, whereas conditioned medium obtained from C/EBPδ-deficient macrophages only minimally affects gemcitabine-induced PDAC cell death. Subsequent analysis of RNA-Seq data identified the pyrimidine metabolism pathway amongst the most significant pathways down-regulated in C/EBPδ-deficient macrophages and size filtration experiments indeed showed that the low molecular weight and free metabolite fraction most effectively induced gemcitabine resistance. In line with a role for pyrimidines, we next show that supplementing macrophage conditioned medium with deoxycytidine overruled the effect of macrophage conditioned media on gemcitabine resistance. Consistently, macrophage C/EBPδ-dependent resistance is specific for gemcitabine and does not affect paclitaxel or 5-FU-induced cytotoxicity. Overall, we thus show that C/EBPδ-dependent deoxycytidine biosynthesis in macrophages induces gemcitabine resistance of pancreatic cancer cells.

Epigenetic modifications underlie the differential adipogenic potential of preadipocytes derived from human subcutaneous fat tissue

AIM

Ceiling culture-derived preadipocytes (ccdPAs) and adipose-derived stem cells (ASCs) can be harvested from human subcutaneous fat tissue using the specific gravity method. Both cell types possess a similar spindle shape without lipid droplets. We previously reported that ccdPAs have a higher adipogenic potential than ASCs, even after a 7-week culture. We performed a genome-wide epigenetic analysis to examine the mechanisms contributing to the adipogenic potential differences between ccdPAs and ASCs.

MATERIALS AND METHODS

Methylation analysis of cytosines followed by guanine (CpG) using a 450K BeadChip was performed on human ccdPAs and ASCs isolated from three metabolically healthy females. Chromatin immunoprecipitation sequencing (ChIP-seq) was performed to evaluate trimethylation at lysine 4 of histone 3 (H3K4me3).

RESULTS

Unsupervised machine learning using t-distributed stochastic neighbor embedding (tSNE) to interpret 450,000-dimensional methylation assay data showed that the cells were divided into ASC and ccdPA groups. In KEGG pathway analysis of 1,543 genes with differential promoter CpG methylation, the peroxisome proliferator-activated receptor (PPAR) and adipocytokine signaling pathways ranked in the top 10 pathways. In the PPAR gamma gene, H3K4me3 peak levels were higher in ccdPAs than in ASCs, whereas promoter CpG methylation levels were significantly lower in ccdPAs than in ASCs. Similar differences in promoter CpG methylation were also seen in the fatty acid-binding protein 4 (FABP4) and leptin genes.

CONCLUSION

We analyzed the epigenetic status of adipogenesis-related genes as a potential mechanism underlying the differences in adipogenic differentiation capability between ASCs and ccdPAs.

Non-Tumor CCAAT/Enhancer-Binding Protein Delta Potentiates Tumor Cell Extravasation and Pancreatic Cancer Metastasis Formation

CCAAT/enhancer-binding protein delta (C/EBPδ) is a transcription factor involved in apoptosis and proliferation, which is downregulated in pancreatic ductal adenocarcinoma (PDAC) cells. Loss of nuclear C/EBPδ in PDAC cells is associated with decreased patient survival and pro-tumorigenic properties in vitro. Interestingly however, next to C/EBPδ expression in tumor cells, C/EBPδ is also expressed by cells constituting the tumor microenvironment and by cells comprising the organs and parenchyma. However, the functional relevance of systemic C/EBPδ in carcinogenesis remains elusive. Here, we consequently assessed the potential importance of C/EBPδ in somatic tissues by utilizing an orthotopic pancreatic cancer model. In doing so, we show that genetic ablation of C/EBPδ does not significantly affect primary tumor growth but has a strong impact on metastases; wildtype mice developed metastases at multiple sites, whilst this was not the case in C/EBPδ^-/- mice. In line with reduced metastasis formation in C/EBPδ^-/- mice, C/EBPδ-deficiency also limited tumor cell dissemination in a specific extravasation model. Tumor cell extravasation was dependent on the platelet-activating factor receptor (PAFR) as a PAFR antagonist inhibited tumor cell extravasation in wildtype mice but not in C/EBPδ^-/- mice. Overall, we show that systemic C/EBPδ facilitates pancreatic cancer metastasis, and we suggest this is due to C/EBPδ-PAFR-dependent tumor cell extravasation.

High-Throughput Screening for CEBPD-Modulating Compounds in THP-1-Derived Reporter Macrophages Identifies Anti-Inflammatory HDAC and BET Inhibitors

This study aimed to identify alternative anti-inflammatory compounds that modulate the activity of a relevant transcription factor, CCAAT/enhancer binding protein delta (C/EBPδ). C/EBPδ is a master regulator of inflammatory responses in macrophages (Mϕ) and is mainly regulated at the level of CEBPD gene transcription initiation. To screen for CEBPD-modulating compounds, we generated a THP-1-derived reporter cell line stably expressing secreted alkaline phosphatase (SEAP) under control of the defined CEBPD promoter (CEBPD::SEAP). A high-throughput screening of LOPAC^®1280 and ENZO^®774 libraries on LPS- and IFN-γ-activated THP-1 reporter Mϕ identified four epigenetically active hits: two bromodomain and extraterminal domain (BET) inhibitors, I-BET151 and Ro 11-1464, as well as two histone deacetylase (HDAC) inhibitors, SAHA and TSA. All four hits markedly and reproducibly upregulated SEAP secretion and CEBPD::SEAP mRNA expression, confirming screening assay reliability. Whereas BET inhibitors also upregulated the mRNA expression of the endogenous CEBPD, HDAC inhibitors completely abolished it. All hits displayed anti-inflammatory activity through the suppression of IL-6 and CCL2 gene expression. However, I-BET151 and HDAC inhibitors simultaneously upregulated the mRNA expression of pro-inflammatory IL-1ß. The modulation of CEBPD gene expression shown in this study contributes to our understanding of inflammatory responses in Mϕ and may offer an approach to therapy for inflammation-driven disorders.

C/EBPβ and C/EBPδ transcription factors: Basic biology and roles in the CNS

CCAAT/enhancer binding protein (C/EBP) β and C/EBPδ are transcription factors of the basic-leucine zipper class which share phylogenetic, structural and functional features. In this review we first describe in depth their basic molecular biology which includes fascinating aspects such as the regulated use of alternative initiation codons in the C/EBPβ mRNA. The physical interactions with multiple transcription factors which greatly opens the number of potentially regulated genes or the presence of at least five different types of post-translational modifications are also remarkable molecular mechanisms that modulate C/EBPβ and C/EBPδ function. In the second part, we review the present knowledge on the localization, expression changes and physiological roles of C/EBPβ and C/EBPδ in neurons, astrocytes and microglia. We conclude that C/EBPβ and C/EBPδ share two unique features related to their role in the CNS: whereas in neurons they participate in memory formation and synaptic plasticity, in glial cells they regulate the pro-inflammatory program. Because of their role in neuroinflammation, C/EBPβ and C/EBPδ in microglia are potential targets for treatment of neurodegenerative disorders. Any strategy to reduce C/EBPβ and C/EBPδ activity in neuroinflammation needs to take into account its potential side-effects in neurons. Therefore, cell-specific treatments will be required for the successful application of this strategy.

Genetic effects of single nucleotide polymorphisms in JAK2 and STAT5A genes on susceptibility of Chinese Holsteins to mastitis

The JAK-STAT pathway plays a key role in host immunity. The present study was designed to evaluate the effects of single nucleotide polymorphisms (SNPs) in STAT5A and JAK2 genes on some serum cytokines, mastitis and milk production traits. Two SNPs (SNP1 43046497A/C and SNP2 43047829G/A) in STAT5A, and four SNPs in JAK2 (SNP3 39652267A/G, SNP4 39630048C/T, SNP5 39631044G/A, and SNP6 39631175T/C) were revealed and genotyped in 268 Chinese Holstein cattle. Fixed model was used to analyze the association of SNPs with phenotypes by general linear model procedure of SAS 9.1. SNP1 and SNP4 were significantly associated with IL-6 and IL-17 (P < 0.05), respectively. In JAK2 gene, SNP3 was highly significant (P < 0.01) and SNP5 was significant (P < 0.05) in association with SCC, whereas, the association of SNP6 was found significant (P < 0.05) with both SCC and SCS. Combination genotype analysis revealed that SNPs in JAK2 gene significantly associated with SCC and SCS were associated significantly with the corresponding phenotypes in combinations as well. The GG genotype of SNP3 individually and in any combination genotypes showed lowest SCC. The dominant effect of SNP1, SNP5 and SNP6 was found highly significant (P < 0.01) on the corresponding phenotypes (IL-6, SCC and SCS). As for haplotype analysis, two haplotypes were revealed between the two SNPs of STAT5A gene and four haplotypes amongst four SNPs in JAK2 gene; strong linkage disequilibrium (D' > 0.9) was observed between all these haplotypes. The results imply that the identified SNPs could be powerful markers to select dairy cattle with improved genetic resistance against mastitis.

Identification of novel Sp1 targets involved in proliferation and cancer by functional genomics

Sp1 is a transcription factor regulating many genes through its DNA binding domain, containing three zinc fingers. We were interested in identifying target genes regulated by Sp1, particularly those involved in proliferation and cancer. Our approach was to treat HeLa cells with a siRNA directed against Sp1 mRNA to decrease the expression of Sp1 and, in turn, the genes activated by this transcription factor. Sp1-siRNA treatment led to a great number of differentially expressed genes as determined by whole genome cDNA microarray analysis. Underexpressed genes were selected since they represent putative genes activated by Sp1 and classified in six Gene Onthology categories, namely proliferation and cancer, mRNA processing, lipid metabolism, glucidic metabolism, transcription and translation. Putative Sp1 binding sites were found in the promoters of the selected genes using the Match™ software. After literature mining, 11 genes were selected for further validation. Underexpression by qRT-PCR was confirmed for the 11 genes plus Sp1 in HeLa cells after Sp1-siRNA treatment. EMSA and ChIP assays were performed to test for binding of Sp1 to the promoters of these genes. We observed binding of Sp1 to the promoters of RAB20, FGF21, IHPK2, ARHGAP18, NPM3, SRSF7, CALM3, PGD and Sp1 itself. Furthermore, the mRNA levels of RAB20, FGF21 and IHPK2 and luciferase activity for these three genes related to proliferation and cancer, were determined after overexpression of Sp1 in HeLa cells, to confirm their regulation by Sp1. Involvement of these three genes in proliferation was validated by gene silencing using polypurine reverse hoogsteen hairpins.

Non-receptor tyrosine kinase 2 reaches its lowest expression levels in human breast cancer during regional nodal metastasis

Almost half of breast Ductal Carcinoma in situ are likely to remain non threatening in situ lesions with no invasion to the surrounding stroma and no metastases. The majority of focal disruptions in myoepithelial (ME) cell layers indicative of invasion onset were found to be overlying epithelial cell clusters with no or substantially reduced estrogen receptor α (ERα) expression. Here we report the down-regulation of tyrosine kinase-2 (TYK2) and up-regulation of strumpellin expression, among other proteins in ERα(-) cells located at disrupted ME layers compared to adjacent ERα(+) cells overlying an intact myoepithelial layer. ERα(+) and ERα(-) cells were microdissected from the same in vivo human breast cancer tissues, proteins were extracted and separated utilizing Differential in-Gel Electrophoresis followed by trypsin digestion, MALDI-TOF analysis, and protein identification. Proteins expressed by ERα(-) cell clusters were found to express higher levels of strumpellin that binds to valosin-containing protein (VCP) to slow-down wound closure and promote growth; and lower levels of TYK2, a jak protein necessary for lineage specific differentiation. TYK2 levels were further analyzed by immunohistochemistry in a cohort composed of 70 patients with broad clinical characteristics. TYK2 levels were minimal in TxN1M0 breast cancers which is the stage where the initial regional lymph node metastasis is observed. Our data highlight the role of TYK2 downregulation in breast cancer cell de-differentitation and initiation of regional metastasis. In addition, the aggressiveness of the ERα(-) cell clusters compared to ERα(+) ones present in the same duct of the same patient was confirmed.

Eicosapentaenoic acid demethylates a single CpG that mediates expression of tumor suppressor CCAAT/enhancer-binding protein delta in U937 leukemia cells

Polyunsaturated fatty acids (PUFAs) inhibit proliferation and induce differentiation in leukemia cells. To investigate the molecular mechanisms whereby fatty acids affect these processes, U937 leukemia cells were conditioned with stearic, oleic, linolenic, α-linolenic, arachidonic, eicosapentaenoic, and docosahexaenoic acids. PUFAs affected proliferation; eicosapentaenoic acid (EPA) was the most potent on cell cycle progression. EPA enhanced the expression of the myeloid lineage-specific transcription factors CCAAT/enhancer-binding proteins (C/EBPβ and C/EBPδ), PU.1, and c-Jun, resulting in increased expression of the monocyte lineage-specific target gene, the macrophage colony-stimulating factor receptor. Indeed, it is known that PU.1 and C/EBPs interact with their consensus sequences on a small DNA fragment of macrophage colony-stimulating factor receptor promoter, which is a determinant for expression. We demonstrated that C/EBPβ and C/EBPδ bind the same response element as a heterodimer. We focused on the enhanced expression of C/EBPδ, which has been reported to be a tumor suppressor gene silenced by promoter hypermethylation in U937 cells. After U937 conditioning with EPA and bisulfite sequencing of the -370/-20 CpG island on the C/EBPδ promoter region, we found a site-specific CpG demethylation that was a determinant for the binding activity of Sp1, an essential factor for C/EBPδ gene basal expression. Our results provide evidence for a new role of PUFAs in the regulation of gene expression. Moreover, we demonstrated for the first time that re-expression of the tumor suppressor C/EBPδ is controlled by the methylation state of a site-specific CpG dinucleotide.

CCAAT/Enhancer Binding Protein-delta (C/EBP-delta) regulates cell growth, migration and differentiation

BACKGROUND

CCAAT/enhancer binding protein-delta (C/EBP-delta) is a member of the highly conserved C/EBP family of basic region leucine zipper transcription factors. C/EBP family members regulate cell growth and differentiation and "loss of function" alterations in C/EBPs have been reported in a variety of human cancers. C/EBP-delta gene expression is upregulated by G0 growth arrest, IL-6 family cytokines and endotoxin treatments. C/EBP-delta exhibits properties of a tumor suppressor gene, including reduced expression and promoter methylation-induced silencing in transformed cell lines and primary tumors. In addition, C/EBP-delta gene expression is repressed by c-Myc, an oncogene that is over-expressed in a wide range of human cancers. "ChIP-chip" studies demonstrated that C/EBP-delta functions as a transcriptional activator of target genes that function in intracellular signal transduction, transcription, DNA binding/repair, cell cycle control, cell adhesion, and apoptosis. Despite progress in determining the biochemical functions of C/EBP-delta, the specific cellular defects that are induced by C/EBP-delta "loss of function" alterations are poorly understood. This study investigated the impact of C/EBP-delta "loss of function" alterations on growth arrest, migration/invasion and differentiation in nontransformed mouse mammary epithelial cells (MECs) and primary mouse embryo fibroblasts (MEFs).

RESULTS

C/EBP-delta siRNA transfected MECs exhibited ~90% reduction in C/EBP-delta mRNA and protein levels. C/EBP-delta siRNA treatment resulted in defective growth arrest as demonstrated by persistently elevated BrdU labeling, 3H-thymidine incorporation and cyclin D1 levels in response to growth arrest treatments. C/EBP-delta siRNA treatment also resulted in increased migration/invasion and defective differentiation. C/EBP-delta knockout MEFs exhibited defective growth arrest and increased proliferation/migration. Re-introduction of C/EBP-delta expression restored the growth arrest response of C/EBP-delta knockout MEFs. Finally, deletion of the C/EBP-delta DNA binding domain or the C/EBP-delta bZIP domain resulted in the loss of C/EBP-delta growth inhibition in clonogenic assays.

CONCLUSIONS

This study demonstrates that C/EBP-delta functions in the regulation of critical cell fate determining programs such as growth arrest, migration, and differentiation. These results support the tumor suppressor function of C/EBP-delta and identify potential mechanisms in which "loss of function" alterations in C/EBP-delta could promote cell transformation and tumorigenesis.

Myc interacts with Max and Miz1 to repress C/EBPdelta promoter activity and gene expression

BACKGROUND

"Loss of function" alterations in CCAAT/Enhancer Binding Proteindelta (C/EBPdelta) have been reported in a number of human cancers including breast, prostate and cervical cancer, hepatocellular carcinoma and acute myeloid leukemia. C/EBPdelta gene transcription is induced during cellular quiescence and repressed during active cell cycle progression. C/EBPdelta exhibits tumor suppressor gene properties including reduced expression in cancer cell lines and tumors and promoter methylation silencing. We previously reported that C/EBPdelta expression is inversely correlated with c-Myc (Myc) expression. Aberrant Myc expression is common in cancer and transcriptional repression is a major mechanism of Myc oncogenesis. A number of tumor suppressor genes are targets of Myc transcriptional repression including C/EBPalpha, p15INK4, p21CIP1, p27KIP1 and p57KIP2. This study investigated the mechanisms underlying Myc repression of C/EBPdelta expression.

RESULTS

Myc represses C/EBPdelta promoter activity in nontransformed mammary epithelial cells in a dose-dependent manner that requires Myc Box II, Basic Region and HLH/LZ domains. Chromatin Immunoprecipitation (ChIP) assays demonstrate that Myc, Miz1 and Max are associated with the C/EBPdelta promoter in proliferating cells, when C/EBPdelta expression is repressed. EMSAs demonstrate that Miz1 binds to a 30 bp region (-100 to -70) of the C/EBPdelta promoter which contains a putative transcription initiator (Inr) element. Miz1 functions exclusively as a repressor of C/EBPdelta promoter activity. Miz1 siRNA expression or expression of a Miz1 binding deficient Myc (MycV394D) construct reduces Myc repression of C/EBPdelta promoter activity. Max siRNA expression, or expression of a Myc construct lacking the HLH/LZ (Max interacting) region, also reduces Myc repression of C/EBPdelta promoter activity. Miz1 and Max siRNA treatments attenuate Myc repression of endogenous C/EBPdelta expression. Myc Box II interacting proteins RuvBl1 (Pontin, TIP49) and RuvBl2 (Reptin, TIP48) enhances Myc repression of C/EBPdelta promoter activity.

CONCLUSION

Myc represses C/EBPdelta expression by associating with the C/EBPdelta proximal promoter as a transient component of a repressive complex that includes Max and Miz1. RuvBl1 and RuvBl2 enhance Myc repression of C/EBPdelta promoter activity. These results identify protein interactions that mediate Myc repression of C/EBPdelta, and possibly other tumor suppressor genes, and suggest new therapeutic targets to block Myc transcriptional repression and oncogenic function.

The cell growth inhibitory transcription factor C/EBPdelta is expressed in human meningiomas in association with low histological grade and proliferation index

CCAAT/enhancer binding protein (C/EBP) delta is a transcription factor which has been demonstrated to mediate the growth arrest of mammary and prostate cancer cell lines. It is induced by several stimuli including inflammatory cytokines. In this study, C/EBPdelta immunohistochemical expression was assessed in 49 meningiomas of different histotype and grade and correlated with a variety of clinico-pathological data and with the overall and recurrence-free survival of the patients. Positive staining was observed in the nuclei of neoplastic cells in 22 out of the 49 cases analyzed. C/EBPdelta expression was significantly associated with a low histological grade and proliferation index, reflected by low Ki-67 labeling index (LI) and mitotic activity, and with the presence of intra-tumoral inflammatory infiltrate and the absence of necrosis. In addition, the absence of C/EBPdelta was significantly correlated with a shorter disease-free interval. Our findings suggest that C/EBPdelta expression may prevent the development of recurrences by inhibition of neoplastic growth in meningiomas. If further studies confirm its induction by inflammatory mediators, this might be exploited in novel therapies to prevent recurrences in meningiomas.

Identification and characterization of CCAAT/Enhancer Binding proteindelta (C/EBPdelta) target genes in G0 growth arrested mammary epithelial cells

BACKGROUND

CCAAT/Enhancer Binding Proteindelta (C/EBPdelta) is a member of the highly conserved C/EBP family of leucine zipper (bZIP) proteins. C/EBPdelta is highly expressed in G0 growth arrested mammary epithelial cells (MECs) and "loss of function" alterations in C/EBPdelta have been associated with impaired contact inhibition, increased genomic instability and increased cell migration. Reduced C/EBPdelta expression has also been reported in breast cancer and acute myeloid leukemia (AML). C/EBPdelta functions as a transcriptional activator, however, only a limited number of C/EBPdelta target genes have been reported. As a result, the role of C/EBPdelta in growth control and the potential mechanisms by which "loss of function" alterations in C/EBPdelta contribute to tumorigenesis are poorly understood. The goals of the present study were to identify C/EBPdelta target genes using Chromatin Immunoprecipitation coupled with a CpG Island (HCG12K) Array gene chip ("ChIP-chip") assay and to assess the expression and potential functional roles of C/EBPdelta target genes in growth control.

RESULTS

ChIP-chip assays identified approximately 100 C/EBPdelta target gene loci which were classified by gene ontology (GO) into cell adhesion, cell cycle regulation, apoptosis, signal transduction, intermediary metabolism, gene transcription, DNA repair and solute transport categories. Conventional ChIP assays validated the ChIP-chip results and demonstrated that 14/14 C/EBPdelta target loci were bound by C/EBPdelta in G0 growth arrested MCF-12A MECs. Gene-specific RT-PCR analysis also demonstrated C/EBPdelta-inducible expression of 14/14 C/EBPdelta target genes in G0 growth arrested MCF-12A MECs. Finally, expression of endogenous C/EBPdelta and selected C/EBPdelta target genes was also demonstrated in contact-inhibited G0 growth arrested nontransformed human MCF-10A MECs and in mouse HC11 MECs. The results demonstrate consistent activation and downstream function of C/EBPdelta in growth arrested human and murine MECs.

CONCLUSION

C/EBPdelta target genes were identified by a global gene array approach and classified into functional categories that are consistent with biological contexts in which C/EBPdelta is induced, such as contact-mediated G0 growth arrest, apoptosis, metabolism and inflammation. The identification and validation of C/EBPdelta target genes provides new insights into the mechanistic role of C/EBPdelta in mammary epithelial cell biology and sheds new light on the potential impact of "loss of function" alterations in C/EBPdelta in tumorigenesis.

PIASy represses CCAAT/enhancer-binding protein delta (C/EBPdelta) transcriptional activity by sequestering C/EBPdelta to the nuclear periphery

CCAAT/enhancer binding proteindelta (C/EBPdelta) plays a key role in mammary epithelial cell G(0) growth arrest, and "loss of function" alterations in C/EBPdelta have been reported in breast cancer and acute myeloid leukemia. C/EBPdelta is regulated at the transcriptional, post-transcriptional, and post-translational levels, suggesting tight control of C/EBPdelta content and function. Protein inhibitors of activated STATs (PIASs) regulate a growing number of transcription factors, including C/EBPs. HC11 nontransformed mammary epithelial cells express PIAS3, PIASxbeta, and PIASy, and all three PIAS family members repress C/EBPdelta transcriptional activity. PIASy is the most potent, however, repressing C/EBPdelta transcriptional activity by >80%. PIASy repression of C/EBPdelta transcriptional activity is dependent upon interaction between the highly conserved PIASy N-terminal nuclear matrix binding domain (SAPD) and the C/EBPdelta transactivation domain (TAD). PIASy repression of C/EBPdelta transcriptional activity is independent of histone deacetylase activity, PIASy E3 SUMO ligase activity, and C/EBPdelta sumoylation status. PIASy expression is associated with C/EBPdelta translocation from nuclear foci, where C/EBPdelta co-localizes with p300, to the nuclear periphery. PIASy-mediated translocation of C/EBPdelta is dependent upon the PIASy SAPD and C/EBPdelta TAD. PIASy reduces the expression of C/EBPdelta adhesion-related target genes and enhances repopulation of open areas within a cell monolayer in the in vitro "scratch" assay. These results demonstrate that PIASy represses C/EBPdelta by a mechanism that requires interaction between the PIASy SAPD and C/EBPdelta TAD and does not require PIASy SUMO ligase activity or C/EBPdelta sumoylation. PIASy alters C/EBPdelta nuclear localization, reduces C/EBPdelta transcriptional activity, and enhances cell proliferation/migration.

Differential expression in lung and bronchial lymph node of pigs with high and low responses to infection with porcine reproductive and respiratory syndrome virus

One hundred Hampshire x Duroc cross-bred pigs and 100 Nebraska Index line pigs were infected with porcine reproductive and respiratory syndrome virus (PRRSV) and evaluated for resistance and susceptibility. Controls (100/line) were uninfected littermates to infected pigs. Viremia (V), BW change (WTDelta), and rectal temperature at 0, 4, 7, and 14 d postinfection were recorded. Lung, bronchial lymph node (BLN), and blood tissue were collected at necropsy (14 d postinfection). Infected pigs were classified as low or high responders to PRRSV based on the first principal component from principal component analyses of all variables. Low responders to PRRSV (low PRRSV burden) and their uninfected littermates were assigned to the low (L) class. High responders to PRRSV (high PRRSV burden) and their uninfected littermates were assigned to the high (H) class. Infected pigs in the L class had large WTDelta, low V, and few lung lesions; H-class pigs had small WTDelta, high V, and many lung lesions. Ribonucleic acid was extracted from lung and BLN tissue of the 7 highest and 7 lowest responders per line and from each of their control littermates. A control reference design was used, and cDNA from each reference sample tissue was prepared from pooled RNA extracted from 2 control pigs from each line whose infected littermates had a principal component value of 0. Design variables in data analyses were line (Index vs. Hampshire x Duroc), class (H vs. L), treatment (infected vs. uninfected controls), and slide/pig as error. Oligo differential expression was based on P < 0.01 occurring in both lung and BLN. Line and treatment effects were significant for 38 and 541 oligos, respectively, in both lung and BLN. Line x class interaction existed for expression of thymosin beta-4, DEAD box RNA helicase 3, acetyl-cholinesterase, and Homo sapiens X (inactive)-specific transcript in both tissues. Treatment x class existed for expression of CCAAT/enhancer-binding delta protein, nuclear factor of kappa light polypeptide gene enhancer in B cells inhibitor alpha, thioredoxin-interacting protein, major facilitator superfamily domain containing 1, and unknown sequences SS00012040 and SS00012343. Line x treatment and line x treatment x class interactions were not significant. Possible important genetic associations for fine-mapping candidate genes related to response to PRRSV and determining causative alleles were revealed.

Regulation of C/EBPdelta-dependent transactivation by histone deacetylases in intestinal epithelial cells

The C/EBPdelta transcription factor is involved in the positive regulation of the intestinal epithelial cell acute phase response. C/EBPdelta regulation by histone deacetylases (HDACs) during the course of inflammation remains to be determined. Our aim was to examine the effect of HDACs on C/EBPdelta-dependent regulation of haptoglobin, an acute phase protein induced in intestinal epithelial cells in response to pro-inflammatory cytokines. HDAC1, HDAC3, and HDAC4 were expressed in intestinal epithelial cells, as determined by Western blot. GST pull-down assays showed specific HDAC1 interactions with the transcriptional activation and the b-ZIP C/EBPdelta domains, while the co-repressor mSin3A interacts with the C-terminal domain. Immunoprecipitation assays confirmed the interaction between HDAC1 and the N-terminal C/EBPdelta amino acid 36-164 domain. HDAC1 overexpression decreased C/EBPdelta transcriptional activity of the haptoglobin promoter, as assessed by transient transfection and luciferase assays. Chromatin immunoprecipitation analysis showed a displacement of HDAC1 from the haptoglobin promoter in response to inflammatory stimuli and an increased acetylation of histone H3 and H4. HDAC1 silencing by shRNA expression increased both basal and IL-1beta-induced haptoglobin mRNA levels in epithelial intestinal cells. Our results suggest that interactions between C/EBPs and HDAC1 negatively regulate C/EBPdelta-dependent haptoglobin expression in intestinal epithelial cells.

The mouse C/EBPdelta gene promoter is regulated by STAT3 and Sp1 transcriptional activators, chromatin remodeling and c-Myc repression

CCAAT/enhancer binding proteindelta (C/EBPdelta) gene transcription is highly induced in G(0) growth arrested mammary epithelial cells and "loss of function" alterations in C/EBPdelta have been reported in human breast cancer. To gain a better understanding of the positive and negative factors that control C/EBPdelta gene expression we investigated the role of transcriptional activators, coactivators, repressors, histone modifications, chromatin remodeling and basal transcriptional machinery components in growing and growth arrested HC11 mouse mammary epithelial cells. Growth arrest treatments result in increased STAT3 activation (pSTAT3) and increased C/EBPdelta expression. Co-immunoprecipitation and chromatin immunoprecipitation (ChIP) assays demonstrated that pSTAT3 and Sp1 interact and bind to the transcriptionally active C/EBPdelta promoter. ChIP assays performed under exponentially growing (C/EBPdelta non-expressing) conditions demonstrated that the C/EBPdelta promoter is preloaded with transcriptional activators (Sp1 and CREB) and transcriptional machinery components (TBP and RNA Pol II). In contrast, under G(0) growth arrest (C/EBPdelta expressing) conditions ChIP analysis detected pSTAT3, Sp1, NCoA/SRC1, CBP/p300, pCREB, TBP, and serine 2 phosphorylated Pol II (pPol II) in association with the C/EBPdelta proximal promoter. C/EBPdelta promoter-associated histone post-translational modification analysis revealed histone H3 and H4 acetylation and methylation patterns consistent with a constitutively "open" chromatin conformation. Chromatin remodeling experiments demonstrated that BRG1, the ATPase component of the SWI/SNF chromatin remodeling complex, is required for C/EBPdelta transcription. Finally, C/EBPdelta expression is repressed in proliferating mammary epithelial cells by c-Myc via a mechanism that involves the binding of c-Myc:Max dimers to C/EBPdelta promoter-bound Miz-1. These results provide a molecular model of C/EBPdelta transcriptional regulation under G(0) growth arrest conditions.

Ultraviolet radiation (UVR) activates p38 MAP kinase and induces post-transcriptional stabilization of the C/EBPδ mRNA in G0 growth arrested mammary epithelial cells

The G(0) growth arrest (quiescent) state is highly conserved in evolution to promote survival under adverse environmental conditions. To maintain viability, G(0) growth arrested cells limit gene expression to essential growth control and pro-survival genes. CCAAT enhancer binding protein delta (C/EBPdelta), a member of the C/EBP family of nuclear proteins, is highly expressed in G(0) growth arrested mammary epithelial cells (MECs). Although C/EBPdelta gene transcription is elevated during G(0) growth arrest, C/EBPdelta mRNA and protein are relatively short lived, suggesting tight control of the cellular C/EBPdelta content in unstressed, quiescent cells. Treatment of G(0) growth arrested MECs with ultraviolet radiation (UVR) dramatically increases the C/EBPdelta mRNA half-life (approximately 4-fold) and protein content (approximately 3-fold). The mRNA stabilizing effects of UVR treatment are mediated by the C/EBPdelta mRNA 3'untranslated region, which contains an AU rich element. UVR increased p38 MAP kinase (MAPK) activation and SB203580, a p38 MAPK inhibitor, blocked UVR-induced C/EBPdelta mRNA stabilization. UVR increased the nuclear to cytoplasmic translocation of HuR, an ARE-binding protein that functions in mRNA stabilization. Finally, HuR siRNA treatment blocked UVR-induced stabilization of the C/EBPdelta and C/EBPbeta mRNAs but had no effect on C/EBPzeta (CHOP) mRNA stability. In summary, G(0) growth arrested MECs respond to UVR treatment by activating p38 MAPK, increasing HuR translocation and HuR/C/EBPdelta mRNA binding and stabilizing the C/EBPdelta mRNA. These results identify post-transcriptional stabilization of the C/EBPdelta mRNA as a mechanism to increase C/EBPdelta levels in the stress response of quiescent cells to UVR.

Proteasome-mediated CCAAT/enhancer-binding protein delta (C/EBPdelta) degradation is ubiquitin-independent

C/EBPdelta (CCAAT/enhancer-binding protein delta) is a member of the C/EBP family of nuclear proteins that function in the control of cell growth, survival, differentiation and apoptosis. We previously demonstrated that C/EBPdelta gene transcription is highly induced in G(0) growth-arrested mammary epithelial cells but the C/EBPdelta protein exhibits a t(1/2) of only approximately 120 min. The goal of the present study was to investigate the role of C/EBPdelta modification by ubiquitin and C/EBPdelta proteasome-mediated degradation. Structural and mutational analyses demonstrate that an intact leucine zipper is required for C/EBPdelta ubiquitination; however, the leucine zipper does not provide lysine residues for ubiquitin conjugation. C/EBPdelta ubiquitination is not required for proteasome-mediated C/EBPdelta degradation and the presence of ubiquitin does not increase C/EBPdelta degradation by the proteasome. Instead, the leucine zipper stabilizes the C/EBPdelta protein by forming homodimers that are poor substrates for proteasome degradation. To investigate the cellular conditions associated with C/EBPdelta ubiquitination we treated G(0) growth-arrested mammary epithelial cells with DNA-damage- and oxidative-stress-inducing agents and found that C/EBPdelta ubiquitination is induced in response to H2O2. However, C/EBPdelta protein stability is not influenced by H2O2 treatment. In conclusion, our results demonstrate that proteasome-mediated protein degradation of C/EBPdelta is ubiquitin-independent.

Treatment of cultured myotubes with the proteasome inhibitor β-lactone increases the expression of the transcription factor C/EBPβ

The role of the proteasome in the regulation of cellular levels of the transcription factor CCAAT/enhancer-binding protein β (C/EBPβ) is poorly understood. We tested the hypothesis that C/EBPβ levels in cultured myotubes are regulated, at least in part, by proteasome activity. Treatment of cultured L6 myotubes, a rat skeletal muscle cell line, with the specific proteasome inhibitor β-lactone resulted in increased nuclear levels of C/EBPβ as determined by Western blotting and immunofluorescent detection. This effect of β-lactone reflected inhibited degradation of C/EBPβ. Surprisingly, the increased C/EBPβ levels in β-lactone-treated myotubes did not result in increased DNA-binding activity. In additional experiments, treatment of the myotubes with β-lactone resulted in increased nuclear levels of growth arrest DNA damage/C/EBP homologous protein (Gadd153/CHOP), a dominant-negative member of the C/EBP family that can form heterodimers with other members of the C/EBP family and block DNA binding. Coimmunoprecipitation and immunofluorescent detection provided evidence that C/EBPβ and Gadd153/CHOP interacted and colocalized in the nuclei of the β-lactone-treated myotubes. When Gadd153/CHOP expression was downregulated by transfection of myotubes with siRNA targeting Gadd153/CHOP, C/EBPβ DNA-binding activity was restored in β-lactone-treated myotubes. The results suggest that C/EBPβ is degraded by a proteasome-dependent mechanism in skeletal muscle cells and that Gadd153/CHOP can interact with C/EBPβ and block its DNA-binding activity. The observations are important because they increase the understanding of the complex regulation of the expression and activity of C/EBPβ in skeletal muscle.

Degradation of C/EBPβ in cultured myotubes is calpain-dependent

Members of the C/EBP transcription factor family regulate cell differentiation and multiple other cellular functions. The cellular levels of C/EBPalpha, gamma, delta, epsilon, and Gadd153/CHOP are regulated in part by proteasome-dependent degradation. In contrast, mechanisms regulating the degradation of C/EBPbeta are poorly understood. We tested the hypothesis that the degradation of C/EBPbeta is calpain-dependent. Studies were performed in cultured L6 myotubes (a rat skeletal muscle cell line) because we have found previously that C/EBPbeta may be involved in the regulation of muscle proteolysis. Treatment of cultured L6 myotubes with the calpain inhibitors calpeptin and Calpain Inhibitor I and II resulted in increased C/EBPbeta concentrations but did not influence cellular levels of the other C/EBP transcription factor family members. Transfection of myoblasts with a plasmid expressing the endogenous calpain inhibitor calpastatin resulted in increased cellular levels of C/EBPbeta whereas the opposite result was observed in myoblasts overexpressing micro- or m-calpain. Co-immunoprecipitation provided evidence for protein-protein interaction between C/EBPbeta and micro- and m-calpain suggesting that C/EBPbeta may be a calpain substrate. This notion was supported by experiments in which immunoprecipitated C/EBPbeta was incubated with purified micro-calpain in a cell-free system. The increase in C/EBPbeta levels caused by inhibition of calpain activity was accompanied by increased C/EBPbeta DNA-binding and gene activation. The present results suggest that C/EBPbeta is degraded by a calpain-dependent mechanism in skeletal muscle cells and that the role of calpains is specific for C/EBPbeta among different members of the C/EBP transcription factor family.

Promoter methylation reduces C/EBPdelta (CEBPD) gene expression in the SUM-52PE human breast cancer cell line and in primary breast tumors

CCAAT/Enhancer Binding Proteins (C/EBPs) are a highly conserved family of leucine zipper proteins that regulate cell growth and differentiation. C/EBPdelta functions in the initiation and maintenance of mammary epithelial cell G(0) growth arrest and 'loss of function' alterations in C/EBPdelta gene expression have been reported in human breast cancer and in rodent carcinogen-induced mammary tumors. The molecular mechanism underlying reduced C/EBPdelta gene expression in mammary tumorigenesis, however, is unknown. In this report we demonstrate that C/EBPdelta gene expression is undetectable in the SUM-52PE human breast cancer cell line and that silencing of SUM-52PE C/EBPdelta gene expression is due to epigenetic promoter hypermethylation (26/27 CpGs methylated). The hypermethylated SUM-52PE C/EBPdelta gene promoter is associated with reduced levels of acetylated Histone H4, consistent with a closed, transcriptionally inactive chromatin conformation. Treatment with 5'-aza-cytidine and trichostatin A (TSA) re-activates cytokine-induced SUM-52PE C/EBPdelta gene expression. C/EBPdelta gene expression is reduced to virtually undetectable levels in 32% (18/57) of primary human breast tumors. Site-specific CpG methylation was observed in 33% (6/18) of the low C/EBPdelta expressing primary breast tumors. CpG methylation adjacent to the C/EBPdelta proximal promoter Sp1 site was associated with reduced C/EBPdelta expression in a primary breast cancer sample. Electromobility shift assays (EMSA) demonstrated a significant reduction in binding to oligos containing the CpG methylation 5' to the Sp1 binding site. These results demonstrate a direct link between C/EBPdelta gene promoter hyper- and site specific-methylation and reduced C/EBPdelta gene expression in breast cancer cell lines and primary breast tumors.

Gene expression characteristics of CD28null memory phenotype CD8+ T cells and its implication in T-cell aging

Accumulation of CD28(null)CD8(+) T cells is considered as one of the hallmarks of aging in the human immune system. However, the precise changes of CD28(null)CD8(+) T cells, compared to those of the precursor CD28(+)CD8(+) memory T cells, have not been determined. In this study, we present an analysis of the global gene expression profiles of CD28(+) and CD28(null) memory phenotype CD8(+) T cells. These two CD8(+) T subsets exhibited an overall similar gene expression profile with only a few dozen genes that were differentially expressed. A wide range of functions, including co-stimulation, effector activity, signaling, and transcription, were possessed by these differentially expressed genes, reflecting significant functional changes of CD28(null) memory phenotype CD8(+) T cells from their CD28(+) counterparts. In addition, CD28(null) memory CD8(+) T cells expressed several natural killer cell receptors and high levels of granzymes, perforin, and FasL, indicating an increasing capacity for cytotoxicity during memory CD8(+) T-cell aging. Interestingly, in vitro culture of these two subsets with interleukin-15 showed that similar gene expression changes occurred in both subsets. Our analysis provides the gene expression portraits of CD28(null) memory phenotype CD8(+) T cells and alteration from their CD28(+) counterparts and suggests potential mechanisms of T-cell aging.

Neutrophil elastase stimulates MUC1 gene expression through increased Sp1 binding to the MUC1 promoter

We previously reported MUC1 was a cell surface receptor for Pseudomonas aeruginosa, and binding of bacteria to cells was significantly reduced by pretreatment with neutrophil elastase (NE) (Lillehoj EP, Hyun SW, Kim BT, Zhang XG, Lee DI, Rowland S, and Kim KC. Am J Physiol Lung Cell Mol Physiol 280: L181-L187, 2001). The current study was conducted to ascertain NE effects on MUC1 gene transcription, and MUC1 protein synthesis and degradation. A549 human lung carcinoma cells treated with NE exhibited significantly higher MUC1 protein levels in detergent lysates compared with cells treated with vehicle alone. Also, MUC1 protein shed into cell-conditioned medium was rapidly and completely degraded by NE. Actinomycin D blocked NE-stimulated increase in MUC1 protein expression, suggesting a mechanism of increased gene transcription that was confirmed by measurement of quantitatively greater MUC1 mRNA levels in NE-treated cells compared with controls. However, NE did not alter MUC1 mRNA stability, implying increased de novo transcription induced by the protease. NE increased promoter activity in A549 cells transfected with MUC1 gene promoter-luciferase reporter plasmid. This effect of NE was completely blocked by mithramycin A, an inhibitor of Sp1, as well as mutation of one of the putative Sp1 binding sites in MUC1 promoter located at -99/-90 relative to transcription initiation site. EMSA revealed NE enhanced binding of Sp1 to this 10-bp segment in a time-dependent manner. These results indicate the increase in MUC1 gene transcription by NE is mediated through increase in Sp1 binding to -99/-90 segment of MUC1 promoter.

A role of STAT3 in Rho GTPase-regulated cell migration and proliferation

Rho family GTPases and STAT3 act as mediators of cytokine and growth factor signaling in a variety of cellular functions involved in inflammation, tumorigenesis, and development. In the course of searching for their functional connections, we found by using STAT3 knock-out mouse embryonic fibroblasts that RhoA, Rac1, and Cdc42 could cause nonspecific activation of STAT3 promoter-driven luciferase reporter in the absence of STAT3, raising concerns to a body of literature where STAT3 was associated with Rho GTPases based on the reporter system. We also found that although active RhoA, Rac1, and Cdc42 could all mediate Ser-727 and Tyr-705 phosphorylation and nuclear translocation of STAT3, the Rho GTPases were able to induce STAT3 activation independently of the interleukin-6 autocrine pathway, and active RhoA, Rac1, or Cdc42 could not form a stable complex with STAT3 as previously suggested, indicating an unappreciated mechanism of STAT3 activation by the Rho GTPases. The RhoA-induced STAT3 activation partly depended on Rho-associated kinase (ROK) and involved multiple effector signals as revealed by the examination of effector domain mutants of RhoA. Genetic deletion of STAT3 led to a loss of response to RhoA in myosin light chain phosphorylation and actin stress fiber induction but sensitized the cells to RhoA or ROK-stimulated cell migration. STAT3 was required for the RhoA-induced NF-kappaB and cyclin D1 transcription and was involved in NF-kappaB nuclear translocation. Furthermore, loss of STAT3 expression inhibited RhoA-promoted cell proliferation and blocked RhoA or ROK induced anchorage-independent growth. These phenotypic changes in STAT3-/- cells could be rescued by reconstituting STAT3 gene. Our studies carried out in STAT3 null cells demonstrate unambiguously that STAT3 represents an essential effector pathway of Rho GTPases in regulating multiple cellular functions including actin cytoskeleton reorganization, cell migration, gene activation, and proliferation.