1alpha,25-dihydroxycholecalciferol activates binding of CREB to a CRE site in the CD14 promoter and drives promoter activity in a phosphatidylinositol-3 kinase-dependent manner

A hierarchical regulatory network analysis of the vitamin D induced transcriptome reveals novel regulators and complete VDR dependency in monocytes

The transcription factor vitamin D receptor (VDR) is the high affinity nuclear target of the biologically active form of vitamin D₃ (1,25(OH)₂D₃). In order to identify pure genomic transcriptional effects of 1,25(OH)₂D₃, we used VDR cistrome, transcriptome and open chromatin data, obtained from the human monocytic cell line THP-1, for a novel hierarchical analysis applying three bioinformatics approaches. We predicted 75.6% of all early 1,25(OH)₂D₃-responding (2.5 or 4 h) and 57.4% of the late differentially expressed genes (24 h) to be primary VDR target genes. VDR knockout led to a complete loss of 1,25(OH)₂D₃–induced genome-wide gene regulation. Thus, there was no indication of any VDR-independent non-genomic actions of 1,25(OH)₂D₃ modulating its transcriptional response. Among the predicted primary VDR target genes, 47 were coding for transcription factors and thus may mediate secondary 1,25(OH)₂D₃ responses. CEBPA and ETS1 ChIP-seq data and RNA-seq following CEBPA knockdown were used to validate the predicted regulation of secondary vitamin D target genes by both transcription factors. In conclusion, a directional network containing 47 partly novel primary VDR target transcription factors describes secondary responses in a highly complex vitamin D signaling cascade. The central transcription factor VDR is indispensable for all transcriptome-wide effects of the nuclear hormone.

What turns CREB on? And off? And why does it matter?

Altered expression and function of the transcription factor cyclic AMP response-binding protein (CREB) has been identified to play an important role in cancer and is associated with the overall survival and therapy response of tumor patients. This review focuses on the expression and activation of CREB under physiologic conditions and in tumors of distinct origin as well as the underlying mechanisms of CREB regulation by diverse stimuli and inhibitors. In addition, the clinical relevance of CREB is summarized, including its use as a prognostic and/or predictive marker as well as a therapeutic target.

Immunomodulatory effects of Lippia sidoides extract: induction of IL-10 through cAMP and p38 MAPK-dependent mechanisms

Lippia sidoides is an aromatic shrub that grows wild in the northeastern region of Brazil. In local traditional medicine, the aerial portions of this species are used as anti-infectives, antiseptics, spasmolytics, sedatives, hypotensives, and anti-inflammatory agents. In this research, we evaluate the potential immunological properties of Lippia extract through in vitro analysis of its ability to modulate intracellular cyclic adenosine monophosphate (cAMP) levels and interleukin-10 (IL-10) production. These results show that Lippia extract increases intracellular cAMP through the inhibition of phosphodiesterase activity. They also demonstrate that Lippia extract increases IL-10 production in THP-1 monocytes through both an increase in intracellular cAMP and the activation of p38 MAPK. These results suggest that the Lippia-mediated inhibition of phosphodiesterase activity and the subsequent increase in intracellular cAMP may explain some of the biological activities associated with L. sidoides. In addition, the anti-inflammatory activity of L. sidoides may also be due, in part, to its ability to induce IL-10 production through the inhibition of cyclic nucleotide-dependent phosphodiesterase activity and by its activation of the p38 MAPK pathway.

The hydrolase DDAH2 enhances pancreatic insulin secretion by transcriptional regulation of secretagogin through a Sirt1-dependent mechanism in mice

The role of dimethylarginine dimethylaminohydrolase 2 (DDAH2) in glucose metabolism is unknown. Here, we generated DDAH2 transgenic (Tg) mice. These mice had lower plasma glucose levels (60 min: 298±32 vs. 418±35 mg/dl; 120 min: 205±15 vs. 284±20 mg/dl) and higher insulin levels (15 min: 2.1±0.2 vs. 1.5±0.1 ng/ml; 30 min: 1.8±0.1 vs. 1.5±0.1 ng/ml) during intraperitoneal glucose tolerance tests when fed a high-fat diet (HFD) compared with HFD-fed wild-type (WT) mice. Glucose-stimulated insulin secretion (GSIS) was increased in Tg islets by 33%. Pancreatic asymmetrical dimethylarginine, nitric oxide, and oxidative stress levels were not correlated with improvements in insulin secretion in Tg mice. Secretagogin, an insulin vesicle docking protein, was up-regulated by 2.7-fold in Tg mice and in pancreatic MIN-6 cells overexpressing DDAH2. GSIS in MIN-6 cells was dependent on DDAH2-induced secretagogin expression. Pancreatic Sirt1, DDAH2, and secretagogin were down-regulated in HFD-fed WT mice by 70, 75, and 85%, respectively. Overexpression of Sirt1 overexpression by 3.9-fold increased DDAH2 and secretagogin expression in MIN-6 cells by 3.2- and 2.5-fold, respectively. DDAH2 overexpression improved GSIS in pancreas-specific Sirt1-deficient mice. In summary, the Sirt1/DDAH2/secretagogin pathway is a novel regulator of GSIS.

A vitamin D3 analog augmented interleukin-8 production by human monocytic cells in response to various microbe-related synthetic ligands, especially NOD2 agonistic muramyldipeptide

Active metabolite vitamin D(3), 1α,25-dihydroxyvitamin D(3), is a pleiotropic factor and exhibits various physiological functions, including immunomodulating activities. In this study, the possible regulation of innate immune responses of human monocytic cells by a vitamin D(3) analog was examined. Human monocytic THP-1 cells were pre-treated with OCT, vitamin D(3) analog, 1α,25-dihydroxy-22-oxavitamin D(3), followed by stimulation with various chemically synthesized Toll-like receptors (TLR) and NOD1 and NOD2 ligands. OCT-treated cells produced more IL-8 than non-treated cells upon stimulation with various chemically-synthesized ligands: TLR2-agonistic lipopeptide (FSL-1), TLR3-agonistic poly I:C, TLR4-agonistic lipid A (E. coli-type LA-15-PP), NOD1-agonistic FK565 and NOD2-agonistic muramyldipeptide (MDP). Among the ligands, MDP was the highest inducer of IL-8 production in OCT-treated THP-1 cells, and IL-8 production increased depending on the treatment time until 72h. OCT up-regulated the expression of NOD2 in THP-1 cells, and OCT-treated cells exhibited higher activation of p38, JNK and ERK in the MAPK pathway, IκBα in the NF-κB pathway, and TAK1 upstream in response to MDP than non-treated cells. Analysis using siRNA against NOD2 and inhibitors of specific signal molecules indicated that the existence of NOD2 and activation of the above signaling molecules are required for enhanced production of IL-8 in OCT-treated THP-1 cells. These findings suggested that NOD2, NF-κB and MAPK pathways are involved in the activity of OCT to augment the response of human monocytic cells to MDP.

1,25-Dihydroxyvitamin D3 promotes a sustained LPS-induced NF-κB-dependent expression of CD55 in human monocytic THP-1 cells

The vitamin D3 system imposes immunosuppressive effects on monocytic cells, in part, by inhibiting NF-κB-dependent expression of proinflammatory mediators. CD55, a cell surface complement regulatory protein that promotes protective and anti-inflammatory properties, is reportedly an NF-κB target gene transiently induced in monocytic cells by the bacterial endotoxin LPS. CD55 is elevated on white cells in women experiencing preterm labor (a pathophysiology commonly associated with bacterial infection) and failure to maintain CD55 was associated with subsequent preterm delivery. We examined the influence of vitamin D3 signaling on LPS-induced expression of CD55 in human monocytic THP-1 cells using quantitative PCR, immunoblot, immunohistochemistry, and NF-κB activation pathway inhibitors. Non-NF-κB targets CD14 and CD11b, which modulate bacterial surveillance and eradication, respectively, were also examined. LPS produced a rapid transient 1.6-fold increase in CD55 mRNA. 1,25-D3 alone did not affect CD55 mRNA expression within the first 48 h. However, in 1,25-D3 pretreated cells, LPS produced a >4-fold immediate and sustained increase in CD55 mRNA and protein expression, which was blocked by NF-κB inhibitors. Our results unexpectedly suggest that vitamin D3 signaling may promote an anti-inflammatory response through an NF-κB-dependent increase in CD55 expression. As expected, LPS or 1,25-D3 alone led to sustained increases in CD14 and CD11b expression. In 1,25-D3 pretreated cells, LPS differentially regulated protein expression - CD14 (21-fold increase) and CD11b (a transient 2-fold decrease) - principally at the posttranscriptional level. The coordinated temporal expression of CD55, CD14 and CD11b would contribute to an anti-inflammatory response by providing protection against complement-mediated cell lysis during pathogen recognition and eradication. Overall, the vitamin D3 system may play a role coordinating an anti-inflammatory response pattern of the host complement immune system. This may be particularly important when considering the high rates of preterm births in blacks, a population that exhibits reduced circulating vitamin D3 levels.

Myeloid cell IL-10 production in response to leishmania involves inactivation of glycogen synthase kinase-3β downstream of phosphatidylinositol-3 kinase

Leishmania disease expression has been linked to IL-10. In this study, we investigated the regulation of IL-10 production by macrophages infected with Leishmania donovani. Infection of either murine or human macrophages brought about selective phosphorylation of Akt-2 in a PI3K-dependent manner. These events were linked to phosphorylation and inactivation of glycogen synthase kinase-3β (GSK-3β) at serine 9, as the latter was abrogated by inhibition of either PI3K or Akt. One of the transcription factors that is negatively regulated by GSK-3β is CREB, which itself positively regulates IL-10 expression. Infection of macrophages with leishmania induced phosphorylation of CREB at serine 133, and this was associated with enhanced CREB DNA binding activity and induction of IL-10. Similar to phosphorylation of GSK-3β, both phosphorylation of CREB at serine 133 and CREB DNA binding activity were abrogated in cells treated with inhibitors of either PI3K or Akt prior to infection. Furthermore, disruption of this pathway either by inhibition of Akt or by overexpression of GSK-3β markedly attenuated IL-10 production in response to leishmania. Thus, GSK-3β negatively regulates myeloid cell IL-10 production in response to leishmania. Switching off GSK-3β promotes disease pathogenesis.

Podophyllotoxin induces CREB phosphorylation and CRE-driven gene expression via PKA but not MAPKs

CRE-driven luciferase reporter is commonly used in drug screening systems involving G protein-coupled receptors (GPCRs). In a screen campaign designed to search for melanocortin-4 receptor (MC4R) agonists, podophyllotoxin, a microtubules disruptor, was found to induce cAMP-responsive element (CRE)-driven reporter expression. MC4R was not involved because podophyllotoxin induced CREB activation and CRE-driven transcription in cells not expressing MC4R. Previous studies indicated that intracellular calcium, PKA, and MAPKs are involved in CREB phosphorylation and activation. Our studies revealed that podophyllotoxin did not affect intracellular calcium level and the phosphorylation state of p38. Podophyllotoxin induced JNK and ERK activation, but blockade of JNK and ERK activation with specific inhibitors had no effect on podophyllotoxin-induced CREB activation and CRE-regulated gene expression. Further experiments revealed that H89, a specific inhibitor of PKA, significantly inhibited podophyllotoxin-induced CREB activation. Podophyllotoxin itself did not alter intracellular cAMP level. Taken together, podophyllotoxin induces CREB activation and CRE-driven gene expression via PKA activation by a cAMP-independent mechanism.

Regulation by 1, 25-dihydroxy-vitamin D3 on altered TLRs expression and response to ligands of monocyte from autoimmune diabetes

BACKGROUND

Altered Toll-like receptors (TLRs) expression and response of monocyte may be associated with insulin sensitivity, obesity and diabetes.

METHODS

Peripheral blood monocytes were respectively collected from 23 healthy controls, 16 type 1 diabetes mellitus (T1DM), and 18 latent autoimmune diabetes in adults (LADA). CD14, TLR2 and TLR4 expression were analyzed by flow cytometer. Moreover, the effect of 1, 25-dihydroxy-vitamin D3 (1,25(OH)(2)D3) on monocyte response to lipoteichoic acid (LTA) and lipopolysaccharide (LPS) was evaluated in vitro by measuring phosphorylation concentration of NF-kappaB-p65 and associated cytokine production.

RESULTS

Monocytes showed significantly higher surface CD14 and TLR4 expressions from LADA and lower CD14 expression from T1DM than controls. TLRs ligands decreased monocyte CD14 expression in T1DM but increased in LADA. Monocyte hyperresponsiveness to ligands was modulated by 1,25(OH)(2)D3 to similar concentration, as compared to controls.

CONCLUSIONS

Monocytes from T1DM and LADA showed similar cellular reactivity towards ligands and 1,25(OH)2D3 was observed to restore this defect to a certain extent in vitro.

Temporal recruitment of transcription factors at the 3',5'-cyclic adenosine 5'-monophosphate-response element of the human GnRH-II promoter

GnRH-II is a potent GnRH subtype involved in modulating OVCAR-3 cell proliferation and the invasive properties of JEG-3 cells, and an atypical cAMP-response element (CRE) in the human GnRH-II promoter influences its activation. We demonstrated that the GnRH-II promoter is activated by 8-bromoadenosine-cAMP in several cell lines including alphaT3, TE671, JEG-3, and OVCAR-3 cells and that cAMP enhances GnRH-II mRNA levels in JEG-3 and OVCAR-3 cells. Moreover, 8-bromoadenosine-cAMP increases cAMP response element-binding protein (CREB) phosphorylation in JEG-3 and OVCAR-3 cells and augments CBP and CCAAT/enhancer-binding protein (C/EBP)-beta coimmunoprecipitation with phosphorylated CREB (p-CREB) in a temporally defined manner from nuclear extracts. When CREB, CBP, and C/EBPbeta levels were knocked down by small interfering RNA, reductions in any of these transcription factors reduced cAMP-enhanced GnRH-II promoter activity and GnRH-II mRNA levels in JEG-3 and OVCAR-3 cells. Importantly, chromatin immunoprecipitation assay showed that p-CREB bound the CRE within the endogenous GnRH-II promoter within 1 h and that p-CREB association with C/EBPbeta occurs within 2 h of cAMP stimulation, coincident with the first appearance of C/EBPbeta at the CRE. By contrast, maximum interactions between p-CREB and CBP do not occur until at least 4 h after cAMP stimulation, and this is reflected in the progressive loading of CBP at the CRE at 2-4 h, as demonstrated by chromatin immunoprecipitation. Taken together, these data suggest that p-CREB, C/EBPbeta, and CBP are recruited to the CRE of the GnRH-II promoter in a temporarily defined manner to enhance its transcription in JEG-3 and OVCAR-3 cells in response to cAMP.

Myeloid cell differentiation in response to calcitriol for expression CD11b and CD14 is regulated by myeloid zinc finger-1 protein downstream of phosphatidylinositol 3-kinase

Immature cells of the mononuclear phagocyte series differentiate in response to calcitriol. This is accompanied by increased expression of both CD11b and CD14 and has been shown to be phosphatidylinositol 3-kinase (PI3K) dependent. The events downstream of PI3K that regulate mononuclear phagocyte gene expression, however, remain to be fully understood. In the present study, we show that incubation of THP-1 cells with calcitriol brings about activation of the myeloid zinc finger-1 (MZF-1) transcription factor dependent upon PI3K. In addition, we show that the proximal promoter regions of both CD11b and CD14 contain functional MZF-1 binding sites that are calcitriol responsive. Site-directed mutagenesis of the putative MZF-1 elements abolished MZF-1 binding to the promoters of both CD11b and CD14. Not only did calcitriol treatment increase MZF-1 DNA binding activity to these sites, but it also up-regulated cellular levels of MZF-1. Silencing of MZF-1 resulted in a markedly blunted response to calcitriol for induction of both CD11b and CD14 mRNA transcript levels. Cell surface expression of CD11b and CD14 was also reduced, but to a lesser extent. Taken together, these results show that MZF-1 is involved downstream of PI3K in a calcitriol-induced signaling pathway leading to myeloid cell differentiation and activation of CD11b and CD14.

Identification of a calcitriol-regulated Sp-1 site in the promoter of human CD14 using a combined western blotting electrophoresis mobility shift assay (WEMSA)

Calcitriol (1α, 25-dihydroxyvitamin D₃) induces the expression of CD14 in mononuclear phagocytes. The mechanisms accounting for this have been unclear since the promoter of CD14 does not contain a canonical vitamin D response element (VDRE). Calcitriol has been shown to regulate the activity of the transcription factor Sp-1 and our analysis of the proximal promoter of CD14 indicated the presence of four Sp-1-like binding sequences. To identify which of these sites might be involved in the response to calcitriol, we used a system incorporating an electrophoretic mobility shift assay (EMSA) coupled to Western blot analysis (WEMSA). Using WEMSA, we found that only one of the Sp-1-like binding sequences, located at position -91 to -79 (relative to the transcription start site), bound the transcription factor Sp1. Sp-1 binding to this site was demonstrable using nuclear extracts from control cells. Notably, binding activity was attenuated in nuclear extracts prepared from cells that had been incubated with calcitriol, thus suggesting Sp-1 involvement in calcitriol induction of CD14 expression. Notably, these results show that like EMSA, WEMSA can be broadly applied to aid in the identification of transcription factors involved in regulating gene expression. WEMSA, however, offers a number of distinct advantages when compared with conventional EMSA. Antibodies used for WEMSA often provide less ambiguous signals than those used in EMSA, and these do not have to recognize epitopes under native conditions. In addition, WEMSA does not require the use of labeled oligos, thus eliminating a significant expense associated with EMSA.