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Histone deacetylases (HDACs) and microRNAs (miRs) have pro-survival roles, but the mechanism behind this is unclear. Repression of ceramide synthase 1 (CerS1), altering C(18) -ceramide generation, was linked to drug resistance and metastasis. Here we report that the CerS1 promoter was repressed by HDAC1-dependent inhibition of Sp1 recruitment to two specific GC-boxes spanning the -177 and -139 region. Moreover, an alternatively spliced variant CerS1 mRNA (CerS1-2) was detected mainly in cancer cells or primary tumour tissues compared to controls, which was targeted by miR-574-5p for degradation. A specific 3'UTR-targeting site, localized within the retained intron between exons 6 and 7, was identified, and its mutation, or miR-574-5p knockdown prevented the degradation of CerS1-2 mRNA. Interference with HDAC1 and miR-574-5p reconstituted CerS1-2 expression and C(18) -ceramide generation in multiple human cancer cell lines, which subsequently inhibited proliferation and anchorage-independent growth. Accordingly, knockdown of CerS1 partially protected cancer cells from MS-275/miR-574-5p siRNA-mediated growth inhibition. Thus, these data suggest that the HDAC1/miR-574-5p axis might provide a novel therapeutic target to reconstitute tumour suppressor CerS1/ceramide signalling.
IHF and HU are two heterodimeric nucleoid-associated proteins (NAP) that belong to the same protein family but interact differently with the DNA. IHF is a sequence-specific DNA-binding protein that bends the DNA by over 160°. HU is the most conserved NAP, which binds non-specifically to duplex DNA with a particular preference for targeting nicked and bent DNA. Despite their importance, the in vivo interactions of the two proteins to the DNA remain to be described at a high resolution and on a genome-wide scale. Further, the effects of these proteins on gene expression on a global scale remain contentious. Finally, the contrast between the functions of the homo- and heterodimeric forms of proteins deserves the attention of further study. Here we present a genome-scale study of HU- and IHF binding to the Escherichia coli K12 chromosome using ChIP-seq. We also perform microarray analysis of gene expression in single- and double-deletion mutants of each protein to identify their regulons. The sequence-specific binding profile of IHF encompasses ∼30% of all operons, though the expression of <10% of these is affected by its deletion suggesting combinatorial control or a molecular backup. The binding profile for HU is reflective of relatively non-specific binding to the chromosome, however, with a preference for A/T-rich DNA. The HU regulon comprises highly conserved genes including those that are essential and possibly supercoiling sensitive. Finally, by performing ChIP-seq experiments, where possible, of each subunit of IHF and HU in the absence of the other subunit, we define genome-wide maps of DNA binding of the proteins in their hetero- and homodimeric forms.
Using a model of medroxyprogesterone acetate (MPA)-induced mouse mammary tumors that transit through different stages of hormone dependence, we previously reported that the activation of the phosphatidylinositol 3-kinase (PI3K)/AKT (protein kinase B) pathway is critical for the growth of hormone-independent (HI) mammary carcinomas but not for the growth of hormone-dependent (HD) mammary carcinomas. The objective of this work was to explore whether the activation of the PI3K/AKT pathway is responsible for the changes in tumor phenotype and for the transition to autonomous growth. We found that the inhibition of the PI3K/AKT/mTOR (mammalian target of rapamycin) pathway suppresses HI tumor growth. In addition, we were able to induce mammary tumors in mice in the absence of MPA by inoculating HD tumor cells expressing a constitutively active form of AKT1, myristoylated AKT1 (myrAKT1). These tumors were highly differentiated and displayed a ductal phenotype with laminin-1 and cytokeratin 8 expression patterns typical of HI tumors. Furthermore, myrAKT1 increased the tumor growth of IBH-6 and IBH-7 human breast cancer cell lines. In the estrogen-dependent IBH-7 cell line, myrAKT1 induced estrogen-independent growth accompanied by the expression of the adhesion markers focal adhesion kinase and E-cadherin. Finally, we found that cells expressing myrAKT1 exhibited increased phosphorylation of the progesterone receptor at Ser190 and Ser294 and of the estrogen receptor α at Ser118 and Ser167, independently of exogenous MPA or estrogen supply. Our results indicate that the activation of the PI3K/AKT/mTOR pathway promotes tissue architecture remodeling and the activation of steroid receptors.
KCNE2 functions as an auxiliary subunit in voltage-gated K and HCN channels in the heart. Genetic variations in KCNE2 have been linked to long QT syndrome. The underlying mechanisms are not entirely clear. One of the issues is whether KCNE2 protein is expressed in ventricles. We use adenovirus-mediated genetic manipulations of adult cardiac myocytes to validate two antibodies (termed Ab1 and Ab2) for their ability to detect native KCNE2 in the heart. Ab1 faithfully detects native KCNE2 proteins in spontaneously hypertensive rat and guinea pig hearts. In both cases, KCNE2 protein is more abundant in ventricles than in atria. In both ventricular and atrial myocytes, KCNE2 protein is preferentially distributed on the cell surface. Ab1 can detect a prominent KCNE2 band in human ventricular muscle from nonfailing hearts. The band intensity is much fainter in atria and in failing ventricles. Ab2 specifically detects S98 phosphorylated KCNE2. Through exploring the functional significance of S98 phosphorylation, we uncover a novel mechanism by which KCNE2 modulates the human ether-a-go-go related gene (hERG) current amplitude: by accelerating hERG protein degradation and thus reducing the hERG protein level on the cell surface. S98 phosphorylation appears to be required for this modulation, so that S98 dephosphorylation leads to an increase in hERG/rapid delayed rectifier current amplitude. Our data confirm that KCNE2 protein is expressed in the ventricles of human and animal models. Furthermore, KCNE2 can modulate its partner channel function not only by altering channel conductance and/or gating kinetics, but also by affecting protein stability.
We have isolated and characterized a fatty acid binding protein from the liver of the orange-spotted grouper (Epinephelus coioides). Amino acid sequence similarity of the Ec-FABP (E. coioides-FABP) was highest to FABP10s isolated from the livers of catfish, chicken, salamander and iguana. The open-reading frame of the Ec-FABP codes for a protein of 14.0 kDa with a calculated isoelectric point of 8.5. We first expressed a FABP10 protein from orange-spotted grouper (E. coioides) in Pichia pastoris, and then characterized the antioxidative potential of our recombinant Ec-FABP by DCF fluorescence assay. RT-PCR assays showed that endogenous Ec-FABP mRNA is most strongly expressed in liver with the most abundance and intestine. Change in the groupers' blood cells respiratory burst activity was examined during and after exposure to the pH and temperature stress using flow cytometry. Further analysis of Ec-FABP gene expression in liver tissue by quantitative real-time PCR demonstrated that Ec-FABP transcript levels increased when the fish were exposed to both pH and temperature stress, but the time when its mRNA expression level peaked differed under these stresses. Western blot analyses confirmed that the Ec-FABP protein was strongly expressed in the liver after exposure to the pH and temperature stress. These results suggest that Ec-FABP expression is stimulated by pH and temperature stress and that it may play important roles in general adaptive and antioxidant responses.
CLN5 disease, late infantile variant phenotype neuronal ceroid lipofuscinosis, is a severe neurodegenerative disease caused by mutations in the CLN5 gene, which encodes a lysosomal protein of unknown function. Cln5-deficiency in mice leads to loss of thalamocortical neurons, and glial activation, but the underlying mechanisms are poorly understood. We have now studied the gene expression of Cln5 in the mouse brain and show that it increases gradually with age and differs between neurons and glia, with the highest expression in microglia. In Cln5(-/-) mice, we documented early and significant microglial activation that was already evident at 3 months of age. Loss of Cln5 also leads to defective myelination in vitro and in the developing mouse brain. This was accompanied by early alterations in serum lipid profiles, dysfunctional cellular metabolism and lipid transport in Cln5(-/-) mice. Taken together, these data provide significant new information about events associated with Cln5-deficiency, revealing altered myelination and disturbances in lipid metabolism, together with an early neuroimmune response.
Tau hyperphosphorylation has been implicated in the pathogenesis of a variety of forms of human epilepsy. Here we investigated whether treatment with sodium selenate, a drug which reduces pathological hyperphosphorylated tau by enhancement of PP2A activity, would inhibit seizures in rodent models. In vitro, sodium selenate reduced tau phosphorylation in human neuroblastoma cells and reversed the increase in tau phosphorylation induced by the PP2A inhibitor, okadaic acid. Sodium selenate treatment was then tested against three different rodent seizure models. Firstly the propensity of 6-Hz electrical corneal stimulation to induce seizures in adult mice was assessed following acute treatment with different doses of sodium selenate. Secondly, the number of seizures induced by pentylenetetrazole (PTZ) was quantified in rats following chronic sodium selenate treatment via drinking water. Finally, amygdala kindled rats were chronically treated with sodium selenate in drinking water and the length and the severity of the seizures evoked by stimulation of the amygdala recorded. The results demonstrated a dose-dependent protection of sodium selenate against 6-Hz stimulation induced seizures, and significant reduction in the total number of seizures following PTZ injection. Amygdala kindled rats chronically treated with sodium selenate had significantly shorter seizure duration compared controls, with more pronounced effects observed as the duration of treatment increased. The results of this study indicate that targeting hyperphosphorylated tau by treatment with sodium selenate has anti-seizure effects in a broad range of rodent models, and may represent a novel approach to treatment of patients with epilepsy.
It is well known that antidepressants both improve mood and increase the rate at which the dentate gyrus (DG) generates new neurons. In addition to the implications of neurogenesis for mood regulation, the production and survival of granule cells has also been implicated in learning and memory. Despite this evidence, the results of studies on the effect of antidepressants on memory have been mixed. A critical piece of data that may be missing from previous studies, however, is insight into (a) the location that newborn neurons migrate to following fluoxetine administration and (b) their ability to express normal patterns of activity-related genes. Here we demonstrate a finding that may resolve the discrepancy in the effects fluoxetine-induced neurogenesis on mood and memory: after 5 weeks delay, the net additional neurons generated in animals given the antidepressant fluoxetine during treatment are functionally normal, but preferentially accumulate (due to changes in migration and/or survival) in an area of the DG that is not recruited by spatial memory tasks.
All-trans-retinoic-acid (ATRA)-induced differentiation of human myeloid leukemia cells is characterized by persistent mitogen-activated protein kinase (MAPK) signaling. Fragmentary data suggests Src family kinase (SFK) inhibitors enhance differentiation, and thus have potential therapeutic value. The present study shows that SFK inhibitors PP2 and dasatinib enhance aspects of MAPK signaling and regulate a panel of differentiation markers, including CD11b and p47(phox). HL-60 and NB4 myeloid leukemia cells show accelerated ATRA-induced G1/0 arrest/differentiation with inhibitor co-treatment. We also identified components of a Lyn- and c-Raf-containing MAPK signaling complex augmented by the inhibitors. PP2 and dasatinib increased the ATRA-induced expression of Lyn and c-Raf (total and c-RafpS259) and their interaction. The Lyn-associated serine/threonine kinase, casein kinase II (CK2), also complexed with c-Raf and c-RafpS259, and the kinase suppressor of Ras 1 (KSR1) scaffold protein bound c-Raf, Lyn and extracellular signal-regulated kinase (ERK). c-Raf/ERK association was increased by the inhibitors, which is significant as ERK may cause c-Raf C-terminal domain (CTD) phosphorylation in a putative feedback mechanism. Consistent with this, inhibitor treatment caused more CTD phosphorylation. Lyn knockdown decreased c-Raf CTD and S259 phosphorylation. This is the first evidence suggesting SFK inhibitors enhance ATRA-induced differentiation through a possible feedback loop involving KSR1-scaffolded c-Raf and ERK complexed with Lyn and CK2.
Sympathetic nerve activity and arterial blood pressure responses to static hindlimb muscle contractions are greater in rats with femoral arteries that were previously ligated (24-72 h earlier) than in control rats. Studies further demonstrate that acid-sensing ion channel subtype 3 (ASIC(3)) in thin-fibre muscle afferents contributes to the amplified reflex muscle responses observed in occluded rats, probably due to enhanced ASIC(3) expression in muscle sensory neurons. The purpose of this study was to characterize acid-induced current with activation of ASIC(3) in dorsal root ganglion (DRG) neurons of control rats and rats with 24 h of femoral occlusion using whole-cell patch clamp methods. Also, immunohistochemistry was employed to examine existence of ASIC(3) expression in DRG neurons of thin-fibre afferents. DRG neurons from 4- to 6-week-old rats were labelled by injecting the fluorescence tracer DiI into the hindlimb muscles 4-5 days prior to the recording experiments. The results of this study show that ∼90% of current responses evoked by pH 6.7 in DRG neurons innervating the hindlimb muscles are ASIC(3)-like. The peak current amplitude to pH 6.7 is significantly attenuated with application of rAPETx2, a specific ASIC(3) antagonist. In addition, ASIC(3)-like current responses to pH 6.7 are observed in small, medium and large DRG neurons, and size distribution of DRG neurons is similar in control and occluded animals. However, the peak current amplitude of DRG neuron response induced by ASIC(3) stimulation is larger in occluded rats than that in control rats. Moreover, the percentage of DRG neurons with ASIC(3)-like currents is greater after arterial occlusion compared with control. Furthermore, results from double immunofluorescence experiments show that femoral artery occlusion mainly augments ASIC(3) expression within DRG neurons projecting C-fibre afferents. Taken together, these data suggest that (1) the majority of current responses to pH 6.7 are ASIC(3)-like in DRG neurons with nerve endings in the hindlimb muscles, (2) a greater acid-induced current responding to pH 6.7 develops when hindlimb arterial blood supply is deficient under ischaemic conditions, and (3) increased ASIC(3) expression is largely observed in thin C-fibres of DRG neurons after hindlimb ischaemia.
Early after-depolarization (EAD), or abnormal depolarization during the plateau phase of action potentials, is a hallmark of long-QT syndrome (LQTS). More than 13 genes have been identified as responsible for LQTS, and elevated risks for EADs may depend on genotypes, such as exercise in LQT1 vs. sudden arousal in LQT2 patients. We investigated mechanisms underlying different high-risk conditions that trigger EADs using transgenic rabbit models of LQT1 and LQT2, which lack I(Ks) and I(Kr) (slow and fast components of delayed rectifying K(+) current), respectively. Single-cell patch-clamp studies show that prolongation of action potential duration (APD) can be further enhanced by lowering extracellular potassium concentration ([K(+)](o)) from 5.4 to 3.6 mm. However, only LQT2 myocytes developed spontaneous EADs following perfusion with lower [K(+)](o), while there was no EAD formation in littermate control (LMC) or LQT1 myocytes, although APDs were also prolonged in LMC myocytes and LQT1 myocytes. Isoprenaline (ISO) prolonged APDs and triggered EADs in LQT1 myocytes in the presence of lower [K(+)](o). In contrast, continuous ISO perfusion diminished APD prolongation and reduced the incidence of EADs in LQT2 myocytes. These different effects of ISO on LQT1 and LQT2 were verified by optical mapping of the whole heart, suggesting that ISO-induced EADs are genotype specific. Further voltage-clamp studies revealed that ISO increases L-type calcium current (I(Ca)) faster than I(Ks) (time constant 9.2 s for I(Ca) and 43.6 s for I(Ks)), and computer simulation demonstrated a high-risk window of EADs in LQT2 during ISO perfusion owing to mismatch in the time courses of I(Ca) and I(Ks), which may explain why a sympathetic surge rather than high sympathetic tone can be an effective trigger of EADs in LQT2 perfused hearts. In summary, EAD formation is genotype specific, such that EADs can be elicited in LQT2 myocytes simply by lowering [K(+)](o), while LQT1 myocytes require sympathetic stimulation. Slower activation of I(Ks) than of I(Ca) by ISO may explain why different sympathetic modes, i.e. sympathetic surge vs. high sympathetic tone, are associated with polymorphic ventricular tachycardia in LQTS patients.
Alarmins are endogenous mediators capable of promoting the recruitment and activation of antigen-presenting cells (APCs), including dendritic cells (DCs), that can potentially alert host defense against danger signals. However, the relevance of alarmins to the induction of adaptive immune responses remains to be demonstrated. In this study, we report the identification of HMGN1 (high-mobility group nucleosome-binding protein 1) as a novel alarmin and demonstrate that it contributes to the induction of antigen-specific immune responses. HMGN1 induced DC maturation via TLR4 (Toll-like receptor 4), recruitment of APCs at sites of injection, and activation of NF-κB and multiple mitogen-activated protein kinases in DCs. HMGN1 promoted antigen-specific immune response upon co-administration with antigens, and Hmgn1(-/-) mice developed greatly reduced antigen-specific antibody and T cell responses when immunized with antigens in the presence of lipopolysaccharide (LPS). The impaired ability of Hmgn1(-/-) mice to mount antigen-specific immune responses was accompanied by both deficient DC recruitment at sites of immunization and reduced production of inflammatory cytokines. Bone marrow chimera experiments revealed that HMGN1 derived from nonleukocytes was critical for the induction of antigen-specific antibody and T cell responses. Thus, extracellular HMGN1 acts as a novel alarmin critical for LPS-induced development of innate and adaptive immune responses.
Development of the head skeleton involves reciprocal interactions between cranial neural crest cells (CNCCs) and the surrounding pharyngeal endoderm and ectoderm. Whereas elegant experiments in avians have shown a prominent role for the endoderm in facial skeleton development, the relative functions of the endoderm in growth versus regional identity of skeletal precursors have remained unclear. Here we describe novel craniofacial defects in zebrafish harboring mutations in the Sphingosine-1-phospate (S1P) type 2 receptor (s1pr2) or the S1P transporter Spinster 2 (spns2), and we show that S1P signaling functions in the endoderm for the proper growth and positioning of the jaw skeleton. Surprisingly, analysis of s1pr2 and spns2 mutants, as well as sox32 mutants that completely lack endoderm, reveals that the dorsal-ventral (DV) patterning of jaw skeletal precursors is largely unaffected even in the absence of endoderm. Instead, we observe reductions in the ectodermal expression of Fibroblast growth factor 8a (Fgf8a), and transgenic misexpression of Shha restores fgf8a expression and partially rescues the growth and differentiation of jaw skeletal precursors. Hence, we propose that the S1P-dependent anterior foregut endoderm functions primarily through Shh to regulate the growth but not DV patterning of zebrafish jaw precursors.
Cholesterol metabolism in the brain is distinct from that in other tissues due to the fact that cholesterol itself is unable to pass across the blood-brain barrier. Elimination of brain cholesterol is mainly dependent on a neuronal-specific cytochrome P450, CYP46A1, catalyzing the conversion of cholesterol into 24(S)-hydroxycholesterol (24OHC), which is able to pass the blood-brain barrier. A suitable model for studying this elimination from human neuronal cells has not been described previously. It is shown here that differentiated Ntera2/clone D1 (NT2) cells express the key genes involved in brain cholesterol homeostasis including CYP46A1, and that the expression profiles of the genes observed during neuronal differentiation are those expected to occur in vivo. Thus there was a decrease in the mRNA levels corresponding to cholesterol synthesis enzymes and a marked increase in the mRNA level of CYP46A1. The latter increase was associated with increased levels of CYP46A1 protein and increased production of 24OHC. The magnitude of the secretion of 24OHC from the differentiated NT2 cells into the medium was similar to that expected to occur under in vivo conditions. An alternative to elimination of cholesterol by the CYP46A1 mechanism is elimination by CYP27A1, and the product of this enzyme, 27-hydroxycholesterol (27OHC), is also known to pass the blood-brain barrier. The CYP27A1 protein level decreased during the differentiation of the NT2 cells in parallel with decreased production of 27OHC. The ratio between 24OHC and 27OHC in the medium from the cultured cells increased, by a factor of 13, during the differentiation process. The results suggest that progenitor cells eliminate cholesterol in the form of 27OHC while neurogenesis induces a change to the CYP46A1 dependent pathway. Furthermore this study demonstrates that differentiated NT2 cells are suitable for studies of cholesterol homeostasis in human neurons.
Trypanosomes and Leishmanias are important human parasites whose cellular architecture is centred on the single flagellum. In trypanosomes, this flagellum is attached to the cell along a complex flagellum attachment zone (FAZ), comprising flagellar and cytoplasmic components, the integrity of which is required for correct cell morphogenesis and division. The cytoplasmic FAZ cytoskeleton is conspicuously associated with a sheet of endoplasmic reticulum termed the 'FAZ ER'. In the present work, 3D electron tomography of bloodstream form trypanosomes was used to clarify the nature of the FAZ ER. We also identified TbVAP, a T. brucei protein whose knockdown by RNAi in procyclic form cells leads to a dramatic reduction in the FAZ ER, and in the ER associated with the flagellar pocket. TbVAP is an orthologue of VAMP-associated proteins (VAPs), integral ER membrane proteins whose mutation in humans has been linked to familial motor neuron disease. The localisation of tagged TbVAP and the phenotype of TbVAP RNAi in procyclic form trypanosomes are consistent with a function for TbVAP in the maintenance of sub-populations of the ER associated with the FAZ and the flagellar pocket. Nevertheless, depletion of TbVAP did not affect cell viability or cell cycle progression.
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