Iron–sulfur cluster exchange reactions mediated by the human Nfu protein

Human Nfu is an iron–sulfur cluster protein that has recently been implicated in multiple mitochondrial dysfunctional syndrome (MMDS1). The Nfu family of proteins shares a highly homologous domain that contains a conserved active site consisting of a CXXC motif. There is less functional conservation between bacterial and human Nfu proteins, particularly concerning their Iron–sulfur cluster binding and transfer roles. Herein, we characterize the cluster exchange chemistry of human Nfu and its capacity to bind and transfer a [2Fe–2S] cluster. The mechanism of cluster uptake from a physiologically relevant [2Fe–2S](GS)₄ cluster complex, and extraction of the Nfu-bound iron–sulfur cluster by glutathione are described. Human holo Nfu shows a dimer-tetramer equilibrium with a protein to cluster ratio of 2:1, reflecting the Nfu-bridging [2Fe–2S] cluster. This cluster can be transferred to apo human ferredoxins at relatively fast rates, demonstrating a direct role for human Nfu in the process of [2Fe–2S] cluster trafficking and delivery.     

Instrumental comparison of the determination of Cr³+ uptake by human transferrin

UV-VIS absorbance, inductively coupled plasma-optical emission spectroscopy (ICP-OES), and particle beam/hollow cathode-optical emission spectroscopy (PB/HC-OES) are presented as techniques for determining Cr3+ loading into transferrin (Tf), with and without Fe3+. The methods are compared based on loading percentages (i.e. 100% loading would be equal to 2 M(n+): 1 Tf) determined for Cr3+ loading into apo-transferrin. Spectral interferences and overlapping LMCT bands cause inaccurate chromium (qualitative) and iron (qualitative and quantitative) results for the UV-VIS absorbance method. The ICP-OES and PB/HC-OES methods are in good agreement providing evidence that the PB/HC-OES method is a valid technique for investigating metal-protein complexes. Maximum Cr3+ loading into apo-transferrin over a 24 h period was determined to be 26.8 3.5% by the ICP-OES method and 25.3 2.2% by the PB/HC-OES method. Loading percentages were increased to 49.7 1.9% (ICP-OES) and 55.7 3.2% (PB/HC-OES) when the metal-transferrin solution was allowed to incubate for up to 10 days. Under non-excess carbonate conditions the Cr3+ loading is elevated over a 24 h incubation time, but under physiological conditions the loading is inhibited. Equal loading of Fe3+ and Cr3+ into apo-transferrin was achieved when chromium was at a level more than 5 times in excess of iron. Inhibition of Cr3+ loading was only observed when an excess of Fe3+ was available to bind into apo-transferrin. The ability for Cr3+ to displace Fe3+ from holo-transferrin was observed as small amounts of Cr3+ were loaded into the once occupied metal binding site.     

Is the development of falciparum malaria in the human host limited by the availability of uninfected erythrocytes?

Background  

The development and propagation of malaria parasites in their vertebrate host is a complex process in which various host and parasite factors are involved. Sometimes the evolution of parasitaemia seems to be quelled by parasite load. In order to understand the typical dynamics of evolution of parasitaemia, various mathematical models have been developed. The basic premise ingrained in most models is that the availability of uninfected red blood cells (RBC) in which the parasite develops is a limiting factor in the propagation of the parasite population.     

Low extracellular pH stimulates the production of IL-1β by human monocytes

The development of acidic environments is a hallmark of inflammatory processes of different etiology. We have previously shown that transient exposure to acidic conditions, similar to those encountered in vivo, induces the activation of neutrophils and the phenotypic maturation of dendritic cells. We here report that extracellular acidosis (pH 6.5) selectively stimulates the production and the secretion of IL-1β by human monocytes without affecting the production of TNF-α, IL-6 and the expression of CD40, CD80, CD86, and HLA-DR. Stimulation of IL-1β production by pH 6.5-treated monocytes was shown to be dependent on caspase-1 activity, and it was also observed using peripheral blood mononuclear cells instead of isolated monocytes. Contrasting with the results in monocytes, we found that pH 6.5 did not stimulate any production of IL-1β by macrophages. Changes in intracellular pH seem to be involved in the stimulation of IL-1β production. In fact, monocytes cultured at pH 6.5 undergo a fall in the values of intracellular pH while the inhibitor of the Na+/H+ exchanger, 5-(N-ethyl-N-isopropyl)amiloride induced both, a decrease in the values of intracellular pH and the stimulation of IL-1β production. Real time quantitative PCR assays indicated that monocytes cultured either at pH 6.5 or in the presence of 5-(N-ethyl-N-isopropyl)amiloride expressed higher levels of pro-IL-1β mRNA suggesting that low values of intracellular pH enhance the production of IL-1β, at least in part, by stimulating the synthesis of its precursor.     

Relaxation by β3-adrenoceptor agonists of the isolated human internal anal sphincter

AimsIn this study, responses of β₃-adrenoceptor agonists were examined on human isolated internal anal sphincter (IAS) in order to explore their relaxant effects on hypertonicity of IAS.Main methodsThe relaxant efficacy (E_max) and potency (? logIC₅₀) of BRL37344 and SR58611A, β₃-adrenoceptor agonists, were examined in contracted IAS muscle strips. The presence of β₃-adrenoceptors, and changes in intracellular calcium and cyclic nucleotide levels in IAS muscle were tested by Western blotting, epifluorescence microscopy and enzyme immunoassay, respectively.Key findingsBRL37344 and SR58611A relaxed contracted IAS muscle (E_max = 27 ± 3% and 35 ± 3%; -logIC₅₀ = 6.26 ± 0.24 and 4.87 ± 0.13; respectively). These relaxant responses were blocked by SR59230A, a selective β₃-antagonist but not by β₁/β₂-selective antagonists, neuronal inhibitor or inhibition of nitric oxide synthase. The E_max of β₃-agonists was similar to that of β₂-selective agonists but smaller than that of isoprenaline (nonselective agonist) or β₁-selective agonists. BRL37344 (100 μM) increased cAMP (1.5-fold) without cGMP change, and depressed intracellular calcium signal. β₃-Adrenoceptor expression was smaller than that of β₁- and β₂-adrenoceptors.SignificanceThis is the first study demonstrating the presence of β₃-adrenoceptor in human IAS muscle and β₃-mediated relaxation of augmented sphincter tone. However, direct β₃-relaxation appears smaller than that obtained for nonselective agonists which may limit their potential use in the treatment of anorectal hypertonicity disorders.     

Bmi-1 extends the life span of normal human oral keratinocytes by inhibiting the TGF-β signaling

We previously demonstrated that Bmi-1 extended the in vitro life span of normal human oral keratinocytes (NHOK). We now report that the prolonged life span of NHOK by Bmi-1 is, in part, due to inhibition of the TGF-β signaling pathway. Serial subculture of NHOK resulted in replicative senescence and terminal differentiation and activation of TGF-β signaling pathway. This was accompanied with enhanced intracellular and secreted TGF-β1 levels, phosphorylation of Smad2/3, and increased expression of p15^INK4B and p57^KIP2. An ectopic expression of Bmi-1 in NHOK (HOK/Bmi-1) decreased the level of intracellular and secreted TGF-β1 induced dephosphorylation of Smad2/3, and diminished the level of p15^INK4B and p57^KIP2. Moreover, Bmi-1 expression led to the inhibition of TGF-β-responsive promoter activity in a dose-specific manner. Knockdown of Bmi-1 in rapidly proliferating HOK/Bmi-1 and cancer cells increased the level of phosphorylated Smad2/3, p15^INK4B, and p57^KIP2. In addition, an exposure of senescent NHOK to TGF-β receptor I kinase inhibitor or anti-TGF-β antibody resulted in enhanced replicative potential of cells. Taken together, these data suggest that Bmi-1 suppresses senescence of cells by inhibiting the TGF-β signaling pathway in NHOK.     

Glucuronidation of the steroid enantiomers ent-17β-estradiol, ent-androsterone and ent-etiocholanolone by the human UDP-glucuronosyltransferases

Steroids enantiomers are interesting compounds for detailed exploration of drug metabolizing enzymes, such as the UDP-glucuronosyltransferases (UGTs). We have now studied the glucuronidation of the enantiomers of estradiol, androsterone and etiocholanolone by the 19 human UGTs of subfamilies 1A, 2A and 2B. The results reveal that the pattern of human UGTs of subfamily 2B that glucuronidate ent-17β-estradiol, particularly 2B15 and 2B17, resembles the glucuronidation of epiestradiol (17α-estradiol) rather than 17β-estradiol, the main physiological estrogen. The UGTs of subfamilies 1A and 2A exhibit higher degree of regioselectivity than enantioselectivity in the conjugation of these estradiols, regardless of whether the activity is primarily toward the non-chiral site, 3-OH (UGT1A1, UGT1A3, UGT1A7, UGT1A8 and, above all, UGT1A10), or the 17-OH (UGT1A4). In the cases of etiocholanolone and androsterone, glucuronidation of the ent-androgens, like the conjugation of the natural androgens, is mainly catalyzed by UGTs of subfamilies 2A and 2B. Nevertheless, the glucuronidation of ent-etiocholanolone and ent-androsterone by both UGT2B7 and UGT2B17 differs considerably from their respective activity toward the corresponding endogenous androgens, whereas UGT2A1-catalyzed conjugation is much less affected by the stereochemistry differences. Kinetic analyses reveal that the K(m) value of UGT2A1 for ent-estradiol is much higher than the corresponding value in the other two high activity enzymes, UGT1A10 and UGT2B7. Taken together, the results highlight large enantioselectivity differences between individual UGTs, particularly those of subfamily 2B.     

Regional mapping of the human gene for lysosomal α-glucosidase by in situ hybridization

Summary The current approach to the chromosomal localization of genes coding for lysosomal enzymes has been the correlation of enzymatic and karyotypic analyses of human-rodent somatic cell hybrids. The feasibility of regional mapping depends on the availability of human cells with informative chromosomal rearrangements. In this communication we report the first localization of a gene coding for a lysosomal enzyme by in situ hybridization. The application of an acid -glucosidase cDNA probe to normal human chromosomes allowed direct regional mapping of the -glucosidase locus (GAA) to the region q23q25 of chromosome 17.     

The intrinsic stability of the human prion β-sheet region investigated by molecular dynamics

Human prion diseases are neurodegenerative disorders associated to the misfolding of the prion protein (PrP). Common features of prion disorders are the fibrillar amyloid deposits and the formation of prefibrillar oligomeric species also suggested as the origin of cytotoxicity associated with diseases. Although the process of PrP misfolding has been extensively investigated, many crucial aspects of this process remain unclear. We have here carried out a molecular dynamics study to evaluate the intrinsic dynamics of PrP β-sheet, a region that is believed to play a crucial role in prion aggregation. Moreover, as this region mediates protein association in dimeric assemblies frequently observed in prion crystallographic investigations, we also analyzed the dynamics of these intermolecular interactions. The extensive sampling of replica exchange shows that the native antiparallel β-structure of the prion is endowed with a remarkable stability. Therefore, upon unfolding, the persistence of a structured β-region may seed molecular association and influence the subsequent phases of the aggregation process. The analysis of the four-stranded β-sheet detected in the dimeric assemblies of PrP shows a tendency of this region to form dynamical structured states. The impact on the β-sheet structure and dynamics of disease associated point mutations has also been evaluated.     

Understanding the proteome encoded by “non-coding RNAs”:new insights into human genome

A great number of non-coding RNAs(ncRNAs) account for the majority of the genome. The translation of these ncRNAs has been noted but seriously underestimated due to both technological and theoretical limitations. Based on the development of ribosome profiling(Ribo-seq), full length translating RNA analysis(RNC-seq) and mass spectrometry technology, more and more ncRNAs are being found to be translated in different organism, and some of them can produce functional peptides. While recently, not only individual new functional proteins, but also a new proteome have been experimentally discovered to be encoded by endogenous lncRNAs and circRNAs. These new proteins are of biological significance, suggesting the connection of the translation of ncRNAs to human physiology and diseases. Therefore, an in-depth and systematic understanding of the coding capabilities of ncRNAs is necessary for basic biology and medicine. In this review, we summarize the advances in the field of discovering this new proteome, i.e. "ncRNA-coded" proteins.     

General and unspecific damping by malignancy of the circadian amplitude of circulating human melatonin?

The circadian rhythm of serum melatonin of 39 cancer patients is compared with that of 28 healthy subjects matched by gender and age. Each subject provided 6 blood samples at 4-hour intervals for determination of melatonin by RIA. After log10-transformation, data series were analyzed by single and population-mean cosinor and compared between the two groups and among patients subgrouped by cancer site, stage and treatment. A circadian rhythm (P<0.001) is demonstrated for both groups, with a contributing 12-hour harmonic (P<0.001). In the absence of a difference in MESOR, the circadian amplitude of the cancer patients is smaller than that of the healthy subjects (P=0.003). Numerically, nocturnal (00:00 and 04:00) melatonin concentrations are lower and daytime (08:00-20:00) melatonin concentrations are higher in the cancer patients than in the healthy subjects (P=0.032 at 12:00 and P=0.058 at 16:00). In the age ranges examined, no differences are found with age in either group or by gender in health. No differences are found among cancer patients subgrouped either by site, stage (localized vs. metastasized) or treatment. If these results are validated, other Janus-like (two-faced: stimulation or inhibition, depending on chronome stage) effects of malignancy should be taken into consideration for screening and for timing treatment.     

Suppression of the NF-κB pathway by diesel exhaust particles impairs human antimycobacterial immunity

Epidemiological studies suggest that chronic exposure to air pollution increases susceptibility to respiratory infections, including tuberculosis in humans. A possible link between particulate air pollutant exposure and antimycobacterial immunity has not been explored in human primary immune cells. We hypothesized that exposure to diesel exhaust particles (DEP), a major component of urban fine particulate matter, suppresses antimycobacterial human immune effector cell functions by modulating TLR-signaling pathways and NF-κB activation. We show that DEP and H37Ra, an avirulent laboratory strain of Mycobacterium tuberculosis, were both taken up by the same peripheral human blood monocytes. To examine the effects of DEP on M. tuberculosis-induced production of cytokines, PBMC were stimulated with DEP and M. tuberculosis or purified protein derivative. The production of M. tuberculosis and purified protein derivative-induced IFN-γ, TNF-α, IL-1β, and IL-6 was reduced in a DEP dose-dependent manner. In contrast, the production of anti-inflammatory IL-10 remained unchanged. Furthermore, DEP stimulation prior to M. tuberculosis infection altered the expression of TLR3, -4, -7, and -10 mRNAs and of a subset of M. tuberculosis-induced host genes including inhibition of expression of many NF-κB (e.g., CSF3, IFNG, IFNA, IFNB, IL1A, IL6, and NFKBIA) and IFN regulatory factor (e.g., IFNG, IFNA1, IFNB1, and CXCL10) pathway target genes. We propose that DEP downregulate M. tuberculosis-induced host gene expression via MyD88-dependent (IL6, IL1A, and PTGS2) as well as MyD88-independent (IFNA, IFNB) pathways. Prestimulation of PBMC with DEP suppressed the expression of proinflammatory mediators upon M. tuberculosis infection, inducing a hyporesponsive cellular state. Therefore, DEP alters crucial components of antimycobacterial host immune responses, providing a possible mechanism by which air pollutants alter antimicrobial immunity.     

Manipulation of the host cell membrane by humanγ-herpesviruses EBV and KSHV for pathogenesis

The cell membrane regulates many physiological processes including cellular communication,homing and metabolism. It is therefore not surprising that the composition of the host cell membrane is manipulated by intracellular pathogens. Among these, the human oncogenic herpesviruses Epstein–Barr virus(EBV) and Kaposi's sarcoma-associated herpesvirus(KSHV)exploit the host cell membrane to avoid immune surveillance and promote viral replication.Accumulating evidence has shown that both EBV and KSHV directly encode several similar membrane-associated proteins, including receptors and receptor-specific ligands(cytokines and chemokines), to increase virus fitness in spite of host antiviral immune responses. These proteins are expressed individually at different phases of the EBV/KSHV life cycle and employ various mechanisms to manipulate the host cell membrane. In recent decades, much effort has been made to address how these membrane-based signals contribute to viral tumorigenesis. In this review, we summarize and highlight the recent understanding of how EBV and KSHV similarly manipulate host cell membrane signals, particularly how remodeling of the cell membrane allows EBV and KSHV to avoid host antiviral immune responses and favors their latent and lytic infection.