Allosteric control of dynamin-related protein 1 through a disordered C-terminal Short Linear Motif

The mechanochemical GTPase dynamin-related protein 1 (Drp1) catalyzes mitochondrial and peroxisomal fission, but the regulatory mechanisms remain ambiguous. Here we find that a conserved, intrinsically disordered, six-residue Short Linear Motif at the extreme Drp1 C-terminus, named CT-SLiM, constitutes a critical allosteric site that controls Drp1 structure and function in vitro and in vivo. Extension of the CT-SLiM by non-native residues, or its interaction with the protein partner GIPC-1, constrains Drp1 subunit conformational dynamics, alters self-assembly properties, and limits cooperative GTP hydrolysis, surprisingly leading to the fission of model membranes in vitro. In vivo, the involvement of the native CT-SLiM is critical for productive mitochondrial and peroxisomal fission, as both deletion and non-native extension of the CT-SLiM severely impair their progression. Thus, contrary to prevailing models, Drp1-catalyzed membrane fission relies on allosteric communication mediated by the CT-SLiM, deceleration of GTPase activity, and coupled changes in subunit architecture and assembly-disassembly dynamics.

NMR identification of a conserved Drp1 cardiolipin-binding motif essential for stress-induced mitochondrial fission

Mitochondria form tubular networks that undergo coordinated cycles of fission and fusion. Emerging evidence suggests that a direct yet unresolved interaction of the mechanoenzymatic GTPase dynamin-related protein 1 (Drp1) with mitochondrial outer membrane-localized cardiolipin (CL), externalized under stress conditions including mitophagy, catalyzes essential mitochondrial hyperfragmentation. Here, using a comprehensive set of structural, biophysical, and cell biological tools, we have uncovered a CL-binding motif (CBM) conserved between the Drp1 variable domain (VD) and the unrelated ADP/ATP carrier (AAC/ANT) that intercalates into the membrane core to effect specific CL interactions. CBM mutations that weaken VD-CL interactions manifestly impair Drp1-dependent fission under stress conditions and induce "donut" mitochondria formation. Importantly, VD membrane insertion and GTP-dependent conformational rearrangements mediate only transient CL nonbilayer topological forays and high local membrane constriction, indicating that Drp1-CL interactions alone are insufficient for fission. Our studies establish the structural and mechanistic bases of Drp1-CL interactions in stress-induced mitochondrial fission.

Directed Evolution Using Stabilized Bacterial Peptide Display

Chemically stabilized peptides have attracted intense interest by academics and pharmaceutical companies due to their potential to hit currently "undruggable" targets. However, engineering an optimal sequence, stabilizing linker location, and physicochemical properties is a slow and arduous process. By pairing non-natural amino acid incorporation and cell surface click chemistry in bacteria with high-throughput sorting, we developed a method to quantitatively select high affinity ligands and applied the Stabilized Peptide Evolution by E. coli Display technique to develop disrupters of the therapeutically relevant MDM2-p53 interface. Through in situ stabilization on the bacterial surface, we demonstrate rapid isolation of stabilized peptides with improved affinity and novel structures. Several peptides evolved a second loop including one sequence (K_d = 1.8 nM) containing an i, i+4 disulfide bond. NMR structural determination indicated a bent helix in solution and bound to MDM2. The bicyclic peptide had improved protease stability, and we demonstrated that protease resistance could be measured both on the bacterial surface and in solution, enabling the method to test and/or screen for additional drug-like properties critical for biologically active compounds.

Probing membrane enhanced protein-protein interactions in a minimal redox complex of cytochrome-P450 and P450-reductase

Investigating the interplay in a minimal redox complex of cytochrome-P450 and its reductase is crucial for understanding cytochrome-P450's enzymatic activity. Probing the hotspots of dynamic structural interactions using NMR revealed the engagement of loop residues from P450-reductase to be responsible for the enhanced affinity of CYP450 towards its obligate redox partner.

A Minimal Functional Complex of Cytochrome P450 and FBD of Cytochrome P450 Reductase in Nanodiscs

Structural interactions that enable electron transfer to cytochrome-P450 (CYP450) from its redox partner CYP450-reductase (CPR) are a vital prerequisite for its catalytic mechanism. The first structural model for the membrane-bound functional complex to reveal interactions between the full-length CYP450 and a minimal domain of CPR is now reported. The results suggest that anchorage of the proteins in a lipid bilayer is a minimal requirement for CYP450 catalytic function. Akin to cytochrome-b₅ (cyt-b₅ ), Arg 125 on the C-helix of CYP450s is found to be important for effective electron transfer, thus supporting the competitive behavior of redox partners for CYP450s. A general approach is presented to study protein-protein interactions combining the use of nanodiscs with NMR spectroscopy and SAXS. Linking structural details to the mechanism will help unravel the xenobiotic metabolism of diverse microsomal CYP450s in their native environment and facilitate the design of new drug entities.

Membrane environment drives cytochrome P450's spin transition and its interaction with cytochrome b5

Heme's spin-multiplicity is key in determining the enzymatic function of cytochrome P450 (cytP450). The origin of the low-spin state in ferric P450 is still under debate. Here, we report the first experimental demonstration of P450's membrane interaction altering its spin equilibrium which is accompanied by a stronger affinity for cytochrome b₅. These results highlight the importance of lipid membrane for the function of P450.

NMR structure and localization of a large fragment of the SARS-CoV fusion protein: Implications in viral cell fusion

The lethal Coronaviruses (CoVs), Severe Acute Respiratory Syndrome-associated Coronavirus (SARS-CoV) and most recently Middle East Respiratory Syndrome Coronavirus, (MERS-CoV) are serious human health hazard. A successful viral infection requires fusion between virus and host cells carried out by the surface spike glycoprotein or S protein of CoV. Current models propose that the S2 subunit of S protein assembled into a hexameric helical bundle exposing hydrophobic fusogenic peptides or fusion peptides (FPs) for membrane insertion. The N-terminus of S2 subunit of SARS-CoV reported to be active in cell fusion whereby FPs have been identified. Atomic-resolution structure of FPs derived either in model membranes or in membrane mimic environment would glean insights toward viral cell fusion mechanism. Here, we have solved 3D structure, dynamics and micelle localization of a 64-residue long fusion peptide or LFP in DPC detergent micelles by NMR methods. Micelle bound structure of LFP is elucidated by the presence of discretely folded helical and intervening loops. The C-terminus region, residues F42-Y62, displays a long hydrophobic helix, whereas the N-terminus is defined by a short amphipathic helix, residues R4-Q12. The intervening residues of LFP assume stretches of loops and helical turns. The N-terminal helix is sustained by close aromatic and aliphatic sidechain packing interactions at the non-polar face. ¹⁵N{¹H}NOE studies indicated dynamical motion, at ps-ns timescale, of the helices of LFP in DPC micelles. PRE NMR showed that insertion of several regions of LFP into DPC micelle core. Together, the current study provides insights toward fusion mechanism of SARS-CoV.

Kinetic and Structural Characterization of the Effects of Membrane on the Complex of Cytochrome b 5 and Cytochrome c

Cytochrome b₅ (cytb₅) is a membrane protein vital for the regulation of cytochrome P450 (cytP450) metabolism and is capable of electron transfer to many redox partners. Here, using cyt c as a surrogate for cytP450, we report the effect of membrane on the interaction between full-length cytb₅ and cyt c for the first time. As shown through stopped-flow kinetic experiments, electron transfer capable cytb₅ - cyt c complexes were formed in the presence of bicelles and nanodiscs. Experimentally measured NMR parameters were used to map the cytb₅-cyt c binding interface. Our experimental results identify differences in the binding epitope of cytb₅ in the presence and absence of membrane. Notably, in the presence of membrane, cytb₅ only engaged cyt c at its lower and upper clefts while the membrane-free cytb₅ also uses a distal region. Using restraints generated from both cytb₅ and cyt c, a complex structure was generated and a potential electron transfer pathway was identified. These results demonstrate the importance of studying protein-protein complex formation in membrane mimetic systems. Our results also demonstrate the successful preparation of novel peptide-based lipid nanodiscs, which are detergent-free and possesses size flexibility, and their use for NMR structural studies of membrane proteins.

89 METHYLATION STATUS OF IGF2/H19 DMR3 REGION AFFECTS IN VITRO BLASTOCYST PRODUCTION IN GOAT (CAPRA HIRCUS)

Parthenogenesis has been observed in lower animals but no known instance has been reported in mammals because both maternal and paternal genomes are a fundamental prerequisite for embryogenesis. A major reason for developmental failure of uniparental zygotes is expression of certain genes in a parent-of-origin-specific manner, i.e. genomic imprinting of genes. Out of many imprinted genes identified so far, IGF2/H19 have been extensively studied and known to play an important role in fetal and placental development. Gene IGF2 is expressed by the paternal allele, H19 is transcribed from the maternal allele, and the reciprocal expression of both genes is regulated by the DMR3 region placed upstream of the H19 gene. In the present study we compared the methylation status of IGF2/H19 DMR in parthenogenetic activated (PA) and IVF goat (Capra hircus) blastocyst through bisulphite sequencing. For this, immature oocytes of usable quality were subjected to in vitro maturation and subsequently used for embryo production through parthenogenesis (n = 993) (by calcium ionophore and 6-DMAP activation) and IVF (n = 1096). It was found that embryo production rate at all the embryonic stages (2-cell, 4-cell, 8–16-cell, morula, and blastocyst) was significantly higher (P < 0.05) in parthenogenesis (74.66 ± 3.35%, 61.90 ± 2.73%, 47.83 ± 2.95%, 38.13 ± 5.28%, and 21.11 ± 2.51%, respectively) as compared with IVF (55.21 ± 2.02%, 38.12 ± 2.48%, 28.53 ± 1.67%, 21.57 ± 1.59%, and 8.23 ± 1.02%, respectively). When blastocysts (n = 6 each) were subjected to TUNEL, it was found that PA blastocyst showed significantly higher (P < 0.05) total cell number (217.83 ± 18.80 v. 159.67 ± 13.94) and significantly low (P < 0.05) apoptotic index (2.04 ± 0.25 v. 4.03 ± 0.29) as compared with IVF blastocysts. For the methylation pattern study, we analysed 17 CpG sites on the DMR3 region of the IGF2/H19 gene. Variable methylation pattern was observed within these CpG sites in different clones (n = 15) of PA and IVF blastocyst. The DMR3 region of the IGF2/H19 gene was significantly hypermethylated (P < 0.05) in PA blastocysts as compared with IVF blastocysts (80.39 ± 2.96, 32.55 ± 4.37, respectively), which suggests higher expression of IGF2 in parthenotes. The result suggests IGF2 might play different roles in different species; the same expression pattern of IGF2 is observed in ovine, but a contrary result is found in porcine species. Our results signify the hypermethylation of IGF2/H19 DMR3, which leads to higher expression of IGF2 to support embryonic development at the blastocyst stage. This work was supported by the NFBSFARA Project on Parthenogenetic Goat (CA-4002), New Delhi, India.

90 OVIDUCTAL EPITHELIAL CELLS Co-CULTURE PROMOTES GOAT (CAPRA HIRCUS) IN VITRO PARTHENOGENETIC EMBRYO DEVELOPMENT

Co-culture of pre-implantation embryos with oviducal epithelial cells mimics the in vivo conditions, thus, playing a crucial role in embryo metabolism and gene expression and finally supporting embryonic developmental competence in several ways. Hence, the objective of the present study was to evaluate the effect of goat oviducal epithelial cells (GOEC) co-culture on goat parthenogenetic embryonic development, quality, and relative mRNA abundance of genes related to developmental competence and oxidative stress. The GOEC were obtained from goat oviducts by squeezing and thorough washing with TCM-199 + 10% fetal bovine serum. Goat cumulus–oocyte complexes were collected from slaughterhouse ovaries and matured in TCM-199 + 10% fetal bovine serum supplemented with 5 μg mL−1 of FSH, 10 μg mL−1 of LH, and 1 μg mL−1 of β-oestradiol for 27 h in CO2 incubator with 5% CO2 and at 38.5°C with >95% RH. In vitro matured cumulus–oocyte complexes were denuded and activated with 5 μM calcium ionophore and 2 mM 6-DMAP. Following activation, embryos were co-cultured with and without GOEC (control) in mCR2aa media. The blastocyst development rate was significantly (P < 0.05) higher (23.00 ± 1.15% v. 17.33 ± 1.45%) in the media cultured with GOEC than in control. The total cell number of blastocysts (n = 4) was also found to be significantly more (167.25 ± 17.51 v. 110.25 ± 12.02) than that of control (P < 0.05). However, the apoptotic index (3.76 ± 0.23% v. 7.97 ± 1.99%) was not significantly different in both groups. Further, RNA was isolated from both groups (20 each) of blastocysts on Day 8, and cDNA was prepared. Analysis by qPCR revealed that the relative mRNA abundance of development related genes, i.e. VEGF, BMP4, and CCNB1, showed significantly high (P < 0.05) expression, whereas the expression of CRABP1 was significantly low (P < 0.05) in GOEC co-culture than control. Oxidative stress related genes GPX-1 and SOD2 had comparable expression in both the culture systems, whereas a nonsignificant (P < 0.05) increase in expression of PRDX1 was observed in GOEC co-culture group. In conclusion, co-culture of embryos with GOEC in the simple culture media like mCR2aa helps in improving developmental competence and quality of parthenogenetic embryos. This work was supported by the NFBSFARA Project on Parthenogenetic Goat (CA-4002), New Delhi, India.

Correction: Designed multi-stranded heme binding β-sheet peptides in membrane

Correction for ‘Designed multi-stranded heme binding β-sheet peptides in membrane’ by Areetha D'Souza et al., Chem. Sci., 2016, 7, 2563–2571.

Designed multi-stranded heme binding β-sheet peptides in membrane

Designed peptides demonstrating well-defined structures and functioning in membrane environment are of significant interest in developing novel proteins for membrane active biological processes including enzymes, electron transfer, ion channels and energy conversion. Heme proteins' ability to carry out multiple functions in nature has inspired the design of several helical heme binding peptides and proteins soluble in water and also recently in membrane. Naturally occurring β-sheet proteins are both water and membrane soluble, and are known to bind heme, however, designed heme binding β-sheet proteins are yet to be reported, plausibly because of the complex folding and difficulty in introducing heme binding sites in the β-sheet structures. Here, we describe the design, NMR structures and biochemical functional characterization of four stranded and six stranded membrane soluble β-sheet peptides that bind heme and di-heme, respectively. The designed peptides contain either DP-G or DP-DA residues for the nucleation of β-turns intended to stabilize multi-stranded β-sheet topologies and ligate heme with bis-His coordination between adjacent antiparallel β-strands. Furthermore, we have optimized a high affinity heme binding pocket, Kd ∼ nM range, in the adjacent β-strands by utilizing a series of four stranded β-sheet peptides employing β- and ω-amino acids. We find that there is a progressive increase in cofactor binding affinity in the designed peptides with the alkyl chain length of ω-amino acids. Notably, the six stranded β-sheet peptide binds two molecules of heme in a cooperative fashion. The designed peptides perform peroxidase activity with varying ability and efficiently carried out electron transfer with membrane associated protein cytochrome c. The current study demonstrates the designing of functional β-sheet proteins in a membrane environment and expands the repertoire of heme protein design.

NMR structures and localization of the potential fusion peptides and the pre-transmembrane region of SARS-CoV: Implications in membrane fusion

Severe acute respiratory syndrome-associated coronavirus (SARS-CoV) poses a serious public health hazard. The S2 subunit of the S glycoprotein of SARS-CoV carries out fusion between the virus and the host cells. However, the exact mechanism of the cell fusion process is not well understood. Current model suggests that a conformational transition, upon receptor recognition, of the two heptad core regions of S2 may expose the hydrophobic fusogenic peptide or fusion peptide for membrane insertion. Three regions of the S2 subunit have been proposed to be involved in cell-cell fusion. The N-terminal fusion peptide (FP, residues 770-788), an internal fusion peptide (IFP, residues 873-888) and the pre-transmembrane region (PTM, residues 1185-1202) demonstrated interactions with model lipid membranes and potentially involved in the fusion process. Here, we have determined atomic resolution structures of these three peptides in DPC detergent micelles by solution NMR. FP assumes α-helical conformation with significant distortion at the central Gly residues; enabling a close packing among sidechains of aromatic residues including W, Y and F. The 3-D structure of PMT is characterized by a helix-loop-helix with extensive aromatic interactions within the helices. IFP adopts a rather straight α-helical conformation defined by packing among sidechains of aromatic and aliphatic residues. Paramagnetic spin labeled NMR has demonstrated surface localization of PMT whereas FP and IFP inserted into the micelles. Collectively, data presented in this study will aid in understanding fusion mechanism of SARS-CoV.

Designed di-heme binding helical transmembrane protein

De novo designing of functional membrane proteins is fundamental in terms of understanding the structure, folding, and stability of membrane proteins. In this work, we report the design and characterization of a transmembrane protein, termed HETPRO (HEme-binding Transmembrane PROtein), that binds two molecules of heme in a membrane and catalyzes oxidation/reduction reactions. The primary structure of HETPRO has been optimized in a guided fashion, from an antimicrobial peptide, for transmembrane orientation, defined 3D structure, and functions. HETPRO assembles into a tetrameric form, from an apo dimeric helical structure, in complex with cofactor in detergent micelles. The NMR structure of the apo HETPRO in micelles reveals an antiparallel helical dimer that inserts into the nonpolar core of detergent micelles. The well-defined structure of HETPRO and its ability to bind to heme moieties could be utilized to develop a functional membrane protein mimic for electron transport and photosystems.

Identification and characterization of potent, selective small molecule RIP2 kinase inhibitors (INM6P.422)

NOD1 and NOD2 are cytoplasmic PRRs, which bind peptides derived from bacterial peptidoglycans. Signaling via these receptors involves recruitment and activation of RIP2 kinase, which results in NF-κB- and MAPK-dependent pro-inflammatory cytokine production. To enable a chemical biology approach to evaluate the role of RIP2 in inflammation we screened an in-house compound collection. Optimization of an aminoquinoline template led to the discovery of GSK’214 and related analogs. GSK’214 potently and reversibly inhibited human, rat and mouse RIP2 enzymatic activity (IC50 3-10 nM). Selectivity was demonstrated against a panel of 273 commercially-available kinases. NOD2-mediated signaling induced by muramyl dipeptide (MDP) was used to characterize functional activity, in vitro and in vivo. GSK’214 inhibited cytokine (TNFα, IL1β, IL-6 and IL-8) production (IC50 20 nM) by human monocytes stimulated by MDP, but not by ligands specific for TLR2, TLR4, TLR7, TLR9, IL1R and TNFR. Using an acute mouse peritonitis assay, orally administered GSK’214 inhibited neutrophil influx and cytokine release induced by MDP, but not LPS. Next, we used these inhibitors to probe the role of RIP2 in a murine TNBS-colitis model of intestinal inflammation. Selective inhibition of RIP2 kinase activity reduced disease severity to a degree comparable to prednisolone. These results demonstrate the potential of these inhibitors to elucidate the contribution of RIP2 kinase-dependent signaling in inflammation.

Increase in flavan-3-ols by silencing flavonol synthase mRNA affects the transcript expression and activity levels of antioxidant enzymes in tobacco

Flavonoids are plant secondary metabolites widespread throughout the plant kingdom involved in many physiological and biochemical functions. Amongst the flavonoids, flavan-3-ols (catechin and epicatechin) are known for their direct free radical scavenging activity in vitro, but studies on their antioxidant potential and interaction with antioxidant enzymes in vivo are lacking. Here, the flavonoid pathway was engineered by silencing a gene encoding flavonol synthase (FLS) in tobacco to direct the flow of metabolites towards production of flavan-3-ols. FLS silencing reduced flavonol content 17-53%, while it increased catechin and epicatechin content 51-93% and 18-27%, respectively. The silenced lines showed a significant increase in expression of genes for dihydroflavonol reductase and anthocyanidin synthase, a downstream gene towards epicatechin production, with no significant change in expression of other genes of the flavonoid pathway. Effects of accumulation of flavan-3-ols in FLS silenced lines on transcript level and activities of antioxidant enzymes were studied. Transcripts of the antioxidant enzymes glutathione reductase (GR), ascorbate peroxidase (APx), and catalase (CAT) increased, while glutathione-S-transferase (GST), decreased in FLS silenced lines. Enhanced activity of all the antioxidant enzymes was observed in silenced tobacco lines. To validate the affect of flavan-3-ols on the antioxidant system, in vitro experiments were conducted with tobacco seedlings exposed to two concentrations of catechin (10  and 50 μm) for 2 days. In vitro exposed seedlings produced similar levels of transcripts and activity of antioxidant enzymes as FLS silenced seedlings. Results suggest that flavan-3-ols (catechin) might be increasing activity of GR, Apx and CAT by elevating their mRNAs levels. Since these enzymes are involved in scavenging of reactive oxygen species, this strategy would help in tailoring crops for enhanced catechin production as well as making them tolerant to oxidative stresses.

Role of the APOB Gene Polymorphism (c.12669G>A, p. Gln4154Lys) in Coronary Artery Disease in the Indian Punjabi Population

High concentration of apolipoprotein B (apoB) is a risk factor for coronary artery disease (CAD). The association of the APOB gene polymorphism c.12669G>A, p.Gln4154Lys with the risk of CAD varies considerably in different populations. The present study represents the first investigation regarding the role of this APOB gene polymorphism with CAD in the Indian Punjabi population. We have studied the APOB gene polymorphism c.12669G>A, p.Gln4154Lys and its relationship with lipid, apoB, low-density lipoprotein (LDL) heterogeneity and oxidation in subjects suffering from CAD. The study was conducted on 87 patients with CAD; 75 healthy subjects served as controls. Polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) was used to determine the DNA polymorphism in the APOB gene. Frequency of R- (mutant) allele was significantly high (p <0.05) in CAD patients when compared to controls. Variations in serum lipid levels in the R+R+ and R+R- APOB genotypes were insignificant (p >0.05). However, serum apoB levels were significantly raised (p <0.05) in CAD patients with the R+R- genotype as compared to those with the R+R+ APOB genotype. Coronary artery disease patients had raised significantly raised (p <0.01) Log triglyceride/high density lipoprotein-cholesterol (HDL-C) ratio, apoB carbonyl content and increased malondialdehyde-low density lipoprotein (MDA-LDL levels, irrespective of APOB genotype as compared to controls. Carriers of the R- allele are at higher risk of CAD, probably because of elevated serum apoB levels in the Indian Punjabi population. Overall, it may be concluded that the R- allele might be associated with increased susceptibility towards CAD development in the Indian Punjabi population, and one of the linking factor is the elevation in serum apoB levels. However, this association needs further evaluation in a larger population. Secondly, the robust mechanism behind the positive association of the R- allele with raised serum apoB levels needs to be explored, which might be helpful in the strengthening the observed results.

Proteomics-based approach for identification and purification of human phosphate binding apolipoprotein from amniotic fluid

Human amniotic fluid is of both maternal and fetal origin; it protects the fetus and provides the environment for growth and development of the fetus. We used a proteomics-based approach for targeting and purifying human phosphate binding protein, a member of the DING family of proteins from amniotic fluid, using Blue Sepharose CL-6B, DEAE-Sephacel and gel filtration chromatography. The protein had earlier been reported to be serendipitously purified along with PON1 (paraoxonase 1). It was identified using electro-spray-ionization-time-of-flight mass spectrometry and was found to be human phosphate binding protein. Human phosphate binding proteins have been reported to play a role as phosphate scavengers and may have a protective function against phosphate-related disorders, such as atherosclerosis, diabetes and kidney stones.

In silico characterization of genetic homology in nuclear-encoded apicoplast-targeted genes between Plasmodium falciparum & P. vivax

BACKGROUND & OBJECTIVE

Resistance to anti-malarial drugs by the parasites is one of the major obstacles to malaria control. The primary objective of this work was to find specific nuclear-encoded-apicoplast-targeted genes that are conserved between two different human malaria parasite species, Plasmodium falciparum and P. vivax to find a common drug/vaccine targets for both the species.

METHODS

Using computational genomics, possible nuclear-encoded-apicoplast-targeted genes were identified in P. falciparum genome. With comparative genomic approaches, homologous genes were identified between the two different human malaria species, P. falciparum and P. vivax.

RESULTS

Of the total 545 reported nuclear-encoded-apicoplast-targeted genes in P. falciparum, we could narrow down to as less as five genes that were found to have highly conserved nucleotide stretches in P. vivax. However, two such genes were of importance, as the majority of the protein coding regions (exons) of these genes were found to be highly conserved between them.

INTERPRETATION & CONCLUSION

This preliminary study shows that nuclear-encoded-apicoplast-targeted genes were conserved between the two human malaria parasites and these could be targeted for developing a common drug to cure both forms of malaria.

Ceramide potentiates, but sphingomyelin inhibits, vitamin D-induced keratinocyte differentiation: comparison between keratinocytes and HL-60 cells

Differentiation of epidermal keratinocytes and leukemia HL-60 cells induced by 1,25-dihydroxyvitamin D [1,25(OH)2D] has been reported to be mediated, at least in part, by increases in cellular ceramide levels. Ceramides produced by 1,25(OH)2D-induced sphingomyelin (SM) hydrolysis also contribute to the permeability barrier lipids in keratinocytes. Exogenously supplied SM is taken up by mammalian cells, including keratinocytes, and is incorporated into cellular pools. However, the effects of exogenously added SM on keratinocyte differentiation have not been studied. Therefore, in this study, we compared exogenously added SM with a cell-permeable ceramide for their ability to stimulate keratinocyte differentiation induced by 1,25(OH)2D. Both short-chain ceramide (C2-cer) and SM stimulated the differentiation and inhibited the proliferation of HL-60 cells. As expected, this effect was potentiated by 1,25(OH)2D. However, SM inhibited the differentiation and stimulated the proliferation of keratinocytes. While C2-cer potentiated the effects of 1,25(OH)2D, SM reversed the effects of 1,25(OH)2D on keratinocytes. The ratio of SM to ceramide was significantly different between keratinocytes and HL-60 cells. While the SM level of HL-60 cells were twice that of keratinocytes, keratinocytes contained ten times more ceramides than HL-60 cells, resulting in a ceramide/SM ratio 17 times higher in keratinocytes. Thus, we identified similarities and significant differences in the sphingolipid-mediated cell signaling pathway between keratinocytes and HL-60 cells. While SM stimulated HL-60 cell differentiation, presumably by incorporation into SMase-accessible membrane pools, it inhibited keratinocyte differentiation. In keratinocytes, SM was possibly incorporated into a different cellular pool (barrier lipid pool) or altered membrane phospholipid metabolism and membrane fluidity.

Two domains unique to osteoblast-specific transcription factor Osf2/Cbfa1 contribute to its transactivation function and its inability to heterodimerize with Cbfbeta

Osf2/Cbfa1, hereafter called Osf2, is a member of the Runt-related family of transcription factors that plays a critical role during osteoblast differentiation. Like all Runt-related proteins, it contains a runt domain, which is the DNA-binding domain, and a C-terminal proline-serine-threonine-rich (PST) domain thought to be the transcription activation domain. Additionally, Osf2 has two amino-terminal domains distinct from any other Runt-related protein. To understand the mechanisms of osteoblast gene regulation by Osf2, we performed an extensive structure-function analysis. After defining a short Myc-related nuclear localization signal, a deletion analysis revealed the existence of three transcription activation domains and one repression domain. AD1 (for activation domain 1) comprises the first 19 amino acids of the molecule, which form the first domain unique to Osf2, AD2 is formed by the glutamine-alanine (QA) domain, the second domain unique to Osf2, and AD3 is located in the N-terminal half of the PST domain and also contains sequences unique to Osf2. The transcription repression domain comprises the C-terminal 154 amino acids of Osf2. DNA-binding, domain-swapping, and protein interaction experiments demonstrated that full-length Osf2 does not interact with Cbfbeta, a known partner of Runt-related proteins, whereas a deletion mutant of Osf2 containing only the runt and PST domains does. The QA domain appears to be responsible for preventing this heterodimerization. Thus, our results uncover the unique functional organization of Osf2 by identifying functional domains not shared with other Runt-related proteins that largely control its transactivation and heterodimerization abilities.

Assessment of copper and zinc status in hair and urine of young women descendants of NIDDM parents

The concentration of copper (Cu) and zinc (Zn) in hair and urine were studied in young nonpregnant healthy women whose both parents were diagnosed for noninsulin-dependent diabetes mellitus (NIDDM descendants) and were compared with those of young healthy nonpregnant females with no family history of NIDDM or hypertension (non-NIDDM descendants) and NIDDM patients. The concentration of Zn in hair in NIDDM descendants was significantly higher than that of non-NIDDM descendants (p < 0.001) and insignificantly higher than that of NIDDM patients. The hair Cu concentrations in NIDDM descendant and patients were significantly lower than that of non-NIDDM descendants (p < 0.001). Hyperzincuria was detected in some NIDDM patients and hypocuperuria in all NIDDM descendants and patients. The data suggest that the young healthy NIDDM descendants possess high-Zn and low-Cu reserves in their bodies, and the observed perturbation appears to be associated with Cu-Zn antagonism.

Sero surveillance of HIV infection in high risk groups and in suspected AIDS cases in a New Delhi hospital

A total of 17,824 sera were screened for the presence of HIV 1 + 2 antibodies by Enzyme Immuno Assay (EIA) to determine (i) seroprevalence of HIV infection in hospital high risk groups (ii) time trend of HIV seroprevalence in STD clinic attendees (both STD patients and non STD patients), over a period of six years, (iii) relationship of the STD's with HIV seropositivity (iv) clinical profile and epidemiological characteristics of the AIDS cases. A progressive increase in the HIV seropositive STD patients showing a five fold rise over six years was seen. Most gave history of multipartner sex especially with female CSW's. The most common STD associated with HIV seropositivity was Syphilis followed by Chancroid and Gonorrhoea. All had HIV-1 infection. The AIDS cases (20) presented mainly with tuberculosis, both pulmonary and extrapulmonary. The mode of infection, both in the HIV seropositive and AIDS cases, was mainly heterosexual relationship followed by blood transfusion. In a few cases, infection was perinatally transmitted. In the limited number of HIV positive contacts studied, seven were confirmed as Western Blot positive. HIV infection, although a later introduction in Delhi compared to the coastal cities, has shown a clear increasing trend in the STD patients.

Serum and cerebrospinal fluid concentrations of rifampicin at two dose levels in children with tuberculous meningitis

Twenty patients of tuberculous meningitis (TBM) in age group of 6 months to 10 years included in the study were divided into two groups of 10 patients each. Rifampicin was administered in dosage of 10 mg and 7.5 mg/kg bw to each patient of groups I and II respectively. Drug concentrations in serum and CSF of these patients were measured by a microbiological tube dilution method using a strain of Sarcina lutea. In group I mean serum and CSF concentration was 3.84 micrograms/ml and 0.178 microgram/ml respectively, while in group II it was 2.16 micrograms/ml and 0.206 microgram/ml respectively. These concentrations were many times higher than the MIC against Mycobacterium tuberculosis. Mean percentage penetration of rifampicin in CSF was 5 and 10% in group I and II respectively. We recommend similar studies in large number of children before advocating the therapy with low dose of rifampicin in TBM.

Seroprevalence of cytomegalovirus antibodies in patients attending STD and antenatal clinics

Sera from 368 patients attending sexually transmitted disease (STD) and antenatal clinics were screened for cytomegalovirus (CMV) specific IgG and IgM by indirect ELISA. IgG was detected in 94% of patients tested. CMV IgM seropositivity was found in 8.5% of normal pregnant females and in none of the normal asymptomatic males. CMV-IgM was detected in higher number of patients with STD than in those without STD. There was slightly higher association of CMV IgM antibodies mainly with syphilis in males and chlamydial endocervicitis in females.

Detection of IgM antibodies in pulmonary tuberculosis by ELISA using A60 antigen

An enzyme immunosorbent assay (ELISA) was evaluated as a serodiagnostic test in patients with active tuberculosis (Group I), clinically suspected pulmonary tuberculosis (Group II) and pulmonary diseases other than tuberculosis and normal healthy subjects (Group III). and compared with culture and sputum smear examination results. ELISA was found to have a sensitivity of 77.5% and a specificity of 87.5%. Sputum smear had a sensitivity of 65% and specificity of 100%. In patients clinically suspected to have pulmonary tuberculosis ELISA had a sensitivity of 60%. Thus ELISA using A60 antigen can facilitate the diagnosis of tuberculosis in patients with active as well as suspected pulmonary tuberculosis and can provide results within hours of receipt of samples.

Synergy between vitamin D precursor 25-hydroxyvitamin D and short chain ceramides on keratinocyte proliferation and differentiation

The active vitamin D metabolite, 1,25-dihydroxyvitamin D3 (1,25D), and its analogs induce normal human keratinocyte differentiation and are used for the treatment of psoriasis. Long-term topical use of 1,25D, however, causes hypercalcemia. The precursor of 1,25D, 25-hydroxyvitamin D3 (25D) is converted to 1,25D in the keratinocyte in a regulated manner. The action of 1,25D is reported to be mediated, at least in part, by cellular ceramides in the leukemia cell line, HL-60 cells. Therefore, in this study we evaluated the synergy between 25D and short chain cell permeable ceramides (SCC) or synthetic analogs of ceramides on keratinocyte growth and differentiation in vitro. C2 ceramide (acetyl sphingosine) synergistically enhanced the growth inhibitory effect of 25D and 1,25D in a concentration-dependent manner. Short chain analogs of ceramide-like compounds, neoceramides and pseudoceramides, also inhibited keratinocyte proliferation and acted in synergy with 25D and 1,25D. SCC alone increased transglutaminase and cornified envelope levels. 25D potentiated this prodifferentiating effect of SCC. Twenty-four-hour preincubation with SCC did not alter 25D or 1,25D uptake into keratinocytes. These studies demonstrate a synergy between vitamin D metabolites and ceramides in human keratinocytes and indicate the potential of using 25D as an effective and safer alternative to deliver 1,25D benefits to the epidermis.

Initial and acquired drug resistance of Mycobacterium tuberculosis in east Delhi

One hundred and fifty six strains of Mycobacterium tuberculosis, isolated from cases of pulmonary tuberculosis were subjected to sensitivity test to detect initial and acquired drug resistance to Streptomycin, isoniazid, Rifampicin, Ethambutol and Pyrazinamide. Initial and acquired drug resistance was observed to one or more drugs in 16% and 24.4% of the patients respectively. Strains resistant to Rifampicin and Ethambutol were resistant to Isoniazid also. Drug resistance was unrelated to age and sex of the patients.

Excess bioavailability of zinc may cause obesity in humans

The body weight or body weight/height ratio exhibits a positive linear correlation to hair zinc (Zn) concentration which is more strongly positive in men than in women. The obese of both sexes possess higher Zn concentrations in their hair than those with normal body weight/height. The degree of obesity increases with the increase in the hair Zn concentration.

Serum adenosine deaminase, 5'-nucleotidase & alkaline phosphatase in breast cancer patients

Serum levels of adenosine deaminase (ADA), 5-nucleotidase (5'-NT) and alkaline phosphatase (ALP) were studied in 25 patients of carcinoma breast and 25 normal subjects. Adenosine deaminase was found to be the better probable parameter for the detection of cancer and to assess the development of various stages of cancer whereas 5'-nucleotidase had only diagnostic significance. Serum alkaline phosphatase levels were important for assessing the spread of cancer at secondary sites. After mastectomy a significant decrease was found in the levels of serum ADA and 5'-NT whereas no variations were found in case of serum ALP.