Cyclophilin-D promotes the mitochondrial permeability transition but has opposite effects on apoptosis and necrosis

Cyclophilin-D is a peptidylprolyl cis-trans isomerase of the mitochondrial matrix. It is involved in mitochondrial permeability transition, in which the adenine nucleotide translocase of the inner membrane is transformed from an antiporter to a non-selective pore. The permeability transition has been widely considered as a mechanism in both apoptosis and necrosis. The present study examines the effects of cyclophilin-D on the permeability transition and lethal cell injury, using a neuronal (B50) cell line stably overexpressing cyclophilin-D in mitochondria. Cyclophilin-D overexpression rendered isolated mitochondria far more susceptible to the permeability transition induced by Ca2+ and oxidative stress. Similarly, cyclophilin-D overexpression brought forward the onset of the permeability transition in intact cells subjected to oxidative stress. In addition, in the absence of stress, the mitochondria of cells overexpressing cyclophilin-D maintained a lower inner-membrane potential than those of normal cells. All these effects of cyclophilin-D overexpression were abolished by cyclosporin A. It is concluded that cyclophilin-D promotes the permeability transition in B50 cells. However, cyclophilin-D overexpression had opposite effects on apoptosis and necrosis; whereas NO-induced necrosis was promoted, NO- and staurosporine-induced apoptosis were inhibited. These findings indicate that the permeability transition leads to cell necrosis, but argue against its involvement in apoptosis.

Overexpressed cyclophilin B suppresses apoptosis associated with ROS and Ca2+ homeostasis after ER stress

Prolonged accumulation of misfolded proteins in the endoplasmic reticulum (ER) results in ER stress-mediated apoptosis. Cyclophilins are protein chaperones that accelerate the rate of protein folding through their peptidyl-prolyl cis-trans isomerase (PPIase) activity. In this study, we demonstrated that ER stress activates the expression of the ER-localized cyclophilin B (CypB) gene through a novel ER stress response element. Overexpression of wild-type CypB attenuated ER stress-induced cell death, whereas overexpression of an isomerase activity-defective mutant, CypB/R62A, not only increased Ca(2+) leakage from the ER and ROS generation, but also decreased mitochondrial membrane potential, resulting in cell death following exposure to ER stress-inducing agents. siRNA-mediated inhibition of CypB expression rendered cells more vulnerable to ER stress. Finally, CypB interacted with the ER stress-related chaperones, Bip and Grp94. Taken together, we concluded that CypB performs a crucial function in protecting cells against ER stress via its PPIase activity.

Nitrite accumulation and nitric oxide emission in relation to cellular signaling in nitrite reductase antisense tobacco

An antisense nitrite reductase (NiR, EC 1.7.7.1) tobacco ( Nicotiana tabacum L.) transformant (clone 271) was used to gain insight into a possible correlation between nitrate reductase (NR, EC 1.6.6.1)-dependent nitrite accumulation and nitric oxide (NO(.)) production, and to assess the regulation of signal transduction in response to stress conditions. Nitrite concentrations of clone 271 leaves were 10-fold, and NO(.) emission rates were 100-fold higher than in wild type leaves. Increased protein tyrosine nitration in clone 271 suggests that high NO(.) production resulted in increased peroxynitrite (ONOO(-)) formation. Tyrosine nitration was also observed in vitro by adding peroxynitrite to leaf extracts. As in mammalian cells, NO(.) and derivatives also increased synthesis of proteins like 14-3-3 and cyclophilins, which are both involved in regulation of activity and stability of enzymes.

Cyclophilin D, Somehow a Master Regulator of Mitochondrial Function

Cyclophilin D (CyPD) is an important mitochondrial chaperone protein whose mechanism of action remains a mystery. It is well known for regulating mitochondrial function and coupling of the electron transport chain and ATP synthesis by controlling the mitochondrial permeability transition pore (PTP), but more recent evidence suggests that it may regulate electron transport chain activity. Given its identification as a peptidyl-prolyl, cis-trans isomerase (PPIase), CyPD, is thought to be involved in mitochondrial protein folding, but very few reports demonstrate the presence of this activity. By contrast, CyPD may also perform a scaffolding function, as it binds to a number of important proteins in the mitochondrial matrix and inner mitochondrial membrane. From a clinical perspective, inhibiting CyPD to inhibit PTP opening protects against ischemia⁻reperfusion injury, making modulation of CyPD activity a potentially important therapeutic goal, but the lack of knowledge about the mechanisms of CyPD's actions remains problematic for such therapies. Thus, the important yet enigmatic nature of CyPD somehow makes it a master regulator, yet a troublemaker, for mitochondrial function.

Optimization of an Escherichia coli system for cell-free synthesis of selectively 15N-labelled proteins for rapid analysis by NMR spectroscopy

Cell-free protein synthesis offers rapid access to proteins that are selectively labelled with [15N]amino acids and suitable for analysis by NMR spectroscopy without chromatographic purification. A system based on an Escherichia coli cell extract was optimized with regard to protein yield and minimal usage of 15N-labelled amino acid, and examined for the presence of metabolic by-products which could interfere with the NMR analysis. Yields of up to 1.8 mg of human cyclophilin A per mL of reaction medium were obtained by expression of a synthetic gene. Equivalent yields were obtained using transcription directed by either T7 or tandem phage lambdapR and pL promoters, when the reactions were supplemented with purified phage T7 or E. coli RNA polymerase. Nineteen samples, each selectively labelled with a different 15N-enriched amino acid, were produced and analysed directly by NMR spectroscopy after ultracentrifugation. Cross-peaks from metabolic by-products were evident in the 15N-HSQC spectra of 13 of the samples. All metabolites were found to be small molecules that could be separated readily from the labelled proteins by dialysis. No significant transamination activity was observed except for [15N]Asp, where an enzyme in the cell extract efficiently converted Asp-->Asn. This activity was suppressed by replacing the normally high levels of potassium glutamate in the reaction mixture with ammonium or potassium acetate. In addition, the activity of peptide deformylase appeared to be generally reduced in the cell-free expression system.

High stability of mRNAs postmortem and protocols for their assessment by RT-PCR

Measurement of gene expression is a major area of brain research. We report on the remarkable postmortem stability of a selection of brain mRNAs in both fresh and frozen brain tissue. We describe techniques for extracting total RNA, synthesizing cDNAs from the mRNAs, amplifying specific cDNAs by the polymerase chain reaction technique, and quantitating the products. We chose five genes to study: the housekeeping gene cyclophilin; the complement components C3 and C4; the microtubule associated protein-2 (MAP-2); and the strongly inducible cyclooxygenase COX-2. We found little deterioration in total RNA or in any of the mRNAs in postmortem tissue up to 96 h. When tissue was frozen, stored at -70 degrees C for 15 years and then thawed, there was no evidence of deterioration from storage, but there was gradual deterioration post thawing. All the mRNAs were stable for 1-2 h at 4 degrees C following thawing. Cyclophilin, C3 and C4 mRNAs were still stable after 8 h, MAP-2 and COX-2 mRNAs showed significant deterioration between 2 and 4 h, and COX-2 mRNA showed drastic deterioration between 4 and 8 h. The data give no indication of rapid postmortem degeneration of RNA. Reliable mRNA values may be obtained from postmortem brain with long autolysis times provided the tissue has been kept in the cold, and from frozen tissues for 1-2 h after thawing.

Effects of creatine supplementation on housekeeping genes in human skeletal muscle using real-time RT-PCR

The present study examined the validity and reliability of measuring the expression of various genes in human skeletal muscle using quantitative real-time RT-PCR on a GeneAmp 5700 sequence detection system with SYBR Green 1 chemistry. In addition, the validity of using some of these genes as endogenous controls (i.e., housekeeping genes) when human skeletal muscle was exposed to elevated total creatine levels and exercise was also examined. For all except 28S, linear relationships between the logarithm of the starting RNA concentrations and the cycle threshold (C(T)) values were established for beta-actin, beta2-microglobulin (beta2M), cyclophilin (CYC), and glyceraldehyde-3-phosphate dehydrogenase (GAPDH). We found a linear response between C(T) values and the logarithm of a given amount of starting cDNA for all the genes tested. The overall intra-assay coefficient of variance for these genes was 1.3% and 21% for raw C(T) values and the linear value of 2(-C(T)), respectively. Interassay variability was 2.3% for raw C(T) values and 34% for the linear value of 2(-C(T)). We also examined the expression of various housekeeping genes in human skeletal muscle at days 0, 1, and 5 following oral supplementation with either creatine or a placebo employing a double-blind crossover study design. Treatments were separated by a 5-wk washout period. Immediately following each muscle sampling, subjects performed two 30-s all-out bouts on a cycle ergometer. Creatine supplementation increased (P < 0.05) muscle total creatine content above placebo levels; however, there were no changes (P > 0.05) in C(T) values across the supplementation periods for any of the genes. Nevertheless, 95% confidence intervals showed that GAPDH was variable, whereas beta-actin, beta2M, and CYC were the least varying genes. Normalization of the data to these housekeeping genes revealed variable behavior for beta2M with more stable expressions for both beta-actin and CYC. We conclude that, using real-time RT-PCR, beta-actin or CYC may be used as housekeeping genes to study gene expression in human muscle in experiments employing short-term creatine supplementation combined with high-intensity exercise.

Mitochondrial defects and dysfunction in calcium regulation in glaucomatous trabecular meshwork cells

PURPOSE

Disruption in intracellular calcium ion (Ca(2+)) homeostasis has major effects on health. Persistent Ca(2+) overload induces mitochondrial permeability transition pore (MPTP) opening, which prompts mitochondrial release of calcium (mCICR) and reactive oxygen species (ROS) into the cytosol which, in turn, compromises mitochondrial function. This study was conducted to examine intracellular Ca(2+) levels and mitochondrial vulnerability to Ca(2+) stress in trabecular meshwork (TM) of individuals with primary open-angle glaucoma (POAG).

METHODS

Primary cultures of TM cells from POAG (GTM) and age-matched, nondiseased (NTM) eyes, obtained from postmortem donors eyes by standard surgical trabeculectomy, were treated with the following calcium regulators: the mitochondrial respiratory chain I inhibitor rotenone (ROT); the mitochondrial permeability transition pore (MPTP) inhibitors cyclosporine (Cys) and aristolochic acid (ArA); the Ca(2+) chelators BAPTA/AM or EDTA; the mitochondrial Ca(2+) uniporter inhibitor ruthenium red (RR); the Ca(2+)/Na(+) exchanger inhibitor trifluoperazine; and the inositol 1,4,5-triphosphate receptor type 3 (IP3R) inhibitors 2-aminoethoxydiphenyl borane (2-APB) and xestospongin C (Xe-C). Ca(2+) concentrations in the cytoplasm ([Ca(2+)](c)) and mitochondria ([Ca(2+)](m)) were determined by confocal microscopy and flow cytometry with the fluorescent Ca(2+) indicators fluo-3/AM and rhod-2/AM, respectively. Mitochondrial membrane potential (DeltaPsim) was examined with the fluorescent probe tetramethylrhodamine ethyl ester (TMRE). The expression of cyclophilin D, a protein that induces MPTP opening was also measured.

RESULTS

There was increased [Ca(2+)](c), [Ca(2+)](m), mCICR, MPTP opening, and expression of cyclophilin D and decreased DeltaPsim in POAG TM cells compared with control cells. ROT artificially exacerbated these conditions in GTM cells. Chelation of [Ca(2+)](c) and inhibition of IP3R and MPTP opening suppressed mitochondrial dysfunction and reduced the additional effects of ROT in GTM cells.

CONCLUSIONS

POAG TM cells have defective mitochondrial function, which causes them to be abnormally vulnerable to Ca(2+) stress. The dysfunction in calcium regulation by these cells may contribute to the failure of this tissue to control IOP. Pharmacologic inhibitors of IP3R, MPTP opening, and cyclophilin D could have clinical implications for primary open-angle glaucoma.

Cell surface expression of CD147/EMMPRIN is regulated by cyclophilin 60

CD147, also known as extracellular matrix metalloproteinase inducer, is a regulator of matrix metalloproteinase production and also serves as a signaling receptor for extracellular cyclophilins. Previously, we demonstrated that cell surface expression of CD147 is sensitive to cyclophilin-binding drug cyclosporin A, suggesting involvement of a cyclophilin in the regulation of intracellular transport of CD147. In this report, we identify this cyclophilin as cyclophilin 60 (Cyp60), a distinct member of the cyclophilin family of proteins. CD147 co-immunoprecipitated with Cyp60, and confocal immunofluorescent microscopy revealed intracellular co-localization of Cyp60 and CD147. This interaction with Cyp60 involved proline 211 of CD147, which was shown previously to be critical for interaction between CD147 and another cyclophilin, cyclophilin A, in solution. Mutation of this proline residue abrogated co-immunoprecipitation of CD147 and Cyp60 and reduced surface expression of CD147 on the plasma membrane. Suppression of Cyp60 expression using RNA interference had an effect similar to that of cyclosporin A: reduction of cell surface expression of CD147. These results suggest that Cyp60 plays an important role in the translocation of CD147 to the cell surface. Therefore, Cyp60 may present a novel target for therapeutic interventions in diseases where CD147 functions as a pathogenic factor, such as cancer, human immunodeficiency virus infection, or rheumatoid arthritis.

Curcumin-induced melanoma cell death is associated with mitochondrial permeability transition pore (mPTP) opening

Here we studied the role of mitochondrial permeability transition pore (mPTP) opening in curcumin's cytotoxicity in melanoma cells. In cultured WM-115 melanoma cells, curcumin induced mitochondrial membrane potential (MPP) decrease, cyclophilin-D (CyPD)-adenine nucleotide translocator 1 (ANT-1) (two mPTP components) mitochondrial association and cytochrome C release, indicating mPTP opening. The mPTP blocker sanglifehrin A (SfA) and ANT-1 siRNA-depletion dramatically inhibited curcumin-induced cytochrome C release and WM-115 cell death. CyPD is required for curcumin-induced melanoma cell death. The CyPD inhibitor cyclosporin A (CsA) or CyPD siRNA-depletion inhibited curcumin-induced WM-115 cell death and apoptosis, while WM-115 cells with CyPD over-expression were hyper-sensitive to curcumin. Finally, we found that C6 ceramide enhanced curcumin-induced cytotoxicity probably through facilitating mPTP opening, while CsA and SfA as well as CyPD and ANT-1 siRNAs alleviated C6 ceramide's effect on curcumin in WM-115 cells. Together, these results suggest that curcumin-induced melanoma cell death is associated with mPTP opening.

Increased expression and intramitochondrial translocation of cyclophilin-D associates with increased vulnerability of the permeability transition pore to stress-induced opening during compensated ventricular hypertrophy

Opening of the permeability transition pore (PTP) of mitochondria is a critical permeation event that compromises cell viability and may constitute a factor that participates to the loss of cardiomyocytes in compromised hearts. Mitochondria from hearts with volume overload-induced compensated hypertrophy are more vulnerable to opening of the PTP opening in response to a Ca2+ stress. Several of the factors known to affect PTP opening, including respiratory function, membrane potential, the rate of mitochondrial Ca2+ uptake and endogenous levels of Ca2+ in the mitochondrial matrix, were not altered by volume overload. In contrast, there was an 80% increase in the abundance of the PTP regulating protein cyclophilin-D and a 3.7 fold enhancement of Cyp-D binding to membrane, which all predispose to PTP opening. Mitochondria from volume overloaded animals also displayed elevated rates of production of reactive oxygen species, which may be causally related to both the intramitochondrial translocation of cyclophilin-D and PTP opening, since incubation of cardiac mitochondria with terbutylhydroperoxyde in vitro increased to binding of cyclophilin-D to mitochondrial membranes in a dose-related fashion, except when cyclosporin A (a ligand of cyclophilin D with a known ability to delay PTP opening) was present prior to the addition of terbutylhydroperoxyde. Taken together, these results constitute the first evidence obtained in a pathophysiologic situation that increased abundance of cyclophilin-D within mitochondrial membranes may increase mitochondrial vulnerability to stress, and thus possibly initiate a vicious cycle of cellular dysfunction that may ultimately lead to activation of cell death.

Growth hormone induces eNOS expression and nitric oxide release in a cultured human endothelial cell line

Growth hormone deficiency is linked to cardiovascular disease and particularly increased peripheral vascular resistance. Surprisingly, its role in endothelial nitric oxide (NO) synthetase (eNOS) regulation and NO release is basically unknown. We therefore studied the effects of different doses of somatotropin in cultures of a human endothelial cell line (EAhy926). We investigated expression and activity of eNOS, as well as other target genes known to be deregulated in cardiovascular disease including E-selectin and the lectin-like oxidized low density lipoprotein receptor. Treatment of cultured human endothelial cells with somatotropin resulted in significant (P<0.05) increases of eNOS gene and protein expression, as well as NO release, whereas production of intracellular reactive oxygen species was significantly reduced, at the highest somatotropin dose level. The enhanced eNOS gene/protein expression and enzyme activity correlate well. Our findings are suggestive for a novel role of growth hormone in endothelial biology, and particularly NO production.

Thermodynamic characterization of the interaction of human cyclophilin 18 with cyclosporin A

Isothermal titration calorimetry (ITC) was used to investigate thermodynamic parameters of the cyclosporin A (CsA)-cyclophilin 18 (hCyp18) association reaction. We have calculated the thermodynamic parameters (enthalpy, entropy, heat capacity, and free energy of binding) of the CsA/hCyp18 complexation. All but two methods described in the literature underestimate the affinity to hCyp18 of CsA. We found that the association constant (1.1.10(8) M(-1) at 10 degrees C) of CsA to hCyp18 is in close agreement with the reciprocal of the reported inhibitory constant of the peptidylprolyl cis/trans isomerase activity of hCyp18. Interpretation of the thermodynamic parameters in buffered solution of water, 30% glycerol and D(2)O leads to the conclusion that the highly specific binding of CsA to hCyp18 is mainly mediated through hydrogen bonding and to a lesser degree through hydrophobic interaction. Furthermore, the pH dependence of the association constant was determined and analyzed according to a single proton linkage model, resulting in a pK(a) value of 5.7 in free hCyp18 and below 4.5 in the CsA complexed form. Titration experiments using different single component buffers possessing different heats of ionization allowed us to estimate that statistically half a proton is transferred upon CsA binding from the binding interface of hCyp18 to the buffer at pH 5.5. No proton transfer was detected at pH 7.5. The thermodynamic results are discussed in relation to the published X-ray and NMR structure of the free and CsA complexed hCyp18.

Influence of an altered methylation potential on mRNA methylation and gene expression in HepG2 cells

S-adenosylhomocysteine (AdoHcy), a by-product and inhibitor of S-adenosylmethionine (AdoMet)-dependent methylation reactions, is removed by AdoHcy hydrolase. The ratio of AdoMet and AdoHcy, also termed methylation potential (MP), is a metabolic indicator for cellular methylation status. In the present study, we have investigated the influence of hypoxia and inhibition of AdoHcy hydrolase on MP in HepG2 cells. Furthermore, we studied the impact of deviations in MP on mRNA and DNA methylation and the expression of selected genes: erythropoietin, VEGF-A, AdoHcy hydrolase, cyclophilin, and HIF-1alpha. Under hypoxic conditions, the MP raised from 53.4 +/- 3.3 to 239.4 +/- 24.8, which is the result of increased AdoMet and decreased AdoHcy levels. Inhibition of AdoHcy hydrolase by adenosine-2',3'-dialdehyde leads to a 40-fold reduction of the MP under both normoxic and hypoxic conditions. Hypoxia increases erythropoietin (2.7-fold) and VEGF-A (5-fold) mRNA expression. During a reduced MP erythropoietin mRNA expression is lowered under normoxia and hypoxia by 70%, whereas VEGF-A mRNA expression is only reduced under hypoxic conditions by 60%. The mRNA expression of AdoHcy hydrolase, HIF-1alpha, and cyclophilin is insensitive to an altered MP. Furthermore, decreased MP leads to a highly significant decrease in overall mRNA methylation. Our results show that the mRNA levels of the studied genes respond differentially to changes in MP. This implies that genes with a slower transcription rate and mRNAs with a slower turnover are insensitive to short-term changes in MP.

Dopamine D1 and D2 receptor mRNA up-regulation in the caudate-putamen and nucleus accumbens of rat brains by smoking

Nicotine, the toxic substance that is exclusively absorbed from smoking, produces a wide array of behavior and collectively propels drug-seeking behaviors when abused. The neurotransmitter dopamine (DA) is important in the reward and reinforcing properties of many addictive drugs: however, the effect of nicotine by cigarette smoking itself on the expression of DA receptors in the caudate-putamen (CPu), nucleus accumbens (NAc) and olfactory tubercle (OTu) has not been elucidated completely. Hence, the effects of smoking and nicotine on DA receptors need to be defined. In this research, the effect of smoking and nicotine addiction on the DA D1 and D2 receptors in the rat CPu, NAc and OTu were studied. Adult male Spraque-Dawley (S.D., n=50) rats were administered with cigarette smoke (passive inhaled for 10 min and 1 h, 500 ml x 3 times/day, 4 weeks) and nicotine (oral, 3 mg/day). DA D1 and D2 receptor mRNA levels were determined by in situ hybridization and RNase protection assay (RPA). In the smoking groups (10 min and 1 h), DA D1 and D2 receptor mRNA greatly increased in the CPu and NAc, and most of all in the NAc. The nicotine treated group showed increased expression of DA D1 and D2 receptor mRNA too, but statistically less than in the smoking group. In the smoking group, DA D1 and D2 receptor mRNA levels were significantly higher in the CPu and NAc than in the nicotine group (P<.01). These results suggest that smoking and nicotine administration both influence DA receptor mRNAs in the CPu, NAc and OTu, in terms of up-regulation. The up-regulation was much more evident in the smoking group than in the nicotine group. In conclusion, we believe that smoking up-regulate the DA receptor mRNA expression significantly higher in rat CPu and NAc than nicotine but only a little bit higher in OTu.

Oligo-microarray analysis reveals the role of cyclophilin A in drug resistance

Cyclophilin A (CYPA) belongs to peptidyl prolyl isomerases (PPIases), which catalyze the cis/trans isomerization of prolyl peptide bonds in cellular communication. CYPA has been implicated in several pathological processes, including cancer, inflammatory diseases, and HIV-1 infection. Up-regulation of CYPA has been found to be a common phenomenon in several tumor types, including in hepatocellular carcinoma (HCC). However, the role of CYPA in tumor cells remains unknown. We generated a stable SK-Hep1 cell line and studied the CYPA regulated genes at the transcriptome level. The microarray results reveal that CYPA can up-regulate the expression of many cytokine and drug resistance related genes. Furthermore, we showed that the elevated CYPA expression contributes to drug resistance. We postulate that the over-expression of CYPA in tumors may play a role in clinical resistance to chemotherapy.

Molecular and physiological properties associated with zebra complex disease in potatoes and its relation with Candidatus Liberibacter contents in psyllid vectors

Zebra complex (ZC) disease on potatoes is associated with Candidatus Liberibacter solanacearum (CLs), an α-proteobacterium that resides in the plant phloem and is transmitted by the potato psyllid Bactericera cockerelli (Šulc). The name ZC originates from the brown striping in fried chips of infected tubers, but the whole plants also exhibit a variety of morphological features and symptoms for which the physiological or molecular basis are not understood. We determined that compared to healthy plants, stems of ZC-plants accumulate starch and more than three-fold total protein, including gene expression regulatory factors (e.g. cyclophilin) and tuber storage proteins (e.g., patatins), indicating that ZC-affected stems are reprogrammed to exhibit tuber-like physiological properties. Furthermore, the total phenolic content in ZC potato stems was elevated two-fold, and amounts of polyphenol oxidase enzyme were also high, both serving to explain the ZC-hallmark rapid brown discoloration of air-exposed damaged tissue. Newly developed quantitative and/or conventional PCR demonstrated that the percentage of psyllids in laboratory colonies containing detectable levels of CLs and its titer could fluctuate over time with effects on colony prolificacy, but presumed reproduction-associated primary endosymbiont levels remained stable. Potato plants exposed in the laboratory to psyllid populations with relatively low-CLs content survived while exposure of plants to high-CLs psyllids rapidly culminated in a lethal collapse. In conclusion, we identified plant physiological biomarkers associated with the presence of ZC and/or CLs in the vegetative potato plant tissue and determined that the titer of CLs in the psyllid population directly affects the rate of disease development in plants.

Quantitative proteomic analysis of cyclosporine-induced toxicity in a human kidney cell line and comparison with tacrolimus

The calcineurin-inhibitors (CNIs) cyclosporine (CsA) and tacrolimus (TAC) remain the pillars of modern immunosuppression regimens used in solid organ transplantation. Nephrotoxicity is an adverse effect that limits their successful use. The precise molecular mechanisms underlying this nephrotoxicity remain unclear. Using SILAC together with LC-MALDI-TOF/TOF, we investigated the CNIs-induced proteomic perturbations in renal cells. Among the 495 proteins quantifiable in both forward and reverse SILAC, 69 displayed CsA-induced perturbations: proteins involved in ER-stress/protein folding, apoptosis, metabolism/transport or cytoskeleton pathways were up-regulated, while cyclophilin B as well as nuclear and RNA-processing proteins were down-regulated. Co-administration of CsA with the antioxidant N-acetylcysteine significantly decreased lipid peroxidation and also partially corrected the CsA-induced unfolded protein response. TAC toxicity profile was apparently different from that of CsA, especially without perturbation of cyclophilins A and B, up-regulation of ER-chaperones nor down-regulation of a number of nuclear proteins. These results provide a new insight and are consistent with recent data regarding the molecular mechanisms of CNIs-induced nephrotoxicity. Our findings offer new directions for future research aiming to identify specific biomarkers of CsA nephrotoxicity.

Differential gene expression in Arachis diogoi upon interaction with peanut late leaf spot pathogen, Phaeoisariopsis personata and characterization of a pathogen induced cyclophilin

The wild relatives of peanut are resistant to various economically important diseases including late leaf spot (LLS) caused by Phaeoisariopsis personata, compared with the susceptible cultivated peanut (Arachis hypogaea L.). The interaction of the late leaf spot pathogen, Phaeoisariopsis personata and the highly resistant, diploid peanut wild species, Arachis diogoi was analyzed at the molecular level by differential gene expression studies. Genes up-regulated with in 48 h of pathogen challenge were isolated as partial cDNAs. Some of the isolated genes, which are shown to be involved in the first line of defense in plants, were further characterized with respect to their transcriptional regulation in response to pathogen. Among the isolated clones, two were found to encode cyclophilin like proteins. One of the two isolated partial cDNAs encoding cyclophilin like proteins was extended using 5' RACE. The full length cDNA, designated as AdCyp, was 886 bp in length and encodes a polypeptide of 172 amino acids. Southern hybridization suggests that AdCyp is possibly coded by a single gene and at least one more identical gene is present in Arachis diogoi genome. AdCyp exhibits evolutionary conservation across the kingdoms. Phylogenetic analysis showed that AdCyp belongs to the subgroup I of Group I in cyclophilins. A translational fusion of GFP-AdCyp was found to localize to both cytosol and nucleus. AdCyp transcripts were found to accumulate in response to the treatments with pathogen as well as phytohormones. Constitutive heterologous expression of AdCyp resulted in enhanced resistance to Ralstonia solanacearum and reduced susceptibility towards Phytophthora parasitica var. nicotianae in transgenic tobacco and the resistance was associated with higher transcript levels of various defense related genes.

Cyclophilin B stimulates RNA synthesis by the HCV RNA dependent RNA polymerase

Cyclophilins are cellular peptidyl isomerases that have been implicated in regulating hepatitis C virus (HCV) replication. Cyclophilin B (CypB) is a target of cyclosporin A (CsA), an immunosuppressive drug recently shown to suppress HCV replication in cell culture. Watashi et al. recently demonstrated that CypB is important for efficient HCV replication, and proposed that it mediates the anti-HCV effects of CsA through an interaction with NS5B [Watashi K, Ishii N, Hijikata M, Inoue D, Murata T, Miyanari Y, et al. Cyclophilin B is a functional regulator of hepatitis C virus RNA polymerase. Mol Cell 2005;19:111-22]. We examined the effects of purified CypB proteins on the enzymatic activity of NS5B. Recombinant CypB purified from insect cells directly stimulated NS5B-catalyzed RNA synthesis. CypB increased RNA synthesis by NS5B derived from genotype 1a, 1b, and 2a HCV strains. Stimulation appears to arise from an increase in productive RNA binding. NS5B residue Pro540, a previously proposed target of CypB peptidyl-prolyl isomerase activity, is not required for stimulation of RNA synthesis.

Cyclosporine inhibits mouse cytomegalovirus infection via a cyclophilin-dependent pathway specifically in neural stem/progenitor cells

The potential of neural stem and progenitor cell (NSPC) transplantation in neurodegenerative disease raises a concern about immunosuppressive agents and opportunistic neurotropic pathogens that may interfere with engraftment. Cytomegalovirus (CMV) is an important opportunistic pathogen infecting the central nervous system, where it may remain latent for life, following transplacental transmission. Cyclosporine (Cs), an immunosuppressive drug used in organ transplantation, where its use is associated with CMV reactivation, suppressed murine CMV (MCMV) infection in cultured NSPCs but not in fibroblasts. This activity of Cs appears to be mediated via cyclophilin (CyP) rather than via calcineurin. First, the calcineurin-specific inhibitor FK506 failed to suppress replication. Second, the CyP-specific inhibitor NIM811 strongly suppressed replication in NSPC. NSPCs maintained in the presence of NIM811 retained viral genomes for several weeks without detectable viral gene expression or obvious deleterious effects. The withdrawal of NIM811 reactivated viral replication, suggesting that the inhibitory mechanism was reversible. Finally, inhibition of endogenous CyP A (CyPA) by small interfering RNA also inhibited replication in NSPCs. These results show that MCMV replication depends upon cellular CyPA pathways in NSPCs (in a specific cell type-dependent fashion), that CyPA plays an important role in viral infection in this cell type, and that inhibition of viral replication via CyP leads to persistence of the viral genome without cell damage. Further, the calcineurin-signaling pathway conferring immunosuppression in T cells does not influence viral replication in a detectable fashion.

Modulation of cyclophilin gene expression by N-4-(hydroxyphenyl)retinamide: association with reactive oxygen species generation and apoptosis

To explore the mechanisms underlying the pro-apoptotic effects of the synthetic retinoid N-4-(hydroxyphenyl)retinamide (4-HPR) on LNCaP human prostate cancer cells, we used the differential display-polymerase chain reaction (DD-PCR) technique to identify 4-HPR-responsive genes. RNA extracted from LNCaP cells that had been treated for 24 h with 4-HPR at a dose (2.5 microM) optimal for apoptosis induction was used for DD-PCR analysis using random primers. A differentially expressed 115 bp fragment was cloned and sequenced and then identified in GenBank as having a high degree of homology with several members of the cyclophilin gene family. Northern blot analyses using specific probes for cyclophilin A, cyclophilin D, and the cloned 115-bp fragment were performed on RNA extracted from LNCaP cells and MCF-7 human breast cancer cells treated with 4-HPR, N-acetylcysteine (NAC, an anti-oxidant), 4-HPR plus NAC, cyclosporin A, R-1881 (a synthetic androgen), dehydroepiandrosterone, all-trans retinoic acid, or prednisone. 4-HPR downregulated the transcript detected by the 115-bp fragment. Expression patterns detected by the 115-bp fragment and cyclophilin D probes were identical in response to each treatment; none of these treatments affected cyclophilin A expression. Furthermore, expression of mRNA transcripts detected by the 115-bp fragment and cyclophilin D probes correlated with the generation of reactive oxygen species (ROS), as detected by measurement of 2,7-dichlorofluorescein oxidation. Therefore, members of the cyclophilin gene family, such as cyclophilin D (a component of the mitochondrial permeability transition pore previously linked with oxidative stress and apoptosis), may play a role in the ROS-mediated apoptotic effects of 4-HPR.

Involvement of brain natriuretic peptide signaling pathway in the cardioprotective action of sitagliptin

BACKGROUND

The current study is focusing on the role of brain natriuretic peptide (BNP), a substrate of dipeptidyl peptidase-4 (DPP-4) enzyme, and its signaling survival pathway in the cardioprotective mechanism of sitagliptin, a DPP-4 inhibitor.

METHODS

Male Wistar rats were randomized into 7 groups, sham, I/R, KT-5823 (selective protein kinase (PK) G inhibitor), 5-HD (selective mito-KATP channel blocker), sitagliptin (300mg/kg, po), sitagliptin+KT-5823, and sitagliptin+5-HD. Sitagliptin was administered for 3 days prior to induction of coronary I/R, while either KT-5823 or 5-HD was administered intravenously 5min before coronary ligation.

RESULTS

Pretreatment with sitagliptin provided significant protection against I/R injury as manifested by decreasing, percentage of infarct size, suppressing the elevated ST segment, reducing the increased cardiac enzymes, as well as DPP-4 activity and elevating both heart rate (HR) and left ventricular developed pressure (LVDP). However, the addition of either blocker to sitagliptin regimen reversed partly its cardioprotective effects. Although I/R increased BNP content, it unexpectedly decreased that of cGMP; nevertheless, sitagliptin elevated both parameters, an effect that was not affected by the use of the two blockers. On the molecular level, sitagliptin decreased caspase-3 activity and downregulated the mRNA levels of BNP, Bax, and Cyp D, while upregulated that of Bcl2. The use of either KT-5823 or 5-HD with sitagliptin hindered its effect on the molecular markers tested.

CONCLUSIONS

The results of the present study suggest that the cardioprotective effect of sitagliptin is mediated partly, but not solely, through the BNP/cGMP/PKG survival signaling pathway.

Splicing factors differentially expressed in psoriasis alter mRNA maturation of disease-associated EDA+ fibronectin

The EDA+ fibronectin splicing variant is overexpressed in psoriatic non-lesional epidermis and sensitizes keratinocytes to mitogenic signals. However, regulation of its abundance is only partially understood. In our recent cDNA microarray experiment, we identified three SR-rich splicing factors-splicing factor, arginine/serine-rich 18 (SFRS18), peptidyl-prolyl cis-trans isomerase G (PPIG), and luc-7 like protein 3 (LUC7L3)-which might be implicated in the preactivated states of keratinocytes in psoriatic non-involved skin and could also contribute to the regulation of fibronectin mRNA maturation. In this study, we investigated the role of LUC7L3, PPIG, and SFRS18 in psoriasis and in the mRNA maturation process of fibronectin. Regarding tissue staining experiments, we were able to demonstrate a characteristic distribution of the splicing factors in healthy, psoriatic non-involved and involved epidermis. Moreover, the expression profiles of these SR-rich proteins were found to be very similar in synchronized keratinocytes. Contribution of splicing facwwtors to the EDA+ fibronectin formation was also confirmed: their siRNA silencing leads to altered fibronectin mRNA and protein expression patterns, suggesting the participation in the EDA domain inclusion. Our results indicate that LUC7L3, PPIG, and SFRS18 are not only implicated in EDA+ fibronectin formation, but also that they could possess multiple roles in psoriasis-associated molecular abnormalities.