Mesenchymal Stromal Cell-Based Therapy: New Perspectives and Challenges.

Stem cells have been the focus of intense research opening up new possibilities for the treatment of various diseases. Mesenchymal stromal cells (MSCs) are multipotent cells with relevant immunomodulatory properties and are thus considered as a promising new strategy for immune disease management. To enhance their efficiency, several issues related to both MSC biology and functions are needed to be identified and, most importantly, well clarified. The sources from which MSCs are isolated are diverse and might affect their properties. Both clinicians and scientists need to handle a phenotypic-characterized population of MSCs, particularly regarding their immunological profile. Moreover, it is now recognized that the tissue-reparative effects of MSCs are based on their immunomodulatory functions that are activated following a priming/licensing step. Thus, finding the best ways to pre-conditionate MSCs before their injection will strengthen their activity potential. Finally, soluble elements derived from MSC-secretome, including extracellular vesicles (EVs), have been proposed as a cell-free alternative tool for therapeutic medicine. Collectively, these features have to be considered and developed to ensure the efficiency and safety of MSC-based therapy. By participating to this Special Issue "Mesenchymal Stem/Stromal Cells in Immunity and Disease", your valuable contribution will certainly enrich the content and discussion related to the thematic of MSCs.

Empowering the immune fate of bone marrow mesenchymal stromal cells: gene and protein changes.

OBJECTIVE AND DESIGN: Bone marrow mesenchymal stromal cells (BM-MSCs) are referred as a promising immunotherapeutic cell product. New approaches using empowered MSCs should be developed as for the treatment or prevention of different immunological diseases. Such preconditioning by new licensing stimuli will empower the immune fate of BM-MSCs and, therefore, promote a better and more efficient biological. Here, our main goal was to establish the immunological profile of BM-MSCs following inflammatory priming and in particular their capacity to adjust their immune-related proteome and transcriptome. MATERIAL AND METHODS: To run this study, we have used BM-MSC cell cultures, a pro-inflammatory cytokine cocktail priming, flow cytometry analysis, qPCR and ELISA techniques. RESULTS: Different expression levels of several immunological mediators such as COX-1, COX-2, LIF, HGF, Gal-1, HO-1, IL-11, IL-8, IL-6 and TGF-ß were constitutively observed in BM-MSCs. Inflammation priming substantially but differentially modulated the gene and protein expression profiles of these mediators. Thus, expressions of COX-2, LIF, HGF, IL-11, IL-8 and IL-6 were highly increased/induced and those of COX-1, Gal-1, and TGF-ß were reduced. CONCLUSIONS: Collectively, we demonstrated that BM-MSCs are endowed with a specific and modular regulatory machinery which is potentially involved in immunomodulation. Moreover, BM-MSCs are highly sensitive to inflammation and respond to such signal by properly adjusting their gene and protein expression of regulatory factors. Using such preconditioning may empower the immune fate of MSCs and, therefore, enhance their value for cell-based immunotherapy.

Exacerbation of Aging-Associated and Instability-Induced Murine Osteoarthritis With Deletion of D Prostanoid Receptor 1, a Prostaglandin D2 Receptor.

OBJECTIVE: D prostanoid receptor 1 (DP1), a receptor for prostaglandin D2 , plays important roles in inflammation and cartilage metabolism. However, its role in the pathogenesis of osteoarthritis (OA) remains unknown. This study was undertaken to explore the roles of DP1 in the development of OA in murine models and to evaluate the efficacy of a DP1 selective agonist in the treatment of OA. METHODS: The development of aging-associated OA and destabilization of the medial meniscus (DMM)-induced OA was compared between DP1-deficient (DP1-/- ) and wild-type (WT) mice. The progression of OA was assessed by histology, immunohistochemistry, and micro-computed tomography. Cartilage explants from DP1-/- and WT mice were treated with interleukin-1α (IL-1α) ex vivo, to evaluate proteoglycan degradation. The effect of intraperitoneal administration of the DP1 selective agonist BW245C on OA progression was evaluated in WT mice. RESULTS: Compared to WT mice, DP1-/- mice had exacerbated cartilage degradation in both models of OA, and this was associated with increased expression of matrix metalloproteinase 13 and ADAMTS-5. In addition, DP1-/- mice demonstrated enhanced subchondral bone changes. Cartilage explants from DP1-/- mice showed enhanced proteoglycan degradation following treatment with IL-1α. Intraperitoneal injection of BW245C attenuated the severity of DMM-induced cartilage degradation and bony changes in WT mice. CONCLUSION: These findings indicate a critical role for DP1 signaling in OA pathogenesis. Modulation of the functions of DP1 may constitute a potential therapeutic target for the development of novel OA treatments.

Lysine-specific demethylase 1-mediated demethylation of histone H3 lysine 9 contributes to interleukin 1ß-induced microsomal prostaglandin E synthase 1 expression in human osteoarthritic chondrocytes.

INTRODUCTION: Microsomal prostaglandin E synthase 1 (mPGES-1) catalyzes the terminal step in the biosynthesis of PGE2, a critical mediator in the pathophysiology of osteoarthritis (OA). Histone methylation plays an important role in epigenetic gene regulation. In this study, we investigated the roles of histone H3 lysine 9 (H3K9) methylation in interleukin 1ß (IL-1ß)-induced mPGES-1 expression in human chondrocytes. METHODS: Chondrocytes were stimulated with IL-1ß, and the expression of mPGES-1 mRNA was evaluated using real-time RT-PCR. H3K9 methylation and the recruitment of the histone demethylase lysine-specific demethylase 1 (LSD1) to the mPGES-1 promoter were evaluated using chromatin immunoprecipitation assays. The role of LSD1 was further evaluated using the pharmacological inhibitors tranylcypromine and pargyline and small interfering RNA (siRNA)-mediated gene silencing. The LSD1 level in cartilage was determined by RT-PCR and immunohistochemistry. RESULTS: The induction of mPGES-1 expression by IL-1ß correlated with decreased levels of mono- and dimethylated H3K9 at the mPGES-1 promoter. These changes were concomitant with the recruitment of the histone demethylase LSD1. Treatment with tranylcypromine and pargyline, which are potent inhibitors of LSD1, prevented IL-1ß-induced H3K9 demethylation at the mPGES-1 promoter and expression of mPGES-1. Consistently, LSD1 gene silencing with siRNA prevented IL-1ß-induced H3K9 demethylation and mPGES-1 expression, suggesting that LSD1 mediates IL-1ß-induced mPGES-1 expression via H3K9 demethylation. We show that the level of LSD1 was elevated in OA compared to normal cartilage. CONCLUSION: These results indicate that H3K9 demethylation by LSD1 contributes to IL-1ß-induced mPGES-1 expression and suggest that this pathway could be a potential target for pharmacological intervention in the treatment of OA and possibly other arthritic conditions.

Expression of peroxisome proliferator-activated receptors α, ß, γ, and H- and L-prostaglandin D synthase during osteoarthritis in the spontaneous hartley guinea pig and experimental dog models.

OBJECTIVE: To investigate the expression of peroxisome proliferator-activated receptors (PPAR) α, ß, and γ, and hematopoietic and lipocalin-type prostaglandin D synthase (H- and L-PGDS) over the course of osteoarthritis (OA) in the spontaneous Hartley guinea pig and the anterior cruciate ligament transection dog models. METHODS: Guinea pigs were sacrificed at 2 (control group), 4, 8, and 12 months of age (n = 5 per group). Non-operated (control) and operated dogs were sacrificed at 4, 8, and 12 weeks postsurgery. Cartilage was evaluated histologically using the Osteoarthritis Research Society International (OARSI) guidelines. The expression of PPAR-α, ß, γ, and H- and L-PGDS was evaluated by real-time PCR and immunohistochemistry. The nonparametric Spearman test was used for correlation analysis. RESULTS: PPAR-α, ß, and γ were detected in medial tibial plateau from control animals in both the spontaneous and surgical models. Levels of PPAR-α and ß did not change over the course of OA, whereas PPAR-γ levels decreased during progression of disease. We also observed that the expression of H-PGDS remained unchanged, whereas L-PGDS increased over the course of OA. PPAR-γ levels correlated negatively, whereas L-PGDS levels correlated positively, with the histological score of OA. CONCLUSION: The level of PPAR-γ decreased, whereas level of L-PGDS increased during the progression of OA. These data suggest that reduced expression of PPAR-γ may contribute to the pathogenesis of OA, whereas enhanced expression of L-PGDS may be part of a reparative process.

Egr-1 contributes to IL-1-mediated down-regulation of peroxisome proliferator-activated receptor γ expression in human osteoarthritic chondrocytes.

INTRODUCTION: Peroxisome proliferator-activated receptor (PPAR)γ has been shown to exhibit anti-inflammatory and anti-catabolic properties and to be protective in animal models of osteoarthritis (OA). We have previously shown that interleukin-1ß (IL-1) down-regulates PPARγ expression in human OA chondrocytes. However, the mechanisms underlying this effect have not been well characterized. The PPARγ promoter harbors an overlapping Egr-1/specificity protein 1 (Sp1) binding site. In this study, our objective was to define the roles of Egr-1 and Sp1 in IL-1-mediated down-regulation of PPARγ expression. METHODS: Chondrocytes were stimulated with IL-1 and the expression levels of Egr-1 and Sp1 mRNAs and proteins were evaluated using real-time reverse transcriptase-polymerase chain reaction (RT-PCR) and Western blotting, respectively. The role of de novo protein synthesis was evaluated using the protein synthesis inhibitor cycloheximide (CHX). The recruitment of Sp1 and Egr-1 to the PPARγ promoter was evaluated using chromatin immunoprecipitation (ChIP) assays. The PPARγ promoter activity was analyzed in transient transfection experiments. The roles of Egr-1 and Sp1 were further evaluated using small interfering RNA (siRNA) approaches. The level of Egr-1 in cartilage was determined using immunohistochemistry. RESULTS: Down-regulation of PPARγ expression by IL-1 requires de novo protein synthesis and was concomitant with the induction of the transcription factor Egr-1. Treatment with IL-1 induced Egr-1 recruitment and reduced Sp1 occupancy at the PPARγ promoter. Overexpression of Egr-1 potentiated, whereas overexpression of Sp1 alleviated, the suppressive effect of IL-1 on the PPARγ promoter, suggesting that Egr-1 may mediate the suppressive effect of IL-1. Consistently, Egr-1 silencing prevented IL-1-mediated down-regulation of PPARγ expression. We also showed that the level of Egr-1 expression was elevated in OA cartilage compared to normal cartilage. CONCLUSIONS: Our results indicate that induction and recruitment of Egr-1 contributed to the suppressive effect of IL-1 on PPARγ expression. They also suggest that modulation of Egr-1 levels in the joint may have therapeutic potential in OA.

Inhibition of interleukin-1beta-induced matrix metalloproteinases 1 and 13 production in human osteoarthritic chondrocytes by prostaglandin D2.

OBJECTIVE: To investigate the effects of prostaglandin D2 (PGD2) on interleukin-1beta (IL-1beta)-induced matrix metalloproteinase 1 (MMP-1) and MMP-13 expression in human chondrocytes and the signaling pathways involved in these effects. METHODS: Chondrocytes were stimulated with IL-1 in the presence or absence of PGD2, and expression of MMP-1 and MMP-13 proteins was evaluated by enzyme-linked immunosorbent assay. Messenger RNA (mRNA) expression and promoter activity were analyzed by real-time reverse transcription-polymerase chain reaction and transient transfections, respectively. The role of the PGD2 receptors D prostanoid receptor 1 (DP1) and chemoattractant receptor-like molecule expressed on Th2 cells (CRTH2) was evaluated using specific agonists and antibody-blocking experiments. The contribution of the cAMP/protein kinase A (PKA) pathway was determined using cAMP-elevating agents and PKA inhibitors. RESULTS: PGD2 decreased in a dose-dependent manner IL-1-induced MMP-1 and MMP-13 protein and mRNA expression as well as their promoter activation. DP1 and CRTH2 were expressed and functional in chondrocytes. The effect of PGD2 was mimicked by BW245C, a selective agonist of DP1, but not by 13,14-dihydro-15-keto-PGD2, a selective agonist of CRTH2. Furthermore, treatment with an anti-DP1 antibody reversed the effect of PGD2, indicating that the inhibitory effect of PGD2 is mediated by DP1. The cAMP-elevating agents 8-Br-cAMP and forskolin suppressed IL-1-induced MMP-1 and MMP-13 expression, and the PKA inhibitors KT5720 and H89 reversed the inhibitory effect of PGD2, suggesting that the effect of PGD2 is mediated by the cAMP/PKA pathway. CONCLUSION: PGD2 inhibits IL-1-induced production of MMP-1 and MMP-13 by chondrocytes through the DP1/cAMP/PKA signaling pathway. These data also suggest that modulation of PGD2 levels in the joint may have therapeutic potential in the prevention of cartilage degradation.

Peroxisome proliferator-activated receptor gamma1 expression is diminished in human osteoarthritic cartilage and is downregulated by interleukin-1beta in articular chondrocytes.

Peroxisome proliferator-activated receptor gamma (PPARgamma) is a nuclear receptor involved in the regulation of many cellular processes. We and others have previously shown that PPARgamma activators display anti-inflammatory and chondroprotective properties in vitro and improve the clinical course and histopathological features in an experimental animal model of osteoarthritis (OA). However, the expression and regulation of PPARgamma expression in cartilage are poorly defined. This study was undertaken to investigate the quantitative expression and distribution of PPARgamma in normal and OA cartilage and to evaluate the effect of IL-1beta, a prominent cytokine in OA, on PPARgamma expression in cultured chondrocytes. Immunohistochemical analysis revealed that the levels of PPARgamma protein expression were significantly lower in OA cartilage than in normal cartilage. Using real-time RT-PCR, we demonstrated that PPARgamma1 mRNA levels were about 10-fold higher than PPARgamma2 mRNA levels, and that only PPARgamma1 was differentially expressed: its levels in OA cartilage was 2.4-fold lower than in normal cartilage (p < 0.001). IL-1 treatment of OA chondrocytes downregulated PPARgamma1 expression in a dose- and time-dependent manner. This effect probably occurred at the transcriptional level, because IL-1 decreases both PPARgamma1 mRNA expression and PPARgamma1 promoter activity. TNF-alpha, IL-17, and prostaglandin E2 (PGE2), which are involved in the pathogenesis of OA, also downregulated PPARgamma1 expression. Specific inhibitors of the mitogen-activated protein kinases (MAPKs) p38 (SB203580) and c-Jun N-terminal kinase (SP600125), but not of extracellular signal-regulated kinase (PD98059), prevented IL-1-induced downregulation of PPARgamma1 expression. Similarly, inhibitors of NF-kappaB signaling (pyrrolidine dithiocarbamate, MG-132, and SN-50) abolished the suppressive effect of IL-1. Thus, our study demonstrated that PPARgamma1 is downregulated in OA cartilage. The pro-inflammatory cytokine IL-1 may be responsible for this downregulation via a mechanism involving activation of the MAPKs (p38 and JNK) and NF-kappaB signaling pathways. The IL-1-induced downregulation of PPARgamma expression might be a new and additional important process by which IL-1 promotes articular inflammation and cartilage degradation.

Alterations of metabolic activity in human osteoarthritic osteoblasts by lipid peroxidation end product 4-hydroxynonenal.

4-Hydroxynonenal (HNE), a lipid peroxidation end product, is produced abundantly in osteoarthritic (OA) articular tissues, but its role in bone metabolism is ill-defined. In this study, we tested the hypothesis that alterations in OA osteoblast metabolism are attributed, in part, to increased levels of HNE. Our data showed that HNE/protein adduct levels were higher in OA osteoblasts compared to normal and when OA osteoblasts were treated with H2O2. Investigating osteoblast markers, we found that HNE increased osteocalcin and type I collagen synthesis but inhibited alkaline phosphatase activity. We next examined the effects of HNE on the signaling pathways controlling cyclooxygenase-2 (COX-2) and interleukin-6 (IL-6) expression in view of their putative role in OA pathophysiology. HNE dose-dependently decreased basal and tumour necrosis factor-alpha (TNF-alpha)-induced IL-6 expression while inducing COX-2 expression and prostaglandin E2 (PGE2) release. In a similar pattern, HNE induces changes in osteoblast markers as well as PGE2 and IL-6 release in normal osteoblasts. Upon examination of signaling pathways involved in PGE2 and IL-6 production, we found that HNE-induced PGE2 release was abrogated by SB202190, a p38 mitogen-activated protein kinase (MAPK) inhibitor. Overexpression of p38 MAPK enhanced HNE-induced PGE2 release. In this connection, HNE markedly increased the phosphorylation of p38 MAPK, JNK2, and transcription factors (CREB-1, ATF-2) with a concomitant increase in the DNA-binding activity of CRE/ATF. Transfection experiments with a human COX-2 promoter construct revealed that the CRE element (-58/-53 bp) was essential for HNE-induced COX-2 promoter activity. However, HNE inhibited the phosphorylation of IkappaBalpha and subsequently the DNA-binding activity of nuclear factor-kappaB. Overexpression of IKKalpha increased TNF-alpha-induced IL-6 production. This induction was inhibited when TNF-alpha was combined with HNE. These findings suggest that HNE may exert multiple effects on human OA osteoblasts by selective activation of signal transduction pathways and alteration of osteoblastic phenotype expression and pro-inflammatory mediator production.

Expression and regulation of microsomal prostaglandin E synthase-1 in human osteoarthritic cartilage and chondrocytes.

OBJECTIVE: Elevated production of prostaglandin E2 (PGE2) plays an important role in the pathogenesis of arthritis. Recently, an inducible microsomal prostaglandin E synthase-1 (mPGES-1) was identified. This enzyme is functionally coupled with cyclooxygenase-2 (COX-2) and converts the COX product PGH2 to PGE2. We analyzed expression of mPGES-1 in human normal and osteoarthritic (OA) cartilage and determined the effect of different inflammatory agonists on the expression of mPGES-1 in OA chondrocytes. METHODS: Expression of mPGES-1 mRNA and protein in cartilage was determined by quantitative real-time reverse transcriptase-polymerase chain reaction and immunohistochemistry, respectively. OA chondrocytes were treated with different inflammatory agents, and mPGES-1 protein expression was evaluated by Western blot. Activation of the mPGES-1 promoter was assessed in transient transfection experiments. RESULTS: Levels of mPGES-1 mRNA and protein were markedly elevated in OA versus normal cartilage. Treatment of chondrocytes with interleukin 1beta (IL-1beta) induced expression of mPGES-1 protein in a dose- and time-dependent manner. This appears to occur at the transcriptional level, as IL-1beta induced expression of mPGES-1 mRNA and the activity of this gene promoter. Tumor necrosis factor-alpha (TNF-alpha) and IL-17 also upregulated expression of mPGES-1 protein and displayed a synergistic effect with IL-1beta. Peroxisome proliferator-activated receptor-gamma ligands, 15-deoxy-delta(12,14)-prostaglandin J2 and troglitazone, inhibited IL-1beta-induced mPGES-1 protein expression, an effect that was reversed by exogenous PGE2. CONCLUSION: Our study shows that mPGES-1 expression is upregulated in OA versus normal cartilage and that proinflammatory cytokines increased mPGES-1 expression in chondrocytes. These data suggest that mPGES-1 may prove to be an interesting therapeutic target for controlling PGE2 synthesis.

Molecular basis of gyrase poisoning by the addiction toxin CcdB.

Gyrase is an ubiquitous bacterial enzyme that is responsible for disentangling DNA during DNA replication and transcription. It is the target of the toxin CcdB, a paradigm for plasmid addiction systems and related bacterial toxin-antitoxin systems. The crystal structure of CcdB and the dimerization domain of the A subunit of gyrase (GyrA14) dictates an open conformation for the catalytic domain of gyrase when CcdB is bound. The action of CcdB is one of a wedge that stabilizes a dead-end covalent gyrase:DNA adduct. Although CcdB and GyrA14 form a globally symmetric complex where the two 2-fold axes of both dimers align, the complex is asymmetric in its details. At the centre of the interaction site, the Trp99 pair of CcdB stacks with the Arg462 pair of GyrA14, explaining why the Arg462Cys mutation in the A subunit of gyrase confers resistance to CcdB. Overexpression of GyrA14 protects Escherichia coli cells against CcdB, mimicking the action of the antidote CcdA.

Inhibition of interleukin-1beta-induced cyclooxygenase 2 expression in human synovial fibroblasts by 15-deoxy-Delta12,14-prostaglandin J2 through a histone deacetylase-independent mechanism.

OBJECTIVE: The cyclooxygenase (COX) metabolite, 15-deoxy-Delta(12,14)-prostaglandin J(2) (15d-PGJ(2)), has been reported to inhibit the expression of a number of genes involved in the pathogenesis of arthritis. However, its effects on COX-2 remain controversial. We undertook this study to investigate the effects of 15d-PGJ(2) on interleukin-1beta (IL-1beta)-induced COX-2 expression in human synovial fibroblasts (HSFs). METHODS: HSFs were cultured with IL-1beta in the absence or presence of 15d-PGJ(2), and the levels of COX-2 protein and messenger RNA (mRNA) expression were evaluated using Western blotting and real-time reverse transcriptase-polymerase chain reaction, respectively. COX-2 promoter activity was analyzed in transient transfection experiments. Chromatin immunoprecipitation assays were performed to evaluate the level of histone acetylation and the recruitment of histone deacetylases (HDACs) 1, 2, and 3 and histone acetylase (HAT) p300 to the COX-2 promoter. RESULTS: IL-1beta-induced COX-2 protein and mRNA expression, as well as COX-2 promoter activation, were inhibited by 15d-PGJ(2). Troglitazone, a selective peroxisome proliferator-activated receptor gamma (PPARgamma) ligand, enhanced COX-2 expression, while GW9662, a specific PPARgamma antagonist, relieved the suppressive effect of 15d-PGJ(2). IL-1beta-induced histone H3 acetylation was selectively blocked by 15d-PGJ(2). The reduction of histone H3 acetylation did not correlate with the recruitment of HDACs to the COX-2 promoter. Also, treatment with the specific HDAC inhibitor, trichostatin A, did not relieve the suppressive effect of 15d-PGJ(2), indicating that HDACs are not involved in the inhibitory effect of 15d-PGJ(2). Furthermore, 15d-PGJ(2) blocked IL-1beta-induced recruitment of p300 to the COX-2 promoter, which may be the mechanism for decreased histone H3 acetylation and COX-2 expression. In accordance with this, overexpression of p300, but not of a mutant p300 lacking HAT activity, relieved the inhibitory effect of 15d-PGJ(2) on COX-2 promoter activation. CONCLUSION: These data suggest that 15d-PGJ(2) can inhibit IL-1beta-induced COX-2 expression by an HDAC-independent mechanism, probably by interfering with HAT p300.

Activation of peroxisome proliferator-activated receptor gamma inhibits interleukin-1beta-induced membrane-associated prostaglandin E2 synthase-1 expression in human synovial fibroblasts by interfering with Egr-1.

Membrane-associated prostaglandin (PG) E(2) synthase-1 (mPGES-1) catalyzes the conversion of PGH(2) to PGE(2), which contributes to many biological processes. Peroxisome proliferator-activated receptor gamma (PPARgamma) is a ligand-activated transcription factor and plays an important role in growth, differentiation, and inflammation in different tissues. Here, we examined the effect of PPARgamma ligands on interleukin-1beta (IL-1beta)-induced mPGES-1 expression in human synovial fibroblasts. PPARgamma ligands 15-deoxy-Delta(12,14) prostaglandin J(2) (15d-PGJ(2)) and the thiazolidinedione troglitazone (TRO), but not PPARalpha ligand Wy14643, dose-dependently suppressed IL-1beta-induced PGE(2) production, as well as mPGES-1 protein and mRNA expression. 15d-PGJ(2) and TRO suppressed IL-1beta-induced activation of the mPGES-1 promoter. Overexpression of wild-type PPARgamma further enhanced, whereas overexpression of a dominant negative PPARgamma alleviated, the suppressive effect of both PPARgamma ligands. Furthermore, pretreatment with an antagonist of PPARgamma, GW9662, relieves the suppressive effect of PPARgamma ligands on mPGES-1 protein expression, suggesting that the inhibition of mPGES-1 expression is mediated by PPARgamma. We demonstrated that PPARgamma ligands suppressed Egr-1-mediated induction of the activities of the mPGES-1 promoter and of a synthetic reporter construct containing three tandem repeats of an Egr-1 binding site. The suppressive effect of PPARgamma ligands was enhanced in the presence of a PPARgamma expression plasmid. Electrophoretic mobility shift and supershift assays for Egr-1 binding sites in the mPGES-1 promoter showed that both 15d-PGJ(2) and TRO suppressed IL-1beta-induced DNA-binding activity of Egr-1. These data define mPGES-1 and Egr-1 as novel targets of PPARgamma and suggest that inhibition of mPGES-1 gene transcription may be one of the mechanisms by which PPARgamma regulates inflammatory responses.

The highly conserved TldD and TldE proteins of Escherichia coli are involved in microcin B17 processing and in CcdA degradation.

Microcin B17 (MccB17) is a peptide antibiotic produced by Escherichia coli strains carrying the pMccB17 plasmid. MccB17 is synthesized as a precursor containing an amino-terminal leader peptide that is cleaved during maturation. Maturation requires the product of the chromosomal tldE (pmbA) gene. Mature microcin is exported across the cytoplasmic membrane by a dedicated ABC transporter. In sensitive cells, MccB17 targets the essential topoisomerase II DNA gyrase. Independently, tldE as well as tldD mutants were isolated as being resistant to CcdB, another natural poison of gyrase encoded by the ccd poison-antidote system of plasmid F. This led to the idea that TldD and TldE could regulate gyrase function. We present in vivo evidence supporting the hypothesis that TldD and TldE have proteolytic activity. We show that in bacterial mutants devoid of either TldD or TldE activity, the MccB17 precursor accumulates and is not exported. Similarly, in the ccd system, we found that TldD and TldE are involved in CcdA and CcdA41 antidote degradation rather than being involved in the CcdB resistance mechanism. Interestingly, sequence database comparisons revealed that these two proteins have homologues in eubacteria and archaebacteria, suggesting a broader physiological role.