Mycobacterium tuberculosis chaperonin 10 stimulates bone resorption: a potential contributory factor in Pott's disease

Chaperonin: Co-chaperonin Interactions

Co-chaperonins function together with chaperonins to mediate ATP-dependent protein folding in a variety of cellular compartments. Chaperonins are evolutionarily conserved and form two distinct classes, namely, group I and group II chaperonins. GroEL and its co-chaperonin GroES form part of group I and are the archetypal members of this family of protein folding machines. The unique mechanism used by GroEL and GroES to drive protein folding is embedded in the complex architecture of double-ringed complexes, forming two central chambers that undergo conformational rearrangements that enable protein folding to occur. GroES forms a lid over the chamber and in doing so dislodges bound substrate into the chamber, thereby allowing non-native proteins to fold in isolation. GroES also modulates allosteric transitions of GroEL. Group II chaperonins are functionally similar to group I chaperonins but differ in structure and do not require a co-chaperonin. A significant number of bacteria and eukaryotes house multiple chaperonin and co-chaperonin proteins, many of which have acquired additional intracellular and extracellular biological functions. In some instances, co-chaperonins display contrasting functions to those of chaperonins. Human HSP60 (HSPD) continues to play a key role in the pathogenesis of many human diseases, in particular autoimmune diseases and cancer. A greater understanding of the fascinating roles of both intracellular and extracellular Hsp10 on cellular processes will accelerate the development of techniques to treat diseases associated with the chaperonin family.

Determination of variable region sequences from hybridoma immunoglobulins that target Mycobacterium tuberculosis virulence factors

Mycobacterium tuberculosis (Mtb) infects one-quarter of the world's population. Mtb and HIV coinfections enhance the comorbidity of tuberculosis (TB) and AIDS, accounting for one-third of all AIDS-associated mortalities. Humoral antibody to Mtb correlates with TB susceptibility, and engineering of Mtb antibodies may lead to new diagnostics and therapeutics. The characterization and validation of functional immunoglobulin (Ig) variable chain (IgV) sequences provide a necessary first step towards developing therapeutic antibodies against pathogens. The virulence-associated Mtb antigens SodA (Superoxide Dismutase), KatG (Catalase), PhoS1/PstS1 (regulatory factor), and GroES (heat shock protein) are potential therapeutic targets but lacked IgV sequence characterization. Putative IgV sequences were identified from the mRNA of hybridomas targeting these antigens and isotype-switched into a common immunoglobulin fragment crystallizable region (Fc region) backbone, subclass IgG2aκ. Antibodies were validated by demonstrating recombinant Ig assembly and secretion, followed by the determination of antigen-binding specificity using ELISA and immunoblot assay.

Vitamin D receptor activated by vitamin D administration alleviates Mycobacterium tuberculosis-induced bone destruction by inhibiting NFκB-mediated aberrant osteoclastogenesis

Clinically, bone destruction caused by Mycobacterium tuberculosis was serious especially in patients with vitamin D (VD) deficiency. However, the role of VD in M. tuberculosis-induced bone destruction remains clear. In this context, we investigate the role of VD and vitamin D receptor (VDR) in the M. tuberculosis-induced bone destruction. First, we infected RAW264.7 and bone marrow-derived macrophages (BMMs) with Mycobacterium bovis Bacillus Calmette-Guérin (M. bovis BCG) in vitro. Then, we activated VDR through VD administration. TRAP and FAK staining, bone resorption assays, immunofluorescence staining, qPCR, and western blot were carried out. In vivo, the M. tuberculosis-induced osteolytic model on the murine skull was established and the μCT and histological analyses were performed. We found that VDR and TRAP were upregulated in bone tuberculosis tissue and proved that M. tuberculosis infection promoted osteoclastogenesis in RAW264.7 and BMMs. VD could inhibit osteoclasts differentiation, fusion, and bone resorption dose-dependently. However, when VDR was knocked down, the inhibitory effect of VD on osteoclasts disappeared. In mechanism, activation of VDR inhibits the phosphorylation of IκB α, thereby inhibiting NFκB signaling pathway and alleviating osteoclastogenesis. Furthermore, in the skull osteolysis model, VD administration reduced osteolysis, but not in VDR^-/- mice. Our study, for the first time, demonstrates that activation of VDR by VD administration inhibits M. tuberculosis-induced bone destruction. Our results reveal that VD and VDR are potential therapeutic targets for M. tuberculosis-induced bone destruction, and are of great clinical significance for the development of new therapeutic strategies.

Mycobacterium tuberculosis infection increases the number of osteoclasts and inhibits osteoclast apoptosis by regulating TNF-α-mediated osteoclast autophagy

Osteoarticular tuberculosis, a chronic inflammatory disease characterized by Mycobacterium tuberculosis (M.tb) infection, has become a serious problem in China. The present study was conducted to determine the mechanism of action of tumor necrosis factor (TNF)-α in the pathogenesis of osteoarticular tuberculosis. The number of osteoclasts in osteoarticular tuberculosis tissue samples was detected by tartrate-resistant acid phosphatase staining. Autophagy and apoptosis of osteoclasts were detected by western blotting, reverse transcription-quantitative PCR, transmission electron microscopy and TUNEL staining. The results showed that autophagy and the number of osteoclasts increased in the lesions of patients with osteoarticular tuberculosis compared with osteoarthritis samples. Moreover, activation of osteoclast autophagy inhibited the apoptosis of osteoclasts infected with M.tb, and increased the expression level of TNF-α. The results showed that TNF-α enhanced the autophagic activity of M.tb-infected osteoclasts and inhibited cell apoptosis. These findings indicated that M.tb infection induced osteoclast production and inhibited osteoclast apoptosis by regulating TNF-α-mediated osteoclast autophagy, revealing a new mechanism for TNF-α in the pathogenesis of osteoarticular tuberculosis.

The osteoclast, a target cell for microorganisms

Bone is a highly adaptive tissue with regenerative properties that is subject to numerous diseases. Infection is one of the causes of altered bone homeostasis. Bone infection happens subsequently to bone surgery or to systemic spreading of microorganisms. In addition to osteoblasts, osteoclasts (OCs) also constitute cell targets for pathogens. OCs are multinucleated cells that have the exclusive ability to resorb bone mineral tissue. However, the OC is much more than a bone eater. Beyond its role in the control of bone turnover, the OC is an immune cell that produces and senses inflammatory cytokines, ingests microorganisms and presents antigens. Today, increasing evidence shows that several pathogens use OC as a host cell to grow, generating debilitating bone defects. In this review, we exhaustively inventory the bacteria and viruses that infect OC and report the present knowledge in this topic. We point out that most of the microorganisms enhance the bone resorption activity of OC. We notice that pathogen interactions with the OC require further investigation, in particular to validate the OC as a host cell in vivo and to identify the cellular mechanisms involved in altered bone resorption. Thus, we conclude that the OC is a new cell target for pathogens; this new research area paves the way for new therapeutic strategies in the infections causing bone defects.

Mycobacterium Tuberculosis in Spinal Tuberculosis

Even in an era of remarkable medical advances, there is an issue of why tuberculosis remains in the list of disastrous diseases, afflicting humans and causing suffering. There has not been a plausible answer to this, and it has been suggested that clinicians and medical scientists could presently not win the war against the tubercle bacilli. With regards to this issue, based on the authors' own clinical and research experiences, in this review, the available literature was revisited in order to address the raised questions and to provide recent information on characteristics of tubercle bacilli and possible ways to more effectively treat tuberculosis.

Chaperonin-co-chaperonin interactions

Co-chaperonins function together with chaperonins to mediate ATP-dependant protein folding in a variety of cellular compartments. GroEL and its co-chaperonin GroES are the only essential chaperones in Escherichia coli and are the archetypal members of this family of protein folding machines. The unique mechanism used by GroEL and GroES to drive protein folding is embedded in the complex architecture of double-ringed complexes, forming two central chambers that undergo structural rearrangements as part of the folding mechanism. GroES forms a lid over the chamber, and in doing so dislodges bound substrate into the chamber, thereby allowing non-native proteins to fold in isolation. GroES also modulates allosteric transitions of GroEL. A significant number of bacteria and eukaryotes house multiple chaperonin and co-chaperonin proteins, many of which have acquired additional intracellular and extracellular biological functions. In some instances co-chaperonins display contrasting functions to those of chaperonins. Human Hsp60 continues to play a key role in the pathogenesis of many human diseases, in particular autoimmune diseases and cancer. A greater understanding of the fascinating roles of both intracellular and extracellular Hsp10, in addition to its role as a co-chaperonin, on cellular processes will accelerate the development of techniques to treat diseases associated with the chaperonin family.

Mycobacterium tuberculosis 10-kDa co-chaperonin regulates the expression levels of receptor activator of nuclear factor-κB ligand and osteoprotegerin in human osteoblasts

The aim of the present study was to investigate the effect of recombinant Mycobacterium tuberculosis (r-Mt) 10-kDa co-chaperonin (cpn10) on the expression of osteoprotegerin (OPG) and receptor activator of nuclear factor-κB ligand (RANKL) in third-generation cultured osteoblasts. The osteoblast-like cultures were isolated from bone fragments taken from patients undergoing surgery. Prior to stimulation with r-Mt cpn10, cells were incubated in serum-free medium for 24 h. r-Mt cpn10 was added into fresh serum-free medium, reaching final concentrations of 0.01–10 μg/ml. The levels of OPG were determined using enzyme-linked immunosorbent assay. Reverse transcription-quantitative polymerase chain reaction (RT-qPCR) analysis was performed to determine the levels of RANKL and OPG mRNA. For measurement of the protein levels of OPG and RANKL, a western blotting assay was performed. r-Mt cpn10 downregulated the protein levels of OPG in the third generation cultured osteoblasts at a dose of 10 μg/ml. RT-qPCR revealed that the OPG mRNA level was decreased by 73% after 4 h and by 85.5% after 8 h following incubation with r-Mt cpn10 (10 μg/ml). Western blot analysis demonstrated similar results for the OPG protein level. In the third-generation cultured osteoblasts, the levels of RANKL mRNA and protein were increased by 2.6- and 1-fold, respectively, following incubation with r-Mt cpn10 (10 μg/ml). Furthermore, the RANKL/OPG ratio was markedly increased by r-Mt cpn10 (10 μg/ml) treatment. In conclusion, the results of the current study demonstrated that r-Mt cpn10 decreased the levels of OPG and increased the levels of RANKL in a dose- and time-dependent manner. Notably, the present study indicated that r-Mt cpn10 exerts its effect on osteoblastic cells by increasing the RANKL/OPG ratio.

A new murine model to study musculoskeletal tuberculosis (short communication)

Musculoskeletal tuberculosis (TB) is a severe extrapulmonary manifestation of chronic Mycobacterium (M.) tuberculosis infection. Considering increasing incidence, multi-drug resistance and associated treatment difficulties, more preclinical research is needed. In this study we developed a murine model for musculoskeletal TB. Mice, intranasally infected with M. tuberculosis, were sacrificed after ten months. Mycobacterial growth was detected in lung and femur homogenates. Ziehl-Neelsen staining of paraffin-embedded femurs showed acid-fast rods in the myelum and Magnetic Resonance Imaging demonstrated osteomyelitis and macronodular tuberculomas. This new murine model of musculoskeletal TB might be of value to further investigate immunologic and radiologic responses.

Mycobacterium tuberculosis escapes from the phagosomes of infected human osteoclasts reprograms osteoclast development via dysregulation of cytokines and chemokines

Spinal tuberculosis is a condition characterized by massive resorption of the spinal vertebrae due to the infection with Mycobacterium tuberculosis (Mtb). However, the pathogenesis of spinal tuberculosis has not been established because it was almost completely eradicated by the establishment of antibiotic treatment in the mid-20th century. In this study, we investigated the inflammatory responses of human multinucleated osteoclasts infected with virulent Mtb strain. We found that the intracellular Mtb infection of multinuclear osteoclasts resulted in the rapid growth of Mtb and an osteolytic response, rather than inflammation. In response to Mtb infection, the mononuclear osteoclast precursors produced proinflammatory cytokines including tumor necrosis factor (TNF)-α, an intrinsic characteristic they share with macrophages. In contrast, highly fused multinucleated osteoclasts incapacitated the production of these cytokines. Instead, the intracellular Mtb inside multinuclear osteoclasts escaped from the endosome/phagosome, leading to a different pattern of osteoclast activation, with the production of chemokines such as CCL5, CCL17, CCL20, CCL22, CCL24, and CCL25. Moreover, intracellular infection with an avirulent Mtb strain resulted in diminished production of these chemokines. These findings indicate that intracellular Mtb infection in multinuclear osteoclasts reprograms osteoclast development via the dysregulation of cytokines and chemokines.

Establishing the diagnosis of tuberculous vertebral osteomyelitis

PURPOSE

The aim of this article has been to analyze the clinical and radiological data suggesting tuberculous vertebral osteomielitis (TVO), and then discuss the steps to be followed to achieve an aetiological diagnosis.

METHODS

A thorough literature search was carried out to identify the best clinical and microbiological evidence for a fast and efficient diagnosis of TVO.

RESULTS

The clinical and radiological diagnosis of spinal tuberculosis suffers from serious limitations, with a high percentage of cases requiring vertebral biopsy to reach a definitive diagnosis. The increasing incidence of multidrug-resistant tuberculosis has highlighted the insufficiency of the histopathological diagnosis and the need for microbiological diagnosis. Unfortunately, the maximum sensitivity of spinal tuberculosis cultures is 80 %, and traditional methods require 6 to 8 weeks for the isolation, identification and sensitivity study. New culture media and identification methods have improved sensitivity and reduced the time required for the identification. Molecular methods have now been integrated into a single test, with identification of the mycobacterium responsible and its sensitivity to rifampicin. Additionally, multiplex-PCR tests have been developed that allow a rapid differential diagnosis between granulomatous spondylodiscitis.

CONCLUSIONS

All patients with subacute inflammatory back or neck pain showing suggestive radiological findings should be studied to rule out TVO. If there is no clear evidence of tuberculosis from another location or indication for surgery, a percutaneous vertebral biopsy should be performed. When TVO is suspected, all spinal or paravertebral tissue samples should be sent simultaneously to pathology and microbiology laboratories for appropriate processing.

A comparative study of pyogenic and tuberculous spondylodiscitis

STUDY DESIGN

We performed a retrospective review of 126 cases of infectious spondylodiscitis over a 4-year period.

OBJECTIVE

Differentiation between pyogenic spondylodiscitis (PS) and tuberculous spondylodiscitis (TS) is essential for deciding on the appropriate therapeutic regimen. The aim of this study was to compare the characteristics of the 2 forms of spondylodiscitis.

SUMMARY OF BACKGROUND DATA

There has been much effort to distinguish the radiologic findings in PS versus TS, but classification based on radiologic findings alone had limitations yet.

METHODS

We compared the predisposing factors or associated illnesses, clinical, radiologic, and laboratory features of microbiologically confirmed cases of PS and TS in 2 university hospitals.

RESULTS

Of 126 patients, 79 had PS and 47 TS. PS was more frequently associated with the followings: previous invasive spinal procedures (PS vs. TS: 32.9% vs. 8.5%), preceding bacteremia (13.9% vs. 0%), chronic renal failure (12.7% vs. 0%), liver cirrhosis (13.9% vs. 0%), fever (temperature >38°C) (48.1% vs. 17.0%), white blood cell counts over 10,000/mm (41.8% vs. 19.1%), fraction of neutrophils >75% (49.4% vs. 27.7%), C-reactive protein levels over 5 mg/dL (58.2% vs. 27.7%), erythrocyte sedimentation rate levels over 40 mm/h (84.4% vs. 66.0%), and ALP levels over 120 IU/L (45.6% vs. 17.0%). TS was frequently associated with active tuberculosis of other organs (0% vs. 31.9%), longer diagnostic delay (47.6 vs. 106.3 days), involvement of thoracic spines (21.5% vs. 38.3%), and involvement of ≥3 spinal levels (11.4% vs. 36.2%).

CONCLUSION

Previous invasive spinal procedures, preceding bacteremia, fever, higher white blood cell counts, C-reactive protein, ALP, and higher fraction of neutrophils are suggestive of PS. Concurrent active tuberculosis, more indolent course and involvement of thoracic spines are suggestive of TS. When the causative organism is not identified despite all efforts at diagnosis, combination of the clinical, radiologic, and laboratory characteristics of the patient is helpful.

Comparison of the moonlighting actions of the two highly homologous chaperonin 60 proteins of Mycobacterium tuberculosis

Evidence is emerging that the two chaperonin (Cpn) 60 proteins of Mycobacterium tuberculosis, Cpn60.1 and Cpn60.2, have moonlighting actions that may contribute to the pathology of tuberculosis. We studied the release of Cpn60.1 from M. tuberculosis and infected macrophage like cells and compared recombinant Cpn60.1 and Cpn60.2 in a range of cell-based assays to determine how similar the actions of these highly homologous proteins are. We now establish that Cpns are similar as follows: (i) Cpn60.1, as it has been shown for Cpn60.2, is released by M. tuberculosis in culture, and Cpn60.1 is furthermore released when the bacterium is in quiescent, but not activated, macrophage like cells, and (ii) both proteins only showed a partial requirement for MyD88 for the induction of proinflammatory cytokine production compared to lipopolysaccharide. However, we also found major differences in the cellular action of Cpns. (i) Cpn60.2 proved to be a more potent stimulator of whole blood leukocytes than Cpn60.1 and was the only one to induce tumor necrosis factor alpha synthesis. (ii) Cpn60.1 bound to ca. 90% of circulating monocytes compared to Cpn60.2, which bound <50% of these cells. Both chaperonins bound to different cell surface receptors, while monocyte activation by both proteins was completely abrogated in TLR4-/- mice, although Cpn60.2 also showed significant requirement for TLR2. Finally, an isogenic mutant lacking cpn60.1, but containing intact cpn60.2, was severely inhibited in generating multinucleate giant cells in an in vitro human granuloma assay. These results clearly show that, despite significant sequence homology, M. tuberculosis Cpn60 proteins interact in distinct ways with human or murine macrophages.

Molecular chaperones and protein-folding catalysts as intercellular signaling regulators in immunity and inflammation

This review critically examines the hypothesis that molecular chaperones and protein-folding catalysts from prokaryotes and eukaryotes can be secreted by cells and function as intercellular signals, principally but not exclusively, for leukocytes. A growing number of molecular chaperones have been reported to function as ligands for selected receptors and/or receptors for specific ligands. Molecular chaperones initially appeared to act primarily as stimulatory signals for leukocytes and thus, were seen as proinflammatory mediators. However, evidence is now emerging that molecular chaperones can have anti-inflammatory actions or, depending on the protein and concentration, anti- and proinflammatory functions. Recasting the original hypothesis, we propose that molecular chaperones and protein-folding catalysts are "moonlighting" proteins that function as homeostatic immune regulators but may also under certain circumstances, contribute to tissue pathology. One of the key issues in the field of molecular chaperone biology relates to the role of microbial contaminants in their signaling activity; this too will be evaluated critically. The most fascinating aspect of molecular chaperones probably relates to evidence for their therapeutic potential in human disease, and ongoing studies are evaluating this potential in a range of clinical settings.

Multiple moonlighting functions of mycobacterial molecular chaperones

Molecular chaperones and protein folding catalysts are normally thought of as intracellular proteins involved in protein folding quality control. However, in the mycobacteria there is increasing evidence to support the hypothesis that molecular chaperones are also secreted intercellular signalling molecules or can control actions at the cell wall or indeed control the composition of the cell wall. The most recent evidence for protein moonlighting in the mycobacteria is the report that chaperonin 60.2 of Mycobacterium tuberculosis is important in the key event in tuberculosis - the entry of the bacterium into the macrophage. This brief overview highlights the potential importance of the moonlighting functions of molecular chaperones in the biology and pathobiology of the mycobacteria.

Caught with their PAMPs down? The extracellular signalling actions of molecular chaperones are not due to microbial contaminants

In recent years, it has been hypothesised that a new signalling system may exist in vertebrates in which secreted molecular chaperones form a dynamic continuum between the cellular stress response and corresponding homeostatic physiological mechanisms. This hypothesis seems to be supported by the finding that many molecular chaperones are released from cells and act as extracellular signals for a range of cells. However, this nascent field of biological research seems to suffer from an excessive criticism that the biological activities of molecular chaperones are due to undefined components of the microbial expression hosts used to generate recombinant versions of these proteins. In this article, a number of the proponents of the cell signalling actions of molecular chaperones take this criticism head-on. They show that sufficient evidence exists to support fully the hypothesis that molecular chaperones have cell-cell signalling actions that are likely to be part of the homeostatic mechanism of the vertebrate.

Unfolding the relationship between secreted molecular chaperones and macrophage activation states

Over the last 20 years, it has emerged that many molecular chaperones and protein-folding catalysts are secreted from cells and function, somewhat in the manner of cytokines, as pleiotropic signals for a variety of cells, with much attention being focused on the macrophage. During the last decade, it has become clear that macrophages respond to bacterial, protozoal, parasitic and host signals to generate phenotypically distinct states of activation. These activation states have been termed 'classical' and 'alternative' and represent not a simple bifurcation in response to external signals but a range of cellular phenotypes. From an examination of the literature, the hypothesis is propounded that mammalian molecular chaperones are able to induce a wide variety of alternative macrophage activation states, and this may be a system for relating cellular or tissue stress to appropriate macrophage responses to restore homeostatic equilibrium.

The two homologous chaperonin 60 proteins of Mycobacterium tuberculosis have distinct effects on monocyte differentiation into osteoclasts

Mycobacterium tuberculosis produces two homologous chaperonin (Cpn)60 proteins, Cpn60.1 and Cpn60.2 (Hsp65). Both proteins stimulate human and murine monocyte cytokine synthesis but, unlike Cpn60 proteins from other microbial species, fail to stimulate the breakdown of cultured murine bone. Here, we have examined the mechanism of action of these proteins on bone remodelling and osteoclastogenesis, induced in vitro in murine calvarial explants and the murine monocyte cell line RAW264.7. Additionally, we have determined their effect on bone remodelling in vivo in an animal model of arthritis. Recombinant Cpn60.1 but not Cpn60.2 inhibited bone breakdown both in vitro, in murine calvaria and in vivo, in experimental arthritis. Analysis of the mechanism of action of Cpn60.1 suggests that this protein works by directly blocking the synthesis of the key osteoclast transcription factor, nuclear factor of activated T cells c1. The detection of circulating immunoreactive intact Cpn60.1 in a small number of patients with tuberculosis but not in healthy controls further suggests that the skeleton may be affected in patients with tuberculosis. Taken together, these findings reveal that M. tuberculosis Cpn60.1 is a potent and novel inhibitor of osteoclastogenesis both in vitro and in vivo and a potential cure for bone-resorptive diseases like osteoporosis.

A Mycobacterium tuberculosis mutant lacking the groEL homologue cpn60.1 is viable but fails to induce an inflammatory response in animal models of infection

The causative agent of tuberculosis, Mycobacterium tuberculosis, has two chaperonin (Cpn60) proteins and one cochaperonin (Cpn10) protein. We show here that cpn60.2 and cpn10, but not cpn60.1, are essential for cell survival. A mutant lacking Cpn60.1 was indistinguishable from the wild-type organism in plate and broth culture and within murine macrophages, although it showed increased sensitivity to high temperature (55 degrees C). However, infection of mice with the Deltacpn60.1 mutant revealed a major difference from the wild-type organism. In spite of having equal numbers of bacteria in infected sites, the Deltacpn60.1 mutant failed to produce granulomatous inflammation in either mice or guinea pigs. This was associated with reduced cytokine expression in infected animals and macrophages. Cell wall lipid acid composition was not altered in the mutant strain. Thus, it appears that Cpn60.1 is an important agent in the regulation of the cytokine-dependent granulomatous response in M. tuberculosis infection.

Identification of novel bacterial plasminogen-binding proteins in the human pathogen Mycobacterium tuberculosis

Binding and activation of human plasminogen (Plg) to generate the proteolytic enzyme plasmin (Plm) have been associated with the invasive potential of certain bacteria. In this work, proteomic analysis together with ligand blotting assays identified several major Plg-binding spots in Mycobacterium tuberculosis soluble extracts (SEs) and culture filtrate proteins. The identity of 15 different proteins was deduced by N-terminal and/or MS and corresponded to DnaK, GroES, GlnA1, Ag85 complex, Mpt51, Mpt64, PrcB, MetK, SahH, Lpd, Icl, Fba, and EF-Tu. Binding of Plg to recombinant M. tuberculosis DnaK, GlnA1, and Ag85B was further confirmed by ELISA and ligand blotting assays. The binding was inhibited by epsilon-aminocaproic acid, indicating that the interaction involved lysine residues. Plg bound to recombinant mycobacterial proteins was activated to Plm by tissue-type Plg activator. In contrast with recombinant proteins, M. tuberculosis SE enhanced several times the Plg activation mediated by the activator. Interestingly, GlnA1 was able to bind the extracellular matrix (ECM) protein fibronectin. Together these results show that M. tuberculosis posses several Plg receptors suggesting that bound Plg to bacteria surface, can be activated to Plm, endowing bacteria with the ability to break down ECM and basal membranes proteins contributing to tissue injury in tuberculosis.

Immunologic response enhances atherosclerosis-type 1 helper T cell (Th1)-to-type 2 helper T cell (Th2) shift and calcified atherosclerosis in Bacillus Calmette-Guerin (BCG)-treated apolipoprotein E-knockout (apo E-/-) mice

Although immunocompetent hosts develop protective type 1 helper T cell (Th1) responses in mycobacterial infections, seroepidemiologic studies show that patients with atherosclerosis commonly express high antibody titers against mycobacterial heat shock protein (HSP) 65 and may develop a nonprotective type 2 helper T cell (Th2) response and advanced disease. These studies were undertaken to define mycobacterial dose requirements and kinetics for development of antibodies to HSP65, the Th1 to Th2 shift of immune response, and calcified atherosclerotic lesion development in the apo E-/- mouse. Fourteen-week apo E-/- female mice were treated intraperitoneally (ip) with heat-killed M. bovis Bacillus Calmette-Guerin (BCG), and 14 days later, cross-sections from the ascending aortas were stained for measurement of lesion size and calcium deposition. At 14 days, 0.01-mg BCG induced Th1 responses against HSP65. In contrast, 1-mg BCG induced splenic PGE2-releasing macrophages with a Th1-to-Th2 shift of responses to HSP65, which was PGE2-dependent. Treatment with 1-mg BCG significantly lowered bone density with increases in marrow osteoclastogenesis and development of calcified lesions in the aorta. At 14 days, 0.01-mg BCG induced Th1-dependent HSP65 responses and did not advance atherosclerosis. In contrast, for 1-mg BCG, a PGE2-dependent Th1-to-Th2 shift of responses to HSP65 and evidence of bone resorption are associated with advanced calcified atherosclerotic lesions.

Effect of fish skin mucus on the soluble proteome of Vibrio salmonicida analysed by 2-D gel electrophoresis and tandem mass spectrometry

Vibrio salmonicida is the causative agent of cold-water vibriosis in farmed marine fish species. Adherence of pathogenic bacteria to mucosal surfaces is considered to be the first steps in the infective processes, and proteins involved are regarded as virulence factors. The global protein expression profile of V. salmonicida, grown with and without the presence of fish skin mucus in the synthetic media, was compared. Increased levels of proteins involved in motility, oxidative stress responses, and general stress responses were demonstrated as an effect of growth in the presence of mucus compared to non-mucus containing media. Enhanced levels of the flagellar proteins FlaC, FlaD and FlaE indicate increased motility capacity, while enhanced levels of the heat shock protein DnaK and the chaperonin GroEL indicate a general stress response. In addition, we observed that peroxidases, TPx.Grx and AhpC, involved in the oxidative stress responses, were induced by mucus proteins. The addition of mucus to the culture medium did not significantly alter the growth rate of V. salmonicida. An analysis of mucus proteins suggests that the mucus layer harbours a protein species that potentially possesses catalytic activity against DNA, and a protein with iron chelating activity. This study represents the first V. salmonicida proteomic analysis, and provides specific insight into the proteins necessary for the bacteria to challenge the skin mucus barrier of the fish.

Tuberculous myelopathy: current aspects of neurologic sequels in the southeast of Iran

OBJECTIVE

The spinal cord may be affected in different ways in the course of tuberculous infection. The objective of this study was to determine the epidemiologic features, clinical manifestations, pathophysiologic mechanisms, neurologic sequels, and treatment outcomes of tuberculous myelopathy in the southeast of Iran in which the disease is endemic.

METHOD

A retrospective study was scheduled. All cases of tuberculous myelopathy treated in our hospital over the last 7 years were reviewed. Only those with histologic or microbiologic confirmation or those who responded to antituberculous therapy were included.

RESULTS

During a 7-year period, 43 cases of tuberculous myelopathy were found. The most frequent clinical manifestations were backache (86%) and fever (67%). Twenty patients were paraparetic or paraplegic and 40% had kyphosis. Imaging studies revealed thoracic and/or lumbar spine involvement in 92% of patients with tuberculous spondylitis. Fifteen, five and two patients had sensorimotor spinal cord syndrome, radiculomyelitis and intramedullary syringomyelic syndrome, respectively. Forty-seven percent required surgical intervention. There was improvement in 81% of the cases.

CONCLUSION

Different pathophysiologic mechanisms acted on the clinical manifestations of spinal neurotuberculosis. A good outcome is expected if the diagnosis is made in the early stages before the appearance of spinal deformity and neurologic deficits.

Heat shock protein 10 and signal transduction: a "capsula eburnea" of carcinogenesis?

To date, little is known either about the physical interactions of heat shock protein 10 (Hsp10) with other proteins within the cell or its involvement in signal transduction pathways. Hsp10 has been considered mainly as a partner of Hsp60 in the Hsp60/10 protein folding machine. Only recently, Hsp10 was reported to interact with proteins involved in deoxyribonucleic acid checkpoint inactivation, termination of M-phase, messenger ribonucleic acid export, import of nuclear proteins, nucleocytoplasmic transport, and pheromone signaling pathways. At the same time, Hsp10 expression can be up-regulated in cancer cells, because it accumulates as the cell transformation progresses. Recent data suggest that Hsp10 may be not only a component of the folding machine but also an active player of the cell signaling network, influencing cell cycle, nucleocytoplasmic transport, and metabolism, with putative roles in the lack of cell differentiation and in the inhibition of apoptosis. In this review, we revise the involvement of Hsp10 in signal transduction pathways and its possible role in cancer etiology.

Cation-mediated interplay of loops in chaperonin-10

The ubiquitously occurring chaperonins consist of a large tetradecameric Chaperonin-60, forming a cylindrical assembly, and a smaller heptameric Chaperonin-10. For a functional protein folding cycle, Chaperonin-10 caps the cylindrical Chaperonin-60 from one end forming an asymmetric complex. The oligomeric assembly of Chaperonin-10 is known to be highly plastic in nature. In Mycobacterium tuberculosis, the plasticity has been shown to be modulated by reversible binding of divalent cations. Binding of cations confers rigidity to the metal binding loop, and also promotes stability of the oligomeric structure. We have probed the conformational effects of cation binding on the Chaperonin-10 structure through fluorescence studies and molecular dynamics simulations. Fluorescence studies show that cation binding induces reduced exposure and flexibility of the dome loop. The simulations corroborate these results and further indicate a complex landscape of correlated motions between different parts of the molecule. They also show a fascinating interplay between two distantly spaced loops, the metal binding "dome loop" and the GroEL-binding "mobile loop", suggesting an important cation-mediated role in the recognition of Chaperonin-60. In the presence of cations the mobile loop appears poised to dock onto the Chaperonin-60 structure. The divalent metal ions may thus act as key elements in the protein folding cycle, and trigger a conformational switch for molecular recognition.

The unusual chaperonins of Mycobacterium tuberculosis

Heat shock proteins (Hsps), also known as molecular chaperones, are a diverse set of proteins that mediate the correct folding, assembly, transport and degradation of other proteins. In addition, Hsps have been shown to play a variety of important roles in immunity, thereby representing prominent antigens in the humoral and cellular immune response. Chaperonins form a sub-group of molecular chaperones that are found in all domains of life. Chaperonins in all bacteria are encoded by the essential groEL and groES genes, also called cpn60 and cpn10 arranged on the bicistronic groESL operon. Interestingly, Mycobacterium tuberculosis contains two copies of the cpn60 genes. The existence of a duplicate set of cpn60 genes in M. tuberculosis, however, has been perplexing. Cpn10 and Cpn60s of M. tuberculosis have been shown to be highly antigenic in nature, eliciting strong B- and T-cell immune responses. Recent work has shown intriguing structural, biochemical and signaling properties of the M. tuberculosis chaperonins. This review details the recent developments in the study of the M. tuberculosis chaperonins.

Stress cytokines: pivotal proteins in immune regulatory networks; Opinion

Stress proteins have three immunological regulatory functions: within the cell, on the cell membrane as signalling receptors, and in the extracellular environment as stress cytokines. They can activate the immune system by providing danger signals or they may downregulate immune and inflammatory responses. In addition, they can modulate immune responses by acting as chaperones for antigenic peptides while they themselves are processed and presented to T cells as self-peptides. We predict that the exploitation of the downregulatory properties of stress cytokines will have therapeutic applications in the treatment of human chronic inflammatory diseases, such as rheumatoid arthritis.

The intercellular signaling activity of the Mycobacterium tuberculosis chaperonin 60.1 protein resides in the equatorial domain

The major heat shock protein, chaperonin 60, has been established to have intercellular signaling activity in addition to its established protein-folding function. Mycobacterium tuberculosis is one of a small proportion of bacteria to encode two chaperonin 60 proteins. We have demonstrated that chaperonin 60.1 from this bacterium is a very active stimulator of human monocytes. To determine structure/function relationships of chaperonin 60.1 we have cloned and expressed the apical, equatorial, and intermediate domains of this protein. We have found that the signaling activity of M. tuberculosis chaperonin 60.1 resides in the equatorial domain. This activity of the recombinant equatorial domain was completely blocked by treating the protein with proteinase K, ruling out lipopolysaccharide contamination as the cause of the cell activation. Blockade of the activity of the equatorial domain by anti-CD14 monoclonal antibodies reveals that this domain activates monocytes by binding to CD14. Looking at the oligomeric state of the active proteins, using native gel electrophoresis and protein cross-linking we found that recombinant M. tuberculosis chaperonin 60.1 fails to form the prototypic tetradecameric structure of chaperonin 60 proteins under the conditions tested and only forms dimers. It is therefore concluded that the monocyte-stimulating activity of M. tuberculosis Cpn60.1 resides in the monomeric subunit and within this subunit the biological activity is due to the equatorial domain.

The Mycobacterium tuberculosis chaperonin 10 monomer exhibits structural plasticity

The conditions which favor dissociation of oligomeric Mycobacterium tuberculosis chaperonin 10 and the solution structure of the monomer were studied by analytical ultracentrifugation, size exclusion chromatography, fluorescence, and circular dichroism spectroscopies. At neutral pH and in the absence of divalent cations, the protein is fully monomeric below approximately a 4.7 microM concentration. Under these conditions the monomer forms completely unfolded and partially folded conformers which are in equilibrium with each other. One conformer accumulates over the others which is stable within a very narrow range of temperatures. It contains a beta-sheet-structured C-terminal half and a mostly disordered N-terminal half. Other components of the equilibrium include partially helical structures which do not completely unfold at high temperature or under strong acidic conditions. Complete unfolding of the monomer occurs in the presence of denaturants or below 14 degrees C. Cold-denaturation is detected at an unusually high temperature and this may be due to the concentration of hydrophobic residues, which is larger in chaperonins than in other globular proteins. Finally, the monomer self-associates in the pH range 5.8-2.9, where it forms small oligomers. A structure-activity relationship was investigated with the sequences known to be involved in the various biological activities of the monomer.

Effect of Mycobacterium tuberculosis chaperonins on bronchial eosinophilia and hyper-responsiveness in a murine model of allergic inflammation

BACKGROUND

Epidemiological evidence suggests that infection with Mycobacterium tuberculosis protects children against asthma. Several laboratories have shown that, in mouse models of allergic inflammation, administration of the whole live tuberculosis vaccine, Mycobacterium bovis bacillus Calmette-Guerin (BCG), prevents ovalbumin (OVA)-induced pulmonary eosinophilia.

OBJECTIVE

The aim of this study was to characterize specific M. tuberculosis molecules that are known to modulate immune responses to see if they affected pulmonary eosinophilia and bronchial hyper-responsiveness.

METHODS

C57Bl/6 mice were sensitized to OVA on days 0 and 7 and subsequently challenged with OVA on day 14 over a 3-day period. Pulmonary eosinophilia and bronchial hyper-responsiveness were measured 24 h following the last antigen challenge. In some groups, mice were pre-treated with M. tuberculosis or M. tuberculosis chaperonins (Cpns)60.1, 60.2 and 10, and the effect of this treatment on the allergic inflammatory response to aerosolized OVA was established.

RESULTS

We show that M. tuberculosis Cpns inhibit allergen-induced pulmonary eosinophilia in the mouse. Of the three Cpns produced by M. tuberculosis, Cpn60.1, Cpn10 and Cpn60.2, the first two are effective in preventing eosinophilia when administered by the intra-tracheal route. Furthermore, the increase in airways sensitivity to inhaled methacholine following OVA challenge of immunized mice was suppressed following treatment with Cpn60.1. The allergic inflammatory response was also characterized by an increase in Th2 cytokines IL-4 and IL-5 in bronchoalveolar lavage fluid, which was also suppressed following treatment with Cpn60.1.

CONCLUSION

These data show that bacterial Cpns can suppress eosinophil recruitment and bronchial hyper-responsiveness in a murine model of allergic inflammation.

The TB structural genomics consortium: a resource for Mycobacterium tuberculosis biology

The TB Structural Genomics Consortium is an organization devoted to encouraging, coordinating, and facilitating the determination and analysis of structures of proteins from Mycobacterium tuberculosis. The Consortium members hope to work together with other M. tuberculosis researchers to identify M. tuberculosis proteins for which structural information could provide important biological information, to analyze and interpret structures of M. tuberculosis proteins, and to work collaboratively to test ideas about M. tuberculosis protein function that are suggested by structure or related to structural information. This review describes the TB Structural Genomics Consortium and some of the proteins for which the Consortium is in the progress of determining three-dimensional structures.

Infection-induced up-regulation of the costimulatory molecule 4-1BB in osteoblastic cells and its inhibitory effect on M-CSF/RANKL-induced in vitro osteoclastogenesis

Bacterial infection sometimes impairs bone metabolism. In this study, we infected the osteoblastic cell line MC3T3-E1 with Mycobacterium bovis bacillus Calmette-Guérin (BCG) and identified genes that were up-regulated in the BCG-infected cells by the suppression subtractive hybridization method. A gene encoding 4-1BB (CD137), a member of the tumor necrosis factor-alpha receptor family, was found to be one of the up-regulated genes. Up-regulation of 4-1BB was also observed by infection with Escherichia coli, Salmonella typhimurium, and Staphylococcus aureus, and by treatment with lipopolysaccharides and heat-killed BCG. Bone marrow cells and the macrophage-like cell lines J774 and RAW264.7 were found to express 4-1BB ligand (4-1BBL). Recombinant 4-1BB (r4-1BB) that was immobilized on culture plates strongly inhibited macrophage colony stimulating factor (M-CSF)/receptor activator of nuclear factor-kappaB ligand (RANKL)-induced in vitro osteoclast formation from bone marrow cells. Anti-4-1BBL antibody also inhibited osteoclast formation to a lesser extent, indicating involvement of reverse signaling through 4-1BBL during inhibition of osteoclast formation. A casein kinase I (CKI) inhibitor markedly suppressed the inhibitory effect of r4-1BB on M-CSF/RANKL-induced osteoclast formation, suggesting that CKI might be involved in 4-1BB/4-1BBL reverse signaling. r4-1BB showed no effects on M-CSF- or RANKL-induced phosphorylation of I-kappaB, ERK1/2, p38, or JNK, whereas RANKL-induced phosphorylation of Akt, a downstream target of phosphatidylinositol 3-kinase (PI3K), was completely abolished by r4-1BB, suggesting that 4-1BB/4-1BBL reverse signaling may interfere with PI3K/Akt pathway. r4-1BB also abolished RANKL-mediated induction of nuclear factor of activated T cells-2. This study may elucidate a novel role of 4-1BB in cell metabolism, especially osteoclastogenesis.

Human chaperonin 60 (Hsp60) stimulates bone resorption: structure/function relationships

It is established that the molecular chaperone, chaperonin 60, from various bacteria and from Homo sapiens has cell-cell signalling activity and is able to induce proinflammatory cytokine synthesis. We previously reported that chaperonin 60 proteins from Gram-negative bacteria, but not mycobacteria, have the capacity to resorb cultured murine calvarial bone. We now report that lipopolysaccharide-low human recombinant chaperonin 60 (Hsp60) is a relatively weak cytokine-inducing agonist but is a potent stimulator of murine calvarial bone resorption. The osteolytic activity of Hsp60 was significantly inhibited by indomethacin, interleukin-1 receptor antagonist, and osteoprotegerin, but 5-lipoxygenase inhibitors were less effective. Analysis of Hsp60 truncation mutants revealed that N-terminal mutants (Delta1-137, Delta1-358, and Delta1-465) retained bone resorbing activity. In contrast, a C-terminal truncation mutant (Delta1-26 + Delta466-573) was inactive. This suggests that the active domain in this protein is found within residues 466-573. It is now established that Hsp60 is present in the blood of the majority of the population with the normal range encompassing levels able to activate bone cells. The possibility exists that this protein could play a role in bone remodelling.

Heat shock proteins as regulators of the immune response

Until recently, heat shock proteins (also known as heat stress proteins) have mostly been regarded as intracellular molecules that mediate a range of essential housekeeping and cytoprotective functions. However, interest in their role as intercellular signalling molecules has been fuelled by the observations that these molecules can be released and are present in the extracellular environment under physiological conditions. They can elicit cytokine production by, and adhesion molecule expression of, a range of cell types, and they can deliver maturation signals and peptides to antigen presenting cells through receptor-mediated interactions. These functions suggest that heat shock proteins could be immunoregulatory agents with potent and widely-applicable therapeutic uses. Furthermore, the induction of self heat shock protein immune reactivity can attenuate autoimmunity and delay transplant rejection, and heat shock proteins derived from tumours and pathogens can elicit specific, protective immunity. This review will focus on this rapidly evolving area of heat shock protein biology.

Mycobacterium tuberculosis chaperonin 10 is secreted in the macrophage phagosome: is secretion due to dissociation and adoption of a partially helical structure at the membrane?

To confirm that Mycobacterium tuberculosis chaperonin 10 (Cpn10) is secreted outside the live bacillus, infected macrophages were examined by electron microscopy. This revealed that the mycobacterial protein accumulates both in the wall of the bacterium and in the matrix of the phagosomes in which ingested mycobacteria survive within infected macrophages. To understand the structural implications underlying this secretion, a structural study of M. tuberculosis Cpn10 was performed under conditions that are generally believed to mimic the membrane environment. It was found that in buffer-organic solvent mixtures, the mycobacterial protein forms two main species, namely, a partially helical monomer that prevails in dilute solutions at room temperature and a dimer that folds into a beta-sheet-dominated structure and prevails in either concentrated protein solutions at room temperature or in dilute solutions at low temperature. A partially helical monomer was also found and was completely associated with negatively charged detergents in a micelle-bound state. Remarkably, zwitterionic lipids had no effect on the protein structure. By using N- and C-truncated forms of the protein, the C- and N-terminal sequences were identified as possessing an amphiphilic helical character and as selectively associating with acidic detergent micelles. When the study was extended to other chaperonins, it was found that human Cpn10 is also monomeric and partially helical in dilute organic solvent-buffer mixtures. In contrast, Escherichia coli Cpn10 is mostly dimeric and predominately beta-sheet in both dilute and concentrated solutions. Interestingly, human Cpn10 also crosses biological membranes, whereas the E. coli homologue is strictly cytosolic. These results suggest that dissociation to partially helical monomers and interaction with acidic lipids may be two important steps in the mechanism of secretion of M. tuberculosis Cpn10 to the external environment.

Mycobacterium tuberculosis chaperonin 10 heptamers self-associate through their biologically active loops

The crystal structure of Mycobacterium tuberculosis chaperonin 10 (cpn10(Mt)) has been determined to a resolution of 2.8 A. Two dome-shaped cpn10(Mt) heptamers complex through loops at their bases to form a tetradecamer with 72 symmetry and a spherical cage-like structure. The hollow interior enclosed by the tetradecamer is lined with hydrophilic residues and has dimensions of 30 A perpendicular to and 60 A along the sevenfold axis. Tetradecameric cpn10(Mt) has also been observed in solution by dynamic light scattering. Through its base loop sequence cpn10(Mt) is known to be the agent in the bacterium responsible for bone resorption and for the contribution towards its strong T-cell immunogenicity. Superimposition of the cpn10(Mt) sequences 26 to 32 and 66 to 72 and E. coli GroES 25 to 31 associated with bone resorption activity shows them to have similar conformations and structural features, suggesting that there may be a common receptor for the bone resorption sequences. The base loops of cpn10s in general also attach to the corresponding chaperonin 60 (cpn60) to enclose unfolded protein and to facilitate its correct folding in vivo. Electron density corresponding to a partially disordered protein subunit appears encapsulated within the interior dome cavity of each heptamer. This suggests that the binding of substrates to cpn10 is possible in the absence of cpn60.

Use of a macrophage cell line for rapid detection of Mycobacterium bovis in diagnostic samples

Mycobacterium bovis isolation on bacteriological media from suspected cases of bovine tuberculosis (TB) demands laborious and time-consuming procedures. Even polymerase chain reaction (PCR) and radiometric analyses are secondary procedures and not alternatives to bacteriological procedures. Therefore, there is a need to develop new techniques aimed at rapid M. bovis detection in diagnostic samples. The human macrophage cell line THP-1 was thus investigated in experiments of M. bovis propagation and isolation from reference lymph node suspensions. THP-1 cells were shown to support a high-titered propagation within 48h of minute amounts of both M. bovis BCG and fully pathogenic M. bovis strain 503. A semi-nested PCR for TB-complex-specific insertion sequence IS6110 revealed M. bovis infection in THP-1 cells. The same was true of a flow cytometry (FC) assay for expression of M. bovis chaperonin 10 in infected cells. The reduced time for isolation and identification of M. bovis (48-72h) and the consistency of the test results make the use of macrophage cell cultures attractive and cost-effective for veterinary laboratories involved in TB surveillance.

Mycobacterium tuberculosis pathogenesis and molecular determinants of virulence

Tuberculosis (TB), one of the oldest known human diseases. is still is one of the major causes of mortality, since two million people die each year from this malady. TB has many manifestations, affecting bone, the central nervous system, and many other organ systems, but it is primarily a pulmonary disease that is initiated by the deposition of Mycobacterium tuberculosis, contained in aerosol droplets, onto lung alveolar surfaces. From this point, the progression of the disease can have several outcomes, determined largely by the response of the host immune system. The efficacy of this response is affected by intrinsic factors such as the genetics of the immune system as well as extrinsic factors, e.g., insults to the immune system and the nutritional and physiological state of the host. In addition, the pathogen may play a role in disease progression since some M. tuberculosis strains are reportedly more virulent than others, as defined by increased transmissibility as well as being associated with higher morbidity and mortality in infected individuals. Despite the widespread use of an attenuated live vaccine and several antibiotics, there is more TB than ever before, requiring new vaccines and drugs and more specific and rapid diagnostics. Researchers are utilizing information obtained from the complete sequence of the M. tuberculosis genome and from new genetic and physiological methods to identify targets in M. tuberculosis that will aid in the development of these sorely needed antitubercular agents.

Virulence and the heat shock response

The major adaptive response to elevation in temperature is the heat shock response that involves the induction of many proteins--called heat shock proteins. These include chaperones, proteases, alternative sigma factors and other regulatory and structural proteins. The heat shock response is also turned on by other stress conditions, such as oxidative stress or pH changes. Bacterial entry into the host organism involves a significant environmental change, which is expected to induce the heat shock response. Indeed, some of the heat shock proteins are themselves virulence factors while others affect pathogenesis indirectly, by increasing bacterial resistance to host defenses or regulating virulence genes. The cross talk between heat shock and virulence genes is discussed.

Type I collagen synthesis by human osteoblasts in response to placental lactogen and chaperonin 10, a homolog of early-pregnancy factor

Recent studies have indicated that maternal skeletal metabolism undergoes significant changes during gestation. The agents that are responsible for eliciting these changes in bone turnover during pregnancy have yet to be defined. We therefore sought to investigate whether chaperonin 10 (Cpn10), a homolog of early-pregnancy factor, or human placental lactogen (PL) were capable of influencing the synthesis of type I collagen by human osteoblasts in vitro. Both Cpn10 and PL are major components of the maternal circulation during pregnancy, but how they might contribute to bone metabolism has not been determined. Type I collagen represents the most abundant component of bone tissue, accounting for approximately 90% of the organic compartment. Both Cpn10 and PL were capable of stimulating the synthesis of type I collagen by human osteoblasts in culture. The inclusion of 17 beta-estradiol or prolactin, however, failed to influence the ability of cells to mobilize type I collagen. These novel findings support a role for PL and Cpn10 in the metabolism of bone tissue during pregnancy. Maternal bone collagen metabolism is clearly an important event during pregnancy, and the identification of the factors responsible will aid our understanding of the regulation of skeletal metabolism during gestation.

Chaperonin 60 unfolds its secrets of cellular communication

The cell biology of the chaperonins (Cpns) has been intensively studied over the past 25 years. These ubiquitous and essential molecules assist proteins to fold into their native state and function to protect proteins from denaturation after stress. The structure of the most widely studied Cpn60, Escherichia coli GroEL, has been solved and its mechanism of protein folding action largely established. But in the last decade, evidence has accumulated to suggest that the Cpn60s have functions in addition to intracellular protein folding, particularly the ability to act as intercellular signals with a wide variety of biological effects. Cpn60 has the ability to stimulate cells to produce proinflammatory cytokines and other proteins involved in immunity and inflammation and may, therefore, provide a link between innate and adaptive immunity. Cpn60s are also thought to be pathogenic factors in a wide range of diseases and have recently been reported to be present in the circulation of normal subjects and those with heart disease. An interesting facet of these proteins is the finding that in spite of significant sequence conservation, individual Cpn60 proteins can express very different biological activities. This review discusses the work to date, which has revealed the cell-cell signaling actions of Cpn60 proteins.

Rhizobium leguminosarum chaperonin 60.3, but not chaperonin 60.1, induces cytokine production by human monocytes: activity is dependent on interaction with cell surface CD14

As part of a program of work to understand the interaction of bacterial chaperonins with human leukocytes, we have examined 2 of the 3 chaperonin 60 (Cpn 60) gene products of the nonpathogenic plant symbiotic bacterium, Rhizobium leguminosarum, for their capacity to induce the production of pro- and antiinflammatory cytokines by human cells. Recombinant R. leguminosarum Cpn 60.1 and 60.3 proteins were added to human monocytes at a range of concentrations, and cytokine production was measured by sandwich enzyme-linked immunosorbent assay. In spite of the fact that the 2 R. leguminosarum Cpn 60 proteins share 74.5% amino acid sequence identity, it was found that Cpn 60.3 induced the production of interleukin (IL)-1beta, tumor necrosis factor alpha, IL-6, IL-8, IL-10, and IL-12, but not IL-4, interferon gamma, or GM-CSF (granulocyte-macrophage colony-stimulating factor), whereas the Cpn 60.1 protein failed to demonstrate any cytokine-inducing activity. The use of neutralizing monoclonal antibodies showed that the cytokine-inducing activity of Cpn 60.3 was dependent on its interaction with CD14. This demonstrates that CD14 mediates not only lipopolysaccharide but also R. leguminosarum Cpn 60.3 cell signaling in human monocytes.