Functional domains of HSP70 stimulate generation of cytokines and chemokines, maturation of dendritic cells and adjuvanticity

Inhibition of human immunodeficiency virus type 1 infection of human CD4+ T cells by microbial HSP70 and the peptide epitope 407-426

Human immunodeficiency virus type 1 (HIV-1) virions contain heat shock proteins (HSP), but these proteins have received limited attention. The objectives of this study were to establish if the microbial 70-kDa HSP exerts an inhibitory effect on the HIV-1 infection of human CD4+ T cells, to identify an inhibitory peptide epitope within the sequence of HSP70, and to evaluate the kinetic features of any inhibitory activity. The results of these studies suggest that microbial HSP70 exerts dose-dependent inhibition on CCR5 (R5) strains of clades B, C, and D of HIV-1 infecting human CD4+ T cells. The site of the HIV-1-inhibitory function was identified within the C-terminal peptide binding domain of HSP70, and the function is expressed by the peptide epitope comprising amino acids 407 to 426. The mechanism of inhibition of HIV-1 infectivity by HSP70 is blocking of the CCR5 coreceptors directly and indirectly by inducing CC chemokines and APOBEC3G. The inhibitory effect of HSP70, its C-terminal fragment, or peptide 407-426 may make HSP70 useful as a microbicidal agent. A potentiating noncognate inhibition of HIV-1 infectivity by combined treatment with HSP70 and monoclonal or polyclonal antibody to CCR5 was demonstrated. This novel strategy may be utilized in therapeutic immunization against HIV-1 infection.

Microbial heat shock protein 70 stimulatory properties have different TLR requirements

Members of the HSP70 family have acquired special significance in immunity. Among other receptors, toll like receptor (TLR)-2 and TLR-4 have been suggested to be involved in HSP70-mediated signalling. We have previously shown that recombinant HSP70 from Trypanosoma cruzi and from Plasmodium falciparum function as adjuvants. In the present study, we have extended the study with other microbial HSPs (mHSPs) and considered of interest to assess the influence of TLR-2 and TLR-4 in mHSP-promoted responses. To test this, we evaluated the adjuvant effect of various mHSP molecules in TLR-2(-/-), TLR-4(-/-) and MyD88(-/-) mice. We show that all the mHSPs tested are strong adjuvants and induced IL-12 production by bone marrow macrophages. However, even within the same family, mHSPs induced different types of immune responses. Furthermore, the mHSPs tested, possess different requirements for signaling through TLRs. Interestingly, Tc70 was found to induce in vivo and in vitro responses in both TLR-2(-/-) and TLR-4(-/-) mice. Possible implications of our findings are taken up in the discussion section.

NK cell-based immunotherapies against tumors

Natural killer (NK) cells provide the first line of defence against pathogens and tumors. Their activation status is regulated by pro-inflammatory cytokines and by ligands that either target inhibitory or activating cell surface receptors belonging to the immunoglobulin-like, C-type lectin or natural cytotoxicity receptor families. Apart from non-classical HLA-E, membrane-bound heat shock protein 70 (Hsp70) has been identified as a tumor-specific recognition structure for NK cells expressing high amounts of the C-type lectin receptor CD94, acting as one component of an activating heterodimeric receptor complex. Full-length Hsp70 protein (Hsp70) or the 14-mer Hsp70 peptide T-K-D-N-N-L-L-G-R-F-E-L-S-G (TKD) in combination with pro-inflammatory cytokines enhances the cytolytic activity of NK cells towards Hsp70 membrane-positive tumors. Based on these findings cytokine/TKD-activated NK cells were adoptively transferred in tumor patients. These findings were compared to results of clinical trials using cytokine-activated NK cells.

Immunostimulatory combinations: designing the next generation of vaccine adjuvants

Agents that activate dendritic cells are essential components for vaccines and can be conceptualized as molecular adjuvants. Other molecular adjuvants affect downstream factors that shape the resulting immune response. This review provides a compendium of recently studied molecular adjuvants, focusing on CD8+ T cell responses, which have important roles in HIV vaccines. Reference is also made to CD8+ T cell antitumor responses, where parallel studies of molecular adjuvants are being pursued. Molecular adjuvants can be considered in the following groups: TNF superfamily molecules such as CD40 ligand; agonists for TLRs; agonists for NAIP, CIITA, HET-E, TP-1-leucine-rich repeat pathway receptors, such as nucleotide-binding and oligomerization domain (NOD)1, NOD2, and cryopyrin; chemokines; ILs; CSFs; IFNs; alarmins; and purinergic P2X7 receptor agonists. Complementing these positively acting agents are strategies to reduce the immunosuppressive effects of CD4+CD25+ regulatory T cells and negatively acting factors such as TGF-beta, IL-10, suppressor of cytokine signaling 1, and programmed cell death-1 using neutralizing antibodies, antisense, and small interfering RNA. Especially effective are combinations of molecular adjuvants, which can elicit a massive expansion of antigen-specific CD8+ T cells and show unprecedented efficacy in vaccine and tumor models. Taken together, these new approaches provide significant incremental progress in the development of vaccines to elicit cell-mediated immunity against HIV and other pathogens.

Intracellular and extracellular functions of heat shock proteins: repercussions in cancer therapy

Stress or heat shock proteins (HSPs) are the most conserved proteins present in both prokaryotes and eukaryotes. Their expression is induced in response to a wide variety of physiological and environmental insults. These proteins play an essential role as molecular chaperones by assisting the correct folding of nascent and stress-accumulated misfolded proteins, and preventing their aggregation. HSPs have a dual function depending on their intracellular or extracellular location. Intracellular HSPs have a protective function. They allow the cells to survive lethal conditions. Various mechanisms have been proposed to account for the cytoprotective functions of HSPs. Several HSPs have also been demonstrated to directly interact with various components of the tightly regulated programmed cell death machinery, upstream and downstream of the mitochondrial events. On the other hand, extracellular located or membrane-bound HSPs mediate immunological functions. They can elicit an immune response modulated either by the adaptive or innate immune system. This review will focus on HSP27, HSP70, and HSP90. We will discuss the dual role of these HSPs, protective vs. immunogenic properties, making a special emphasis in their utility as targets in cancer therapy.

On the brotherhood of the mitochondrial chaperones mortalin and heat shock protein 60

The heat shock chaperones mortalin/mitochondrial heat shock protein 70 (mtHsp70) and Hsp60 are found in multiple subcellular sites and function in the folding and intracellular trafficking of many proteins. The chaperoning activity of these 2 proteins involves different structural and functional mechanisms. In spite of providing an excellent model for an evolutionarily conserved molecular "brotherhood", their individual functions, although overlapping, are nonredundant. As they travel to various locations, both chaperones acquire different binding partners and exert a more divergent involvement in tumorigenesis, cellular senescence, and immunology. An understanding of their functional biology may lead to novel designing and development of therapeutic strategies for cancer and aging.

Releasing signals, secretory pathways, and immune function of endogenous extracellular heat shock protein 72

Heat shock proteins (Hsp) were first characterized as intracellular proteins, which function to limit protein aggregation, facilitate protein refolding, and chaperone proteins. During times of cellular stress, intracellular Hsp levels increase to provide cellular protection. Recently, it has been recognized that Hsp, particularly Hsp72, are also found extracellularly (eHsp72), where they exhibit potent immunomodulatory effects on innate and acquired immunity. Circulating eHsp72 levels also greatly increase during times of stress (i.e., when an organism is exposed to a physical/psychological stressor or suffers from various pathological conditions). It has been proposed that elevated eHsp72 serves a protective role by facilitating immunological responses during times of increased risk of pathogenic challenge and/or tissue damage. This review focuses on the in vivo releasing signals and immunomodulatory function(s) of endogenous eHsp72. In addition, we present data that emphasize the importance of caution when conducting in vitro immunological tests of Hsp72 function.

Heat shock proteins in immunity

This chapter focuses on immunological effects of eukaryotic and microbial heat shock proteins (HSPs), with molecular weights of about 60, 70, and 90 kDa. The search for tumor-specific antigens resulted in the identification of HSPs. They have been found to elicit a potent anti-cancer immune response mediated by the adoptive and innate immune system. Following receptor-mediated uptake of HSP (HSP70 and gp96) peptide complexes by antigen-presenting cells and representation of HSP-chaperoned peptides by MHC class I molecules, a CD8-specific T cell response is induced. Apart from chaperoning immunogenic peptides derived from tumors, bacterial and virally infected cells, they by themselves provide activatory signals for antigen-presenting cells and natural killer (NK) cells. After binding of peptide-free HSP70 to Toll-like receptors, the secretion of pro-inflammatory cytokines is initiated by antigen-presenting cells and thus results in a nonspecific stimulation of the immune system. Moreover, soluble as well as cell membrane-bound HSP70 on tumor cells can directly activate the cytolytic and migratory capacity of NK cells. Apart form cancer, HSPs of different origins, with a molecular weight of about 60, 70, and 90 kDa, also play a pivotal role in viral infections, including human and simian immunodeficiency virus (HIV, SIV), measles, and choriomeningitis. Moreover, HSPs have been found to induce tolerance against autoimmune diseases. In summary, depending on their mode of induction, intracellular/extracellular location, cellular origin (eukaryote/prokaryote), peptide loading status, intracellular ADP/ATP content, concentration, and route of application, HSPs either exert immune activation as danger signals in cancer immunity and mediate protection against infectious diseases or exhibit regulatory activities in controlling and preventing autoimmunity.

Exposure to mycobacteria primes the immune system for evolutionarily diverse heat shock proteins

During stress conditions, such as infection, the synthesis of heat shock proteins (HSPs) in microorganisms is upregulated. Since a high degree of homology exists within each HSP family, we postulated that exposure to microorganisms could prime the immune system for evolutionarily diverse HSPs. We tested this hypothesis by priming mice with three microorganisms, namely, Mycobacterium bovis BCG, Mycobacterium vaccae, and Chlamydia pneumoniae. After this, mice received a dose of the various HSPs. We found that BCG and M. vaccae but not C. pneumoniae primed the immune system for the induction of secondary immunoglobulin G (IgG) responses to most of the HSPs tested. Analysis of the IgG1 and IgG2a profile and gamma interferon production induced against the HSPs revealed the induction of a mixture of responses. We also observed that sera from mice treated with M. vaccae and HSP70 were cross-reactive, but no antibody complexes were observed in their kidneys, which frequently are targets for autoantibody reactions. Our findings add further support for the use of HSPs as effective vaccine adjuvants.

Antimicrobial peptides enhance the candidacidal activity of antifungal drugs by promoting the efflux of ATP from Candida cells

OBJECTIVES

To establish a novel strategy of fungal infection control.

METHODS

We examined the influences of antimicrobial peptides including a synthesized short lactoferrin peptide (FKCRRWQWRM, Peptide 2; Pep2) on the synthesis of Candida cell wall polysaccharides, ergosterol synthesis, membrane permeability and the efflux of ATP.

RESULTS

Colony formation of Candida albicans was synergistically suppressed by a combination of low concentrations of each drug and peptide. All peptides and amphotericin B, but not itraconazole, revealed weak inhibitory activities against ergosterol synthesis and the peptides weakly suppressed the synthesis of Candida cell wall components, glucan, mannan and chitin. Cell membrane permeability was not only increased by these peptides but also clearly increased by both amphotericin B and itraconazole. ATP efflux was however up-regulated by low concentrations of the peptides, especially by Pep2 and Hst5, although both antifungal drugs did not exert any influence on ATP efflux. The expression of the Candida drug resistance genes 1 and 2 (CDR1 and CDR2) was increased by both drugs, but this increase was suppressed by each peptide. In addition, larger amounts of amphotericin B and itraconazole remained in Candida cells in the presence of Pep2 or Hst5 due to the lower excretion. The effects of both peptides on ATP efflux and increase of intercellular amphotericin B and itraconazole were blocked by anion channel inhibitors 4,4'-diisothiocyanatestilbene-2, 2'-disulphonic acid and 5-nitro-2-(3-phenylpropylamino) benzoic acid.

CONCLUSIONS

The examined peptides, especially Pep2 and Hst5, enhance the candidacidal activity of antifungal drugs by promoting anion channel-associated ATP efflux from Candida cells and decreasing efflux of the drugs, which could be useful clinical applications.

Adrenergic receptors mediate stress-induced elevations in extracellular Hsp72

Heat-shock protein concentrations in the blood increase after exposure to a variety of stressors, including trauma and psychological stress. Although the physiological function of extracellular heat shock protein remains controversial, there is evidence that extracellular heat shock protein 72 (Hsp72) can facilitate immunologic responses. The signal(s) that mediate(s) the in vivo elevation of extracellular Hsp72 in the blood after stressor exposure remain(s) unknown. Here we report that Hsp72 increases in the circulation via an α1-adrenergic receptor-mediated signaling pathway. Activation of α1-adrenoceptors results in a rapid increase in circulating Hsp72, and blockade of α1-adrenoceptors prevents the stress-induced rise in circulating Hsp72. Furthermore, our studies exclude a role for β-adrenoceptors, glucocorticoids, and ACTH in mediating stress-induced elevations in circulating extracellular Hsp72. Understanding the signals involved in elevating extracellular Hsp72 could facilitate the use of extracellular Hsp72 to bolster immunity and perhaps prevent exacerbation of inflammatory diseases during stress.

HSP110 induces "danger signals" upon interaction with antigen presenting cells and mouse mammary carcinoma

HSP110 is a large molecular weight heat shock protein highly capable of chaperoning large proteins. When chaperoning tumour antigens, HSP110 is capable of eliciting effective anti-tumour immune responses. In the present study, we have determined whether such immunoadjuvant properties of HSP110 stem from its ability to induce "danger signals" through interaction with antigen presenting cells (APCs) and with tumour cells. In the previous studies, endotoxin contamination of HSP preparations was always a matter of concern and controversy. Therefore, we prepared recombinant HSP110 with low endotoxin concentration at which LPS did not have any effect on dendritic cells (DCs). We then evaluated the ability of the HSP110 to induce "danger signals" while interacting with APCs or mouse mammary carcinoma cell line (MMC), as evaluated by modulation of cell surface receptors and cytokines involved in innate and adaptive immune responses. We also performed competition studies in order to rule out contribution of endotoxin in HSP110 preparations while interacting with DCs and MMC. We showed that low endotoxin HSP110 induced DCs to up-regulate the expression of MHC class II, CD40 and CD86 molecules, and to secrete pro-inflammatory cytokines IL-6, IL-12 and TNF-alpha. Importantly, HSP110 induced MMC to secrete IL-12 and elevate secretion of IL-6 and expression of CD40 molecule. These findings demonstrate that HSP110 acts as a "danger signal" through its interaction with DCs and tumour cells, regardless of its endotoxin component. These immunoadjuvant properties of HSP110 suggest that pre-existing immunity in tumour-bearing individuals,may be due to the release of HSPs from tumours upon necrosis alerting the immune system against the tumours.