The heat shock protein HSP70 promotes mouse NK cell activity against tumors that express inducible NKG2D ligands

The stress-inducible heat shock protein (HSP) 70 is known to function as an endogenous danger signal that can increase the immunogenicity of tumors and induce CTL responses. We show in this study that HSP70 also activates mouse NK cells that recognize stress-inducible NKG2D ligands on tumor cells. Tumor size and the rate of metastases derived from HSP70-overexpressing human melanoma cells were found to be reduced in T and B cell-deficient SCID mice, but not in SCID/beige mice that lack additionally functional NK cells. In the SCID mice with HSP70-overexpressing tumors, NK cells were activated so that they killed ex vivo tumor cells that expressed NKG2D ligands. In the tumors, the MHC class I chain-related (MIC) A and B molecules were found to be expressed. Interestingly, a counter selection was observed against the expression of MICA/B in HSP70-overexpressing tumors compared with control tumors in SCID, but not in SCID/beige mice, suggesting a functional relevance of MICA/B expression. The melanoma cells were found to release exosomes. HSP70-positive exosomes from the HSP70-overexpressing cells, in contrast to HSP70-negative exosomes from the control cells, were able to activate mouse NK cells in vitro to kill YAC-1 cells, which express NKG2D ligands constitutively, or the human melanoma cells, in which MICA/B expression was induced. Thus, HSP70 and inducible NKG2D ligands synergistically promote the activation of mouse NK cells resulting in a reduced tumor growth and suppression of metastatic disease.     

Genetic engineering of the major timothy grass pollen allergen, Phl p 6, to reduce allergenic activity and preserve immunogenicity

On the basis of IgE epitope mapping data, we have produced three allergen fragments comprising aa 1-33, 1-57, and 31-110 of the major timothy grass pollen allergen Phl p 6 aa 1-110 by expression in Escherichia coli and chemical synthesis. Circular dichroism analysis showed that the purified fragments lack the typical alpha-helical fold of the complete allergen. Superposition of the sequences of the fragments onto the three-dimensional allergen structure indicated that the removal of only one of the four helices had led to the destabilization of the alpha helical structure of Phl p 6. The lack of structural fold was accompanied by a strong reduction of IgE reactivity and allergenic activity of the three fragments as determined by basophil histamine release in allergic patients. Each of the three Phl p 6 fragments adsorbed to CFA induced Phl p 6-specific IgG Abs in rabbits. However, immunization of mice with fragments adsorbed to an adjuvant allowed for human use (AluGel-S) showed that only the Phl p 6 aa 31-110 induced Phl p 6-specific IgG Abs. Anti-Phl p 6 IgG Abs induced by vaccination with Phl p 6 aa 31-110 inhibited patients' IgE reactivity to the wild-type allergen as well as Phl p 6-induced basophil degranulation. Our results are of importance for the design of hypoallergenic allergy vaccines. They show that it has to be demonstrated that the hypoallergenic derivative induces a robust IgG response in a formulation that can be used in allergic patients.     

Biphasic perimicrovillar membrane production following feeding by previously starved Dysdercus peruvianus (Hemiptera: Pyrrhocoridae)

The development of perimicrovillar membranes (PMM) from midgut cells of starved and fed Dysdercus peruvianus was studied by using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and assays for specific enzymatic markers of the perimicrovillar membranes (alpha-glucosidase), perimicrovillar space (aminopeptidase) and microvillar membranes (beta-glucosidase). High activities of these enzymes were observed 6h post-feeding and significant production of membranes was observed at 30 h post-feeding. In the gut cells of starved insects, the rough endoplasmic reticulum was organized in concentric bundles, with a greater number of mitochondria in the cellular apex. The presence of electron dense double-membrane vesicles and the production of PMM were not observed in this condition. Thirty hours post-feeding, a disorganization of the rough endoplasmic reticulum was observed, and it was possible to see double-membrane vesicles close to the cell apex. The membrane system formation was evident with a significant development of PMM in the midgut lumen. The luminal surface of the midgut during starvation and up to 48 h post-feeding was monitored using SEM. It was demonstrated that in the starved condition, the PMM was virtually absent from gut cells, except at the base of the microvilli. At 6h post-feeding, the microvilli were already completely covered with PMM, but with a maximum of PMM formation seen at 30 h post-feeding. Signals of PMM degradation were observed 48 h after pulse feeding.     

Treatment-enhanced CD4+Foxp3+ glucocorticoid-induced TNF receptor family related high regulatory tumor-infiltrating T cells limit the effectiveness of cytokine-based immunotherapy

Regulatory T cells can suppress activated CD4+ and CD8+ T effector cells and may serve as an impediment to spontaneous or therapeutic type 1 antitumor immunity. In a previous study, we observed minimal therapeutic impact, but significantly enhanced T cell cross-priming and lesional infiltration of tumor-reactive CD8+ T cells into established CMS4 sarcomas after combined treatment of BALB/c mice with rFLt3 ligand (rFL) and recombinant GM-CSF (rGM-CSF). In this study, we show that this cytokine regimen also results in the profound enhancement of CD4+ tumor-infiltrating lymphocytes (TIL) expressing FoxP3, IL-10, and TGF-beta mRNA, with 50 or 90% of CD4+ TIL coexpressing the CD25 and glucocorticoid-induced TNFR family related molecules, respectively. Intracellular staining for Foxp3 protein revealed that combined treatment with rFL plus rGM-CSF results in a significant increase in CD4+Foxp3+ T cells in the spleen of both control and tumor-bearing mice, and that nearly half of CD4+ TIL expressed this marker. In addition, CD4+ TIL cells were of an activated/memory (ICOS(high)CD62L(low)CD45RB(low)) phenotype and were capable of suppressing allospecific T cell proliferation and IFN-gamma production from (in vivo cross-primed) anti-CMS4 CD8+ T cells in vitro, via a mechanism at least partially dependent on IL-10 and TGF-beta. Importantly, in vivo depletion of CD4+ T cells resulted in the ability of previously ineffective, rFL plus rGM-CSF therapy-induced CD8+ T cells to now mediate tumor regression.     

The 2.7 A crystal structure of the autoinhibited human c-Fms kinase domain

c-Fms, a member of the Platelet-derived Growth Factor (PDGF) receptor family of receptor tyrosine kinases (RTKs), is the receptor for macrophage colony stimulating factor (CSF-1) that regulates proliferation, differentiation and survival of cells of the mononuclear phagocyte lineage. Abnormal expression of c-fms proto-oncogene is associated with a significant number of human pathologies, including a variety of cancers and rheumatoid arthritis. Accordingly, c-Fms represents an attractive therapeutic target. To further understand the regulation of c-Fms, we determined the 2.7 A resolution crystal structure of the cytosolic domain of c-Fms that comprised the kinase domain and the juxtamembrane domain. The structure reveals the crucial inhibitory role of the juxtamembrane domain (JM) that binds to a hydrophobic site immediately adjacent to the ATP binding pocket. This interaction prevents the activation loop from adopting an active conformation thereby locking the c-Fms kinase into an autoinhibited state. As observed for other members of the PDGF receptor family, namely c-Kit and Flt3, three JM-derived tyrosine residues primarily drive the mechanism for autoinhibition in c-Fms, therefore defining a common autoinhibitory mechanism within this family. Moreover the structure provides an understanding of c-Fms inhibition by Gleevec as well as providing a platform for the development of more selective inhibitors that target the inactive conformation of c-Fms kinase.     

Dual selection pressure by drugs and HLA class I-restricted immune responses on human immunodeficiency virus type 1 protease

To determine the influence of human immunodeficiency virus type 1 (HIV-1)-specific CD8+ T cells on the development of drug resistance mutations in the HIV-1 protease, we analyzed protease sequences from viruses from a human leukocyte antigen class I (HLA class I)-typed cohort of 94 HIV-1-positive individuals. In univariate statistical analyses (Fisher's exact test), minor and major drug resistance mutations as well as drug-associated polymorphisms showed associations with HLA class I alleles. All correlations with P values of 0.05 or less were considered to be relevant without corrections for multiple tests. A subset of these observed correlations was experimentally validated by enzyme-linked immunospot assays, allowing the definition of 10 new epitopes recognized by CD8+ T cells from patients with the appropriate HLA class I type. Several drug resistance-associated mutations in the protease acted as escape mutations; however, cells from many patients were still able to generate CD8+ T cells targeting the escape mutants. This result presumably indicates the usage of different T-cell receptors by CD8+ T cells targeting these epitopes in these patients. Our results support a fundamental role for HLA class I-restricted immune responses in shaping the sequence of the HIV-1 protease in vivo. This role may have important clinical implications both for the understanding of drug resistance pathways and for the design of therapeutic vaccines targeting drug-resistant HIV-1.     

CARMA1 coiled-coil domain is involved in the oligomerization and subcellular localization of CARMA1 and is required for T cell receptor-induced NF-kappaB activation

T lymphocyte (T cell) activation and proliferation is induced by the activation of multiple signal transduction pathways. Earlier studies indicate that CARMA1, a Caspase Recruitment Domain (CARD) and Membrane-associated GUanylate Kinase domain (MAGUK)-containing scaffold protein, plays an essential role in NF-kappaB activation induced by the costimulation of T cell receptor (TCR) and CD28 molecules. However, the molecular mechanism by which CARMA1 mediates TCR-CD28 costimulation-induced NF-kappaB activation is not fully understood. Here we show that CARMA1 is constitutively oligomerized. This oligomerization of CARMA1 is through its Coiled-coil domain. Disruption of the predicted structure of the Coiled-coil domain of CARMA1 impaired its oligomerization and, importantly, abrogated CARMA1-mediated NF-kappaB activation. Interestingly, disruption of the CC1 domain abrogates CARMA1 localization, whereas disruption of the CC2 domain seems to inhibit CARMA1 self-association. Together, our results demonstrate that the oligomerization of CARMA1 is required for TCR-induced NF-kappaB activation.     

History-dependence of isometric muscle force: effect of prior stretch or shortening amplitude

It is well-recognised that steady-state isometric muscle force is decreased following active shortening (force depression, FD) and increased following active stretch (force enhancement, FE). It has also been demonstrated that passive muscle force is increased following active stretch (passive FE). Several studies have reported that FD increases with shortening amplitude and that FE and passive FE increase with stretch amplitude. Here, we investigate whether these trends continue with further increases in shortening or stretch amplitude. Experiments were performed using in situ cat soleus muscles (n=8 for FD; n=7 for FE and passive FE). FD, FE and passive FE were measured after shortening or stretch contractions that covered as wide a range of amplitudes as practically possible without damaging the muscles. FD increased approximately linearly with shortening amplitude, over the full range of amplitudes investigated. This is consistent with the hypothesis that FD arises from a stress-induced inhibition of crossbridges. FE increased with stretch amplitude only up to a point, and then levelled off. Passive FE, and the transient increase in force at the end of stretch, showed relationships to stretch amplitude that were qualitatively very similar to the relationship for FE, increasing only until the same critical stretch amplitude had been reached. We conclude that FE and passive FE do not increase with stretch amplitude under all circumstances. This finding has important consequences for determining the mechanisms underlying FE and passive FE because any mechanism that is proposed to explain them must be able to predict it.     

The crystal structure and mutational binding analysis of the extracellular domain of the platelet-activating receptor CLEC-2

The human C-type lectin-like molecule CLEC-2 is expressed on the surface of platelets and signaling through CLEC-2 causes platelet activation and aggregation. CLEC-2 is a receptor for the platelet-aggregating snake venom protein rhodocytin. It is also a newly identified co-receptor for human immunodeficiency virus type 1 (HIV-1). An endogenous ligand has not yet been identified. We have solved the crystal structure of the extracellular domain of CLEC-2 to 1.6-A resolution, and identified the key structural features involved in ligand binding. A semi-helical loop region and flanking residues dominate the surface that is available for ligand binding. The precise distribution of hydrophobic and electrostatic features in this loop will determine the nature of any endogenous ligand with which it can interact. Major ligand-induced conformational change in CLEC-2 is unlikely as its overall fold is compact and robust. However, ligand binding could induce a tilt of a 3-10 helical portion of the long loop region. Mutational analysis and surface plasmon resonance binding studies support these observations. This study provides a framework for understanding the effects of rhodocytin venom binding on CLEC-2 and for understanding the nature of likely endogenous ligands and will provide a basis for rational design of drugs to block ligand binding.