Calreticulin is an interleukin-3-sensitive calcium-binding protein in human basophil leukocytes

Signaling pathways activated by a protease allergen in basophils

Allergic diseases represent a significant burden in industrialized countries, but why and how the immune system responds to allergens remain largely unknown. Because many clinically significant allergens have proteolytic activity, and many helminths express proteases that are necessary for their life cycles, host mechanisms likely have evolved to detect the proteolytic activity of helminth proteases, which may be incidentally activated by protease allergens. A cysteine protease, papain, is a prototypic protease allergen that can directly activate basophils and mast cells, leading to the production of cytokines, including IL-4, characteristic of the type 2 immune response. The mechanism of papain's immunogenic activity remains unknown. Here we have characterized the cellular response activated by papain in basophils. We find that papain-induced IL-4 production requires calcium flux and activation of PI3K and nuclear factor of activated T cells. Interestingly, papain-induced IL-4 production was dependent on the immunoreceptor tyrosine-based activation motif (ITAM) adaptor protein Fc receptor γ-chain, even though the canonical ITAM signaling was not activated by papain. Collectively, these data characterize the downstream signaling pathway activated by a protease allergen in basophils.

Evidence of pathway-specific basophil anergy induced by peanut oral immunotherapy in peanut-allergic children

BACKGROUND

In Westernized countries, over 1% of the population is allergic to peanuts or tree nuts, which carries a risk of severe allergic reactions. Several studies support the efficacy of peanut oral immunotherapy (OIT) for reducing the clinical sensitivity of affected individuals; however, the mechanisms of this effect are still being characterized. One mechanism that may contribute is the suppression of effector cells, such as basophils. Basophil anergy has been characterized in vitro as a pathway-specific hyporesponsiveness; however, this has not been demonstrated to occur in vivo.

OBJECTIVE

To evaluate the hypothesis that basophil anergy occurs in vivo due to chronic allergen exposure in the setting of a clinical oral immunotherapy trial.

METHODS

Samples of peripheral blood were obtained from subjects during a placebo-controlled clinical trial of peanut OIT. Basophil reactivity to in vitro stimulation with peanut allergen and controls was assessed by the upregulation of activation markers, CD63 and CD203c, measured by flow cytometry.

RESULTS

The upregulation of CD63 following stimulation of the IgE receptor, either specifically with peanut allergen or non-specifically with anti-IgE antibody, was strongly suppressed by active OIT. However, OIT did not significantly suppress this response in basophils stimulated by the distinct fMLP receptor pathway. In the subset of subjects with egg sensitization, active peanut OIT also suppressed CD63 upregulation in response to stimulation with egg allergen. Allergen OIT also suppressed the upregulation of CD203c including in response to stimulation with IL-3 alone.

CONCLUSION

Peanut OIT induces a hyporesponsive state in basophils that is consistent with pathway-specific anergy previously described in vitro. This suggests the hypothesis that effector cell anergy could contribute to clinical desensitization.

Thioredoxin Txnl1/TRP32 is a redox-active cofactor of the 26 S proteasome

The 26 S proteasome is a large proteolytic machine, which degrades most intracellular proteins. We found that thioredoxin, Txnl1/TRP32, binds to Rpn11, a subunit of the regulatory complex of the human 26 S proteasome. Txnl1 is abundant, metabolically stable, and widely expressed and is present in the cytoplasm and nucleus. Txnl1 has thioredoxin activity with a redox potential of about -250 mV. Mutant Txnl1 with one active site cysteine replaced by serine formed disulfide bonds to eEF1A1, a substrate-recruiting factor of the 26 S proteasome. eEF1A1 is therefore a likely physiological substrate. In response to knockdown of Txnl1, ubiquitin-protein conjugates were moderately stabilized. Hence, Txnl1 is the first example of a direct connection between protein reduction and proteolysis, two major intracellular protein quality control mechanisms.

The application of proteomics technology to thrombosis research: the identification of potential therapeutic targets in cardiovascular disease

Thrombus formation underpins the development of cardiovascular diseases, including acute coronary syndromes and ischaemic stroke. A number of well-characterised cardiovascular risk factors which contribute to the development of the majority of cardiovascular events have been identified, including dyslipidaemia, hypertension and diabetes. Individuals with type 2 diabetes mellitus (T2DM) have a 3- to 5-fold increased risk for development of cardiovascular disease (CVD). They may have a cluster of haemostatic abnormalities, including elevated levels of plasminogen activator inhibitor-1 (PAI-1) and fibrinogen, which contribute to acute thrombotic events. It is clear that additional unidentified risk factors contribute to the pathogenesis of cardiovascular events, and so the search for novel biomarkers and effectors, particularly in individuals with T2DM, remains a major challenge of cardiovascular medicine. Plasma and cellular proteins which contribute to thrombus formation have the potential to confer a pro-thrombotic state and represent a link between genotype, environment and disease phenotype. The comprehensive analysis of these proteins is now increasingly facilitated through the continued development of proteomic technologies which provide multifaceted approaches to the identification of novel biomarkers and/or effectors of thrombus formation and on which future anticoagulant and thrombolytic therapies may be based. This review provides an overview of current proteomic technologies. It focuses on the recent studies in which these technologies have been applied in the search for novel proteins that may confer increased risk of acute cardiovascular diseases and therefore that may influence disease progression and therapy.

Adrm1, a putative cell adhesion regulating protein, is a novel proteasome-associated factor

We have identified Adrm1 as a novel component of the regulatory ATPase complex of the 26 S proteasome: Adrm1 was precipitated with an antibody to proteasomes and vice versa. Adrm1 co-migrated with proteasomes on gel-filtration chromatography and non-denaturing polyacrylamide gel electrophoresis. Adrm1 has been described as an interferon-gamma-inducible, heavily glycosylated membrane protein of 110 kDa. However, we found Adrm1 in mouse tissues only as a 42 kDa peptide, corresponding to the mass of the non-glycosylated peptide chain, and it could not be induced in HeLa cells with interferon. Adrm1 was present almost exclusively in soluble 26 S proteasomes, albeit a small fraction was membrane-associated, like proteasomes. Adrm1 was found in cells in amounts equimolar with S6a, a 26 S proteasome subunit. HeLa cells contain no pool of free Adrm1 but recombinant Adrm1 could bind to pre-existing 26 S proteasomes in cell extracts. Adrm1 may be distantly related to the yeast proteasome subunit Rpn13, mutants of which are reported to display no obvious phenotype. Accordingly, knock-down of Adrm1 in HeLa cells had no effect on the amount of proteasomes, or on degradation of bulk cell protein, or accumulation of polyubiquitinylated proteins. This indicates that Adrm1 has a specialised role in proteasome function.

Isolation and characterization of human apolipoprotein M-containing lipoproteins

Apolipoprotein M (apoM) is a novel apolipoprotein with unknown function. In this study, we established a method for isolating apoM-containing lipoproteins and studied their composition and the effect of apoM on HDL function. ApoM-containing lipoproteins were isolated from human plasma with immunoaffinity chromatography and compared with lipoproteins lacking apoM. The apoM-containing lipoproteins were predominantly of HDL size; approximately 5% of the total HDL population contained apoM. Mass spectrometry showed that the apoM-containing lipoproteins also contained apoJ, apoA-I, apoA-II, apoC-I, apoC-II, apoC-III, paraoxonase 1, and apoB. ApoM-containing HDL (HDL(apoM+)) contained significantly more free cholesterol than HDL lacking apoM (HDL(apoM-)) (5.9 +/- 0.7% vs. 3.2 +/- 0.5%; P < 0.005) and was heterogeneous in size with both small and large particles. HDL(apoM+) inhibited Cu(2+)-induced oxidation of LDL and stimulated cholesterol efflux from THP-1 foam cells more efficiently than HDL(apoM-). In conclusion, our results suggest that apoM is associated with a small heterogeneous subpopulation of HDL particles. Nevertheless, apoM designates a subpopulation of HDL that protects LDL against oxidation and stimulates cholesterol efflux more efficiently than HDL lacking apoM.

Identification and characterization of glucoamylase from the fungus Thermomyces lanuginosus

The glucoamylase from the thermophilic fungus Thermomyces lanuginosus has a molecular weight of 66 kDa and was characterized with isoelectric point, pH and temperature optimum of 3.8-4.0, 5.0 and 70 degrees C, respectively. In addition, the activation energy is 60.4 kJ/mol, Km is 3.5 mM and kcat is 25.3 s(-1). The glucoamylase was partially sequenced on the protein level, and the complete glucoamylase gene including its promoter (but excluding its terminator region) was cloned and sequenced. The glucoamylase protein comprises 617 amino acid residues and shows 60% identity with the glucoamylase from the thermophilic fungus Talaromyces emersonii. cDNA encoding Thermomyces lanuginosus glucoamylase was expression cloned into Pichia pastoris, producing approximately 7.4 U/ml. It was concluded that alternative mRNA splicing as it might occur in Aspergillus niger glucoamylase is not responsible for the occurrence of different glucoamylase isoforms in Thermomyces lanuginosus.

p21Waf1 inhibits granulocytic differentiation of 32Dcl3 cells

Defining the molecular mechanisms that prevent myeloid progenitor cells from maturing is important because defects in maturation contribute to the development of myeloproliferative and myelodysplastic diseases. IL-3 is an important developmental factor for myeloid progenitor cells in vivo and is required to maintain the undifferentiated state in the 32Dcl3 cell line. The mechanisms employed by IL-3 to block differentiation, however, are not well understood. 32Dcl3 cells are myeloid progenitor cells of murine origin with high basal levels of p21waf1/cip1 (p21) expression. Our laboratory has previously reported that p21 levels decreased as CD34+-derived myeloid progenitor cells underwent terminal granulopoiesis in vitro. The effect of p21 upon the expression of genes associated with granulocytic differentiation has been unexplored, however. Since IL-3 maintains high levels of p21 in 32Dcl3 cells, we tested the hypothesis that p21 is an inhibitor of myeloid differentiation. Our findings demonstrate that siRNA knockdown of murine p21 is correlated with premature expression of the primary granule proteins myeloperoxidase and proteinase-3, proteins not abundant in cells maintained as myeloblasts by IL-3. Rescue with human p21 in these cells suppressed premature granule protein expression. p21 knockdown was also found to accelerate morphologic granulocytic differentiation in 32Dcl3 cells stimulated with G-CSF. Since high expression levels of p21 and overexpression of the IL-3 receptor have been correlated with poor outcomes in acute myeloid leukemias (AML), differentiation blockade by p21 may be one mechanism that contributes to AML pathogenesis.

Identification of a major protein on the cytosolic face of caveolae

Cav-p60, a specific and ubiquitous caveolar protein, was immunoprecipitated from solubilized rat adipocyte plasma membranes and identified as similar to a GeneBank entry annotated mouse polymerase transcript release factor (PTRF) by MALDI-TOF and MS-MS of major fragments. Cloning and virtual translation of the corresponding rat adipocyte cDNA sequence revealed 98.7% identity with mouse PTRF. In vitro translation of this sequence produced a protein, which was recognized by antibodies to both cav-p60 and PTRF. EM gold labeling studies showed that a rabbit antiserum against murine PTRF immunolabeled caveolae specifically in adipocytes from both mouse and rat. In view of the reported function of the protein, which is exerted in the cell nucleus, its subcellular localization was investigated. We found that the protein could be purified by differential solubilization of a plasma membrane fraction followed by SDS-PAGE, and that the protein was as abundant as caveolin in this fraction. We were unable to detect the protein in cell nuclei by subcellular fractionation or fluorescence microscopy. The results show that in a large number of cell types, PTRF is essentially located to caveolae, and that each caveola harbors many copies of the protein. Consequently, we suggest the name Cavin for this protein.

Prodefensins are matrix proteins of specific granules in human neutrophils

Defensins are potent antimicrobial and proinflammatory peptides. The human neutrophil defensins human neutrophil peptide (HNP)-1-3 are synthesized as 94 amino acide (aa) preproHNPs, which are converted to 75 aa proHNPs by cotranslational removal of a 19 aa endoplasmic reticulum signal peptide. At the promyelocytic stage of myelopoiesis, proHNPs are further proteolytically modified and accumulate in azurophil granules as 29-30 aa HNPs. In contrast, proHNPs produced by more mature myeloid cells are not subjected to proteolytic cleavage and undergo a high degree of constitutive exocytosis. The proHNPs are devoid of antimicrobial potential, and the significance of their secretion is unknown. To investigate whether mature neutrophils contain proHNPs, we developed antibodies against proHNP-1 by DNA immunization of rabbits. In addition, antibodies against the 45 aa proHNP pro-piece were raised by conventional immunization procedures. These antibodies allowed detection of proHNPs in homogenates of peripheral blood neutrophils. The proHNPs were isolated by affinity chromatography, and their identity was confirmed by mass spectrometry and N-terminal aa sequence analysis. Finally, the neutrophil proHNPs were identified as novel matrix proteins of specific granules by subcellular fractionation experiments, release studies, and immunoelectron microscopy. Thus, human neutrophils not only store large amounts of mature defensins in azurophil granules but also contain a more easily mobilized reservoir of unprocessed prodefensins in specific granules.

Cysteine-rich secretory protein 3 is a ligand of alpha1B-glycoprotein in human plasma

Human cysteine-rich secretory protein 3 (CRISP-3; also known as SGP28) belongs to a family of closely related proteins found in mammals and reptiles. Some mammalian CRISPs are known to be involved in the process of reproduction, whereas some of the CRISPs from reptiles are neurotoxin-like substances found in lizard saliva or snake venom. Human CRISP-3 is present in exocrine secretions and in secretory granules of neutrophilic granulocytes and is believed to play a role in innate immunity. On the basis of the relatively high content of CRISP-3 in human plasma and the small size of the protein (28 kDa), we hypothesized that CRISP-3 in plasma was bound to another component. This was supported by size-exclusion chromatography and immunoprecipitation of plasma proteins. The binding partner was identified by mass spectrometry as alpha(1)B-glycoprotein (A1BG), which is a known plasma protein of unknown function and a member of the immunoglobulin superfamily. We demonstrate that CRISP-3 is a specific and high-affinity ligand of A1BG with a dissociation constant in the nanomolar range as evidenced by surface plasmon resonance. The A1BG-CRISP-3 complex is noncovalent with a 1:1 stoichiometry and is held together by strong electrostatic forces. Similar complexes have been described between toxins from snake venom and A1BG-like plasma proteins from opossum species. In these cases, complex formation inhibits the toxic effect of snake venom metalloproteinases or myotoxins and protects the animal from envenomation. We suggest that the A1BG-CRISP-3 complex displays a similar function in protecting the circulation from a potentially harmful effect of free CRISP-3.