The diversity of the DnaJ/Hsp40 family, the crucial partners for Hsp70 chaperones

DnaJ/Hsp40 (heat shock protein 40) proteins have been preserved throughout evolution and are important for protein translation, folding, unfolding, translocation, and degradation, primarily by stimulating the ATPase activity of chaperone proteins, Hsp70s. Because the ATP hydrolysis is essential for the activity of Hsp70s, DnaJ/Hsp40 proteins actually determine the activity of Hsp70s by stabilizing their interaction with substrate proteins. DnaJ/Hsp40 proteins all contain the J domain through which they bind to Hsp70s and can be categorized into three groups, depending on the presence of other domains. Six DnaJ homologs have been identified in Escherichia coli and 22 in Saccharomyces cerevisiae. Genome-wide analysis has revealed 41 DnaJ/Hsp40 family members (or putative members) in humans. While 34 contain the typical J domains, 7 bear partially conserved J-like domains, but are still suggested to function as DnaJ/ Hsp40 proteins. DnaJA2b, DnaJB1b, DnaJC2, DnaJC20, and DnaJC21 are named for the first time in this review; all other human DnaJ proteins were dubbed according to their gene names, e.g. DnaJA1 is the human protein named after its gene DNAJA1. This review highlights the progress in studying the domains in DnaJ/Hsp40 proteins, introduces the mechanisms by which they interact with Hsp70s, and stresses their functional diversity. Received 27 April 2006; received after revision 5 June 2006; accepted 19 July 2006     

Gamma delta T cell receptors

Gamma delta (γ δ) T cells are among the least understood components of the immune system. While these cells appear to contribute uniquely to host immune competence, defining their functions in the context of host biology and pathology has been difficult. This is largely because it is unclear what antigens the γ δ T cell receptor repertoire is directed against. During the past year, there have been noteworthy advances in this area. Their significance in the context of γ δ T cell biology is discussed. Received 19 January 2006; received after revision 16 March 2006; accepted 26 May 2006     

The importance of HLA-G expression in embryos,trophoblast cells,and embryonic stem cells

The nonclassical HLA-G molecule is a trophoblast-specific molecule present in almost every pregnancy. It differs from classical HLA class I molecules by the low degree of allelic variants and the high diversity of protein structures. HLA-G is reported to be a tolerogenic molecule that acts on cells of both innate and adaptive immunity. At the maternal–fetal interface HLA-G seems to be responsible largely for the reprogramming of local maternal immune response. This review will focus on the HLA-G gene expression profile in pregnancy, in preimplantation embryos, and in human embryonic stem cells with emphasis on the structural diversity of the HLA-G protein and its potential functional and diagnostic implications.     

The effect of αB-crystallin and Hsp27 on the availability of translation initiation factors in heat-shocked cells

The mechanism of the translational thermotolerance provided by the small heat shock proteins (sHsps) αB-crystallin or Hsp27 is unknown. We show here that Hsp27, but not αB-crystallin, increased the pool of mobile stress granule-associated enhanced green fluorescent protein (EGFP)-eukaryotic translation initiation factor (eIF)4E in heat-shocked cells, as determined by fluorescence recovery after photobleaching. Hsp27 also partially prevented the sharp decrease in the pool of mobile cytoplasmic EGFP-eIF4G. sHsps did not prevent the phosphorylation of eIF2α by a heat shock, but promoted dephosphorylation during recovery. Expression of the C-terminal fragment of GADD34, which causes constitutive dephosphorylation of eIF2α, fully compensated for the stimulatory effect of αB-crystallin on protein synthesis in heat-shocked cells, but only partially for that of Hsp27. Our data show that sHsps do not prevent the inhibition of protein synthesis upon heat shock, but restore translation more rapidly by promoting the dephosphorylation of eIF2α and, in the case of Hsp27, the availability of eIF4E and eIF4G. Received 9 December 2005; received after revision 16 January 2006; accepted 23 January 2006     

The endothelial cell protein C receptor: cell surface conductor of cytoprotective coagulation factor signaling

Increasing evidence links blood coagulation proteins with the regulation of acute and chronic inflammatory disease. Of particular interest are vitamin K-dependent proteases, which are generated as a hemostatic response to vascular injury, but can also initiate signal transduction via interactions with vascular receptors. The endothelial cell protein C receptor (EPCR) is a multi-ligand vitamin K-dependent protein receptor for zymogen and activated forms of plasma protein C and factor VII. Although the physiological role of the EPCR-FVII(a) interaction is not well-understood, protein C binding to EPCR facilitates rapid generation of APC in response to excessive thrombin generation, and is a central requirement for the multiple signal-transduction cascades initiated by APC on both vascular endothelial and innate immune cells. Exciting recent studies have highlighted the emerging role of EPCR in modulating the cytoprotective properties of APC in a number of diverse inflammatory disorders. In this review, we describe the structure–function relationships, signal transduction pathways, and cellular interactions that enable EPCR to modulate the anticoagulant and anti-inflammatory properties of its vitamin K-dependent protein ligands, and examine the relevance of EPCR to both thrombotic and inflammation-associated disease.     

Inflammasomes: current understanding and open questions

The innate immune system relies on its capability to detect invading microbes, tissue damage, or stress via evolutionarily conserved receptors. The nucleotide-binding domain leucine-rich repeat (NLR)-containing family of pattern recognition receptors includes several proteins that drive inflammation in response to a wide variety of molecular patterns. In particular, the NLRs that participate in the formation of a molecular scaffold termed the “inflammasome” have been intensively studied in past years. Inflammasome activation by multiple types of tissue damage or by pathogen-associated signatures results in the autocatalytic cleavage of caspase-1 and ultimately leads to the processing and thus secretion of pro-inflammatory cytokines, most importantly interleukin (IL)-1β and IL-18. Here, we review the current knowledge of mechanisms leading to the activation of inflammasomes. In particular, we focus on the controversial molecular mechanisms that regulate NLRP3 signaling and highlight recent advancements in DNA sensing by the inflammasome receptor AIM2.     

Long-term changes in tyrosine phosphorylation of the abundant nuclear proteins during granulocytic differentiation of HL-60 cells

The two-dimensional electrophoretic patterns of nuclear proteins and their tyrosine phosphorylation were compared for HL-60 cells before and after differentiation induction to granulocytes by dimethyl sulfoxide, all-trans retinoic acid and N ⁶,O ²-dibutyryl adenosine 3′5′-cyclic monophosphate. Regardless of the inducer used, some nuclear proteins, which are tyrosine-phosphorylated in proliferating HL-60 cells, undergo gradual dephosphorylation 12–72 h after induction of differentiation, followed by drastic dephosphorylation during maturation to granulocytes. At least 13 nuclear proteins with a molecular mass of 35–110 kDa are dephosphorylated, and 6 nuclear proteins undergo tyrosine phosphorylation. Analysis of the nuclear proteins differentially extracted by salt and detergents indicates that changes in their tyrosine phosphorylation during the maturation stage of differentiating granulocytes occur mainly in proteins which are abundant in nucleoplasm, chromatin and residual nuclear structures. The abundance of these proteins, residing in the nuclear structures, and their long-term modification in phosphorylation during the maturation stages of differentiation strongly suggest that tyrosine phosphorylation of these proteins is involved in reorganization of the differentiating cell nucleus. Received 21 September 1998; received after revision 24 November 1998; accepted 3 December 1998     

Immune biology of Ag-specific γδ T cells in infections

Accumulating evidence suggests that human γδ T cells act as non-classical T cells and contribute to both innate and adaptive immune responses in infections. Vγ2 Vδ2 T (also termed Vγ9 Vδ2 T) cells exist only in primates, and in humans represent a dominant circulating γδ T-cell subset. Primate Vγ2 Vδ2 T cells are the only γδ T cell subset capable of recognizing microbial phosphoantigen. Since nonhuman primate Vγ2 Vδ2 T cells resemble their human counterparts, in-depth studies have been undertaken in macaques to understand the biology and function of human Vγ2 Vδ2 T cells. This article reviews the recent progress for immune biology of Vγ2 Vδ2 T cells in infections.     

Modulation of γδ T cell responses by TLR ligands

Toll-like receptors (TLR) are pattern-recognition receptors that recognize a broad variety of structurally conserved molecules derived from microbes. The recognition of TLR ligands functions as a primary sensor of the innate immune system, leading to subsequent indirect activation of the adaptive immunity as well as none-immune cells. However, TLR are also expressed by several T cell subsets, and the respective ligands can directly modulate their effector functions. The present review summarizes the recent findings of γδ T cell modulation by TLR ligands. TLR1/2/6, 3, and 5 ligands can act directly in combination with T cell receptor (TCR) stimulation to enhance cytokine/chemokine production of freshly isolated human γδ T cells. In contrast to human γδ T cells, murine and bovine γδ T cells can directly respond to TLR2 ligands with increased proliferation and cytokine production in a TCR-independent manner. Indirect stimulatory effects on IFN-γ production of human and murine γδ T cells via TLR-ligand activated dendritic cells have been described for TLR2, 3, 4, 7, and 9 ligands. In addition, TLR3 and 7 ligands indirectly increase tumor cell lysis by human γδ T cells, whereas ligation of TLR8 abolishes the suppressive activity of human tumor-infiltrating Vδ1 γδ T cells on αβ T cells and dendritic cells. Taken together, these data suggest that TLR-mediated signals received by γδ T cells enhance the initiation of adaptive immune responses during bacterial and viral infection directly or indirectly. Moreover, TLR ligands enhance cytotoxic tumor responses of γδ T cells and regulate the suppressive capacity of γδ T cells.     

Calorie restriction and the nutrient sensing signaling pathways

Calorie restriction (CR) is the most potent regimen known to extend the life span in multiple species. CR has also been shown to ameliorate several age-associated disorders in mammals and perhaps humans. CR induces diverse metabolic changes in organisms, and it is currently unclear whether and how these metabolic changes lead to life span extension. Recent studies in model systems have provided insight into the molecular mechanisms by which CR extends life span. In this review, we summarize and provide recent updates on multiple nutrient signaling pathways that have been connected to CR and longevity regulation. The roles of highly conserved longevity regulators – the Sirtuin family – in CR are also discussed. Received 25 August 2006; received after revision 9 October 2006; accepted 13 December 2006     

Peutz-Jeghers syndrome: clinicopathology and molecular alterations

Peutz-Jeghers syndrome (PJS, OMIM 175200) is an unusual inherited intestinal polyposis syndrome associated with distinct peri-oral blue/black freckling [1–9]. Variable penetrance and clinical heterogeneity make it difficult to determine the exact frequency of PJS [4]. PJS is a cancer predisposition syndrome. Affected individuals are at high risk for intestinal and extra-intestinal cancers. In 1997, linkage studies mapped PJS to chromosome 19p [10, 11], and subsequently a serine/threonine kinase gene defect (LKB1) was noted in a majority of PJS cases [12, 13]. A phenotypically similar syndrome has been produced in an LKB1 mouse knockout model [14–18]. Several PJS kindred without LKB1 mutations have been described, suggesting other PJS loci [19–22]. The management of PJS is complex and evolving. New endoscopic technologies may improve management of intestinal polyposis. Identification of specific genetic mutations and their targets will more accurately assess the clinical course, and help gage the magnitude of cancer risk for affected individuals. Received 20 February 2006; received after revision 5 May 2006; accepted 15 June 2006     

Maternal signals for progeny prevention against allergy and asthma

Allergy and asthma are chronic inflammatory diseases which result from complex gene–environment interactions. Recent evidence indicates the importance of prenatal and postnatal developmental processes in terms of maturation of balanced immune responses. According to the current view, gene–environment interactions during a restricted time frame are responsible for programming of the immune system in favor of allergic immune mechanisms later in life. The interaction between genes and environment is complex and only partially understood; however, heritable epigenetic modifications including chemical additions in and alternative packaging of the DNA have been shown to play a crucial role in this context. Novel data indicate that epigenetic mechanisms contribute to the development of T-helper cell function. Environmental factors, including diesel exhaust particles (DEP), vitamins and tobacco smoke, operate through such mechanisms. Furthermore, the role of environmental microbes provides another and maybe even more important group of exogenous exposures which operates in this critical time frame.     

Hsp70 chaperones: Cellular functions and molecular mechanism

Hsp70 proteins are central components of the cellular network of molecular chaperones and folding catalysts. They assist a large variety of protein folding processes in the cell by transient association of their substrate binding domain with short hydrophobic peptide segments within their substrate proteins. The substrate binding and release cycle is driven by the switching of Hsp70 between the low-affinity ATP bound state and the high-affinity ADP bound state. Thus, ATP binding and hydrolysis are essential in vitro and in vivo for the chaperone activity of Hsp70 proteins. This ATPase cycle is controlled by co-chaperones of the family of J-domain proteins, which target Hsp70s to their substrates, and by nucleotide exchange factors, which determine the lifetime of the Hsp70-substrate complex. Additional co-chaperones fine-tune this chaperone cycle. For specific tasks the Hsp70 cycle is coupled to the action of other chaperones, such as Hsp90 and Hsp100.Received 21 October 2004; received after revision 24 November 2004; accepted 6 December 2004     

Establishment of intestinal homeostasis during the neonatal period

The intestinal mucosa faces the challenge of regulating the balance between immune tolerance towards commensal bacteria, environmental stimuli and food antigens on the one hand, and induction of efficient immune responses against invading pathogens on the other hand. This regulatory task is of critical importance to prevent inappropriate immune activation that may otherwise lead to chronic inflammation, tissue disruption and organ dysfunction. The most striking example for the efficacy of the adaptive nature of the intestinal mucosa is birth. Whereas the body surfaces are protected from environmental and microbial exposure during fetal life, bacterial colonization and contact with potent immunostimulatory substances start immediately after birth. In the present review, we summarize the current knowledge on the mechanisms underlying the transition of the intestinal mucosa during the neonatal period leading to the establishment of a stable, life-long host–microbial homeostasis. The environmental exposure and microbial colonization during the neonatal period, and also the influence of maternal milk on the immune protection of the mucosa and the role of antimicrobial peptides, are described. We further highlight the molecular mechanisms of innate immune tolerance in neonatal intestinal epithelium. Finally, we link the described immunoregulatory mechanisms to the increased susceptibility to inflammatory and infectious diseases during the neonatal period.     

Recent structural studies of carbohydrate-binding modules

Carbohydrate-binding modules (CBMs) are found in many carbohydrate-active enzymes. CBMs bind to a range of polysaccharides, their primary function being to increase the catalytic efficiency of the carbohydrate-active enzymes against soluble and/or insoluble substrates. CBMs bind to their target ligands with high specificities and affinities. Thus, CBM systems are excellent models to study the mechanism of protein-carbohydrate interaction. To date, CBMs have been classified into 45 different families and many structural and functional studies have been reported. At present, three-dimensional structures of CBMs from 31 different families have been determined. These structures demonstrate that the fold most commonly found in CBMs is the β-sandwich. In the past few years, about 10 new structures from different families have been reported. These enable detailed classification of CBM structures. This article reviews recent structural and functional studies of CBMs and discusses the sub-classification of β-sandwich CBMs. Received 28 April 2006; received after revision 12 July 2006; accepted 14 September 2006     

Role of vasostatin-1 C-terminal region in fibroblast cell adhesion

Fibroblast adhesion can be modulated by proteins released by neuroendocrine cells and neurons, such as chromogranin A (CgA) and its N-terminal fragment vasostatin-1 (VS-1, CgA_1–78). We have investigated the mechanisms of the interaction of VS-1 with fibroblasts and of its pro-adhesive activity and have found that the proadhesive activity of VS-1 relies on its interaction with the fibroblast membrane via a phospholipid-binding amphipathic α-helix located within residues 47–66, as well as on the interaction of the adjacent C-terminal region 67–78, which is structurally similar to ezrin–radixin–moesin-binding phosphoprotein 50 (a membrane-cytoskeleton adapter protein), with other cellular components critical for the regulation of cell cytoskeleton.     

Structural characterization of two papaya chitinases, a family GH19 of glycosyl hydrolases

Two chitinases, able to use tetra-N-acetylglucosamine, chitin and chitosan as substrates, were characterized after purification from Carica papaya latex. The complete amino acid sequence of the major form and about 40% of the minor one were determined through proteolytic digestions and mass spectroscopy analysis. Sequencing demonstrated that both papaya chitinases are members of the family 19 of glycosyl hydrolases (GH19). Based on the known 3-D structures of other members of family GH19, it was expected that papaya chitinases would adopt all-alpha structures. However, circular dichroism and infrared spectroscopy indicated, for the papaya chitinases, a content of 15–20% of extended structures besides the expected 40% of alpha helices. Since the fully sequenced papaya chitinase contains a large number of proline residues the possibility that papaya chitinase contains polyproline II stretches was examined in the context of their resistance against proteolytic degradation. Received 11 July 2006; received after revision 13 October 2006; accepted 25 October 2006