PubMed Health⌕ Search

Biomedical subjects

Jacques Neefjes

Publications and source records attributed to Jacques Neefjes.

At least 19 recordsLinked to original sources
PubMed2005

The many roads to cross-presentation.

Cross-presentation of extracellular antigens by MHC class I molecules is required for priming cytotoxic T lymphocytes (CTLs) at locations remote from the site of infection. Various mechanisms have been proposed to explain cross-presentation. One such mechanism involves the fusion of the endoplasmic reticulum (ER) with the endosomal-phagosomal system, in which the machinery required for peptide loading of MHC class I molecules is introduced directly into the phagosome. Here, we discuss the evidence for and against the ER-phagosome concept as well as other possible mechanisms of cross-presentation.

Animals↗
PubMed2005

RhoB regulates endosome transport by promoting actin assembly on endosomal membranes through Dia1.

Rho GTPases are crucial regulators of the actin cytoskeleton and they play a role in the control of membrane trafficking. In contrast to the close family members RhoA and RhoC, RhoB localises to endosomes and delays epidermal growth factor receptor traffic. Here, we show that activated RhoB induces the peripheral distribution of endosomes, which align along subcortical actin stress fibres and are surrounded by an actin coat. The Diaphanous-related formin, Dia1, is recruited to endosomes by activated RhoB. Dia1 is required for the formation of the actin coat around endosomes downstream of RhoB, connecting membrane trafficking with the regulation of actin dynamics.

Actins↗
PubMed2005

HFE cross-talks with the MHC class I antigen presentation pathway.

HFE is a protein known to be involved in iron metabolism; yet, other than its homology with major histocompatibility complex (MHC) class I molecules, it has not been described as having an immunologic function. Here we report that peripheral blood mononuclear cells (PBMCs) from patients with hereditary hemochromatosis (HH) carrying the C282Y mutation in HFE have reduced cell-surface expression of MHC class I due to an enhanced endocytosis rate of MHC class I molecules caused by premature peptide and beta2-microglobulin dissociation. This faster turnover also leads to increased expression levels of cell-surface free class I heavy chains in mutant PBMCs. Biochemical analysis indicates an earlier peptide loading and endoplasmic reticulum maturation of MHC class I molecules in C282Y mutant cells. Thermostability assays further showed that in HFE mutants the MHC class I peptide loading gives rise to low-stability heterotrimers that dissociate prematurely during its intracellular traffic. The present results suggest the existence of an intriguing cross-talk between a particular HFE mutation and the classical MHC class I route. These findings constitute the first description of peptide presentation pathway abnormalities linked to HFE and provide additional evidence for the occurrence of immunologic defects in patients with HH.

Antigen Presentation↗
PubMed2005

Varicelloviruses avoid T cell recognition by UL49.5-mediated inactivation of the transporter associated with antigen processing.

Detection and elimination of virus-infected cells by cytotoxic T lymphocytes depends on recognition of virus-derived peptides presented by MHC class I molecules. A critical step in this process is the translocation of peptides from the cytoplasm into the endoplasmic reticulum by the transporter associated with antigen processing (TAP). Here, we identified the bovine herpesvirus 1-encoded UL49.5 protein as a potent inhibitor of TAP. The expression of UL49.5 results in down-regulation of MHC class I molecules at the cell surface and inhibits detection and lysis of the cells by cytotoxic T lymphocytes. UL49.5 homologs encoded by two other varicelloviruses, pseudorabies-virus and equine herpesvirus 1, also block TAP. Homologs of UL49.5 are widely present in herpesviruses, acting as interaction partners for glycoprotein M, but in several varicelloviruses UL49.5 has uniquely evolved additional functions that mediate its participation in TAP inhibition. Inactivation of TAP by UL49.5 involves two events: inhibition of peptide transport through a conformational arrest of the transporter and degradation of TAP by proteasomes. UL49.5 is degraded along with TAP via a reaction that requires the cytoplasmic tail of UL49.5. Thus, UL49.5 represents a unique immune evasion protein that inactivates TAP through a unique two-tiered process.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2005

Cross-presentation by intercellular peptide transfer through gap junctions.

Major histocompatibility complex (MHC) class I molecules present peptides that are derived from endogenous proteins. These antigens can also be transferred to professional antigen-presenting cells in a process called cross-presentation, which precedes initiation of a proper T-cell response; but exactly how they do this is unclear. We tested whether peptides can be transferred directly from the cytoplasm of one cell into the cytoplasm of its neighbour through gap junctions. Here we show that peptides with a relative molecular mass of up to approximately 1,800 diffuse intercellularly through gap junctions unless a three-dimensional structure is imposed. This intercellular peptide transfer causes cytotoxic T-cell recognition of adjacent, innocent bystander cells as well as activated monocytes. Gap-junction-mediated peptide transfer is restricted to a few coupling cells owing to the high cytosolic peptidase activity. We present a mechanism of antigen acquisition for cross-presentation that couples the antigen presentation system of two adjacent cells and is lost in most tumours: gap-junction-mediated intercellular peptide coupling for presentation by bystander MHC class I molecules and transfer to professional antigen presenting cells for cross-priming.

Antigen Presentation↗
PubMed2005

Spatial separation of HLA-DM/HLA-DR interactions within MIIC and phagosome-induced immune escape.

Major Histocompatibility Complex (MHC) class II molecules, including Human Leukocyte Antigen (HLA)-DR, present peptide fragments from proteins degraded in the endocytic pathway. HLA-DR is targeted to late-endocytic structures named MHC class II-containing Compartments (MIIC), where it interacts with HLA-DM. This chaperone stabilizes HLA-DR during peptide exchange and is critical for successful peptide loading. To follow this process in living cells, we have generated cells containing HLA-DR3/Cyan Fluorescent Protein (CFP), HLA-DM/Yellow Fluorescent Protein (YFP), and invariant chain. HLA-DR/DM interactions were observed by Fluorescence Resonance Energy Transfer (FRET). These interactions were pH insensitive, yet occurred only in internal structures and not at the limiting membrane of MIIC. In a cellular model of infection, phagosomes formed a limiting membrane surrounding internalized Salmonella. HLA-DR and HLA-DM did not interact in Salmonella-induced vacuoles, and HLA-DR was not loaded with antigens. The absence of HLA-DR/DM interactions at the limiting membrane prevents local loading of MHC class II molecules in phagosomes. This may allow these bacteria to successfully evade the immune system.

Cell Line↗
PubMed2005

Presenting antigen presentation in living cells using biophysical techniques.

The combination of genetically encoded fluorescent probes and advanced microscopic techniques has dramatically propelled the understanding of cell biology. Highly complex reactions can now be studied in detail in a relatively cost-effective and easy manner and, perhaps most importantly, in the context of a single living cell. In the past decade, numerous reports have uncovered the localization of key molecules in virtually all cellular processes. However, there remains a need for more accurate determination of genuine protein-protein interactions and quantification of highly dynamic processes, which has resulted in the revival of several biophysical techniques. Recent applications of these techniques have deepened understanding of processes involved in antigen presentation to the immune system.

Antigen Presentation↗
PubMed2005

Chaperoning antigen presentation by MHC class II molecules and their role in oncogenesis.

Tumor vaccine development aimed at stimulating the cellular immune response focuses mainly on MHC class I molecules. This is not surprising since most tumors do not express MHC class II or CD1 molecules. Nevertheless, the most successful targets for cancer immunotherapy, leukemia and melanoma, often do express MHC class II molecules, which leaves no obvious reason to ignore MHC class II molecules as a mediator in anticancer immune therapy. We review the current state of knowledge on the process of MHC class II-restricted antigen presentation and subsequently discuss the consequences of MHC class II expression on tumor surveillance and the induction of an efficient MHC class II mediated antitumor response in vivo and after vaccination.

Antigen Presentation↗
PubMed2005

Rab proteins, connecting transport and vesicle fusion.

Small GTPases of the Rab family control timing of vesicle fusion. Fusion of two vesicles can only occur when they have been brought into close contact. Transport by microtubule- or actin-based motor proteins will facilitate this process in vivo. Ideally, transport and vesicle fusion are linked activities. Active, GTP-bound Rab proteins dock on specific compartments and are therefore perfect candidates to control transport of the different compartments. Recently, a number of Rab proteins were identified that control motor protein recruitment to their specific target membranes. By cycling through inactive and active states, Rab proteins are able to control motor protein-mediated transport and subsequent fusion of intracellular structures in both spatial and timed manners.

Animals↗
PubMed2005

Association of BMI1 with polycomb bodies is dynamic and requires PRC2/EZH2 and the maintenance DNA methyltransferase DNMT1.

Polycomb group (PcG) proteins are epigenetic chromatin modifiers involved in heritable gene repression. Two main PcG complexes have been characterized. Polycomb repressive complex 2 (PRC2) is thought to be involved in the initiation of gene silencing, whereas Polycomb repressive complex 1 (PRC1) is implicated in the stable maintenance of gene repression. Here, we investigate the kinetic properties of the binding of one of the PRC1 core components, BMI1, with PcG bodies. PcG bodies are unique nuclear structures located on regions of pericentric heterochromatin, found to be the site of accumulation of PcG complexes in different cell lines. We report the presence of at least two kinetically different pools of BMI1, a highly dynamic and a less dynamic fraction, which may reflect BMI1 pools with different binding capacities to these stable heterochromatin domains. Interestingly, PRC2 members EED and EZH2 appear to be essential for BMI1 recruitment to the PcG bodies. Furthermore, we demonstrate that the maintenance DNA methyltransferase DNMT1 is necessary for proper PcG body assembly independent of DNMT-associated histone deacetylase activity. Together, these results provide new insights in the mechanism for regulation of chromatin silencing by PcG proteins and suggest a highly regulated recruitment of PRC1 to chromatin.

Cells, Cultured↗
PubMed2004

Dynein-mediated vesicle transport controls intracellular Salmonella replication.

Salmonella typhimurium survives and replicates intracellular in a membrane-bound compartment, the Salmonella-containing vacuole (SCV). In HeLa cells, the SCV matures through interactions with the endocytic pathway, but Salmonella avoids fusion with mature lysosomes. The exact mechanism of the inhibition of phagolysosomal fusion is not understood. Rab GTPases control several proteins involved in membrane fusion and vesicular transport. The small GTPase Rab7 regulates the transport of and fusion between late endosomes and lysosomes and associates with the SCV. We show that the Rab7 GTPase cycle is not affected on the SCV. We then manipulated a pathway downstream of the small GTPase Rab7 in HeLa cells infected with Salmonella. Expression of the Rab7 effector RILP induces recruitment of the dynein/dynactin motor complex to the SCV. Subsequently, SCV fuse with lysosomes. As a result, the intracellular replication of Salmonella is inhibited. Activation of dynein-mediated vesicle transport can thus control intracellular survival of Salmonella.

Adaptor Proteins, Signal Transducing↗
PubMed2004

Tamoxifen resistance by a conformational arrest of the estrogen receptor alpha after PKA activation in breast cancer.

Using a novel approach that detects changes in the conformation of ERalpha, we studied the efficacy of anti-estrogens to inactivate ERalpha under different experimental conditions. We show that phosphorylation of serine-305 in the hinge region of ERalpha by protein kinase A (PKA) induced resistance to tamoxifen. Tamoxifen bound but then failed to induce the inactive conformation, invoking ERalpha-dependent transactivation instead. PKA activity thus induces a switch from antagonistic to agonistic effects of tamoxifen on ERalpha. In clinical samples, we found that downregulation of a negative regulator of PKA, PKA-RIalpha, was associated with tamoxifen resistance prior to treatment. Activation of PKA by downregulation of PKA-RIalpha converts tamoxifen from an ERalpha inhibitor into a growth stimulator, without any effect on ICI 182780 (Fulvestrant).

Antineoplastic Agents, Hormonal↗
PubMed2004

A major role for TPPII in trimming proteasomal degradation products for MHC class I antigen presentation.

Intracellular proteins are degraded by the proteasome, and resulting peptides surviving cytoplasmic peptidase activity can be presented by MHC class I molecules. Here, we show that intracellular aminopeptidases degrade peptides within seconds, almost irrespectively of amino acid sequence. N- but not C-terminal extension increases the half-life of peptides until they are 15 amino acids long. Beyond 15 amino acids, peptides are exclusively trimmed by the peptidase TPPII, which displays both exo- and endopeptidase activity. Surprisingly, most proteasomal degradation products are handled by TPPII before presentation by MHC class I molecules. We define three distinct proteolytic activities during antigen processing in vivo. Proteasome-generated peptides relevant for antigen presentation are mostly 15 amino acids or longer. These require TPPII activity for further trimming before becoming substrates for other peptidases and MHC class I. The heterogeneous pool of aminopeptidases will process TPPII products into MHC class I peptides and beyond.

Amino Acid Sequence↗
PubMed2003

Interference with T cell receptor-HLA-DR interactions by Epstein-Barr virus gp42 results in reduced T helper cell recognition.

Epstein-Barr virus (EBV) persists lifelong in infected hosts despite the presence of antiviral immunity. Many viral antigens are expressed during lytic infection. Thus, for EBV to spread, it must have evolved effective ways to evade immune recognition. Here, we report that HLA class II-restricted antigen presentation to T helper cells is hampered in the presence of the lytic-phase protein gp42. This interference with T cell activation involves association of gp42 with class II peptide complexes. Using HLA-DR tetramers, we identify a block in T cell receptor (TCR)-class II interactions imposed by gp42 as the underlying mechanism. EBV gp42 sterically clashes with TCR Valpha-domains as visualized by superimposing the crystal structures for gp42-HLA-DR1 and TCR-MHC class II complexes. Blocking TCR recognition provides a previously undescribed strategy for viral immune evasion.

Flow Cytometry↗
PubMed2003

Stable expression of MHC class I heavy chain/HLA-DO complexes at the plasma membrane.

Major histocompatibility complex (MHC) class I and II molecules present antigenic fragments to the immune system. MHC-like chaperones, like HLA-DM, HLA-DO and tapasin support peptide loading. HLA class I heavy chains require association with beta 2-microglobulin and peptide for endoplasmic reticulum (ER) exit. Likewise, HLA-DO is only able to leave the ER by association to DM. Here we show that HLA-DO and free MHC class I heavy chains associate into a stable complex early during biosynthesis and are expressed at the plasma membrane as a complex. These DO/heavy chain complexes are found on DO-transfected cells and on low amounts on human B cells.

B-Lymphocytes↗
PubMed2003

Peptide diffusion, protection, and degradation in nuclear and cytoplasmic compartments before antigen presentation by MHC class I.

Antigenic peptides generated by the proteasome have to survive a peptidase-containing environment for presentation by MHC class I molecules. We have visualized the fate and dynamics of intracellular peptides in living cells. We show that peptides are distributed over two different but interconnected compartments, the cytoplasm and the nucleus, and diffuse rapidly through and between these compartments. Since TAP is excluded from the nuclear face of the nuclear envelope, nuclear peptides have to leave the nucleus to contact TAP. Thereby, these peptides encounter cytosolic peptidases that degrade peptides within seconds unless bound to chromatin. Since peptide degradation is far more efficient than translocation, many peptides will be lost for antigen presentation by MHC class I molecules.

ATP-Binding Cassette Transporters↗