Biomedical subjects

Joost Neijssen

Publications and source records attributed to Joost Neijssen.

4 recordsLinked to original sources

PubMed2005

Leucine aminopeptidase is not essential for trimming peptides in the cytosol or generating epitopes for MHC class I antigen presentation.

To detect viral infections and tumors, CD8+ T lymphocytes monitor cells for the presence of antigenic peptides bound to MHC class I molecules. The majority of MHC class I-presented peptides are generated from the cleavage of cellular and viral proteins by the ubiquitin-proteasome pathway. Many of the oligopeptides produced by this process are too long to stably bind to MHC class I molecules and require further trimming for presentation. Leucine aminopeptidase (LAP) is an IFN-inducible cytosolic aminopeptidase that can trim precursor peptides to mature epitopes and has been thought to play an important role in Ag presentation. To examine the role of LAP in generating MHC class I peptides in vivo, we generated LAP-deficient mice and LAP-deficient cell lines. These mutant mice and cells are viable and grow normally. The trimming of peptides in LAP-deficient cells is not reduced under basal conditions or after stimulation with IFN. Similarly, there is no reduction in presentation of peptides from precursor or full-length Ag constructs or in the overall supply of peptides from cellular proteins to MHC class I molecules even after stimulation with IFN. After viral infection, LAP-deficient mice generate normal CTL responses to seven epitopes from three different viruses. These data demonstrate that LAP is not an essential enzyme for generating most MHC class I-presented peptides and reveal redundancy in the function of cellular aminopeptidases.

Amino Acid Sequence↗

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↗

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

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↗