Different endocytic compartments are involved in the tight association of class II molecules with processed hen egg lysozyme and ribonuclease A in B cells (original) (raw)
Related papers
European Journal of Immunology, 1993
The invariant chain (Ii) binds to newly synthesized major histocompatibility complex (MHC) class11 molecules and is targeted to an acidic compartment where it is degraded.To evaluate its role on the conformation and the subcellular distribution of murine MHC class I1 molecules we have established stable L cell transfectants expressing class I1 IAk heterodimers alone or in conjunction with p31 and p41 Ii chains. In these cells, class I1 molecules were present under three forms: ap heterodimers bearing high mannose carbohydrate moieties, and fully glycosylated aB heterodimers that are sensitive or resistant to sodium dodecyl sulfate dissociation at 20 "C. The latter class I1 molecules called compact heterodimers, were here highly induced in Ii-positive cells. Using in situ iodination of endosomal compartments, class I1 heterodimers were detected in late endosomal compartments essentially as compact forms in Ii-positive cells, and as non-compact forms in Ii-negative cells. Using confocal microscopy, IAk molecules were located in compartments distinct from early endosomes labeled with transferrin, but partially coincident with vesicles containing fluid-phase markers, and highly coincident with compartments containing large amounts of cathepsins B, D, H, and L in Ii-positive and Ii-negative cells. At the ultrastructural level, class I1 molecules were mostly present in multivesicular bodies, even without Ii expression. But Ii chains were needed to induce an efficient presentation of the hen egg lysozyme antigen and were sufficient to promote a major conformational change of the late endosomal, and/or lysosomal resident, class I1 molecules. Ii molecules are presumably playing a chaperoning function favoring the association of peptides with class I1 molecules in endosomal compartments.
MHC Class II-Associated Invariant Chain-Induced Enlarged Endosomal Structures: A Morphological Study
Experimental Cell Research, 1997
teins, the a-and b-chains, which immediately associate The major histocompatibility complex class II-asso-with the invariant chain (Ii) 2 after synthesis in the ciated invariant chain is believed to direct newly syn-endoplasmic reticulum (ER) . Ii is thought to have thesized class II to endocytic compartments. Invariant at least two important functions in antigen presentachain synthesized at high levels in transiently transtion. Association of Ii with class II prevents binding of fected cells induces formation of large vesicular strucantigen created in the ER or Golgi [4], and the cytosolic tures. We have examined the effect of stable expression tail of Ii contains signals which direct class II molecules of invariant chain in human fibroblasts by light and to endosomes . In endosomes Ii is degraded and electron microscopy. Invariant chain expression drathe class II molecules may bind antigen.
European Journal of Immunology, 1993
We have tested the involvement of the invariant chains (Ii) p31 and p41 in the presentation of peptides derived from hen egg lysozyme (HEL) constructs targeted to different intracellular compartments within transfected fibroblasts. The endogenous HEL constructs were either present in the cytosol (HELc), secreted (HELs), or linked to the mammalian (KDEL C-terminal sequence that causes retention of HEL in the endoplasmic reticulum (ER)/pre-Golgi recycling compartment (HELr). Using Ii-negative antigen-presenting cells, the presentation of HELr to a HEL 46-61 specificT cell hybridoma was far less efficient than the presentation of the HELs. High levels of Ii expression enhanced drastically the presentation of the HEL 46-61 determinant derived from both HELr and HELs. HELr and HELs presentation was fully sensitive to lysosomotropic agents such as chloroquine, indicating that the formation of complexes between major histocompatibility complex (MHC) class I1 molecules and determinants derived from endogenous antigens entering the secretory pathway is taking place in an acidic compartment. The degradation and dissociation of Ii might be a prerequisite for the efficient presentation of endogenously derived determinants by MHC class I1 molecules, as for the presentation of most exogenous antigens.
Subcellular localization and sorting of MHC class II molecules
Biology of the Cell, 1991
Class !I reslricted T cells are usually stimulated by intraceHularly processed exogenous antigens bound to class H molecules. The binding of antigenic peptides to class [i molecules occurs in intraceHular acidic compartments after dissociation of the invariant chain (li) (1). In murine B lympboma cells antigenic peptides can gain access to a pool of recycling class il molecules whereas in L transfected fibroblasts they meet newly synthesized class !! molecules targeted to endnsomul compartments (2). Using confocal microscopy and immunoelectron microscopy together with biochemical techniques we showed that class H molecules are enriched in structures related to prelysesomes atul/or lysesontes independently of invariant chain expression (3). Early endosomes containing internalized transferrin are devoid of class 11 molecules. in murine L cells MHC class Ii rich compartments contain lysnsomal enzymes such as cathepsins. The receptor for iysnsomal enzymes bearing the monnse-6-phes121e motif is also Wesent in such compartments. Moreover these compamnents are localized in the endocytotic pathway since they are accessible to intmudized ovalbumin. Electron microscopy using the immunopemxydase technique or immunogold labelling shows mutivesiculer organeHcs specifically labeled with the anti-class II (i-Ak) monuclonal antibody. These organelles are also heavily labeled with a polyclonal antibody directed asainst the Mannose-6-pbosphate receptor (M6PR). These studies point to the role of prelysosomiul / lysosomul compertments in antigen presentation. We wond~ whether class 11 nmlecules, as the M6PR, are specifically tm'geted to these compartments after their biosynthesis. To visualize the soiling of class II molecules at the level of the trans Golgi Network we use the drug Brefaldin A (4). In a first step class II molecules am massively retained in the endoplamic reticulum. After removal of the drag, class II molecules are accumulated in the Golgi apparatns and stated to igelysmomal compartments by a clathrin dependent mechanism suggesting that specific adresses exist for sorting of MIIC class II molecules.
Journal of Experimental Medicine, 1995
In human B lymphoblastoid cell lines, the majority of major histocompatibility complex (MHC) class II heterodimers are located on the cell surface and in endocytic compartments, while invariant chain (Ii)-associated class II molecules represent biosynthetic intermediates which are present mostly in the endoplasmic reticulum and Golgi complex. To investigate the origin of the MHC class II-positive compartments and their relation to early endosomes, the intracellular distribution of MHC class II molecules and Ii in relation to endocytic tracers was studied in human lymphoblastoid B cells by immunoelectronmicroscopy on ultrathin cryosections. Cross-linking of surface immunoglobulins, followed by a brief period of internalization of the immune complexes, did not alter the intracellular distribution of MHC class II molecules. While early endosomes were abundantly labeled for the cross-linked immunoglobulins, < 1% of total MHC class II molecules were detectable in early endosomes. MHC ...
The Journal of Cell Biology, 1997
Major histocompatibility complex class II molecules are synthesized as a nonameric complex consisting of three αβ dimers associated with a trimer of invariant (Ii) chains. After exiting the TGN, a targeting signal in the Ii chain cytoplasmic domain directs the complex to endosomes where Ii chain is proteolytically processed and removed, allowing class II molecules to bind antigenic peptides before reaching the cell surface. Ii chain dissociation and peptide binding are thought to occur in one or more postendosomal sites related either to endosomes (designated CIIV) or to lysosomes (designated MIIC). We now find that in addition to initially targeting αβ dimers to endosomes, Ii chain regulates the subsequent transport of class II molecules. Under normal conditions, murine A20 B cells transport all of their newly synthesized class II I-Ab αβ dimers to the plasma membrane with little if any reaching lysosomal compartments. Inhibition of Ii processing by the cysteine/serine protease inh...
Journal of Biological Chemistry, 1996
We have previously identified an intracellular compartment involved in the association between processed lysozyme and IA k major histocompatibility complex class II molecules (called the lysozyme-loading compartment (LLC)). Here, we show that the LLC polypeptide composition analyzed by two-dimensional gel electrophoresis shares similarities with that of early endosomes, but not with that of late endosomes. The transferrin receptor, a well known marker for both early and recycling endosomes, colocalizes with IA k molecules in LLC. Moreover, both transferrin and fluid-phase markers have access to LLC after 15 min of internalization. In the presence of concanamycin B, SDS-stable dimer formation and transport of class II molecules out of LLC are impaired. In contrast, nocodazole treatment has no effect. These results suggest that LLC is a specialized compartment of the recycling pathway involved in lysozyme loading and in the targeting of lysozyme-major histocompatibility class II complexes toward the cell surface.