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Ii chain controls the transport of major histocompatibility complex class II molecules to and from lysosomes.

Brachet V, Raposo G, Amigorena S, Mellman I - J. Cell Biol. (1997)

Bottom Line: Major histocompatibility complex class II molecules are synthesized as a nonameric complex consisting of three alpha beta dimers associated with a trimer of invariant (Ii) chains.Our results suggest that alterations in the rate or efficiency of Ii chain processing can alter the postendosomal sorting of class II molecules, resulting in the increased accumulation of alpha beta dimers in lysosome-like MIIC.Thus, simple differences in Ii chain processing may account for the highly variable amounts of class II found in lysosomal compartments of different cell types or at different developmental stages.

View Article: PubMed Central - PubMed

Affiliation: Institut Curie, Section de Recherche Institut National de la Santé et de la Recherche Médicale CJF-95.01, Paris, France.

ABSTRACT
Major histocompatibility complex class II molecules are synthesized as a nonameric complex consisting of three alpha beta 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 alpha beta 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-A(b) alpha beta dimers to the plasma membrane with little if any reaching lysosomal compartments. Inhibition of Ii processing by the cysteine/serine protease inhibitor leupeptin, however, blocked transport to the cell surface and caused a dramatic but selective accumulation of I-A(b) class II molecules in lysosomes. In leupeptin, I-A(b) dimers formed stable complexes with a 10-kD NH2-terminal Ii chain fragment (Ii-p10), normally a transient intermediate in Ii chain processing. Upon removal of leupeptin, Ii-p10 was degraded and released, I-A(b) dimers bound antigenic peptides, and the peptide-loaded dimers were transported slowly from lysosomes to the plasma membrane. Our results suggest that alterations in the rate or efficiency of Ii chain processing can alter the postendosomal sorting of class II molecules, resulting in the increased accumulation of alpha beta dimers in lysosome-like MIIC. Thus, simple differences in Ii chain processing may account for the highly variable amounts of class II found in lysosomal compartments of different cell types or at different developmental stages.

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Immunogold localization of MHC class II molecules in leupeptin-treated cells. Ultrathin cryosections were immunogold labeled with the anti–class II mAb M5.114 and protein A–gold (PAG-10). (A) In control cells, MHC class II molecules are found on the  plasma membrane, in intracellular compartments characterized by the presence of internal membranes. (B) In leupeptin-treated cells (18-h  treatment), MHC class II molecules were detected on the plasma membrane and accumulate in electron-dense compartments displaying  internal membranes. Bars, 120 nm.
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Figure 6: Immunogold localization of MHC class II molecules in leupeptin-treated cells. Ultrathin cryosections were immunogold labeled with the anti–class II mAb M5.114 and protein A–gold (PAG-10). (A) In control cells, MHC class II molecules are found on the plasma membrane, in intracellular compartments characterized by the presence of internal membranes. (B) In leupeptin-treated cells (18-h treatment), MHC class II molecules were detected on the plasma membrane and accumulate in electron-dense compartments displaying internal membranes. Bars, 120 nm.

Mentions: To further define the compartments where αβ–Ii-p10 complexes accumulated, leupeptin-treated and control cells were analyzed by immunoelectron microscopy on ultrathin cryosections. In nontreated cells, MHC class II molecules, detected by the anti–mouse MHC class II mAb M5.114, were found predominantly at the plasma membrane and very occasionally in clathrin-coated pits. A fraction of the class II molecules was also visualized intracellularly in tubules and vesicles that often displayed intraluminal membranes (Fig. 6 A). Since these vesicles were negative for lysosomal membrane markers, they are likely to be CIIV or early endosomes (see below). They were, however, strongly reminiscent of CIIV structures isolated from A20 cells by FFE (Amigorena et al., 1994).


Ii chain controls the transport of major histocompatibility complex class II molecules to and from lysosomes.

Brachet V, Raposo G, Amigorena S, Mellman I - J. Cell Biol. (1997)

Immunogold localization of MHC class II molecules in leupeptin-treated cells. Ultrathin cryosections were immunogold labeled with the anti–class II mAb M5.114 and protein A–gold (PAG-10). (A) In control cells, MHC class II molecules are found on the  plasma membrane, in intracellular compartments characterized by the presence of internal membranes. (B) In leupeptin-treated cells (18-h  treatment), MHC class II molecules were detected on the plasma membrane and accumulate in electron-dense compartments displaying  internal membranes. Bars, 120 nm.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2139866&req=5

Figure 6: Immunogold localization of MHC class II molecules in leupeptin-treated cells. Ultrathin cryosections were immunogold labeled with the anti–class II mAb M5.114 and protein A–gold (PAG-10). (A) In control cells, MHC class II molecules are found on the plasma membrane, in intracellular compartments characterized by the presence of internal membranes. (B) In leupeptin-treated cells (18-h treatment), MHC class II molecules were detected on the plasma membrane and accumulate in electron-dense compartments displaying internal membranes. Bars, 120 nm.
Mentions: To further define the compartments where αβ–Ii-p10 complexes accumulated, leupeptin-treated and control cells were analyzed by immunoelectron microscopy on ultrathin cryosections. In nontreated cells, MHC class II molecules, detected by the anti–mouse MHC class II mAb M5.114, were found predominantly at the plasma membrane and very occasionally in clathrin-coated pits. A fraction of the class II molecules was also visualized intracellularly in tubules and vesicles that often displayed intraluminal membranes (Fig. 6 A). Since these vesicles were negative for lysosomal membrane markers, they are likely to be CIIV or early endosomes (see below). They were, however, strongly reminiscent of CIIV structures isolated from A20 cells by FFE (Amigorena et al., 1994).

Bottom Line: Major histocompatibility complex class II molecules are synthesized as a nonameric complex consisting of three alpha beta dimers associated with a trimer of invariant (Ii) chains.Our results suggest that alterations in the rate or efficiency of Ii chain processing can alter the postendosomal sorting of class II molecules, resulting in the increased accumulation of alpha beta dimers in lysosome-like MIIC.Thus, simple differences in Ii chain processing may account for the highly variable amounts of class II found in lysosomal compartments of different cell types or at different developmental stages.

View Article: PubMed Central - PubMed

Affiliation: Institut Curie, Section de Recherche Institut National de la Santé et de la Recherche Médicale CJF-95.01, Paris, France.

ABSTRACT
Major histocompatibility complex class II molecules are synthesized as a nonameric complex consisting of three alpha beta 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 alpha beta 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-A(b) alpha beta dimers to the plasma membrane with little if any reaching lysosomal compartments. Inhibition of Ii processing by the cysteine/serine protease inhibitor leupeptin, however, blocked transport to the cell surface and caused a dramatic but selective accumulation of I-A(b) class II molecules in lysosomes. In leupeptin, I-A(b) dimers formed stable complexes with a 10-kD NH2-terminal Ii chain fragment (Ii-p10), normally a transient intermediate in Ii chain processing. Upon removal of leupeptin, Ii-p10 was degraded and released, I-A(b) dimers bound antigenic peptides, and the peptide-loaded dimers were transported slowly from lysosomes to the plasma membrane. Our results suggest that alterations in the rate or efficiency of Ii chain processing can alter the postendosomal sorting of class II molecules, resulting in the increased accumulation of alpha beta dimers in lysosome-like MIIC. Thus, simple differences in Ii chain processing may account for the highly variable amounts of class II found in lysosomal compartments of different cell types or at different developmental stages.

Show MeSH
Related in: MedlinePlus