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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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Leupeptin treatment causes MHC class II  molecules to accumulate in  lgp-containing structures by  immunofluorescence microscopy. Control or leupeptintreated (3 h, 2 mM leupeptin)  I-Ab–expressing A20 cells  were fixed, permeabilized,  and then stained for MHC  class II (FITC, using mAb  Y3P, two upper panels) vs  lgp-B (TRITC, using mAb  GL2A7, lower two panels).  In control cells, the small  amount of intracellular MHC  class II was localized to structures that were generally  negative for lgp-B. These  probably represented CIIVs  and early endosomes. Leupeptin treatment, however,  induced extensive colocalization of class II and lgp-B.
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Figure 4: Leupeptin treatment causes MHC class II molecules to accumulate in lgp-containing structures by immunofluorescence microscopy. Control or leupeptintreated (3 h, 2 mM leupeptin) I-Ab–expressing A20 cells were fixed, permeabilized, and then stained for MHC class II (FITC, using mAb Y3P, two upper panels) vs lgp-B (TRITC, using mAb GL2A7, lower two panels). In control cells, the small amount of intracellular MHC class II was localized to structures that were generally negative for lgp-B. These probably represented CIIVs and early endosomes. Leupeptin treatment, however, induced extensive colocalization of class II and lgp-B.

Mentions: Using confocal microscopy, we next asked if the p70-containing vesicles were of endosomal or lysosomal origin. As expected, most of the I-Ab class II molecules detected using mAb Y3P in control cells were observed at the cell surface (Fig. 4). Some intracellular staining was observed in ∼40% of the class II–expressing cells, however. Intracellular class II was observed in poorly resolved vesicles in the perinuclear region. These structures were negative for Ii chain (not shown) and also negative for the late endosome/lysosome membrane marker lgp-B/lamp-2 (Fig. 4, lower left).


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)

Leupeptin treatment causes MHC class II  molecules to accumulate in  lgp-containing structures by  immunofluorescence microscopy. Control or leupeptintreated (3 h, 2 mM leupeptin)  I-Ab–expressing A20 cells  were fixed, permeabilized,  and then stained for MHC  class II (FITC, using mAb  Y3P, two upper panels) vs  lgp-B (TRITC, using mAb  GL2A7, lower two panels).  In control cells, the small  amount of intracellular MHC  class II was localized to structures that were generally  negative for lgp-B. These  probably represented CIIVs  and early endosomes. Leupeptin treatment, however,  induced extensive colocalization of class II and lgp-B.
© Copyright Policy
Related In: Results  -  Collection

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

Figure 4: Leupeptin treatment causes MHC class II molecules to accumulate in lgp-containing structures by immunofluorescence microscopy. Control or leupeptintreated (3 h, 2 mM leupeptin) I-Ab–expressing A20 cells were fixed, permeabilized, and then stained for MHC class II (FITC, using mAb Y3P, two upper panels) vs lgp-B (TRITC, using mAb GL2A7, lower two panels). In control cells, the small amount of intracellular MHC class II was localized to structures that were generally negative for lgp-B. These probably represented CIIVs and early endosomes. Leupeptin treatment, however, induced extensive colocalization of class II and lgp-B.
Mentions: Using confocal microscopy, we next asked if the p70-containing vesicles were of endosomal or lysosomal origin. As expected, most of the I-Ab class II molecules detected using mAb Y3P in control cells were observed at the cell surface (Fig. 4). Some intracellular staining was observed in ∼40% of the class II–expressing cells, however. Intracellular class II was observed in poorly resolved vesicles in the perinuclear region. These structures were negative for Ii chain (not shown) and also negative for the late endosome/lysosome membrane marker lgp-B/lamp-2 (Fig. 4, lower left).

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