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Related leucine-based cytoplasmic targeting signals in invariant chain and major histocompatibility complex class II molecules control endocytic presentation of distinct determinants in a single protein.

Zhong G, Romagnoli P, Germain RN - J. Exp. Med. (1997)

Bottom Line: Some protein determinants, however, do not require Ii for effective class II presentation, although endocytic processing is still necessary.Elimination or mutation of this signal reduces the rate of re-entry of mature surface class II molecules into the endocytic pathway.This permits capture of protein fragments produced optimally under distinct conditions of pH and proteolytic activity.

View Article: PubMed Central - PubMed

Affiliation: Lymphocyte Biology Section, National Institute of Allergy and Infectious Disease, National Institutes of Health, Bethesda, Maryland 20892-1892, USA.

ABSTRACT
Leucine-based signals in the cytoplasmic tail of invariant chain (Ii) control targeting of newly synthesized major histocompatibility complex class II molecules to the endocytic pathway for acquisition of antigenic peptides. Some protein determinants, however, do not require Ii for effective class II presentation, although endocytic processing is still necessary. Here we demonstrate that a dileucine-based signal in the cytoplasmic tail of the class II beta chain is critical for this Ii-independent presentation. Elimination or mutation of this signal reduces the rate of re-entry of mature surface class II molecules into the endocytic pathway. Antigen presentation controlled by this signal does not require newly synthesized class II molecules and appears to involve determinants requiring only limited proteolysis for exposure, whereas the opposite is true for li-dependent determinants. This demonstrates that related leucine-based trafficking signals in li and class II control the functional presentation of protein determinants with distinct processing requirements, suggesting that the peptide binding sites of newly synthesized versus mature class II molecules are made available for antigen binding in distinct endocytic compartments under the control of these homologous cytoplasmic signals. This permits capture of protein fragments produced optimally under distinct conditions of pH and proteolytic activity.

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Differential requirements for Ii coexpression and for  the cytoplasmic tail of the class II  Aβ chain in the presentation of  distinct determinants of HEL.  RBLs stably transfected with  constructs encoding the indicated Aαk and Aβk proteins with  or without Ii p31 were used as  APCs for mouse T hybridomas  specific for the indicated determinants. IL-2 production at 24 h is  presented as OD obtained using  an IL-2–specific capture ELISA.  The data represent one of three  independent experiments.
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Figure 3: Differential requirements for Ii coexpression and for the cytoplasmic tail of the class II Aβ chain in the presentation of distinct determinants of HEL. RBLs stably transfected with constructs encoding the indicated Aαk and Aβk proteins with or without Ii p31 were used as APCs for mouse T hybridomas specific for the indicated determinants. IL-2 production at 24 h is presented as OD obtained using an IL-2–specific capture ELISA. The data represent one of three independent experiments.

Mentions: In certain cells, leucine-based targeting signals in the Ii cytoplasmic tail are important for the endocytic accumulation of newly synthesized class II molecules (4–9). However, this is not true in all cells, and the localization of class II to late endocytic structures has been observed in several cell expressing class II without Ii (26–28). Pinet et al. have reported that presentation of a hemagglutinin determinant by DR is independent of Ii, but requires uncharacterized internalization signals in the cytoplasmic tails of the class II α and β chains (31). Smiley et al. (32) have also shown a role for class II cytoplasmic tails in antigen presentation and suggested that a dileucinebased motif in the β chain may be involved in this function. To assess whether signals in the cytoplasmic tails of the Ak molecule itself are involved in the presentation of 34-45 or 116-129, RBLs were stably transfected with constructs expressing various combinations of wild-type Ak or Ak tail deletion mutants with or without Ii, and clones with comparable levels of surface class II and intracellular Ii selected. As with COS and rat-2 cells, efficient presentation of 46-61, but not 34-45 and 116-129, by wild-type Ak expressed by RBLs depends on Ii (Fig. 3). Although cells expressing wild-type Ak alone can effectively stimulate 34-45– and 116-129–specific T cells after HEL exposure, truncation of the β chain tail prevents this presentation. Examination of presentation of the three determinants by cells with the β tail deleted Ak coexpressed with Ii revealed that each determinant has a distinctive combination of requirements for either Ii or the β chain tail. The 46-61 and 34-45 determinants are both presented well by cells expressing I-Ak with a truncated β chain tail together with Ii, but Ii expression does not rescue the ability of β tail deleted class II molecules to present 116-129. Therefore, the efficient presentation of 46-61 requires Ii irrespective of the presence or absence of the class II β chain tail, presentation of 34-45 requires either intact class II tail or Ii and the class II β tail is required for the presentation of 116-129 and this function cannot be replaced by Ii. Similar data were obtained using transiently transfected COS cells (data not shown).


Related leucine-based cytoplasmic targeting signals in invariant chain and major histocompatibility complex class II molecules control endocytic presentation of distinct determinants in a single protein.

Zhong G, Romagnoli P, Germain RN - J. Exp. Med. (1997)

Differential requirements for Ii coexpression and for  the cytoplasmic tail of the class II  Aβ chain in the presentation of  distinct determinants of HEL.  RBLs stably transfected with  constructs encoding the indicated Aαk and Aβk proteins with  or without Ii p31 were used as  APCs for mouse T hybridomas  specific for the indicated determinants. IL-2 production at 24 h is  presented as OD obtained using  an IL-2–specific capture ELISA.  The data represent one of three  independent experiments.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2196034&req=5

Figure 3: Differential requirements for Ii coexpression and for the cytoplasmic tail of the class II Aβ chain in the presentation of distinct determinants of HEL. RBLs stably transfected with constructs encoding the indicated Aαk and Aβk proteins with or without Ii p31 were used as APCs for mouse T hybridomas specific for the indicated determinants. IL-2 production at 24 h is presented as OD obtained using an IL-2–specific capture ELISA. The data represent one of three independent experiments.
Mentions: In certain cells, leucine-based targeting signals in the Ii cytoplasmic tail are important for the endocytic accumulation of newly synthesized class II molecules (4–9). However, this is not true in all cells, and the localization of class II to late endocytic structures has been observed in several cell expressing class II without Ii (26–28). Pinet et al. have reported that presentation of a hemagglutinin determinant by DR is independent of Ii, but requires uncharacterized internalization signals in the cytoplasmic tails of the class II α and β chains (31). Smiley et al. (32) have also shown a role for class II cytoplasmic tails in antigen presentation and suggested that a dileucinebased motif in the β chain may be involved in this function. To assess whether signals in the cytoplasmic tails of the Ak molecule itself are involved in the presentation of 34-45 or 116-129, RBLs were stably transfected with constructs expressing various combinations of wild-type Ak or Ak tail deletion mutants with or without Ii, and clones with comparable levels of surface class II and intracellular Ii selected. As with COS and rat-2 cells, efficient presentation of 46-61, but not 34-45 and 116-129, by wild-type Ak expressed by RBLs depends on Ii (Fig. 3). Although cells expressing wild-type Ak alone can effectively stimulate 34-45– and 116-129–specific T cells after HEL exposure, truncation of the β chain tail prevents this presentation. Examination of presentation of the three determinants by cells with the β tail deleted Ak coexpressed with Ii revealed that each determinant has a distinctive combination of requirements for either Ii or the β chain tail. The 46-61 and 34-45 determinants are both presented well by cells expressing I-Ak with a truncated β chain tail together with Ii, but Ii expression does not rescue the ability of β tail deleted class II molecules to present 116-129. Therefore, the efficient presentation of 46-61 requires Ii irrespective of the presence or absence of the class II β chain tail, presentation of 34-45 requires either intact class II tail or Ii and the class II β tail is required for the presentation of 116-129 and this function cannot be replaced by Ii. Similar data were obtained using transiently transfected COS cells (data not shown).

Bottom Line: Some protein determinants, however, do not require Ii for effective class II presentation, although endocytic processing is still necessary.Elimination or mutation of this signal reduces the rate of re-entry of mature surface class II molecules into the endocytic pathway.This permits capture of protein fragments produced optimally under distinct conditions of pH and proteolytic activity.

View Article: PubMed Central - PubMed

Affiliation: Lymphocyte Biology Section, National Institute of Allergy and Infectious Disease, National Institutes of Health, Bethesda, Maryland 20892-1892, USA.

ABSTRACT
Leucine-based signals in the cytoplasmic tail of invariant chain (Ii) control targeting of newly synthesized major histocompatibility complex class II molecules to the endocytic pathway for acquisition of antigenic peptides. Some protein determinants, however, do not require Ii for effective class II presentation, although endocytic processing is still necessary. Here we demonstrate that a dileucine-based signal in the cytoplasmic tail of the class II beta chain is critical for this Ii-independent presentation. Elimination or mutation of this signal reduces the rate of re-entry of mature surface class II molecules into the endocytic pathway. Antigen presentation controlled by this signal does not require newly synthesized class II molecules and appears to involve determinants requiring only limited proteolysis for exposure, whereas the opposite is true for li-dependent determinants. This demonstrates that related leucine-based trafficking signals in li and class II control the functional presentation of protein determinants with distinct processing requirements, suggesting that the peptide binding sites of newly synthesized versus mature class II molecules are made available for antigen binding in distinct endocytic compartments under the control of these homologous cytoplasmic signals. This permits capture of protein fragments produced optimally under distinct conditions of pH and proteolytic activity.

Show MeSH
Related in: MedlinePlus