Limits...
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.

Show MeSH

Related in: MedlinePlus

Only the 46-61 determinant is highly dependent on  Ii coexpression with Ak for its effective presentation. COS cells  transfected with cDNA expression constructs encoding either  Ak or Ak and the p31 form of  mouse Ii were used as APCs  with the indicated concentrations of HEL for stimulation of  T hybridomas specific for the  indicated determinants of HEL.  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


getmorefigures.php?uid=PMC2196034&req=5

Figure 2: Only the 46-61 determinant is highly dependent on Ii coexpression with Ak for its effective presentation. COS cells transfected with cDNA expression constructs encoding either Ak or Ak and the p31 form of mouse Ii were used as APCs with the indicated concentrations of HEL for stimulation of T hybridomas specific for the indicated determinants of HEL. 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: We next reexamined the Ii dependence of presentation of the three determinants. The lack of a requirement for newly synthesized proteins suggested that Ii-associated class II molecules would not be required for presentation of 34-45 or 116-129, in contrast to 46-61. COS cells were transiently transfected with plasmid constructs encoding I-Ak α and β chains or I-Ak plus mouse Ii 31, and the transfectants were monitored for class II surface expression levels by FACS®. All transfectant pools used in these experiments expressed equivalent levels of Ak as detected with mAb H116.32 (data not shown), in agreement with our earlier data showing that in COS, Ii coexpression does not noticeably increase surface levels of Ak (38). COS transfectants expressing Ak alone efficiently present 34-45 and 116-129, but not 46-61. Cotransfection with Ii dramatically increases the presentation of 46-61 (Fig. 2 A), but has little effect on presentation of 34-45 and 116-129 (Fig. 2, B and C). Again, these data are consistent with studies using rat-2 transfectants and the differential requirement for protein export from the secretory pathway for presentation of the three determinants.


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)

Only the 46-61 determinant is highly dependent on  Ii coexpression with Ak for its effective presentation. COS cells  transfected with cDNA expression constructs encoding either  Ak or Ak and the p31 form of  mouse Ii were used as APCs  with the indicated concentrations of HEL for stimulation of  T hybridomas specific for the  indicated determinants of HEL.  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 2: Only the 46-61 determinant is highly dependent on Ii coexpression with Ak for its effective presentation. COS cells transfected with cDNA expression constructs encoding either Ak or Ak and the p31 form of mouse Ii were used as APCs with the indicated concentrations of HEL for stimulation of T hybridomas specific for the indicated determinants of HEL. 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: We next reexamined the Ii dependence of presentation of the three determinants. The lack of a requirement for newly synthesized proteins suggested that Ii-associated class II molecules would not be required for presentation of 34-45 or 116-129, in contrast to 46-61. COS cells were transiently transfected with plasmid constructs encoding I-Ak α and β chains or I-Ak plus mouse Ii 31, and the transfectants were monitored for class II surface expression levels by FACS®. All transfectant pools used in these experiments expressed equivalent levels of Ak as detected with mAb H116.32 (data not shown), in agreement with our earlier data showing that in COS, Ii coexpression does not noticeably increase surface levels of Ak (38). COS transfectants expressing Ak alone efficiently present 34-45 and 116-129, but not 46-61. Cotransfection with Ii dramatically increases the presentation of 46-61 (Fig. 2 A), but has little effect on presentation of 34-45 and 116-129 (Fig. 2, B and C). Again, these data are consistent with studies using rat-2 transfectants and the differential requirement for protein export from the secretory pathway for presentation of the three determinants.

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