title: Wortmannin, a phosphatidylinositol 3-kinase inhibitor, blocks the assembly of peptide-MHC class II complexes.
abstract: Peptide-class II complexes are assembled in endocytic, lysosome-like compartments where newly synthesized class II molecules are targeted from the trans-Golgi network (TGN). Recent studies have implicated phosphatidylinositol 3-kinase (PI3-kinase) as an essential component in membrane trafficking from the TGN to lysosomes. Here, using subcellular fractionation, we show PI3-kinase activity associated with subcellular fractions which contain the class II peptide-loading compartment (IIPLC) in B cells. At concentrations required for inhibition of PI3-kinase activity in vivo, wortmannin blocked the processing and presentation of antigen by B cells to T cells. Treatment of B cells with wortmannin significantly limited the proteolytic degradation of invariant chain and the formation of peptide-class II complexes. Subcellular fractionation coupled with pulse-chase analyses showed that invariant chain and class II molecules trafficked to the IIPLC in wortmannin-treated cells. However, wortmannin prevented the maturation and correct targeting to the IIPLC of cathepsin D, a protease necessary for the degradation of invariant chain and assembly of processed antigen-class II complexes. These results suggest that li-class II complexes traffic to the IIPLC via a pathway that is relatively insensitive to wortmannin, but suggest a role for PI3-kinases in the trafficking of other components necessary for the assembly of processed antigen class II complexes to the IIPLC.
authors.affiliation: Department of Biochemistry, Molecular Biology and Cell Biology, Northwestern University, Evanston, IL 60208, USA.
authors.forename: W
authors.initials: W
authors.lastname: Song
authors.forename: N M
authors.initials: NM
authors.lastname: Wagle
authors.forename: T
authors.initials: T
authors.lastname: Banh
authors.forename: C C
authors.initials: CC
authors.lastname: Whiteford
authors.forename: E
authors.initials: E
authors.lastname: Ulug
authors.forename: S K
authors.initials: SK
authors.lastname: Pierce
mesh_terms: D000730:Androstadienes / Q000494:pharmacology*; D000818:Animals; D017951:Antigen Presentation / Q000187:drug effects*; D002402:Cathepsin D / Q000378:metabolism; D002478:Cells, Cultured; D010856:Columbidae; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D000949:Histocompatibility Antigens Class II / Q000378:metabolism*; D006801:Humans; D051379:Mice; D000081082:Phosphoinositide-3 Kinase Inhibitors; D013347:Subcellular Fractions / Q000378:metabolism; D000077191:Wortmannin
chemical_list: D000730:Androstadienes; D004791:Enzyme Inhibitors; D000949:Histocompatibility Antigens Class II; D000081082:Phosphoinositide-3 Kinase Inhibitors; D002402:Cathepsin D; D000077191:Wortmannin