title: CD40 ligation decreases its protein half-life at the cell surface.
abstract: CD40 is expressed on a variety of tumors; anti-CD40 agonists promote tumor cell apoptosis and subsequent tumor regression. Because the effectiveness of anti-CD40- agonists is dependent upon CD40 surface expression, the current study examined ligation-mediated changes in CD40 protein half-life (t(1/2))( )at the cell surface. This study utilized a CD40(+) epithelial cell line (9HTEo-), a CD40 null epithelial cell line (HT-29) engineered to express either wild-type (WT) or mutant (T254A, Q263A, E235A, Delta201) CD40, and the anti-CD40 antibody G28.5. Ligation of endogenous CD40 expressed on 9HTEo- cells decreased CD40 surface protein t(1/2 )from 13 to 4 h (p <0.05). Ligation of WT-, Q263A-, or T254A-CD40 expressed on engineered HT-29 cells decreased CD40 surface protein t(1/2) from an average of 8 to 4 h (p <0.05); T254A and Q263A contain mutated TNF receptor-associated factor (TRAF)2/3-binding sites. In contrast, ligation of E235A and Delta201-CD40 had no affect on its surface protein t(1/2) (p <0.05); E235A contains a mutated TRAF6-binding site while Delta201 lacks an intact cytoplasmic tail. These results suggest that anti-CD40 agonists decrease CD40 surface protein t(1/2) via a mechanism that involves TRAF6 but not TRAF2/3. The therapeutic implications for CD40-mediated tumor regression are discussed.
authors.affiliation: Department of Physiology and Biophysics, University of Alabama at Birmingham, Birmingham, AL 35294-0005, USA.
authors.forename: Torry A
authors.initials: TA
authors.lastname: Tucker
authors.forename: Lisa M
authors.initials: LM
authors.lastname: Schwiebert
mesh_terms: D019943:Amino Acid Substitution; D000911:Antibodies, Monoclonal / Q000276:immunology*; D000937:Antigen-Antibody Reactions / Q000276:immunology*; D001665:Binding Sites / Q000235:genetics; D019921:Biotinylation; D019013:CD40 Antigens / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D002460:Cell Line; D004847:Epithelial Cells / Q000166:cytology / Q000378:metabolism; D019073:HT29 Cells; D006207:Half-Life; D006801:Humans; D017384:Sequence Deletion; D048029:TNF Receptor-Associated Factor 6 / Q000235:genetics / Q000378:metabolism; D014162:Transfection; D047988:Tumor Necrosis Factor Receptor-Associated Peptides and Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D000911:Antibodies, Monoclonal; D019013:CD40 Antigens; D048029:TNF Receptor-Associated Factor 6; D047988:Tumor Necrosis Factor Receptor-Associated Peptides and Proteins