Sci. STKE, 8 October 2002
Heat Shock Proteins CD40 Takes Heat Shock Proteins into the Cell
Heat shock proteins (HSPs), many of which function as molecular chaperones, can act extracellularly on professional antigen-presenting cells (APCs) to stimulate a powerful immune response against tumor and viral antigens. APCs respond to HSP by increasing production of proinflammatory cytokines, and internalize HSP bound to antigens, eventually presenting these antigens to T cells. Becker et al. demonstrate that CD40, a member of the tumor necrosis factor receptor family that is critical to B cell function and plays a role in autoimmunity, mediates the uptake of HSP bound to peptide, implicating CD40 in the specific immunostimulatory response. The authors investigated the interaction of human Hsp70, an HSP with an NH2-terminal nucleotide-binding (ATPase) domain and a COOH-terminal peptide-binding domain that binds peptide in the ADP-bound state, with CD40, a cell-surface receptor previously implicated in the general inflammatory response to HSP. Stimulating a murine macrophage cell line with bacterial lipopolysaccharide increased binding of biotinylated Hsp70, or Hsp70 loaded with biotinylated peptide, and increased levels of CD40 detectable by immunoblot. Transfected Cos-7 cells expressing CD40 bound labeled Hsp70, whereas untransfected cells did not. The authors used an in vitro pull-down assay to demonstrate that Hsp70 bound directly to the exoplasmic domain of CD40 and that binding was enhanced by ADP. Recombinant NH2-terminal domain competed with full-length Hsp70 for binding to CD40, whereas the COOH-terminal domain did not. Peptide substrate that bound to Hsp70 enhanced binding, whereas the Hsp70 cochaperone Hip inhibited binding. The Hsp70-peptide complex induced intracellular signaling in HEK293T cells transfected with CD40, as determined by immunoblot analysis of phosphorylated (activated) p38, and Hsp70 elicited internalization of fluorescently labeled peptide. These data indicate a role for CD40 in the specific, as well as the general, adjuvant response to HSP and suggest that CD40 binding to Hsp70 shares features with cochaperone-Hsp70 interaction.
Citation: CD40 Takes Heat Shock Proteins into the Cell. Sci. STKE 2002, tw368 (2002).
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