Dissecting the Roles of CD91 in Heat Shock Protein-Mediated Cancer Immunosurveillance

Our lab has shown that cancer immunosurveillance is dependent on CD91, a receptor for heat shock proteins (HSPs), which is expressed on antigen-presenting cells (APCs). HSP-chaperoned tumor antigens are cross-presented following endocytosis by CD91. Binding of HSPs to CD91 also initiates an intracellular signaling pathway that is poorly understood. Two tyrosine residues on the intracellular domain (β-chain) of CD91 become phosphorylated following HSP binding, leading to downstream activation of NF-kB and STAT1. We found that the immunogenic HSPs differentially utilize these two phosphorylation sites on CD91 for downstream signaling resulting in unique cytokine profiles and co-stimulation capacity. We investigate here the CD91-interacting adaptor proteins and kinases by crosslinking and co-immunoprecipitation of CD91 and its signaling complex following stimulation with each immunogenic HSP (gp96, calreticulin or hsp70). Mass spectrometry studies with gp96 identified the adaptor protein Shc and two other receptor tyrosine kinase associated with CD91. Inhibition of these kinases leads to a significant decrease in gp96-mediated cytokine production. Further work is being done to elucidate the remainder of this signaling network for each HSP and examine any differences between APC types. This project will aid in better understanding of how CD91-mediated signaling differentially activates effector cytokine profiles in APCs. This knowledge can be used in the development of new therapeutic approaches to enhance immunosurveillance of cancers and to better eradicate established disease.