Moonlighting Functions of Heat Shock Protein 90

Abstract

Hsp90 is a highly expressed and ubiquitous chaperone in eukaryotes and bacteria. It works with hundreds of client proteins and is regulated by dozens of co-chaperones. Its functions in folding, stabilizing, assembling and disassembling proteins and complexes that are involved in many key processes in the cell, including antigen cross-presentation, stabilization of the cytoskeleton, signaling pathways, stabilization of steroid receptors and other transcription factors, assembly and disassembly of transcription machinery, DNA repair, and the cell cycle. This ubiquitous and versatile intracellular protein is found to have even more functions outside the cell. In this review we discuss the idea that Hsp90 is a moonlighting protein with roles as a secreted cytokine and as a cell surface apoptotic signal and receptor for bacterial cells and lipopolysaccharide.