Dual Functions of Heat Shock Proteins : Molecular Chaperones Inside of Cells and Danger Signals Outside of Cells

• Published in: Nihon Haipāsāmia Gakkai shi Vol. 23; no. 1; pp. 11 - 22
• Main Authors: OHTSUKA, KENZO, KAWASHIMA, DAISUKE, ASAI, MIDORI
• Format: Journal Article
• Language: English
• Published: Japanese Society for Thermal Medicine 20-03-2007
• Subjects: danger signals; extracellular HSPs; heat shock proteins (HSPs); molecular chaperones; protein folding diseases
• ISSN: 0911-2529; 1881-9516
• DOI: 10.3191/thermalmedicine.23.11

Heat shock proteins (HSPs) are induced by various environmental (physical, chemical and biological) stresses in virtually all organisms. Most HSPs are also synthesized constitutively at normal growth temperatures, and possess fundamental and indispensable functions in protein biogenesis through their role as molecular chaperones. HSPs also play a role in protecting cells from deleterious and proteotoxic stresses. Although the molecular chaperone functions of HSPs are usually conducted inside of cells, recent reports indicate that HSPs can also be detected on the cell surface and outside of cells in the cellular milieu. HSPs have been shown to be secreted by the exosome pathway, and they are released from cells which have died through necrosis. There is growing evidence that these extracellular HSPs derived from dead cells, or purified exogenous HSPs can stimulate the innate immune system. Thus, HSPs can be considered to be a danger signal or warning signal to tissues or an organism. In this review, the dual functions of HSPs, as molecular chaperones inside of cells and as warning signals outside of cells, is discussed.