Heat Shock Proteins (HSPs)
Heat shock proteins (HSPs) are a highly conserved family of stress response proteins that are induced upon exposure to environmental stresses such as heat, cold, or oxidative stress. Most HSPs act as molecular chaperones to facilitate the folding of cellular proteins, prevent protein aggregation, and target improperly folded proteins to specific degradative pathways. In addition, a subset of HSPs regulates apoptotic signaling pathways. While some HSPs are anti-apoptotic (HSP27, HSP70, HSP90), others promote apoptosis (HSP10, HSP60). HSP27, HSP70, and HSP90 all inhibit the formation of the apoptosome by binding to either cytochrome c (HSP27), or APAF-1 (HSP70, HSP90), subsequently preventing the maturation and activation of caspase-9. HSP70 can also inhibit apoptosis by blocking the release of Apoptosis Inducing Factor (AIF) from the mitochondria. HSP60, with or without HSP10, promotes the proteolytic processing of pro-caspase-3 to induce apoptosis.