title: Stress inhibits nucleocytoplasmic shuttling of heat shock protein hsc70.
abstract: Heat shock proteins of the hsp/hsc70 family are essential chaperones, implicated in the stress response, aging, and a growing number of human diseases. At the molecular level, hsc70s are required for the proper folding and intracellular targeting of polypeptides as well as the regulation of apoptosis. Cytoplasmic members of the hsp/hsc70 family are believed to shuttle between nuclei and cytoplasm; they are found in both compartments of unstressed cells. Our experiments demonstrate that actin filament-destabilizing drugs trigger the nuclear accumulation of hsc70s in unstressed and heat-shocked cells recovering from stress. Using human-mouse heterokaryons, we show that stress inhibits shuttling and sequesters the chaperone in nuclei. The inhibition of hsc70 shuttling upon heat shock is only transient, and transport is reestablished when cells recover from stress. Hsc70 shuttling is controlled by hsc70 retention in the nucleus, a process that is mediated by two distinct mechanisms, ATP-sensitive binding of hsc70s to chaperone substrates and, furthermore, the association with nucleoli. The nucleolar protein fibrillarin and ribosomal protein rpS6 were identified as components that show an increased association with hsc70s in the nucleus upon stress exposure. Together, our data suggest that stress abolishes the exit of hsc70s from the nucleus to the cytoplasm, thereby limiting their function to the nuclear compartment. We propose that during recovery from stress hsc70s are released from nuclear and nucleolar anchors, which is a prerequisite to restore shuttling.
authors.affiliation: Department of Physiology, McGill University, 3655 Promenade Sir William Osler, Montreal, Quebec, H3G 1Y6, Canada.
authors.forename: Mohamed
authors.initials: M
authors.lastname: Kodiha
authors.forename: Angel
authors.initials: A
authors.lastname: Chu
authors.forename: Omar
authors.initials: O
authors.lastname: Lazrak
authors.forename: Ursula
authors.initials: U
authors.lastname: Stochaj
mesh_terms: D000255:Adenosine Triphosphate / Q000502:physiology; D000266:Adenylyl Imidodiphosphate / Q000502:physiology; D000818:Animals; D002459:Cell Fusion; D002467:Cell Nucleus / Q000187:drug effects / Q000378:metabolism*; D003593:Cytoplasm / Q000187:drug effects / Q000378:metabolism*; D050883:HSC70 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism*; D006367:HeLa Cells; D006358:Hot Temperature; D006801:Humans; D051379:Mice; D041681:NIH 3T3 Cells; D011485:Protein Binding; D021381:Protein Transport
chemical_list: D050883:HSC70 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins; C494371:HSPA8 protein, human; C494372:Hspa8 protein, mouse; D000266:Adenylyl Imidodiphosphate; D000255:Adenosine Triphosphate