title: Nucleocytoplasmic shuttling of p62/SQSTM1 and its role in recruitment of nuclear polyubiquitinated proteins to promyelocytic leukemia bodies.
abstract: p62, also known as sequestosome1 (SQSTM1), A170, or ZIP, is a multifunctional protein implicated in several signal transduction pathways. p62 is induced by various forms of cellular stress, is degraded by autophagy, and acts as a cargo receptor for autophagic degradation of ubiquitinated targets. It is also suggested to shuttle ubiquitinated proteins for proteasomal degradation. p62 is commonly found in cytosolic protein inclusions in patients with protein aggregopathies, it is up-regulated in several forms of human tumors, and mutations in the gene are linked to classical adult onset Paget disease of the bone. To this end, p62 has generally been considered to be a cytosolic protein, and little attention has been paid to possible nuclear roles of this protein. Here, we present evidence that p62 shuttles continuously between nuclear and cytosolic compartments at a high rate. The protein is also found in nuclear promyelocytic leukemia bodies. We show that p62 contains two nuclear localization signals and a nuclear export signal. Our data suggest that the nucleocytoplasmic shuttling of p62 is modulated by phosphorylations at or near the most important nuclear localization signal, NLS2. The aggregation of p62 in cytosolic bodies also regulates the transport of p62 between the compartments. We found p62 to be essential for accumulation of polyubiquitinated proteins in promyelocytic leukemia bodies upon inhibition of nuclear protein export. Furthermore, p62 contributed to the assembly of proteasome-containing degradative compartments in the vicinity of nuclear aggregates containing polyglutamine-expanded Ataxin1Q84 and to the degradation of Ataxin1Q84.
authors.affiliation: Molecular Cancer Research Group, Institute of Medical Biology, University of Tromsø, 9037 Tromsø, Norway.
authors.forename: Serhiy
authors.initials: S
authors.lastname: Pankiv
authors.forename: Trond
authors.initials: T
authors.lastname: Lamark
authors.forename: Jack-Ansgar
authors.initials: JA
authors.lastname: Bruun
authors.forename: Aud
authors.initials: A
authors.lastname: Øvervatn
authors.forename: Geir
authors.initials: G
authors.lastname: Bjørkøy
authors.forename: Terje
authors.initials: T
authors.lastname: Johansen
mesh_terms: D021581:Active Transport, Cell Nucleus / Q000235:genetics; D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics / Q000378:metabolism*; D000067696:Ataxin-1; D000067528:Ataxins; D006367:HeLa Cells; D006801:Humans; D045586:Intranuclear Inclusion Bodies / Q000235:genetics / Q000378:metabolism*; D042581:Intranuclear Space / Q000378:metabolism*; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D019913:Nuclear Localization Signals / Q000235:genetics / Q000378:metabolism*; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D010455:Peptides / Q000235:genetics / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex / Q000235:genetics / Q000378:metabolism; D000071456:Sequestosome-1 Protein; D054875:Ubiquitination
chemical_list: C000593749:ATXN1 protein, human; D048868:Adaptor Proteins, Signal Transducing; D000067696:Ataxin-1; D000067528:Ataxins; D009419:Nerve Tissue Proteins; D019913:Nuclear Localization Signals; D009687:Nuclear Proteins; D010455:Peptides; C099718:SQSTM1 protein, human; D000071456:Sequestosome-1 Protein; C097188:polyglutamine; D046988:Proteasome Endopeptidase Complex