title: p62/SQSTM1 in autophagic clearance of a non-ubiquitylated substrate.
abstract: Proteolytic systems and the aggresome pathway contribute to preventing accumulation of cytotoxic aggregation-prone proteins. Although polyubiquitylation is usually required for degradation or aggresome formation, several substrates are processed independently of ubiquitin through a poorly understood mechanism. Here, we found that p62/SQSTM1, a multifunctional adaptor protein, was involved in the selective autophagic clearance of a non-ubiquitylated substrate, namely an aggregation-prone isoform of STAT5A (STAT5A_ΔE18). By using a cell line that stably expressed STAT5A_ΔE18, we investigated the properties of its aggregation and degradation. We found that STAT5A_ΔE18 formed non-ubiquitylated aggresomes and/or aggregates by impairment of proteasome functioning or autophagy. Transport of these aggregates to the perinuclear region was inhibited by trichostatin A or tubacin, inhibitors of histone deacetylase (HDAC), indicating that the non-ubiquitylated aggregates of STAT5A_ΔE18 were sequestered into aggresomes in an HDAC6-dependent manner. Moreover, p62 was bound to STAT5A_ΔE18 through its PB1 domain, and the oligomerization of p62 was required for this interaction. In p62-knockdown experiments, we found that p62 was required for autophagic clearance of STAT5A_ΔE18 but not for its aggregate formation, suggesting that the binding of p62 to non-ubiquitylated substrates might trigger their autophagic clearance.
authors.affiliation: Department of Basic Geriatrics, Research Institute for Neurological Diseases and Geriatrics, Kyoto Prefectural University of Medicine, Kawaramachi-Hirokoji, Kyoto 602-8566, Japan.
authors.forename: Yoshihisa
authors.initials: Y
authors.lastname: Watanabe
authors.forename: Masaki
authors.initials: M
authors.lastname: Tanaka
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics / Q000378:metabolism*; D000813:Anilides / Q000494:pharmacology; D001343:Autophagy / Q000235:genetics; D055785:Gene Knockdown Techniques; D006367:HeLa Cells; D000073864:Histone Deacetylase 6; D056572:Histone Deacetylase Inhibitors / Q000494:pharmacology; D006655:Histone Deacetylases / Q000378:metabolism*; D006801:Humans; D006877:Hydroxamic Acids / Q000494:pharmacology; D009154:Mutation / Q000235:genetics; D011485:Protein Binding; D055503:Protein Multimerization / Q000235:genetics; D021381:Protein Transport / Q000187:drug effects; D059748:Proteolysis; D050799:STAT5 Transcription Factor / Q000235:genetics / Q000378:metabolism*; D000071456:Sequestosome-1 Protein; D019076:Transgenes / Q000235:genetics; D054875:Ubiquitination
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D000813:Anilides; D056572:Histone Deacetylase Inhibitors; D006877:Hydroxamic Acids; C099718:SQSTM1 protein, human; D050799:STAT5 Transcription Factor; D000071456:Sequestosome-1 Protein; C474316:tubacin; C012589:trichostatin A; C433811:HDAC6 protein, human; D000073864:Histone Deacetylase 6; D006655:Histone Deacetylases