title: Targeting SQSTM1/p62 induces cargo loading failure and converts autophagy to apoptosis via NBK/Bik.
abstract: In selective autophagy, the adaptor protein SQSTM1/p62 plays a critical role in recognizing/loading cargo (e.g., malfolded proteins) into autophagosomes for lysosomal degradation. Here we report that whereas SQSTM1/p62 levels fluctuated in a time-dependent manner during autophagy, inhibition or knockdown of Cdk9/cyclin T1 transcriptionally downregulated SQSTM1/p62 but did not affect autophagic flux. These interventions, or short hairpin RNA (shRNA) directly targeting SQSTM1/p62, resulted in cargo loading failure and inefficient autophagy, phenomena recently described for Huntington's disease neurons. These events led to the accumulation of the BH3-only protein NBK/Bik on endoplasmic reticulum (ER) membranes, most likely by blocking loading and autophagic degradation of NBK/Bik, culminating in apoptosis. Whereas NBK/Bik upregulation was further enhanced by disruption of distal autophagic events (e.g., autophagosome maturation) by chloroquine (CQ) or Lamp2 shRNA, it was substantially diminished by inhibition of autophagy initiation (e.g., genetically by shRNA targeting Ulk1, beclin-1, or Atg5 or pharmacologically by 3-methyladenine [3-MA] or spautin-1), arguing that NBK/Bik accumulation stems from inefficient autophagy. Finally, NBK/Bik knockdown markedly attenuated apoptosis in vitro and in vivo. Together, these findings identify novel cross talk between autophagy and apoptosis, wherein targeting SQSTM1/p62 converts cytoprotective autophagy to an inefficient form due to cargo loading failure, leading to NBK/Bik accumulation, which triggers apoptosis.
authors.affiliation: Department of Medicine, Virginia Commonwealth University and Massey Cancer Center, Richmond, Virginia, USA.
authors.forename: Shuang
authors.initials: S
authors.lastname: Chen
authors.affiliation: Department of Medicine, Virginia Commonwealth University and Massey Cancer Center, Richmond, Virginia, USA.
authors.forename: Liang
authors.initials: L
authors.lastname: Zhou
authors.affiliation: Department of Medicine, Virginia Commonwealth University and Massey Cancer Center, Richmond, Virginia, USA National Engineering Laboratory for Druggable Gene and Protein Screening, Northeast Normal University, Changchun, Jilin, China.
authors.forename: Yu
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: Department of Medicine, Virginia Commonwealth University and Massey Cancer Center, Richmond, Virginia, USA Department of Hematology, Beijing Chaoyang Hospital of Capital Medical University, Beijing, China.
authors.forename: Yun
authors.initials: Y
authors.lastname: Leng
authors.affiliation: Department of Medicine, Virginia Commonwealth University and Massey Cancer Center, Richmond, Virginia, USA.
authors.forename: Xin-Yan
authors.initials: XY
authors.lastname: Pei
authors.affiliation: Department of Medicine, Virginia Commonwealth University and Massey Cancer Center, Richmond, Virginia, USA.
authors.forename: Hui
authors.initials: H
authors.lastname: Lin
authors.affiliation: Department of Lymphoma and Myeloma, University of Texas M. D. Anderson Cancer Center, Houston, Texas, USA.
authors.forename: Richard
authors.initials: R
authors.lastname: Jones
authors.affiliation: Department of Lymphoma and Myeloma, University of Texas M. D. Anderson Cancer Center, Houston, Texas, USA.
authors.forename: Robert Z
authors.initials: RZ
authors.lastname: Orlowski
authors.affiliation: Department of Medicine, Virginia Commonwealth University and Massey Cancer Center, Richmond, Virginia, USA ydai@vcu.edu stgrant@vcu.edu.
authors.forename: Yun
authors.initials: Y
authors.lastname: Dai
authors.affiliation: Department of Medicine, Virginia Commonwealth University and Massey Cancer Center, Richmond, Virginia, USA Department of Biochemistry, Virginia Commonwealth University and Massey Cancer Center and Virginia Institute of Molecular Medicine, Richmond, Virginia, USA ydai@vcu.edu stgrant@vcu.edu.
authors.forename: Steven
authors.initials: S
authors.lastname: Grant
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects*; D051017:Apoptosis Regulatory Proteins / Q000235:genetics / Q000378:metabolism*; D001343:Autophagy / Q000187:drug effects*; D001897:Boronic Acids / Q000494:pharmacology; D000069286:Bortezomib; D045744:Cell Line, Tumor; D002478:Cells, Cultured; D056906:Cyclin T / Q000378:metabolism; D042863:Cyclin-Dependent Kinase 9 / Q000378:metabolism; D003513:Cycloheximide / Q000494:pharmacology; D005419:Flavonoids / Q000494:pharmacology; D005786:Gene Expression Regulation; D006360:Heat-Shock Proteins / Q000378:metabolism*; D006801:Humans; D007211:Indoles; D007976:Leupeptins / Q000494:pharmacology; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D024101:Mitochondrial Proteins / Q000235:genetics / Q000378:metabolism*; D010880:Piperidines / Q000494:pharmacology; D021381:Protein Transport / Q000187:drug effects*; D011719:Pyrazines / Q000494:pharmacology; D011758:Pyrroles / Q000494:pharmacology; D034741:RNA, Small Interfering / Q000494:pharmacology; D000071456:Sequestosome-1 Protein
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D000970:Antineoplastic Agents; D051017:Apoptosis Regulatory Proteins; C096820:BIK protein, human; C111741:Bik protein, mouse; D001897:Boronic Acids; D056906:Cyclin T; D005419:Flavonoids; D006360:Heat-Shock Proteins; D007211:Indoles; D007976:Leupeptins; D008565:Membrane Proteins; D024101:Mitochondrial Proteins; D010880:Piperidines; D011719:Pyrazines; D011758:Pyrroles; D034741:RNA, Small Interfering; C099718:SQSTM1 protein, human; D000071456:Sequestosome-1 Protein; C101343:Sqstm1 protein, mouse; C077990:alvocidib; D000069286:Bortezomib; D003513:Cycloheximide; D042863:Cyclin-Dependent Kinase 9; C520962:obatoclax; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde