title: p38(MAPK)-regulated induction of p62 and NBR1 after photodynamic therapy promotes autophagic clearance of ubiquitin aggregates and reduces reactive oxygen species levels by supporting Nrf2-antioxidant signaling.
abstract: Emerging evidence indicates that oxidative stress instigates the formation of ubiquitin (Ub) aggregates, substrates of autophagy, through a process requiring the ubiquitin binding adaptors p62/SQSTM1 and NBR1. Here, we have investigated the role of p62 and NBR1 in cell survival after hypericin-mediated photodynamic therapy (Hyp-PDT), a procedure known to incite robust reactive oxygen species (ROS)-based endoplasmic reticulum stress and autophagy pathways. We found that Hyp-PDT stimulated the formation of p62- and NBR1-associated Ub aggregates in normal and cancer cells, which were ultimately removed by autophagy, through a mechanism partially regulated by p38(MAPK). In line with this, genetic or pharmacological p38(MAPK) inhibition reduced p62 and NBR1 levels and aggregate formation and impaired Nrf2 activation, thus increasing photo-oxidative stress and cell death. p62-deficient cells, or cells lacking p62 and with reduced levels of NBR1 (through siRNA knockdown), also displayed reduced aggregate formation but exhibited attenuated ROS levels, reduced caspase activation, and improved survival after Hyp-PDT. The increased resistance to photo-oxidative stress exhibited by cells lacking p62 and/or NBR1 was overruled by the inhibition of p38(MAPK), which restored cytotoxic ROS levels, thus indicating the relevance of this signal in the control of cell viability. Taken together these findings provide evidence that in photodynamically treated cells a p38(MAPK)-regulated pathway coordinates the p62/NBR1-mediated clearance of cytosolic aggregates and mitigates PDT-induced proteotoxicity. They also reveal that a functional p38(MAPK)-Nrf2 signal is required to keep ROS levels in check and protect against PDT-induced proteotoxicity, independent of aggregate formation.
authors.affiliation: Cell Death Research & Therapy Laboratory, Cellular and Molecular Medicine Department, KU Leuven - University of Leuven, 3000 Leuven, Belgium; Virology and Immunology Unit, GiGA-R, GiGA B34, University of Liège, 4000 Liège, Belgium.
authors.forename: Noemí
authors.initials: N
authors.lastname: Rubio
authors.affiliation: Cell Death Research & Therapy Laboratory, Cellular and Molecular Medicine Department, KU Leuven - University of Leuven, 3000 Leuven, Belgium.
authors.forename: Julien
authors.initials: J
authors.lastname: Verrax
authors.affiliation: Cell Death Research & Therapy Laboratory, Cellular and Molecular Medicine Department, KU Leuven - University of Leuven, 3000 Leuven, Belgium.
authors.forename: Michael
authors.initials: M
authors.lastname: Dewaele
authors.affiliation: Cell Death Research & Therapy Laboratory, Cellular and Molecular Medicine Department, KU Leuven - University of Leuven, 3000 Leuven, Belgium.
authors.forename: Tom
authors.initials: T
authors.lastname: Verfaillie
authors.affiliation: Molecular Cancer Research Group, Department of Medical Biology, University of Tromsø, 9037 Tromsø, Norway.
authors.forename: Terje
authors.initials: T
authors.lastname: Johansen
authors.affiliation: Virology and Immunology Unit, GiGA-R, GiGA B34, University of Liège, 4000 Liège, Belgium. Electronic address: jpiette@ulg.ac.be.
authors.forename: Jacques
authors.initials: J
authors.lastname: Piette
authors.affiliation: Cell Death Research & Therapy Laboratory, Cellular and Molecular Medicine Department, KU Leuven - University of Leuven, 3000 Leuven, Belgium. Electronic address: Patricia.Agostinis@med.kuleuven.be.
authors.forename: Patrizia
authors.initials: P
authors.lastname: Agostinis
mesh_terms: D000818:Animals; D000873:Anthracenes; D001343:Autophagy / Q000187:drug effects / Q000235:genetics* / Q000528:radiation effects; D002460:Cell Line; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects / Q000378:metabolism* / Q000528:radiation effects; D005786:Gene Expression Regulation; D055786:Gene Knockout Techniques; D006367:HeLa Cells; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D008027:Light; D051379:Mice; D051267:NF-E2-Related Factor 2 / Q000235:genetics* / Q000378:metabolism; D010084:Oxidation-Reduction; D010569:Perylene / Q000031:analogs & derivatives / Q000494:pharmacology; D066329:Protein Aggregates; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D011506:Proteins / Q000235:genetics* / Q000378:metabolism; D059748:Proteolysis; D016601:RNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology; D017382:Reactive Oxygen Species / Q000378:metabolism; D015398:Signal Transduction; D025801:Ubiquitin / Q000235:genetics / Q000378:metabolism; D048051:p38 Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000378:metabolism
chemical_list: D000873:Anthracenes; D047908:Intracellular Signaling Peptides and Proteins; C549756:NBR1 protein, human; D051267:NF-E2-Related Factor 2; C495635:NFE2L2 protein, human; C118585:P62 protein, human; D066329:Protein Aggregates; D047428:Protein Kinase Inhibitors; D011506:Proteins; D016601:RNA-Binding Proteins; D011838:Radiation-Sensitizing Agents; D017382:Reactive Oxygen Species; D025801:Ubiquitin; D010569:Perylene; C004965:hypericin; D048051:p38 Mitogen-Activated Protein Kinases
keywords: Autophagy; ER stress; Free radicals; NBR1; PDT; Photodynamic stress; Proteotoxicity; ROS; p62