Similarly, transient depletion of OPTN using two different siRNA targeting OPTN (siOPTN #1 and siOPTN #2) for 48 hours in HeLa cells stably expressing CFP-htt ex1 Q103 led to an increased number of cells containing aggregates as well as insoluble CFP-htt ex1 Q103 compared to control cells expressing OPTN (Fig. model of ALS. A more severe phenotype is observed when optineurin is depleted in zebrafish carrying ALS mutations. Furthermore, TANK1 binding kinase 1 (TBK1) is co-localized with optineurin on protein aggregates and is important in clearance of protein aggregates through the autophagy-lysosome pathway. TBK1 phosphorylates optineurin at position Ser-177 and regulates its ability to interact with autophagy modifiers. This study provides evidence for a ubiquitin-independent function of optineurin in autophagic clearance of protein aggregates as well as additional relevance for TBK1 as an upstream regulator of the autophagic pathway. (Thurston et al., 2009; Wild et al., 2011) or in the general movement of autophagosomes by binding to microtubules (Pankiv et al., 2010), respectively. Optineurin (OPTN) is a 577 amino acid protein of versatile functions which interacts with a variety Cilostazol of proteins involved in membrane and vesicle trafficking (Rab8, huntingtin, myosin VI), cellular morphogenesis, NF-B regulation, signal transduction, transcription regulation and cellular division control (Hattula and Peranen, 2000; Anborgh et al., 2005; Sahlender et al., 2005; Zhu et al., 2007; del Toro et al., 2009; Kachaner et al., 2012). Mutations in OPTN gene have been associated with normal-tension glaucoma, primary open-angle glaucoma (Sarfarazi and Rezaie, 2003; Chalasani et al., 2009), Pagets disease (Albagha et al., 2010; Chung et al., 2010) and ALS (Maruyama et al., 2010; Del Bo et al., 2011; van Blitterswijk et al., 2012). Recently, OPTN was characterized as an autophagy adaptor protein which regulates selective autophagy of ubiquitin-coated cytosolic This OPTN function depends on the phosphorylation of its LC3-interacting motif by the protein kinase TANK-binding kinase 1 (TBK1) (Wild et al., 2011). OPTN has been shown to co-localize with protein inclusions in ALS (Maruyama et al., 2010), HD (Schwab et al., 2012) and many other neurodegenerative diseases (Osawa et al., 2011). However, little is known about the role of OPTN in neurodegenerative disorders, particularly in respect to the autophagy-mediated degradation of misfolded protein inclusions. In this report, we use different aggregation-prone protein models: short fragment of the protein huntingtin carrying an extended polyglutamine (polyQ) mutation (htt ex1 Q103) and superoxide dismutase 1 (SOD1) protein carrying point mutations at position Gly-93 (SOD1 G93C or SOD1 G93A), commonly used as models of HD and ALS, respectively (Witan et al., 2008; Filimonenko et al., 2010). We show that Cilostazol OPTN recognizes htt ex1 Q103 and SOD1 G93C aggregates through its C-terminal coiled-coil domain in a ubiquitin-independent manner and actively participates in the degradation of both htt ex1 Q103 and SOD1 G93C inclusions. Furthermore, we provide evidence for the hypothesis that the degradation of htt ex1 Q103 and SOD1 G93C aggregates is regulated by OPTN via phosphorylation of OPTN Ser-177 by TBK1. Finally, OPTN depletion in wild-type zebrafish causes a motor axonopathy phenotype similar to the phenotype reported in a zebrafish model of ALS generated by overexpression of mutant form of SOD1. RESULTS OPTN interacts with aggregating proteins involved in ALS and HD Recently, mutations in the gene encoding OPTN have been associated with some familial and sporadic forms of ALS. OPTN is frequently detected in protein inclusions in neurons of ALS and HD patients (Maruyama et al., 2010; Schwab et al., 2012). To address the possible interaction of OPTN with protein aggregates involved in neurodegenerative pathologies, we transiently transfected HeLa cells with GFP-SOD1 G93C mutant. This mutation has been identified in ALS patients and is responsible for familial cases of ALS (Gaudette et al., 2000). We also used HeLa cells stably transfected with CFP-htt ex1 Q103 as a well-known model of HD (Filimonenko et al., 2010). The interaction between OPTN and Cilostazol SOD1 G93C or htt ex1 Q103 aggregates was studied Cilostazol using co-immunostaining, immunoprecipitation and binding experiments. Confocal analyses indicated that OPTN readily co-localized with both SOD1 G93C and htt ex1 Q103 Sirt6 inclusions (Fig. 1A, upper panels). Similarly, we observed a co-localization of ubiquitin, p62 and LC3 with SOD1 G93C and htt ex1 Q103 aggregates (Fig. 1A). To further confirm OPTN interaction with SOD1 G93C inclusions, we co-expressed wild-type SOD1 (SOD1 wt) or mutant SOD1 G93C with a wild-type HA-OPTN (HA-OPTN wt) in HeLa cells. Wild-type HA-OPTN co-immunoprecipitated only with the aggregation-prone SOD1 G93C mutant and.