Dysfunction of Optineurin in Amyotrophic Lateral Sclerosis and Glaucoma.

Neurodegenerative disorders, including amyotrophic lateral sclerosis (ALS), frontotemporal dementia, and glaucoma, affect millions of people worldwide. ALS is caused by the loss of motor neurons in the spinal cord, brainstem, and brain, and genetic mutations are responsible for 10% of all ALS cases. Glaucoma is characterized by the loss of retinal ganglion cells and is the most common cause of irreversible blindness. Interestingly, mutations in OPTN, encoding optineurin, are associated with both ALS and glaucoma. Optineurin is a highly abundant protein involved in a wide range of cellular processes, including the inflammatory response, autophagy, Golgi maintenance, and vesicular transport. In this review, we summarize the role of optineurin in cellular mechanisms implicated in neurodegenerative disorders, including neuroinflammation, autophagy, and vesicular trafficking, focusing in particular on the consequences of expression of mutations associated with ALS and glaucoma. This review, therefore showcases the impact of optineurin dysfunction in ALS and glaucoma.

Myosin VI and branched actin filaments mediate membrane constriction and fission of melanosomal tubule carriers.

Vesicular and tubular transport intermediates regulate organellar cargo dynamics. Transport carrier release involves local and profound membrane remodeling before fission. Pinching the neck of a budding tubule or vesicle requires mechanical forces, likely exerted by the action of molecular motors on the cytoskeleton. Here, we show that myosin VI, together with branched actin filaments, constricts the membrane of tubular carriers that are then released from melanosomes, the pigment containing lysosome-related organelles of melanocytes. By combining superresolution fluorescence microscopy, correlative light and electron microscopy, and biochemical analyses, we find that myosin VI motor activity mediates severing by constricting the neck of the tubule at specific melanosomal subdomains. Pinching of the tubules involves the cooperation of the myosin adaptor optineurin and the activity of actin nucleation machineries, including the WASH and Arp2/3 complexes. The fission and release of these tubules allows for the export of components from melanosomes, such as the SNARE VAMP7, and promotes melanosome maturation and transfer to keratinocytes. Our data reveal a new myosin VI- and actin-dependent membrane fission mechanism required for organelle function.

Protein aggregation in amyotrophic lateral sclerosis.

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease characterized by the aggregation of ubiquitinated proteins in affected motor neurons. Recent studies have identified several new molecular constituents of ALS-linked cellular aggregates, including FUS, TDP-43, OPTN, UBQLN2 and the translational product of intronic repeats in the gene C9ORF72. Mutations in the genes encoding these proteins are found in a subgroup of ALS patients and segregate with disease in familial cases, indicating a causal relationship with disease pathogenesis. Furthermore, these proteins are often detected in aggregates of non-mutation carriers and those observed in other neurodegenerative disorders, supporting a widespread role in neuronal degeneration. The molecular characteristics and distribution of different types of protein aggregates in ALS can be linked to specific genetic alterations and shows a remarkable overlap hinting at a convergence of underlying cellular processes and pathological effects. Thus far, self-aggregating properties of prion-like domains, altered RNA granule formation and dysfunction of the protein quality control system have been suggested to contribute to protein aggregation in ALS. The precise pathological effects of protein aggregation remain largely unknown, but experimental evidence hints at both gain- and loss-of-function mechanisms. Here, we discuss recent advances in our understanding of the molecular make-up, formation, and mechanism-of-action of protein aggregates in ALS. Further insight into protein aggregation will not only deepen our understanding of ALS pathogenesis but also may provide novel avenues for therapeutic intervention.

Optineurin is potentially associated with TDP-43 and involved in the pathogenesis of inclusion body myositis.

AIMS: Increasing evidences suggest a similarity in the pathophysiological mechanisms of neuronal cell death in amyotrophic lateral sclerosis (ALS) and myofibre degeneration in sporadic inclusion body myositis (sIBM). The aim of this study is to elucidate the involvement of ALS-causing proteins in the pathophysiological mechanisms in sIBM. METHODS: Skeletal muscle biopsy specimens of five patients with sIBM, two with oculopharyngeal muscular dystrophy (OPMD), three with polymyositis (PM), three with dermatomyositis (DM), three with neurogenic muscular atrophy, and three healthy control subjects were examined. We analysed the expression and localization of familial ALS-causing proteins, including transactive response DNA binding protein-43 (TDP-43), fused in sarcoma/translocated in liposarcoma (FUS/TLS), Cu/Zn superoxide dismutase (SOD1) and optineurin (OPTN) by immunohistochemistry. RESULTS: TDP-43, OPTN and, to a lesser extent, FUS/TLS were more frequently accumulated in the cytoplasm in patients with sIBM and OPMD than in patients with PM, DM, neurogenic muscular atrophy, or healthy control subjects. SOD1 was accumulated in a small percentage of myofibres in patients with sIBM and OPMD, and to a very small extent in patients with PM and DM. Confocal microscopy imaging showed that TDP-43 proteins more often colocalized with OPTN than with FUS/TLS, p62 and phosphorylated Tau. CONCLUSIONS: These findings suggest that OPTN in cooperation with TDP-43 might be involved in the pathophysiological mechanisms of skeletal muscular degeneration in myopathy with rimmed vacuoles. Further investigation into these mechanisms is therefore warranted.

Autophagy receptors link myosin VI to autophagosomes to mediate Tom1-dependent autophagosome maturation and fusion with the lysosome.

Autophagy targets pathogens, damaged organelles and protein aggregates for lysosomal degradation. These ubiquitylated cargoes are recognized by specific autophagy receptors, which recruit LC3-positive membranes to form autophagosomes. Subsequently, autophagosomes fuse with endosomes and lysosomes, thus facilitating degradation of their content; however, the machinery that targets and mediates fusion of these organelles with autophagosomes remains to be established. Here we demonstrate that myosin VI, in concert with its adaptor proteins NDP52, optineurin, T6BP and Tom1, plays a crucial role in autophagy. We identify Tom1 as a myosin VI binding partner on endosomes, and demonstrate that loss of myosin VI and Tom1 reduces autophagosomal delivery of endocytic cargo and causes a block in autophagosome-lysosome fusion. We propose that myosin VI delivers endosomal membranes containing Tom1 to autophagosomes by docking to NDP52, T6BP and optineurin, thereby promoting autophagosome maturation and thus driving fusion with lysosomes.

Toward an integrative view of Optineurin functions.

This review highlights recent advances in our understanding of the mechanisms of Optineurin (Optn) action and its implication in diseases. Optn has emerged as a key player regulating various physiological processes, including membrane trafficking, protein secretion, cell division and host defense against pathogens. Furthermore, there is growing evidence for an association of Optn mutations with human diseases such as primary open-angle glaucoma, amyotrophic lateral sclerosis and Paget's disease of bone. Optn functions depend on its precise subcellular localization and its interaction with other proteins. Here, we review the mechanisms that allow Optn to ensure a timely and spatially coordinated integration of different physiological processes and discuss how their deregulation may lead to different pathologies.

Plk1-dependent phosphorylation of optineurin provides a negative feedback mechanism for mitotic progression.

Plk1 activation is required for progression through mitotic entry to cytokinesis. Here we show that at mitotic entry, Plk1 phosphorylates Optineurin (Optn) at serine 177 and that this dissociates Optn from the Golgi-localized GTPase Rab8, inducing its translocation into the nucleus. Mass spectrometry analysis revealed that Optn is associated with a myosin phosphatase complex (MP), which antagonizes the mitotic function of Plk1. Our data also indicate that Optn functionally connects this complex to Plk1 by promoting phosphorylation of the myosin phosphatase targeting subunit 1 (MYPT1). Accordingly, silencing Optn expression increases Plk1 activity and induces abscission failure and multinucleation, which were rescued upon expression of wild-type (WT) Optn, but not a phospho-deficient mutant (S177A) that cannot translocate into the nucleus during mitosis. Overall, these results highlight an important role of Optn in the spatial and temporal coordination of Plk1 activity.

Cellular and molecular biology of optineurin.

Optineurin is a gene linked to glaucoma, amyotrophic lateral sclerosis, other neurodegenerative diseases, and Paget's disease of bone. This review describes the characteristics of optineurin and summarizes the cellular and molecular biology investigations conducted so far on optineurin. Data from a number of laboratories indicate that optineurin is a cytosolic protein containing 577 amino acid residues. Interacting with proteins such as myosin VI, Rab8, huntingtin, transferrin receptor, and TANK-binding kinase 1, optineurin is involved in basic cellular functions including protein trafficking, maintenance of the Golgi apparatus, as well as NF-κB pathway, antiviral, and antibacteria signaling. Mutation or alteration of homeostasis of optineurin (such as overexpression or knockdown) results in adverse consequences in the cells, leading to the development of neurodegenerative diseases including glaucoma.

[Identification of a new causative gene of amyotrophic lateral sclerosis; optineurin].

Amyotrophic lateral sclerosis (ALS) is a devastating disorder characterized by degeneration of motor neurons of the primary motor cortex, brainstem and spinal cord. ALS patients die within 3 to 5 years without respiratory support. Detecting the causing gene is necessary to elucidate ALS. We identified mutations of optineurin (OPTN) in ALS. We found three types of mutation of OPTN: a homozygous deletion of exon 5, a homozygous Q398X nonsense mutation and a heterozygous E478G missense mutation within its ubiquitin-binding domain. Cell transfection experiments showed that the nonsense and missense mutations of OPTN abolished the inhibition of activation of nuclear factor kappa B. The missense mutation revealed a cytoplasmic distribution different from that of the wild type. A case with the E478G mutation showed OPTN-immunoreactive cytoplasmic retention, and Golgi fragmentation was identified in 70% of the anterior horn cells. TDP-43- or SOD1-positive inclusions of sporadic and SOD1 cases of ALS were also immunolabelled with anti-OPTN antibodies. Furthermore, optineurin is co-localized with fused in sarcoma (FUS) in basophilic inclusions of ALS with FUS mutation and in basophilic inclusion body disease. Our findings suggest that OPTN is involved in the great part of pathogenesis of ALS.

Hypothesis of optineurin as a new common risk factor in normal-tension glaucoma and Alzheimer's disease.

Growing evidences suggest a link between normal tension glaucoma (NTG) and Alzheimer's disease (AD). Both of them are progressive neurodegenerative disorders. Recently researches provide a clue that optineurin may be a new common underlying risk factor involved in NTG and AD. OPTINEURIN (OPTN) gene coding for "optineurin" protein is identified as the causative gene in NTG. Interestingly, optineurin was also found in neurofibrillary tangles and dystrophic neurites in AD, as well as other neurodegenerative diseases. This suggested a new hypothesis for neurodegeneration in AD involving chronic optineurin neurotoxicity, mimicking NTG at the molecular level. A theoretical relationship between optineurin, NTG and AD seems to exist. Indicating that optineurin may play a role in both NTG and AD will shed new light on the link between these two diseases and lead to a better understanding of the common mechanisms underlying NTG and AD.

Functional analysis of the novel C-terminal domains of S pombe transcription factor IIIA.

Transcription factor IIIA from S.pombe exhibits a novel structural organization compared to its homologues in other species. TFIIIA from S.cerevisiae or vertebrates contains a total of nine C(2)H(2) zinc-finger domains and a non-zinc finger region at its C terminus. In addition, the S.cerevisiae protein possesses an 81-amino acid spacer between zinc fingers eight and nine. In contrast, the S.pombe TFIIIA sequence includes ten potential zinc finger motifs, with a 53-amino acid spacer between fingers nine and ten. Zinc finger nine of the S.pombe protein deviates from the consensus for a C(2)H(2) zinc finger, however, in that it does not include an appropriately positioned second Zn(2+)-coordinating histidine. We demonstrate here, through analysis of mutated forms of the protein, that the non-canonical ninth zinc finger is functional in both DNA binding and transcription. In addition, we have shown that the spacer preceding finger ten and finger ten itself are essential for the transcriptional function of S.pombe TFIIIA, but neither is required for wild-type 5S rRNA gene-binding activity.