Potentiation of amyotrophic lateral sclerosis (ALS)-associated TDP-43 aggregation by the proteasome-targeting factor, ubiquilin 1.
ABSTRACT TDP-43 (43-kDa TAR DNA-binding domain protein) is a major constituent of ubiquitin-positive cytoplasmic aggregates present in neurons of patients with fronto-temporal lobular dementia and amyotrophic lateral sclerosis (ALS). The pathologic significance of TDP-43 aggregation is not known; however, dominant mutations in TDP-43 cause a subset of ALS cases, suggesting that misfolding and/or altered trafficking of TDP-43 is relevant to the disease process. Here, we show that the presenilin-binding protein ubiquilin 1 (UBQLN) plays a role in TDP-43 aggregation. TDP-43 interacted with UBQLN both in yeast and in vitro, and the carboxyl-terminal ubiquitin-associated domain of UBQLN was both necessary and sufficient for binding to polyubiquitylated forms of TDP-43. Overexpression of UBQLN recruited TDP-43 to detergent-resistant cytoplasmic aggregates that colocalized with the autophagosomal marker, LC3. UBQLN-dependent aggregation required the UBQLN UBA domain, was mediated by non-overlapping regions of TDP-43, and was abrogated by a mutation in UBQLN previously linked to Alzheimer disease. Four ALS-associated alleles of TDP-43 also coaggregated with UBQLN, and the extent of aggregation correlated with in vitro UBQLN binding affinity. Our findings suggest that UBQLN is a polyubiquitin-TDP-43 cochaperone that mediates the autophagosomal delivery and/or proteasome targeting of TDP-43 aggregates.
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ABSTRACT: Ubiquilin1 (UBQLN1) is a ubiquitin-like domain and a ubiquitin-associated domain containing protein that has been reported to be involved in shuttling proteins to the proteasome, especially during endoplasmic reticulum-associated protein degradation. Thus, UBQLN1 function has been shown to be critical for combating a number of neurological disorders caused by protein aggregation, such as amyotrophic lateral sclerosis, Alzheimer's disease and Huntington's disease. A role for UBQLN1 in regulating processes involved in tumorigenesis has not been demonstrated. Herein, we show that loss of UBQLN1 causes increased cell migration and invasion, actin cytoskeleton reorganization and induction of epithelial-to-mesenchymal transition (EMT). Loss of UBQLN1 results in a significant decrease in the expression of epithelial markers including E-cadherin and claudin1, whereas expression of mesenchymal markers including Vimentin, Snail and ZEB1 are significantly elevated. Interestingly, we found that ZEB1 is required for induction of mesenchymal-like properties following loss of UBQLN1 and ZEB1 is capable of repressing expression of UBQLN1, suggesting a physiological, reciprocal regulation of EMT by UBQLN1 and ZEB1. Further, we find evidence for a role for UBQLN2 in also regulating EMT and cell migration. These observations have potential clinical relevance because the UBQLN1 gene is lost and underexpressed in a large percentage of human cancer cell lines, and primary human lung cancer samples and recurrent mutations in all five UBQLN family members have been identified in human lung cancers. Taken together, our results suggest for the first time a role for UBQLN family members in cancer biology.Oncogene advance online publication, 21 April 2014; doi:10.1038/onc.2014.97.Oncogene 04/2014; · 7.36 Impact Factor
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ABSTRACT: Mutations in valosin-containing protein (VCP) cause a rare, autosomal dominant disease called inclusion body myopathy associated with Paget disease of bone and frontotemporal dementia (IBMPFD). One-third of patients with IBMPFD develop frontotemporal dementia, characterized by an extensive neurodegeneration in the frontal and temporal lobes. Neuropathologic hallmarks include nuclear and cytosolic inclusions positive to ubiquitin and transactive response DNA-binding protein 43 (TDP-43) in neurons and glial activation in affected regions. However, the pathogenic mechanisms by which mutant VCP triggers neurodegeneration remain unknown. Herein, we generated a mouse model selectively overexpressing a human mutant VCP in neurons to study pathogenic mechanisms of mutant VCP-mediated neurodegeneration and cognitive impairment. The overexpression of VCPA232E mutation in forebrain regions produced significant progressive impairments of cognitive function, including deficits in spatial memory, object recognition, and fear conditioning. Although overexpressed or endogenous VCP did not seem to focally aggregate inside neurons, TDP-43 and ubiquitin accumulated with age in transgenic mouse brains. TDP-43 was also found to co-localize with stress granules in the cytosolic compartment. Together with the appearance of high-molecular-weight TDP-43 in cytosolic fractions, these findings demonstrate the mislocalization and accumulation of abnormal TDP-43 in the cytosol of transgenic mice, which likely lead to an increase in cellular stress and cognitive impairment. Taken together, these results highlight an important pathologic link between VCP and cognition.American Journal Of Pathology 06/2013; 183(2):504. · 4.52 Impact Factor
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ABSTRACT: Ubiquilins are proteins that function as ubiquitin receptors in eukaryotes. Mutations in two ubiquilin-encoding genes have been linked to the genesis of neurodegenerative diseases. However, ubiquilin functions are still poorly understood. In this study, evolutionary and functional data are combined to determine the origin and diversification of the ubiquilin gene family and to characterize novel potential roles of ubiquilins in mammalian species, including humans. The analysis of more than six hundred sequences allowed characterizing ubiquilin diversity in all the main eukaryotic groups. Many organisms (e. g. fungi, many animals) have single ubiquilin genes, but duplications in animal, plant, alveolate and excavate species are described. Seven different ubiquilins have been detected in vertebrates. Two of them, here called UBQLN5 and UBQLN6, had not been hitherto described. Significantly, marsupial and eutherian mammals have the most complex ubiquilin gene families, composed of up to 6 genes. This exceptional mammalian-specific expansion is the result of the recent emergence of four new genes, three of them (UBQLN3, UBQLN5 and UBQLNL) with precise testis-specific expression patterns that indicate roles in the postmeiotic stages of spermatogenesis. A gene with related features has independently arisen in species of the Drosophila genus. Positive selection acting on some mammalian ubiquilins has been detected. The ubiquilin gene family is highly conserved in eukaryotes. The infrequent lineage-specific amplifications observed may be linked to the emergence of novel functions in particular tissues.BMC Evolutionary Biology 03/2014; 14(1):63. · 3.29 Impact Factor