Distinctive binding properties of human monoclonal LGI1 autoantibodies determine pathogenic mechanisms.

Autoantibodies against leucine-rich glioma inactivated 1 (LGI1) are found in patients with limbic encephalitis and focal seizures. Here, we generate patient-derived monoclonal antibodies (mAbs) against LGI1. We explore their sequences and binding characteristics, plus their pathogenic potential using transfected HEK293T cells, rodent neuronal preparations, and behavioural and electrophysiological assessments in vivo after mAb injections into the rodent hippocampus. In live cell-based assays, LGI1 epitope recognition was examined with patient sera (n = 31), CSFs (n = 11), longitudinal serum samples (n = 15), and using mAbs (n = 14) generated from peripheral B cells of two patients. All sera and 9/11 CSFs bound both the leucine-rich repeat (LRR) and the epitempin repeat (EPTP) domains of LGI1, with stable ratios of LRR:EPTP antibody levels over time. By contrast, the mAbs derived from both patients recognized either the LRR or EPTP domain. mAbs against both domain specificities showed varied binding strengths, and marked genetic heterogeneity, with high mutation frequencies. LRR-specific mAbs recognized LGI1 docked to its interaction partners, ADAM22 and ADAM23, bound to rodent brain sections, and induced internalization of the LGI1-ADAM22/23 complex in both HEK293T cells and live hippocampal neurons. By contrast, few EPTP-specific mAbs bound to rodent brain sections or ADAM22/23-docked LGI1, but all inhibited the docking of LGI1 to ADAM22/23. After intrahippocampal injection, and by contrast to the LRR-directed mAbs, the EPTP-directed mAbs showed far less avid binding to brain tissue and were consistently detected in the serum. Post-injection, both domain-specific mAbs abrogated long-term potentiation induction, and LRR-directed antibodies with higher binding strengths induced memory impairment. Taken together, two largely dichotomous populations of LGI1 mAbs with distinct domain binding characteristics exist in the affinity matured peripheral autoantigen-specific memory pools of individuals, both of which have pathogenic potential. In human autoantibody-mediated diseases, the detailed characterization of patient mAbs provides a valuable method to dissect the molecular mechanisms within polyclonal populations.

Phenotypic bases of NOTCH2NLC GGC expansion positive neuronal intranuclear inclusion disease in a Southeast Asian cohort.

Neuronal intranuclear inclusion disease (NIID) is a neurodegenerative disorder associated with GGC repeats of >60 to 500 copies in the 5'-untranslated region of NOTCH2NLC. The clinical and genetic characterization of NIID outside of East Asia remains unknown. We identified twelve patients who underwent genetic testing using long-read sequencing or repeat primed polymerase chain reaction. All were positive for a GGC repeat expansion; the median repeat length was 107 (range 92-138). Ten were Chinese and two of Malay ethnicity. Age at onset ranged from 50 to 69 years. Eight (66.7%) patients had dementia, while four (33.3%) patients were oligosymptomatic, without typical NIID symptoms of dementia, Parkinsonism, or muscle weakness. GGA interruptions within the GGC expansion were present in four patients; the number of GGA interruptions was highest (6.71%) in the patient with the earliest age at onset (50 years). Median plasma neurofilament light level was 47.3 pg/mL in seven patients (range 26-380 pg/mL). The highest level (380 pg/mL) was found in one patient who experienced an encephalitic episode. Overall, we describe a cohort of genetically confirmed NIID patients from Southeast Asia and provide further information that the presence of GGA interruptions within GGC repeat expansions may serve as a potential genetic modifier in NIID.

Identifying patients with neuronal intranuclear inclusion disease in Singapore using characteristic diffusion-weighted MR images.

PURPOSE: Adult-onset neuronal intranuclear inclusion disease (NIID) is a rare neurodegenerative disorder described mainly in the Japanese population, with characteristic DWI abnormalities at the junction between gray and white matter. We identify possible cases of NIID in the picture archive and communication system (PACS) of a tertiary neurological referral hospital in Singapore and describe their radiological features. METHODS: The neuroradiology imaging database was reviewed using keyword search of radiological reports to identify patients who had "subcortical U fibre" abnormalities on DWI. MRI were retrospectively reviewed, and those fulfilling inclusion criteria were invited for skin biopsy to detect nuclear inclusions by light and electron microscopy. RESULTS: Twelve Chinese patients (nine female; median age 70.5 years) were enrolled. Seven patients were being assessed for dementia and five for other neurological indications. In all patients, DWI showed distinctive subcortical high signal with increased average apparent diffusion coefficient (ADC), involving frontal, parietal, and temporal more than occipital lobes; the corpus callosum and external capsule were affected in some patients. On T2-weighted images, cerebral and cerebellar atrophy and white matter hyperintensity of Fazekas grade 2 and above were seen in all patients. Three patients underwent skin biopsy; all were positive for intranuclear hyaline inclusion bodies on either p62 staining or electron microscopy, which are pathognomonic for NIID. CONCLUSION: Previously undiagnosed patients with NIID can be identified by searching for abnormalities at the junction between gray and white matter on DWI in PACS and subsequently confirmed by skin biopsy. Radiologists should recognize the distinctive neuroimaging pattern of this dementing disease.

A retrospective review of a tertiary Hospital's isolation and de-isolation policy for suspected pulmonary tuberculosis.

BACKGROUND: Effective protocols for the isolation and de-isolation of patients with suspected pulmonary tuberculosis (PTB) are essential determinants of health-care costs. Early de-isolation needs to be balanced with the need to prevent nosocomial transmission of PTB. The aim of our study was to evaluate the efficiency of our hospital's current protocol for isolating and de-isolating patients with suspected PTB, in particular assessing the timeliness to de-isolation of patients with AFB smear negative respiratory samples. METHODS: We retrospectively reviewed 121 patients with suspected PTB who were admitted to our hospital's isolation ward. We analyzed the time spent in isolation, the total number of respiratory samples that were collected for each patient and the time taken from collection of the first respiratory sample to release of the result of third respiratory sample for acid-fast bacilli (AFB) smear. We also calculated the direct cost of isolation for each patient. RESULTS: The mean and median number of AFB smears for each patient was three. Thirty percent of patients had four or more AFB smears taken and 20% were de-isolated before the results of three negative AFB smears were obtained. The mean duration of isolation was significantly shorter in patients who had fewer than three negative AFB smears compared to those who had three or more negative AFB smears (three days vs. five days, p <0.01). The mean cost in patients who were de-isolated before three negative smears were obtained was USD 947 compared to USD 1,636 in those were only de-isolated after three negative AFB smears (p <0.01). CONCLUSIONS: Our study suggests that our institution's current infection control policy for the isolation of patients with suspected PTB is fairly satisfactory, but may need to be tightened further to prevent true cases of PTB being de-isolated prematurely. However, there may be instances when patients could potentially be de-isolated more quickly without risk to others, thus saving on the use of limited resources and costs to patients.

Parkin enhances the expression of cyclin-dependent kinase 6 and negatively regulates the proliferation of breast cancer cells.

Although mutations in the parkin gene are frequently associated with familial Parkinsonism, emerging evidence suggests that parkin also plays a role in cancers as a putative tumor suppressor. Supporting this, we show here that parkin expression is dramatically reduced in several breast cancer-derived cell lines as well as in primary breast cancer tissues. Importantly, we found that ectopic parkin expression in parkin-deficient breast cancer cells mitigates their proliferation rate both in vitro and in vivo, as well as reduces the capacity of these cells to migrate. Cell cycle analysis revealed the arrestment of a significant percentage of parkin-expressing breast cancer cells at the G1-phase. However, we did not observe significant changes in the levels of the G1-associated cyclin D1 and E. On the other hand, the level of cyclin-dependent kinase 6 (CDK6) is dramatically and selectively elevated in parkin-expressing breast cancer cells, the extent of which correlates well with the expression of parkin. Interestingly, a recent study demonstrated that CDK6 restrains the proliferation of breast cancer cells. Taken together, our results support a negative role for parkin in tumorigenesis and provide a potential mechanism by which parkin exerts its suppressing effects on breast cancer cell proliferation.

Parkin blushed by PINK1.

Mutations in the PTEN-induced putative kinase 1 (PINK1) are a common cause of autosomal recessive Parkinson's disease. In a recent issue of Nature, two independent reports by and show that loss of Drosophila PINK1 leads to defects in mitochondrial function resulting in male sterility, apoptotic muscle degeneration, and minor loss of dopamine neurons that is rescued by overexpression of the ubiquitin E3 ligase, parkin. Thus, PINK1 and parkin appear to function in a common pathway suggesting a convergence of the two genes most commonly associated with autosomal recessive PD.

Autophagy-mediated clearance of aggresomes is not a universal phenomenon.

Aggresomes are juxtanuclear inclusion bodies that have been proposed to act as staging grounds for the disposal of protein aggregates via the autophagic route. To examine whether the composition of an aggresome influences its clearance by autophagy, we ectopically expressed a variety of aggregation-prone proteins in cultured cells to generate aggresomes that differ in their protein content. We found that whereas aggresomes generated in cells expressing mutant huntingtin or mutant tau, or co-expressing synphilin-1 and alpha-synuclein, are amenable to clearance by autophagy, those produced in AIMP2 (p38)- or mutant desmin-expressing cells are apparently resistant to autophagic clearance. Notably, AIMP2 (p38)- and desmin-positive inclusions fail to recruit key components of the autophagic/lysosomal system. However, by altering the composition of inclusions, 'autophagy-resistant' aggresomes could be rendered 'autophagy-susceptible'. Taken together, our results demonstrate that not all aggresomes are efficiently primed for autophagic clearance and highlight a certain degree of selectivity for the supposedly non-discriminative pathway.

Lysine 63-linked ubiquitination promotes the formation and autophagic clearance of protein inclusions associated with neurodegenerative diseases.

Although ubiquitin-enriched protein inclusions represent an almost invariant feature of neurodegenerative diseases, the mechanism underlying their biogenesis remains unclear. In particular, whether the topology of ubiquitin linkages influences the dynamics of inclusions is not well explored. Here, we report that lysine 48 (K48)- and lysine 63 (K63)-linked polyubiquitination, as well as monoubiquitin modification contribute to the biogenesis of inclusions. K63-linked polyubiquitin is the most consistent enhancer of inclusions formation. Under basal conditions, ectopic expression of K63 mutant ubiquitin in cultured cells promotes the accumulation of proteins and the formation of intracellular inclusions in the apparent absence of proteasome impairment. When co-expressed with disease-associated tau and SOD1 mutants, K63 ubiquitin mutant facilitates the formation of tau- and SOD-1-positive inclusions. Moreover, K63-linked ubiquitination was found to selectively facilitate the clearance of inclusions via autophagy. These data indicate that K63-linked ubiquitin chains may represent a common denominator underlying inclusions biogenesis, as well as a general cellular strategy for defining cargo destined for the autophagic system. Collectively, our results provide a novel mechanistic route that underlies the life cycle of an inclusion body. Harnessing this pathway may offer innovative approaches in the treatment of neurodegenerative disorders.

Cellular expression, localization and interactions of the product of the human MOST-1 gene associated with breast and prostate cancers.

We previously isolated and characterized the novel human gene MOST-1 (C8orf17) that is ubiquitously expressed in all cancer cell lines tested but differentially expressed in normal adult tissues. MOST-1 maps to chromosome region 8q24.2 whose amplification is frequently associated with breast and prostate cancers. RT-PCR analyses of breast and prostatic biopsies revealed MOST-1 overexpression and/or amplification in high-grade carcinomas. We raised and characterized a polyclonal antibody against a MOST-1-specific synthetic peptide. in vitro expression of MOST-1 protein revealed a tendency to exist as high molecular mass isoforms which are SDS-insoluble upon thermal stress. MOST-1 displayed cytoplasmic localization in four human cell lines (hTERT-HME1 normal mammary epithelial, MCF7 breast adenocarcinoma, PrEC normal prostate epithelial and DU145 prostate carcinoma), with polar expression during cell division. Knockdown of MOST-1 expression in DU145 cells resulted in reduced cell proliferation but enhanced apoptosis implying a putative mitogenic role of MOST-1. Yeast two-hybrid analyses demonstrated interaction with seven human proteins, most of which are overexpressed in tumors or involved in metabolic pathways. The interacting proteins were creatine kinase, Gardner feline sarcoma v-FGR oncogene product, telethonin, SNC73 protein, ferritin light chain, peripheral benzodiazepine receptor, and immunoglobulin C (mu) and C (delta) heavy chain. Co-immunoprecipitation assays validated the interactions of MOST-1 with the latter three proteins. Our results suggest that MOST-1 is associated with cell survival, proliferation and progression of cancer cells.

Role of the ubiquitin proteasome system in Parkinson's disease.

Parkinson's disease (PD) is the most common neurodegenerative movement disorder. Although a subject of intense research, the etiology of PD remains poorly understood. Recently, several lines of evidence have implicated an intimate link between aberrations in the ubiquitin proteasome system (UPS) and PD pathogenesis. Derangements of the UPS, which normally functions as a type of protein degradation machinery, lead to alterations in protein homeostasis that could conceivably promote the toxic accumulation of proteins detrimental to neuronal survival. Not surprisingly, various cellular and animal models of PD that are based on direct disruption of UPS function reproduce the most prominent features of PD. Although persuasive, new developments in the past few years have in fact raised serious questions about the link between the UPS and PD. Here I review current thoughts and controversies about their relationship and discuss whether strategies aimed at mitigating UPS dysfunction could represent rational ways to intervene in the disease. Publication history: Republished from Current BioData's Targeted Proteins database (TPdb; http://www.targetedproteinsdb.com).

Parkin mediates nonclassical, proteasomal-independent ubiquitination of synphilin-1: implications for Lewy body formation.

It is widely accepted that the familial Parkinson's disease (PD)-linked gene product, parkin, functions as a ubiquitin ligase involved in protein turnover via the ubiquitin-proteasome system. Substrates ubiquitinated by parkin are hence thought to be destined for proteasomal degradation. Because we demonstrated previously that parkin interacts with and ubiquitinates synphilin-1, we initially expected synphilin-1 degradation to be enhanced in the presence of parkin. Contrary to our expectation, we found that synphilin-1 is normally ubiquitinated by parkin in a nonclassical, proteasomal-independent manner that involves lysine 63 (K63)-linked polyubiquitin chain formation. Parkin-mediated degradation of synphilin-1 occurs appreciably only at an unusually high parkin to synphilin-1 expression ratio or when primed for lysine 48 (K48)-linked ubiquitination. In addition we found that parkin-mediated ubiquitination of proteins within Lewy-body-like inclusions formed by the coexpression of synphilin-1, alpha-synuclein, and parkin occurs predominantly via K63 linkages and that the formation of these inclusions is enhanced by K63-linked ubiquitination. Our results suggest that parkin is a dual-function ubiquitin ligase and that K63-linked ubiquitination of synphilin-1 by parkin may be involved in the formation of Lewy body inclusions associated with PD.

The 350-fold compacted Fugu parkin gene is structurally and functionally similar to human Parkin.

Mutations in the human parkin gene (huParkin) are the predominant genetic cause of familial parkinsonism. The huParkin locus, spanning about 1.4 Mb, is one of the largest in the human genome. Despite its huge size, huParkin codes for a rather short transcript of about 4.5 kb. To gain an insight into the structure, function and evolutionary history of huParkin, we have characterized the pufferfish [Fugu rubripes (Fugu)] ortholog of huParkin. A remarkable feature of the Fugu parkin gene (fuparkin) is its unusually compact size. It spans only about 4 kb and is thus 350-fold smaller than its human ortholog. The Fugu and human parkin genes are otherwise highly similar in their genomic organization and expression pattern. Furthermore, like human Parkin, Fugu parkin also functions as an ubiquitin ligase. These shared features between fuparkin and huParkin suggest that the physiological function and regulation of the parkin gene are conserved during the evolution of vertebrates. Conceivably, the compact locus of fuparkin could serve as a useful model to understand the transcriptional regulation of huParkin.

Proteasome inhibition promotes Parkin-Ubc13 interaction and lysine 63-linked ubiquitination.

Disruption of the ubiquitin-proteasome system, which normally identifies and degrades unwanted intracellular proteins, is thought to underlie neurodegeneration. Supporting this, mutations of Parkin, a ubiquitin ligase, are associated with autosomal recessive parkinsonism. Remarkably, Parkin can protect neurons against a wide spectrum of stress, including those that promote proteasome dysfunction. Although the mechanism underlying the preservation of proteasome function by Parkin is hitherto unclear, we have previously proposed that Parkin-mediated K63-linked ubiquitination (which is usually uncoupled from the proteasome) may serve to mitigate proteasomal stress by diverting the substrate load away from the machinery. By means of linkage-specific antibodies, we demonstrated here that proteasome inhibition indeed promotes K63-linked ubiquitination of proteins especially in Parkin-expressing cells. Importantly, we further demonstrated that the recruitment of Ubc13 (an E2 that mediates K63-linked polyubiquitin chain formation exclusively) by Parkin is selectively enhanced under conditions of proteasomal stress, thus identifying a mechanism by which Parkin could promote K63-linked ubiquitin modification in cells undergoing proteolytic stress. This mode of ubiquitination appears to facilitate the subsequent clearance of Parkin substrates via autophagy. Consistent with the proposed protective role of K63-linked ubiquitination in times of proteolytic stress, we found that Ubc13-deficient cells are significantly more susceptible to cell death induced by proteasome inhibitors compared to their wild type counterparts. Taken together, our study suggests a role for Parkin-mediated K63 ubiquitination in maintaining cellular protein homeostasis, especially during periods when the proteasome is burdened or impaired.

Parkin pathway activation mitigates glioma cell proliferation and predicts patient survival.

Mutations in the parkin gene, which encodes a ubiquitin ligase, are a major genetic cause of parkinsonism. Interestingly, parkin also plays a role in cancer as a putative tumor suppressor, and the gene is frequently targeted by deletion and inactivation in human malignant tumors. Here, we investigated a potential tumor suppressor role for parkin in gliomas. We found that parkin expression was dramatically reduced in glioma cells. Restoration of parkin expression promoted G(1) phase cell-cycle arrest and mitigated the proliferation rate of glioma cells in vitro and in vivo. Notably, parkin-expressing glioma cells showed a reduction in levels of cyclin D1, but not cyclin E, and a selective downregulation of Akt serine-473 phosphorylation and VEGF receptor levels. In accordance, cells derived from a parkin-null mouse model exhibited increased levels of cyclin D1, VEGF receptor, and Akt phosphorylation, and divided significantly faster when compared with wild-type cells, with suppression of these changes following parkin reintroduction. Clinically, analysis of parkin pathway activation was predictive for the survival outcome of patients with glioma. Taken together, our study provides mechanistic insight into the tumor suppressor function of parkin in brain tumors and suggests that measurement of parkin pathway activation may be used clinically as a prognostic tool in patients with brain tumor.

Protein misfolding and aggregation in Parkinson's disease.

Protein aggregation as a result of misfolding is a common theme underlying neurodegenerative diseases. In Parkinson's disease (PD), research on protein misfolding and aggregation has taken center stage following the association of alpha-synuclein gene mutations with familial forms of the disease, and importantly, the identification of the protein as a major component of Lewy bodies, a pathological hallmark of PD. Fueling this excitement is the subsequent identification of another PD-linked gene, parkin, as a ubiquitin ligase associated with the proteasome, a major intracellular protein degradation machinery that destroys unwanted, albeit mainly soluble, proteins. Notably, a role for parkin in the clearance of insoluble protein aggregates via macroautophagy has also been implicated by more recent studies. Paradoxically, like alpha-synuclein, parkin is also prone to misfolding, especially in the presence of age-related stress. Similarly, protein misfolding can also affect the function of other key PD-linked genes such as DJ-1, PINK1, and perhaps also LRRK2. Here, we discuss the role of protein misfolding and aggregation in PD, and how impairments of the various cellular protein quality systems could precipitate these events and lead to neuronal demise. Towards the end of our discussion, we also revisited the role of Lewy body formation in PD.

Relative sensitivity of parkin and other cysteine-containing enzymes to stress-induced solubility alterations.

Loss of parkin function is a predominant cause of familial Parkinsonism. Emerging evidence also suggests that parkin expression variability may confer a risk for sporadic Parkinson disease. We have recently demonstrated that a wide variety of Parkinson disease-linked stressors, including dopamine (DA), induce parkin solubility alterations and promote its aggregation within the cell, a phenomenon that may underlie the progressive susceptibility of the brain to degeneration. The vulnerability of parkin to stress-induced modification is likely due to its abundance of cysteine residues. Here, we performed a comprehensive mutational analysis and demonstrate that Cys residues residing both within and outside of the RING-IBR (in between RING fingers)-RING domain of parkin are important in maintaining its solubility. The majority of these Cys residues are highly conserved in parkin across different species and potentially fulfil important structural roles. Further, we found that both parkin and HHARI (human homologue of Drosophila ariadne), another RING-IBR-RING-type ubiquitin ligase, are comparably more susceptible to solubility alterations induced by oxidative and nitrosative stress when compared with other non-RING-IBR-RING Cys-containing enzymes. However, parkin appears to be uniquely sensitive to DA-mediated stress, the specificity of which is likely due to DA modification of 2 Cys residues on parkin (Cys-268 and Cys-323) that are distinct from other RING-IBR-RING members.

Alterations in the solubility and intracellular localization of parkin by several familial Parkinson's disease-linked point mutations.

Mutations in the parkin gene, which encodes a ubiquitin ligase, are currently recognized as the main contributor to familial forms of Parkinson's disease (PD). A simple assumption about the effects of PD-linked mutations in parkin is that they impair or ablate the enzyme activity. However, a number of recent studies, including ours, have indicated that many disease-linked point mutants of parkin retain substantial catalytic activity. To understand how the plethora of mutations on parkin contribute to its dysfunction, we have conducted a systematic analysis of a significant number of parkin point mutants (22 in total), which represent the majority of parkin missense/nonsense mutations reported to date. We found that more than half of these mutations, including many located outside of the parkin RING fingers, produce alteration in the solubility of parkin which influences its detergent extraction property. This mutation-mediated alteration in parkin solubility is also associated with its propensity to form intracellular, aggresome-like, protein aggregates. However, they do not represent sites where parkin substrates become sequestered. As protein aggregation sequesters the functional forms away from their normal sites of action, our results suggest that alterations in parkin solubility and intracellular localization may underlie the molecular basis of the loss of function caused by several of its mutations.