PNMA2 forms immunogenic non-enveloped virus-like capsids associated with paraneoplastic neurological syndrome

The paraneoplastic Ma antigen (PNMA) proteins are associated with cancer-induced paraneoplastic syndromes that present with an autoimmune response and neurological symptoms. Why PNMA proteins are associated with this severe autoimmune disease is unclear. PNMA genes are predominantly expressed in the central nervous system and are ectopically expressed in some tumors. We show that PNMA2, which has been co-opted from a Ty3 retrotransposon, encodes a protein that is released from cells as non-enveloped virus-like capsids. Recombinant PNMA2 capsids injected into mice induce autoantibodies that preferentially bind external "spike" PNMA2 capsid epitopes, whereas a capsid-assembly-defective PNMA2 protein is not immunogenic. PNMA2 autoantibodies in cerebrospinal fluid of patients with anti-Ma2 paraneoplastic disease show similar preferential binding to spike capsid epitopes. PNMA2 capsid-injected mice develop learning and memory deficits. These observations suggest that PNMA2 capsids act as an extracellular antigen, capable of generating an autoimmune response that results in neurological deficits.

UBQLN2 restrains the domesticated retrotransposon PEG10 to maintain neuronal health in ALS

Amyotrophic Lateral Sclerosis (ALS) is a fatal neurodegenerative disease characterized by progressive motor neuron dysfunction and loss. A portion of ALS cases are caused by mutation of the proteasome shuttle factor Ubiquilin 2 (UBQLN2), but the molecular pathway leading from UBQLN2 dysfunction to disease remains unclear. Here, we demonstrate that UBQLN2 regulates the domesticated gag-pol retrotransposon 'paternally expressed gene 10 (PEG10)' in human cells and tissues. In cells, the PEG10 gag-pol protein cleaves itself in a mechanism reminiscent of retrotransposon self-processing to generate a liberated 'nucleocapsid' fragment, which uniquely localizes to the nucleus and changes the expression of genes involved in axon remodeling. In spinal cord tissue from ALS patients, PEG10 gag-pol is elevated compared to healthy controls. These findings implicate the retrotransposon-like activity of PEG10 as a contributing mechanism in ALS through the regulation of gene expression, and restraint of PEG10 as a primary function of UBQLN2.

Global proteomics of Ubqln2-based murine models of ALS

Familial neurodegenerative diseases commonly involve mutations that result in either aberrant proteins or dysfunctional components of the proteolytic machinery that act on aberrant proteins. UBQLN2 is a ubiquitin receptor of the UBL/UBA family that binds the proteasome through its ubiquitin-like domain and is thought to deliver ubiquitinated proteins to proteasomes for degradation. UBQLN2 mutations result in familial amyotrophic lateral sclerosis (ALS)/frontotemporal dementia in humans through an unknown mechanism. Quantitative multiplexed proteomics was used to provide for the first time an unbiased and global analysis of the role of Ubqln2 in controlling the composition of the proteome. We studied several murine models of Ubqln2-linked ALS and also generated Ubqln2 null mutant mice. We identified impacts of Ubqln2 on diverse physiological pathways, most notably serotonergic signaling. Interestingly, we observed an upregulation of proteasome subunits, suggesting a compensatory response to diminished proteasome output. Among the specific proteins whose abundance is linked to UBQLN2 function, the strongest hits were the ubiquitin ligase TRIM32 and two retroelement-derived proteins, PEG10 and CXX1B. Cycloheximide chase studies using induced human neurons and HEK293 cells suggested that PEG10 and TRIM32 are direct clients. Although UBQLN2 directs the degradation of multiple proteins via the proteasome, it surprisingly conferred strong protection from degradation on the Gag-like protein CXX1B, which is expressed from the same family of retroelement genes as PEG10. In summary, this study charts the proteomic landscape of ALS-related Ubqln2 mutants and identifies candidate client proteins that are altered in vivo in disease models and whose degradation is promoted by UBQLN2.

ALS/FTD mutations in UBQLN2 impede autophagy by reducing autophagosome acidification through loss of function

Mutations in UBQLN2 cause amyotrophic lateral sclerosis (ALS), frontotemporal dementia (FTD), and other neurodegenerations. However, the mechanism by which the UBQLN2 mutations cause disease remains unclear. Alterations in proteins involved in autophagy are prominent in neuronal tissue of human ALS UBQLN2 patients and in a transgenic P497S UBQLN2 mouse model of ALS/FTD, suggesting a pathogenic link. Here, we show UBQLN2 functions in autophagy and that ALS/FTD mutant proteins compromise this function. Inactivation of UBQLN2 expression in HeLa cells reduced autophagic flux and autophagosome acidification. The defect in acidification was rescued by reexpression of wild type (WT) UBQLN2 but not by any of the five different UBQLN2 ALS/FTD mutants tested. Proteomic analysis and immunoblot studies revealed P497S mutant mice and UBQLN2 knockout HeLa and NSC34 cells have reduced expression of ATP6v1g1, a critical subunit of the vacuolar ATPase (V-ATPase) pump. Knockout of UBQLN2 expression in HeLa cells decreased turnover of ATP6v1g1, while overexpression of WT UBQLN2 increased biogenesis of ATP6v1g1 compared with P497S mutant UBQLN2 protein. In vitro interaction studies showed that ATP6v1g1 binds more strongly to WT UBQLN2 than to ALS/FTD mutant UBQLN2 proteins. Intriguingly, overexpression of ATP6v1g1 in UBQLN2 knockout HeLa cells increased autophagosome acidification, suggesting a therapeutic approach to overcome the acidification defect. Taken together, our findings suggest that UBQLN2 mutations drive pathogenesis through a dominant-negative loss-of-function mechanism in autophagy and that UBQLN2 functions as an important regulator of the expression and stability of ATP6v1g1. These findings may have important implications for devising therapies to treat UBQLN2-linked ALS/FTD.

Abstract B196: Examining proteasome sensitivity of lymphoid malignancy: Ubiquilin 1 (Ubqln1) is required for BCR-induced proliferation of B cells

Careful regulation of protein levels is essential to cellular life, and the ubiquitin proteasome system is a major way in which cells coordinate the degradation of proteins. In addition to regulating steady state protein degradation, the ubiquitin proteasome system assists in major proteome reorganizations, including the response to cellular stresses and the completion of major milestones such as differentiation, stimulation, and cell division. Lymphocytes are a useful model with which to understand the regulation of protein degradation because they undergo dramatic proteome reorganization upon receptor:ligand interactions, and because some lymphocytic malignancies are uniquely sensitive to treatment with proteasome inhibitors. We have previously shown that B lymphocytes require Ubiquilin 1 (Ubqln1), an extrinsic proteasome receptor, for their proliferation downstream of BCR stimulation. Ubqlns help to facilitate the degradation of ubiquitinated protein by simultaneously binding the cap of the proteasome and ubiquitinated client proteins, but until recently the clients of Ubqln1, as well as the consequences of Ubqln1 loss, were unknown. The lack of Ubqln1 resulted in accumulation of mislocalized mitochondrial proteins and induced a block in protein synthesis downstream of BCR stimulation, which resulted in cell cycle inhibition. This work implicated a role for Ubqln1 both in immune activation as well as B cell malignancy. Unexpectedly, TLR stimulation was normal in Ubqln1-deficienT-cells. Two major hypotheses for this specificity involve unique signal transduction pathway activation, and overexpression of mitochondrial proteins downstream of BCR activation. In fact, dysregulation of BCR signal transduction cascades and upregulation of OXPHOS genes define common and partially overlapping subtypes of diffuse large B-cell lymphoma (DLBCL). Currently, we aim to resolve these hypotheses with both in vivo and in vitro approaches. These studies will sharpen our understanding of B-cell cancer susceptibility to perturbation of the ubiquitin proteasome system and of Ubqln1 function.

Citation Format: Alexandra M. Whiteley, Eric Brown, Daniel Finley. Examining proteasome sensitivity of lymphoid malignancy: Ubiquilin 1 (Ubqln1) is required for BCR-induced proliferation of B cells [abstract]. In: Proceedings of the Fourth CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; Sept 30-Oct 3, 2018; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2019;7(2 Suppl):Abstract nr B196.

Ubiquilin1 promotes antigen-receptor mediated proliferation by eliminating mislocalized mitochondrial proteins

Ubiquilins (Ubqlns) are a family of ubiquitin receptors that promote the delivery of hydrophobic and aggregated ubiquitinated proteins to the proteasome for degradation. We carried out a proteomic analysis of a B cell lymphoma-derived cell line, BJAB, that requires UBQLN1 for survival to identify UBQLN1 client proteins. When UBQLN1 expression was acutely inhibited, 120 mitochondrial proteins were enriched in the cytoplasm, suggesting that the accumulation of mitochondrial client proteins in the absence of UBQLN1 is cytostatic. Using a Ubqln1^−/− mouse strain, we found that B cell receptor (BCR) ligation of Ubqln1^−/− B cells led to a defect in cell cycle entry. As in BJAB cells, mitochondrial proteins accumulated in BCR-stimulated cells, leading to protein synthesis inhibition and cell cycle block. Thus, UBQLN1 plays an important role in clearing mislocalized mitochondrial proteins upon cell stimulation, and its absence leads to suppression of protein synthesis and cell cycle arrest.

Two-surgeon approach to thoracic outlet syndrome: long-term outcome

An orthopaedic surgeon and a vascular surgeon jointly conducted 30 operations for thoracic outlet syndrome in 27 patients, having done the preoperative assessments in conjunction with a neurologist. Anterior scalenectomy was performed by the supraclavicular route except in one case where the infraclavicular route was used. The further surgical procedure was tailored to the abnormalities identified--i.e. resection of cervical rib or band, or medial scalenectomy. The first rib was spared. At median follow-up of 37 months (range 3-228) results were judged excellent or good on 26/30 sides (87%); on the three occasions when scalenectomy alone was performed, the results were only fair or poor. There were no major complications and no patient required reoperation. The long-term outcome in this series suggests that, with multidisciplinary assessment and two-surgeon operative treatment, good results can be obtained by the supraclavicular route without resection of the first rib.

High-dose intravenous immunoglobulin in the treatment of Guillain-Barré syndrome: a preliminary open study

We report the effects of intravenous gamma-globulin (IVGG) in severe Guillain-Barré syndrome (GBS) in a small open study. Seven patients were given IVGG (0.4 g/kg/day) for 5 consecutive days. At the start of treatment all had progressing limb weakness and none could stand unaided. Within 24 h all but one patient started to improve, without the expected plateau phase, and progress was maintained with a mean time to independent walking of 14 days. One patient started treatment 9 h prior to ventilation for 15 days but was walking independently 31 days after admission. This study provides further evidence that IVGG is a promising therapeutic alternative to plasmapheresis in GBS. The rapidity of the response to IVGG raises the possibility that a single dose regimen might be equally or more effective.

Contrast-enhanced lesions on computerised tomography in multiple sclerosis

Two patients are described in whom computerised tomography revealed contrast-enhanced lesions in the early stages of multiple sclerosis. Such lesions may be differentiated from tumours by their transient nature, lack of space-occupying effect, and localisation in the white matter. Contrast enhancement in demyelinating disease is probably related to local breakdown of the blood-brain barrier.

Selective impairment of topographical memory: a single case study

We describe a patient who developed topographical memory loss after a closed head injury. His symptoms and the psychological test results indicate a selective deficit of topographical memory, his perceptual and spatial skills being relatively unimpaired.

Mercury pigmentation from industrial exposure. An ultrastructural and analytical electron microscopic study

A study has been made of facial pigmentation resulting from industrial inorganic mercury exposure. Electron microscopy has shown electron-dense 400--900 nm aggregates of 12 nm particles in dermal macrophages and free in the dermis. Use of the analytical electron microscope has enabled direct confirmation of the presence of mercury in these aggregates. The unexpected finding of coexistent selenium is discussed.

Prosopagnosia: a clinical, psychological, and anatomical study of three patients

Three patients with prosopagnosia are described of whom two had right occipital lesions. An analysis of visual and perceptual functions demonstrated a defect in perceptual classification which appeared to be stimulus-specific. A special mechanism for facial recognition is postulated, and the importance of the right sided posterior lesion is stressed.

Congenital myasthenia gravis: clinical and HLA studies in two brothers

Two brothers with congenital myasthenia gravis are described. In both, ptosis and ophthalmoplegia responded poorly to oral anticholinesterase therapy and to thymectomy. The brothers had two different HLA haplotypes and neither had the HLA-A1-B8-DW3 haplotypes which are commonly associated with myathenia gravis in adult-onset cases.

Progressive encephalomyelitis with rigidity

Two cases of encephalomyelitis are described in which the major clinical manifestation was muscular rigidity and stimulus-sensitive muscular spasms. It is suggested, from pathological evidence, that this rigidity was of spinal origin, and that this disorder is a rare but recognizable entity. Comparison is made with previously reported cases of rigidity of spinal origin, including encephalitis lethargica, and with 'subacute myoclonic spinal neuronitis' and the 'stiff man syndrome.'