Binding of Superantigen Toxins into the CD28 Homodimer Interface Is Essential for Induction of Cytokine Genes That Mediate Lethal Shock

Bacterial superantigen toxins bind directly to the dimer interface of CD28, the principal co-stimulatory receptor, to induce a lethal cytokine storm, and peptides that prevent this binding can suppress superantigen lethality

PI31 expression prevents neuronal degeneration in a mouse Parkinson Disease model

AbstractAge-related neurodegenerative diseases pose a major unmet health need since no effective treatment strategies are currently available. These disorders are defined by the accumulation of abnormal protein aggregates that impair synaptic function and cause progressive neuronal degeneration. Therefore, stimulating protein clearance mechanisms may be neuro-protective. The proteasome regulator PI31 promotes local protein degradation at synapses by mediating fast proteasome transport in neurites, and loss of PI31 function causes neuronal degeneration. Here we show that transgenic expression of PI31 in a mouse Parkinson’s Disease model preserves neuronal function and greatly extends animal health and lifespan. These results indicate that targeting the PI31-pathway may have therapeutic value for treating neurodegenerative disorders.</jats:p

PSMD5 Inactivation Promotes 26S Proteasome Assembly during Colorectal Tumor Progression

Abstract Protein degradation by the ubiquitin–proteasome system (UPS) is central to protein homeostasis and cell survival. The active 26S proteasome is a large protease complex consisting of a catalytic 20S subunit and 19S regulatory particles. Cancer cells are exposed to considerable protein overload due to high metabolic rates, reprogrammed energy metabolism, and aneuploidy. Here we report a mechanism that facilitates the assembly of active 26S proteasomes in malignant cells. Upon tumorigenic transformation of the gut epithelium, 26S proteasome assembly was significantly enhanced, but levels of individual subunits were not changed. This enhanced assembly of 26S proteasomes increased further with tumor progression and was observed specifically in transformed cells, but not in other rapidly dividing cells. Moreover, expression of PSMD5, an inhibitor of proteasome assembly, was reduced in intestinal tumors and silenced with tumor progression. Reexpression of PSMD5 in tumor cells caused decreased 26S assembly and accumulation of polyubiquitinated proteins. These results suggest that inhibition of cancer-associated proteasome assembly may provide a novel therapeutic strategy to selectively kill cancer cells. Significance: Enhanced cancer-associated proteasome assembly is a major stress response that allows tumors to adapt to and to withstand protein overload. Graphical Abstract: http://cancerres.aacrjournals.org/content/canres/78/13/3458/F1.large.jpg. Cancer Res; 78(13); 3458–68. ©2018 AACR.</jats:p

The proteasome regulator PI31 is required for protein homeostasis, synapse maintenance and neuronal survival in mice

AbstractProteasome-mediated degradation of intracellular proteins is essential for cell function and survival. The proteasome-binding protein PI31 (Proteasomal Inhibitor of 31kD) promotes 26S assembly and functions as an adapter for proteasome transport in axons. As localized protein synthesis and degradation is especially critical in neurons, we generated a conditional loss of PI31 in spinal motor neurons (MNs) and cerebellar Purkinje cells (PCs). A cKO of PI31 in these neurons caused axon degeneration, neuronal loss and progressive spinal and cerebellar neurological dysfunction. For both MNs and PCs, markers of proteotoxic stress preceded axonal degeneration and motor dysfunction, indicating a critical role for PI31 in neuronal homeostasis. The time course of the loss of MN and PC function in developing mouse CNS suggests a key role for PI31 in human developmental neurological disorders.Statement of SignificanceThe conserved proteasome-binding protein PI31 serves as an adapter to couple proteasomes with cellular motors to mediate their transport to distal tips of neurons where protein breakdown occurs. We generated global and conditional PI31 knockout mouse strains and show that this protein is required for protein homeostasis, and that its conditional inactivation in neurons disrupts synaptic structures and long-term survival. This work establishes a critical role for PI31 and local protein degradation in the maintenance of neuronal architecture, circuitry and function. Because mutations that impair PI31 function cause neurodegenerative diseases in humans, reduced PI31 activity may contribute to age-related neurodegenerative diseases.</jats:sec

Distinct Cytoplasmic Domains in Plexin-A4 Mediate Diverse Responses to Semaphorin 3A in Developing Mammalian Neurons

Deletion analysis reveals how one neuronal guidance cue–receptor pair can produce either axonal retraction or dendritic branching.</jats:p

Regulation of axonal morphogenesis by the mitochondrial protein Efhd1

During development, neurons adjust their energy balance to meet the high demands of robust axonal growth and branching. The mechanisms that regulate this tuning are largely unknown. Here, we show that sensory neurons lacking liver kinase B1 (Lkb1), a master regulator of energy homeostasis, exhibit impaired axonal growth and branching. Biochemical analysis of these neurons revealed reduction in axonal ATP levels, whereas transcriptome analysis uncovered down-regulation of Efhd1 (EF-hand domain family member D1), a mitochondrial Ca2+-binding protein. Genetic ablation of Efhd1 in mice resulted in reduced axonal morphogenesis as well as enhanced neuronal death. Strikingly, this ablation causes mitochondrial dysfunction and a decrease in axonal ATP levels. Moreover, Efhd1 KO sensory neurons display shortened mitochondria at the axonal growth cones, activation of the AMP-activated protein kinase (AMPK)–Ulk (Unc-51–like autophagy-activating kinase 1) pathway and an increase in autophagic flux. Overall, this work uncovers a new mitochondrial regulator that is required for axonal morphogenesis.</jats:p

The proteasome regulator PI31 is required for protein homeostasis, synapse maintenance, and neuronal survival in mice

Significance The conserved proteasome-binding protein PI31 serves as an adapter to couple proteasomes with cellular motors to mediate their transport to distal tips of neurons where protein breakdown occurs. We generated global and conditional PI31 knockout mouse strains and show that this protein is required for protein homeostasis, and that its conditional inactivation in neurons disrupts synaptic structures and long-term survival. This work establishes a critical role for PI31 and local protein degradation in the maintenance of neuronal architecture, circuitry, and function. Because mutations in the PI31 pathway cause neurodegenerative diseases in humans, reduced PI31 activity may contribute to the etiology of these diseases.</jats:p