[Abstract unavailable

Amyotrophic lateral sclerosis (ALS) is an adult-onset neurodegenerative disorder characterized by loss of motor neurons. Dominant mutations in the gene for superoxide dismutase 1 (SOD1) give rise to familial ALS by an unknown mechanism. Here we show that genetic deficiency of mammalian sterile 20-like kinase 1 (MST1) delays disease onset and extends survival in mice expressing the ALS-associated G93A mutant of human SOD1. SOD1(G93A) induces dissociation of MST1 from a redox protein thioredoxin-1 and promotes MST1 activation in spinal cord neurons in a reactive oxygen species-dependent manner. Moreover, MST1 was found to mediate SOD1(G93A)-induced activation of p38 mitogen-activated protein kinase and caspases as well as impairment of autophagy in spinal cord motoneurons of SOD1(G93A) mice. Our findings implicate MST1 as a key determinant of neurodegeneration in ALS.neurotoxicity | ROS A myotrophic lateral sclerosis (ALS) is an adult-onset neurodegenerative disorder characterized by the selective loss of motor neurons in the brain and spinal cord. Whereas most cases (∼90%) of ALS are sporadic (sALS), both sALS and familial ALS (fALS) share similar clinical characteristics, suggestive of common disease mechanisms. Mutations in the gene for superoxide dismutase 1 (SOD1) are one of the most common causes of fALS and give rise to disease as a result of acquired gain-offunction toxicity (1, 2). Studies using the disease-model mice overexpressing ALS-linked mutants of human SOD1 have suggested that many mutations result in oxidative damage and apoptosis in motor neurons (2, 3). The molecular mechanism by which SOD1 mutants induce neurodegeneration remains unclear, however.Mammalian sterile 20 (STE20)-like kinase 1 (MST1) is a multifunctional serine-threonine kinase that belongs to the family of class II germinal center kinases (4-6). MST1 is composed of a catalytic domain in the amino-terminal region, an inhibitory domain in the central region, and a regulatory Salvador/ Rassf/Hippo (SARAH) domain in the carboxyl-terminal region (7,8). The SARAH domain is responsible for the homo-dimerization of MST1, which contributes to the mechanism underlying MST1 activation (7, 9). It also mediates the formation of heteromeric complexes with other SARAH domain-containing proteins such as 45 kDa WW domain protein and Rassf proteins (7,8). MST1 is expressed ubiquitously and is associated with the regulatory mechanisms for many biological events including cell growth, apoptosis, stress response, and senescence (10, 11). In particular, MST1 has been recently suggested to mediate neuronal cell death initiated by oxidative stress (11,12).Given that oxidative stress contributes to the pathogenesis of ALS, we investigated the possible role of MST1 in the neurotoxicity underlying fALS with use of a transgenic mouse model. Results and DiscussionMotor Neurons in sALS Patients and SOD1(G93A) Mice Show Higher Activity of MST1. We first examined MST1 activity in primary motor neurons (PMNs) prepared from the spinal cord of E13 embryos of contro...

Song (2015) Insights into autophagosome maturation revealed by the structures of ATG5 with its interacting partners, Autophagy, 11:1, 75-87, DOI: 10.4161/15548627.2014 Autophagy is a bulky catabolic process that responds to nutrient homeostasis and extracellular stress signals and is a conserved mechanism in all eukaryotes. When autophagy is induced, cellular components are sequestered within an autophagosome and finally degraded by subsequent fusion with a lysosome. During this process, the ATG12-ATG5 conjugate requires 2 different binding partners, ATG16L1 for autophagosome elongation and TECPR1 for lysosomal fusion. In our current study, we describe the crystal structures of human ATG5 in complex with an N-terminal domain of ATG16L1 as well as an internal AIR domain of TECPR1. Both binding partners exhibit a similar a-helical structure containing a conserved binding motif termed AFIM. Furthermore, we characterize the critical role of the C-terminal unstructured region of the AIR domain of TECPR1. These findings are further confirmed by biochemical and cell biological analyses. These results provide new insights into the molecular details of the autophagosome maturation process, from its elongation to its fusion with a lysosome.

Calcium and integrin binding protein 1 (CIB1) is a Ca 2+ -binding protein of 22 kDa that was initially identified as a protein that interacts with integrin α IIb . Although it interacts with various proteins and has been implicated in diverse cellular functions, the molecular mechanism by which CIB1 regulates intracellular signaling networks has remained unclear. We now show that, by targeting apoptosis signal-regulating kinase 1 (ASK1), CIB1 negatively regulates stress-activated MAPK signaling pathways. CIB1 was thus shown to bind to ASK1, to interfere with the recruitment of TRAF2 to ASK1, and to inhibit the autophosphorylation of ASK1 on threonine-838, thereby blocking ASK1 activation. Furthermore, CIB1 mitigated apoptotic cell death initiated either by TNF-α in breast cancer MCF7 cells or by 6-hydroxydopamine (6-OHDA) in dopaminergic cells. Ca 2+ influx induced by membrane depolarization reversed the inhibitory effect of CIB1 on 6-OHDA-induced ASK1 activation and cell death in dopaminergic neurons. These observations thus suggest that CIB1 functions as a Ca 2+ -sensitive negative regulator of ASK1-mediated signaling events.

Amyotrophic lateral sclerosis (ALS) is a late-onset neurodegenerative disease characterized by the selective degeneration of upper and lower motor neurons associated with the abnormal aggregation of ubiquitinated proteins. The molecular mechanisms underlying the pathogenesis of ALS remain unclear, however. Autophagy is a major pathway for the elimination of protein aggregates and damaged organelles and therefore contributes to cellular homeostasis. This catabolic process begins with the formation of the double membrane-bound autophagosome that engulfs portions of the cytoplasm and subsequently fuses with a lysosome to form an autolysosome, in which lysosomal enzymes digest autophagic substrates. Defects at various stages of autophagy have been associated with pathological mutations of several ALS-linked genes including SOD1, p62, TDP-43, and optineurin, suggesting that such defects may play a causative role in the pathogenesis of this condition. In this review, we summarize the dysregulation of autophagy associated with ALS as well as potential therapeutic strategies based on modulation of the autophagic process.