The C9orf72-SMCR8-WDR41 complex is a GAP for small GTPases

ABSTRACT

Massive expansions of the hexanucleotide in C9orf72 are the primary genetic origins of familial amyotrophic lateral sclerosis (ALS) and frontal temporal dementia (FTD). Current studies have found that this repeat sequence participates in the disease process by producing neurotoxic substances and reducing the level of C9orf72 protein; however, the progress in the functional study of C9orf72 is slow. Recently, a stable complex, consisting of C9orf72, SMCR8, and WDR41, has been implicated in regulating membrane trafficking and macroautophagy. We reported the cryo-electron microscopy (cryo-EM) structure of the C9orf72-SMCR8-WDR41 complex (CSW complex), unveiling that the CSW complex is a dimer of heterotrimers. Intriguingly, in the heterotrimer of the C9orf72-SMCR8-WDR41, C9orf72 interacts with SMCR8 in a manner similar to the FLCN-FNIP2 complex. Nevertheless, WDR41 is connected to the DENN domain of SMCR8 through its N-terminal β-strand and C-terminal helix but does not directly interact with C9orf72. Notably, the C9orf72-SMCR8 complex was demonstrated to act as a GAP for RAB8A and RAB11A in vitro.     

An eukaryotic translation initiation factor,AteIF5A‐2, affects cadmium accumulation and sensitivity in Arabidopsis

Cadmium (Cd) is one of the most toxic elements and can be accumulated in plants easily; meanwhile, eIF5A is a highly conserved protein in all eukaryotic organisms. The present work tried to investigate whether eIF5A is involved in Cd accumulation and sensitivity in Arabidopsis (Arabidopsis thaliana L.) by comparing the wild‐type Columbia‐0 (Col‐0) with a knockdown mutant of AteIF5A‐2, fbr12‐3 under Cd stress conditions. The results showed that the mutant fbr12‐3 accumulated more Cd in roots and shoots and had significantly lower chlorophyll content, shorter root length, and smaller biomass, suggesting that downregulation of AteIF5A‐2 makes the mutant more Cd sensitive. Real‐time polymerase chain reaction revealed that the expressions of metal transporters involved in Cd uptake and translocation including IRT1, ZIP1, AtNramp3, and AtHMA4 were significantly increased but the expressions of PCS1 and PCS2 related to Cd detoxification were decreased notably in fbr12‐3 compared with Col‐0. As a result, an increase in MDA and H₂O₂ content but decrease in root trolox, glutathione and proline content under Cd stress was observed, indicating that a severer oxidative stress occurs in the mutant. All these results demonstrated for the first time that AteIF5A influences Cd sensitivity by affecting Cd uptake, accumulation, and detoxification in Arabidopsis.     

Plasma metabonomics as a novel diagnostic approach for major depressive disorder

Major depressive disorder (MDD) is a socially detrimental psychiatric disorder, contributing to increased healthcare expenditures and suicide rates. However, no empirical laboratory-based tests are available to support the diagnosis of MDD. In this study, a NMR-based plasma metabonomic method for the diagnosis of MDD was tested. Proton nuclear magnetic resonance ((1)H NMR) spectra of plasma sampled from first-episode drug-na??ve depressed patients (n = 58) and healthy controls (n = 42) were recorded and analyzed by orthogonal partial least-squares discriminant analysis (OPLS-DA). The OPLS-DA score plots of the spectra demonstrated that the depressed patient group was significantly distinguishable from the healthy control group. Moreover, the method accurately diagnosed blinded samples (n = 26) in an independent replication cohort with a sensitivity and specificity of 92.8% and 83.3%, respectively. Taken together, NMR-based plasma metabonomics may offer an accurate empirical laboratory-based method applicable to the diagnosis of MDD.     

Hfq Is a Global Regulator That Controls the Pathogenicity of Staphylococcus aureus

The Hfq protein is reported to be an RNA chaperone, which is involved in the stress response and the virulence of several pathogens. In E. coli, Hfq can mediate the interaction between some sRNAs and their target mRNAs. But it is controversial whether Hfq plays an important role in S. aureus. In this study, we found that the deletion of hfq gene in S. aureus 8325-4 can increase the surface carotenoid pigments. The hfq mutant was more resistant to oxidative stress but the pathogenicity of the mutant was reduced. We reveal that the Hfq protein can be detected only in some S. aureus strains. Using microarray and qRT-PCR, we identified 116 genes in the hfq mutant which had differential expression from the wild type, most of which are related to the phenotype and virulence of S. aureus. Among the 116 genes, 49 mRNAs can specifically bind Hfq protein, which indicates that Hfq also acts as an RNA binding protein in S. aureus. Our data suggest that Hfq protein of S. aureus is a multifunctional regulator involved in stress and virulence.     

NRADD,a novel membrane protein with a death domain involved in mediating apoptosis in response to ER stress

NRADD (neurotrophin receptor alike death domain protein) is a novel protein with transmembrane and cytoplasmic regions highly homologous to death receptors, particularly p75(NTR). However, the short N-terminal domain is unique. Expression of NRADD induced apoptosis in a number of cell lines. The apoptotic mechanism involved the activation of caspase-8 and execution of apoptosis without requiring mitochondrial components. The activation of this death receptor-like mechanism required the N-terminal domain, which is N-glycosylated and needed for subcellular targeting. Deletion of the N-terminal domain produced a dominant-negative form of NRADD that protected neurons and Schwann cells from a variety of endoplasmic reticulum (ER) stressors. NRADD may therefore be a necessary component for generating an ER-induced proapoptotic signal.     

ApoB-54.8, a truncated apolipoprotein found primarily in VLDL, is associated with a nonsense mutation in the apoB gene and hypobetalipoproteinemia

A new, large kindred with hypobetalipoproteinemia and a previously undescribed truncated form of apolipoprotein B (apoB) has been identified. The asymptomatic, Caucasian male proband (CK, aged 37 years) has total plasma cholesterol, triglyceride, low density lipoprotein-(LDL) cholesterol, high density lipoprotein- (HDL) cholesterol, and apoB concentrations of 108, 131, 32, 50, and 16 mg/dl, respectively. Plasma samples of 11 family members spanning three generations, which had less than 5th percentile concentrations of LDL-cholesterol, contained three apoB bands detected on immunoblots: the normal apoB-100 and apoB-48 and an unusual band of apparent molecular mass of 299,356 +/- 9580 daltons (approximately 54% the molecular weight of apoB-100). Additional immunoblotting experiments using several different anti-apoB monoclonal antibodies showed that the carboxyl terminal of apoB-100 had been deleted somewhere between amino acid residues 2148-2488. A segment of genomic DNA from the proband was amplified by polymerase chain reaction (PCR) between nucleotides 7491-7791 of Exon 26 of the apoB gene. The DNA segment was cloned into pGEM3Zf(-) and sequenced. A C----T transition was found at nucleotide 7665, resulting in a premature stop codon at amino acid residue 2486 corresponding to apoB-54.8. These results were confirmed by direct sequencing of PCR products from three apoB-54.8 positive and three apoB-54.8 negative kindred members. Allele-specific oligonucleotides were used to identify other affected family members. Cosegregation of apoB-54.8 with the C----T transition occurred in all cases. Based on haplotypes constructed from restriction fragment length polymorphism, variable number of tandem repeats, and 5' insertion/deletion analyses and from the presence or absence of apoB-54.8, it was possible to assign a single allele of apoB to the mutation throughout the family. In contrast with other shorter truncations such as apoB-31, apoB-40, and apoB-46, which are found with particles in the HDL density range, and apoB-89 that is found primarily with LDL, apoB-54.8 was found primarily in very low density lipoproteins, much less in LDL, and was virtually absent in HDL. This suggests that the length of the truncation may significantly affect the metabolism of the associated lipoprotein particles.