scholarly journals Inclusion Formation and Toxicity of the ALS Protein RGNEF and Its Association with the Microtubule Network

2020 ◽  
Vol 21 (16) ◽  
pp. 5597 ◽  
Author(s):  
Sonja E. Di Gregorio ◽  
Kathryn Volkening ◽  
Michael J. Strong ◽  
Martin L. Duennwald
Keyword(s):  
Functional Characterization ◽  
Heterozygous Mutation ◽  
Nucleotide Exchange ◽  
Microtubule Network ◽  
Cytoplasmic Inclusions ◽  
Mammalian Cell Lines ◽  
Ubiquitin System ◽  
Nucleotide Exchange Factor ◽  
Associated Proteins ◽  
Split Ubiquitin

The Rho guanine nucleotide exchange factor (RGNEF) protein encoded by the ARHGEF28 gene has been implicated in the neurodegenerative disease amyotrophic lateral sclerosis (ALS). Biochemical and pathological studies have shown that RGNEF is a component of the hallmark neuronal cytoplasmic inclusions in ALS-affected neurons. Additionally, a heterozygous mutation in ARHGEF28 has been identified in a number of familial ALS (fALS) cases that may give rise to one of two truncated variants of the protein. Little is known about the normal biological function of RGNEF or how it contributes to ALS pathogenesis. To further explore RGNEF biology we have established and characterized a yeast model and characterized RGNEF expression in several mammalian cell lines. We demonstrate that RGNEF is toxic when overexpressed and forms inclusions. We also found that the fALS-associated mutation in ARGHEF28 gives rise to an inclusion-forming and toxic protein. Additionally, through unbiased screening using the split-ubiquitin system, we have identified RGNEF-interacting proteins, including two ALS-associated proteins. Functional characterization of other RGNEF interactors identified in our screen suggest that RGNEF functions as a microtubule regulator. Our findings indicate that RGNEF misfolding and toxicity may cause impairment of the microtubule network and contribute to ALS pathogenesis.

scholarly journals DOCK5 functions as a key signaling adaptor that links FcεRI signals to microtubule dynamics during mast cell degranulation

2014 ◽  
Vol 211 (7) ◽  
pp. 1407-1419 ◽  
Author(s):  
Kana Ogawa ◽  
Yoshihiko Tanaka ◽  
Takehito Uruno ◽  
Xuefeng Duan ◽  
Yosuke Harada ◽  
...  
Keyword(s):  
Mast Cell ◽  
Mast Cells ◽  
Secretory Granules ◽  
Mast Cell Degranulation ◽  
Microtubule Dynamics ◽  
Nucleotide Exchange ◽  
Microtubule Network ◽  
Guanine Nucleotide Exchange ◽  
Nucleotide Exchange Factor ◽  
Life Threatening

Mast cells play a key role in the induction of anaphylaxis, a life-threatening IgE-dependent allergic reaction, by secreting chemical mediators that are stored in secretory granules. Degranulation of mast cells is triggered by aggregation of the high-affinity IgE receptor, FcεRI, and involves dynamic rearrangement of microtubules. Although much is known about proximal signals downstream of FcεRI, the distal signaling events controlling microtubule dynamics remain elusive. Here we report that DOCK5, an atypical guanine nucleotide exchange factor (GEF) for Rac, is essential for mast cell degranulation. As such, we found that DOCK5-deficient mice exhibit resistance to systemic and cutaneous anaphylaxis. The Rac GEF activity of DOCK5 is surprisingly not required for mast cell degranulation. Instead, DOCK5 associated with Nck2 and Akt to regulate microtubule dynamics through phosphorylation and inactivation of GSK3β. When DOCK5–Nck2–Akt interactions were disrupted, microtubule formation and degranulation response were severely impaired. Our results thus identify DOCK5 as a key signaling adaptor that orchestrates remodeling of the microtubule network essential for mast cell degranulation.

scholarly journals Unzipping the Secrets of Amyloid Disassembly by the Human Disaggregase

Cells ◽  
2021 ◽  
Vol 10 (10) ◽  
pp. 2745
Author(s):  
Aitor Franco ◽  
Lorea Velasco-Carneros ◽  
Naiara Alvarez ◽  
Natalia Orozco ◽  
Fernando Moro ◽  
...  
Keyword(s):  
Molecular Mechanisms ◽  
Current Knowledge ◽  
Accelerated Aging ◽  
Strong Relationship ◽  
Nucleotide Exchange ◽  
Nucleotide Exchange Factor ◽  
Class B ◽  
Associated Proteins ◽  
Global Health Problem ◽  
J Protein

Neurodegenerative diseases (NDs) are increasingly positioned as leading causes of global deaths. The accelerated aging of the population and its strong relationship with neurodegeneration forecast these pathologies as a huge global health problem in the upcoming years. In this scenario, there is an urgent need for understanding the basic molecular mechanisms associated with such diseases. A major molecular hallmark of most NDs is the accumulation of insoluble and toxic protein aggregates, known as amyloids, in extracellular or intracellular deposits. Here, we review the current knowledge on how molecular chaperones, and more specifically a ternary protein complex referred to as the human disaggregase, deals with amyloids. This machinery, composed of the constitutive Hsp70 (Hsc70), the class B J-protein DnaJB1 and the nucleotide exchange factor Apg2 (Hsp110), disassembles amyloids of α-synuclein implicated in Parkinson’s disease as well as of other disease-associated proteins such as tau and huntingtin. We highlight recent studies that have led to the dissection of the mechanism used by this chaperone system to perform its disaggregase activity. We also discuss whether this chaperone-mediated disassembly mechanism could be used to solubilize other amyloidogenic substrates. Finally, we evaluate the implications of the chaperone system in amyloid clearance and associated toxicity, which could be critical for the development of new therapies.

scholarly journals A G-protein activation cascade from Arl13B to Arl3 and implications for ciliary targeting of lipidated proteins

eLife ◽  
2015 ◽  
Vol 4 ◽  
Author(s):  
Katja Gotthardt ◽  
Mandy Lokaj ◽  
Carolin Koerner ◽  
Nathalie Falk ◽  
Andreas Gießl ◽  
...  
Keyword(s):  
G Protein ◽  
Joubert Syndrome ◽  
Nucleotide Exchange ◽  
Protein Activation ◽  
Guanine Nucleotide Exchange ◽  
Mammalian Cell Lines ◽  
Nucleotide Exchange Factor ◽  
Cargo Proteins ◽  
Switch Regions ◽  
Activation Cascade

Small G-proteins of the ADP-ribosylation-factor-like (Arl) subfamily have been shown to be crucial to ciliogenesis and cilia maintenance. Active Arl3 is involved in targeting and releasing lipidated cargo proteins from their carriers PDE6δ and UNC119a/b to the cilium. However, the guanine nucleotide exchange factor (GEF) which activates Arl3 is unknown. Here we show that the ciliary G-protein Arl13B mutated in Joubert syndrome is the GEF for Arl3, and its function is conserved in evolution. The GEF activity of Arl13B is mediated by the G-domain plus an additional C-terminal helix. The switch regions of Arl13B are involved in the interaction with Arl3. Overexpression of Arl13B in mammalian cell lines leads to an increased Arl3·GTP level, whereas Arl13B Joubert-Syndrome patient mutations impair GEF activity and thus Arl3 activation. We anticipate that through Arl13B’s exclusive ciliary localization, Arl3 activation is spatially restricted and thereby an Arl3·GTP compartment generated where ciliary cargo is specifically released.

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