Microtubule severing by the katanin complex is activated by PPFR-1–dependent MEI-1 dephosphorylation

Katanin is an evolutionarily conserved microtubule (MT)-severing complex implicated in multiple aspects of MT dynamics. In Caenorhabditis elegans, the katanin homologue MEI-1 is required for meiosis, but must be inactivated before mitosis. Here we show that PPFR-1, a regulatory subunit of a trimeric protein phosphatase 4 complex, enhanced katanin MT-severing activity during C. elegans meiosis. Loss of ppfr-1, similarly to the inactivation of MT severing, caused a specific defect in meiosis II spindle disassembly. We show that a fraction of PPFR-1 was degraded after meiosis, contributing to katanin inactivation. PPFR-1 interacted with MEL-26, the substrate recognition subunit of the CUL-3 RING E3 ligase (CRL3MEL-26), which also targeted MEI-1 for post-meiotic degradation. Reversible protein phosphorylation of MEI-1 may ensure temporal activation of the katanin complex during meiosis, whereas CRL3MEL-26-mediated degradation of both MEI-1 and its activator PPFR-1 ensure efficient katanin inactivation in the transition to mitosis.

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Phosphorylation of the microtubule-severing AAA+ enzyme Katanin regulates C. elegans embryo development

The Journal of Cell Biology ◽

10.1083/jcb.201912037 ◽

2020 ◽

Vol 219 (6) ◽

Author(s):

Nicolas Joly ◽

Eva Beaumale ◽

Lucie Van Hove ◽

Lisa Martino ◽

Lionel Pintard

Keyword(s):

Mitotic Spindle ◽

The Other ◽

Meiotic Spindle ◽

Aaa Atpase ◽

C Elegans ◽

Microtubule Severing ◽

Evolutionarily Conserved ◽

Necessary And Sufficient ◽

Fine Tune

The evolutionarily conserved microtubule (MT)-severing AAA-ATPase enzyme Katanin is emerging as a critical regulator of MT dynamics. In Caenorhabditis elegans, Katanin MT-severing activity is essential for meiotic spindle assembly but is toxic for the mitotic spindle. Here we analyzed Katanin dynamics in C. elegans and deciphered the role of Katanin phosphorylation in the regulation of its activity and stability. Katanin is abundant in oocytes, and its levels drop after meiosis, but unexpectedly, a significant fraction is present throughout embryogenesis, where it is dynamically recruited to the centrosomes and chromosomes during mitosis. We show that the minibrain kinase MBK-2, which is activated during meiosis, phosphorylates Katanin at multiple serines. We demonstrate unequivocally that Katanin phosphorylation at a single residue is necessary and sufficient to target Katanin for proteasomal degradation after meiosis, whereas phosphorylation at the other sites only inhibits Katanin ATPase activity stimulated by MTs. Our findings suggest that cycles of phosphorylation and dephosphorylation fine-tune Katanin level and activity to deliver the appropriate MT-severing activity during development.

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The Not4 RING E3 Ligase: A Relevant Player in Cotranslational Quality Control

ISRN Molecular Biology ◽

10.1155/2013/548359 ◽

2013 ◽

Vol 2013 ◽

pp. 1-19 ◽

Cited By ~ 9

Author(s):

Martine A. Collart

Keyword(s):

Quality Control ◽

Ubiquitin Ligase ◽

E3 Ligase ◽

Rna Degradation ◽

The Other ◽

Ring E3 Ligase ◽

Ideal Position ◽

Evolutionarily Conserved ◽

A Subunit ◽

Ring E3

The Not4 RING E3 ligase is a subunit of the evolutionarily conserved Ccr4-Not complex. Originally identified in yeast by mutations that increase transcription, it was subsequently defined as an ubiquitin ligase. Substrates for this ligase were characterized in yeast and in metazoans. Interestingly, some substrates for this ligase are targeted for polyubiquitination and degradation, while others instead are stable monoubiquitinated proteins. The former are mostly involved in transcription, while the latter are a ribosomal protein and a ribosome-associated chaperone. Consistently, Not4 and all other subunits of the Ccr4-Not complex are present in translating ribosomes. An important function for Not4 in cotranslational quality control has emerged. In the absence of Not4, the total level of polysomes is reduced. In addition, translationally arrested polypeptides, aggregated proteins, and polyubiquitinated proteins accumulate. Its role in quality control is likely to be related on one hand to its importance for the functional assembly of the proteasome and on the other hand to its association with the RNA degradation machines. Not4 is in an ideal position to signal to degradation mRNAs whose translation has been aborted, and this defines Not4 as a key player in the quality control of newly synthesized proteins.

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The UBC27–AIRP3 ubiquitination complex modulates ABA signaling by promoting the degradation of ABI1 in Arabidopsis

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.2007366117 ◽

2020 ◽

Vol 117 (44) ◽

pp. 27694-27702

Author(s):

Wenbo Pan ◽

Baoying Lin ◽

Xiaoyuan Yang ◽

Lijing Liu ◽

Ran Xia ◽

...

Keyword(s):

Drought Tolerance ◽

Protein Phosphatase ◽

Regulatory Mechanism ◽

Drought Response ◽

Aba Signaling ◽

Ring E3 Ligase ◽

Ubiquitin Conjugating Enzyme ◽

Ubiquitination System ◽

Aba Insensitive ◽

Ring E3

Abscisic acid (ABA) is the key phytohormone in plant drought tolerance and stress adaptation. The clade A protein phosphatase 2Cs (PP2Cs) like ABI1 (ABA-INSENSITIVE 1) work as coreceptors of ABA and regulate multiple ABA responses. Ubiquitination of ABI1 has been proven to play important regulatory roles in ABA signaling. However, the specific ubiquitin conjugating enzyme (E2) involved is unknown. Here, we report that UBC27 is an active E2 that positively regulates ABA signaling and drought tolerance. UBC27 forms the E2-E3 pair with the drought regulator RING E3 ligase AIRP3. Both UBC27 and AIRP3 interact with ABI1 and affect the ubiquitination and degradation of ABI1. ABA activates the expression ofUBC27, inhibits the proteasome degradation of UBC27, and enhances the interaction between UBC27 and ABI1 to increase its activity. These findings uncover a regulatory mechanism in ABA signaling and drought response and provide a further understanding of the plant ubiquitination system and ABA signaling pathway.

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Novel perspectives of target-binding by the evolutionarily conserved PP4 phosphatase

Open Biology ◽

10.1098/rsob.200343 ◽

2020 ◽

Vol 10 (12) ◽

pp. 200343

Author(s):

Zoltan Karman ◽

Zsuzsanna Rethi-Nagy ◽

Edit Abraham ◽

Lilla Fabri-Ordogh ◽

Akos Csonka ◽

...

Keyword(s):

Protein Phosphatase ◽

Substrate Recognition ◽

Proline Content ◽

New Class ◽

Binding Partners ◽

Evolutionarily Conserved ◽

Tryptophan Residues ◽

Consensus Motifs ◽

Target Binding ◽

And Function

Protein phosphatase 4 (PP4) is an evolutionarily conserved and essential Ser/Thr phosphatase that regulates cell division, development and DNA repair in eukaryotes. The major form of PP4, present from yeast to human, is the PP4c-R2-R3 heterotrimeric complex. The R3 subunit is responsible for substrate-recognition via its EVH1 domain. In typical EVH1 domains, conserved phenylalanine, tyrosine and tryptophan residues form the specific recognition site for their target's proline-rich sequences. Here, we identify novel binding partners of the EVH1 domain of the Drosophila R3 subunit, Falafel, and demonstrate that instead of binding to proline-rich sequences this EVH1 variant specifically recognizes atypical ligands, namely the FxxP and MxPP short linear consensus motifs. This interaction is dependent on an exclusively conserved leucine that replaces the phenylalanine invariant of all canonical EVH1 domains. We propose that the EVH1 domain of PP4 represents a new class of the EVH1 family that can accommodate low proline content sequences, such as the FxxP motif. Finally, our data implicate the conserved Smk-1 domain of Falafel in target-binding. These findings greatly enhance our understanding of the substrate-recognition mechanisms and function of PP4.

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SMK-1/PPH-4.1–mediated silencing of the CHK-1 response to DNA damage in early C. elegans embryos

The Journal of Cell Biology ◽

10.1083/jcb.200705182 ◽

2007 ◽

Vol 179 (1) ◽

pp. 41-52 ◽

Cited By ~ 16

Author(s):

Seung-Hwan Kim ◽

Antonia H. Holway ◽

Suzanne Wolff ◽

Andrew Dillin ◽

W. Matthew Michael

Keyword(s):

Dna Damage ◽

Protein Phosphatase ◽

Cell Cycle Progression ◽

Germ Line ◽

Embryonic Cell ◽

Regulatory Subunit ◽

Ataxia Telangiectasia Mutated ◽

C Elegans ◽

Early Embryos ◽

Embryonic Cell Cycle

During early embryogenesis in Caenorhabditis elegans, the ATL-1–CHK-1 (ataxia telangiectasia mutated and Rad3 related–Chk1) checkpoint controls the timing of cell division in the future germ line, or P lineage, of the animal. Activation of the CHK-1 pathway by its canonical stimulus DNA damage is actively suppressed in early embryos so that P lineage cell divisions may occur on schedule. We recently found that the rad-2 mutation alleviates this checkpoint silent DNA damage response and, by doing so, causes damage-dependent delays in early embryonic cell cycle progression and subsequent lethality. In this study, we report that mutations in the smk-1 gene cause the rad-2 phenotype. SMK-1 is a regulatory subunit of the PPH-4.1 (protein phosphatase 4) protein phosphatase, and we show that SMK-1 recruits PPH-4.1 to replicating chromatin, where it silences the CHK-1 response to DNA damage. These results identify the SMK-1–PPH-4.1 complex as a critical regulator of the CHK-1 pathway in a developmentally relevant context.

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miR-1 coordinately regulates lysosomal v-ATPase and biogenesis to affect muscle contractility upon proteotoxic challenge during ageing

10.1101/2021.01.21.427623 ◽

2021 ◽

Author(s):

Isabelle Schiffer ◽

Birgit Gerisch ◽

Kazuto Kawamura ◽

Raymond Laboy ◽

Jennifer Hewitt ◽

...

Keyword(s):

Muscle Function ◽

Regulatory Subunit ◽

C Elegans ◽

Evolutionarily Conserved ◽

Atpase Subunits ◽

Muscle Biology ◽

Response To Stress ◽

Pharyngeal Pumping ◽

Lysosomal Acidification

AbstractMuscle function relies on the precise architecture of dynamic contractile elements, which must be fine-tuned to maintain motility throughout life. Muscle is also highly plastic, and remodelled in response to stress, growth, neural and metabolic inputs. The evolutionarily conserved muscle-enriched microRNA, miR-1, regulates distinct aspects of muscle biology during development, but whether it plays a role during ageing is unknown. Here we investigated the role of C. elegans miR-1 in muscle function in response to proteostatic stress during adulthood. mir-1 deletion results in improved mid-life muscle motility, pharyngeal pumping, and organismal longevity under conditions of polyglutamine repeat proteotoxic challenge. We identified multiple vacuolar ATPase subunits as subject to miR-1 control, and the regulatory subunit vha-13/ATP6VIA as a direct target downregulated via its 3’UTR to mediate miR-1 physiology. miR-1 further regulates nuclear localization of lysosomal biogenesis factor HLH-30/TFEB and lysosomal acidification. In summary, our studies reveal that miR-1 coordinately regulates lysosomal v-ATPase and biogenesis to impact muscle function and health during ageing.

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