The molecular mechanism of load adaptation by branched actin networks

  1. Tai-De Li
  2. Peter Bieling  Is a corresponding author
  3. Julian Weichsel
  4. R Dyche Mullins  Is a corresponding author
  5. Daniel A Fletcher  Is a corresponding author
  1. City University of New York, United States
  2. Max Planck Institute of Molecular Physiology, Germany
  3. University of California, Berkeley, United States
  4. University of California, San Francisco, United States

Abstract

Branched actin networks are self-assembling molecular motors that move biological membranes and drive many important cellular processes, including phagocytosis, endocytosis, and pseudopod protrusion. When confronted with opposing forces, the growth rate of these networks slows and their density increases, but the stoichiometry of key components does not change. The molecular mechanisms governing this force response are not well understood, so we used single-molecule imaging and AFM cantilever deflection to measure how applied forces affect each step in branched actin network assembly. Although load forces are observed to increase the density of growing filaments, we find that they actually decrease the rate of filament nucleation due to inhibitory interactions between actin filament ends and nucleation promoting factors. The force-induced increase in network density turns out to result from an exponential drop in the rate constant that governs filament capping. The force dependence of filament capping matches that of filament elongation and can be explained by expanding Brownian Ratchet theory to cover both processes. We tested a key prediction of this expanded theory by measuring the force-dependent activity of engineered capping protein variants and found that increasing the size of the capping protein increases its sensitivity to applied forces. In summary, we find that Brownian Ratchets underlie not only the ability of growing actin filaments to generate force but also the ability of branched actin networks to adapt their architecture to changing loads.

Data availability

Source Data files have been provided for the top and bottom panels of Figure 1c. Movies 1-3 contain source data for Figures 1-4.

Article and author information

Author details

  1. Tai-De Li

    Advanced Science Research Center, City University of New York, New York, United States
    Competing interests
    The authors declare that no competing interests exist.
  2. Peter Bieling

    Department of Systemic Cell Biology, Max Planck Institute of Molecular Physiology, Dortmund, Germany
    For correspondence
    peter.bieling@mpi-dortmund.mpg.de
    Competing interests
    The authors declare that no competing interests exist.
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0002-7458-4358
  3. Julian Weichsel

    Department of Chemistry, University of California, Berkeley, Berkeley, United States
    Competing interests
    The authors declare that no competing interests exist.
  4. R Dyche Mullins

    Department of Cellular and Molecular Pharmacology, University of California, San Francisco, San Francisco, United States
    For correspondence
    Dyche.Mullins@ucsf.edu
    Competing interests
    The authors declare that no competing interests exist.
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0002-0871-5479
  5. Daniel A Fletcher

    Department of Bioengineering and Biophysics, University of California, Berkeley, Berkeley, United States
    For correspondence
    fletch@berkeley.edu
    Competing interests
    The authors declare that no competing interests exist.
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0002-1890-5364

Funding

National Institutes of Health (1R35 GM118119)

  • R Dyche Mullins

National Institutes of Health (R01 GM134137)

  • Daniel A Fletcher

Howard Hughes Medical Institute

  • R Dyche Mullins

Human Frontier Science Program (LT-000843/2010)

  • Peter Bieling

Human Frontier Science Program (CDA00070/2017-2)

  • Peter Bieling

European Molecular Biology Organization (ALTF 854-2009)

  • Peter Bieling

Chan Zuckerberg Initiative

  • Daniel A Fletcher

The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.

Reviewing Editor

  1. Alphee Michelot, Institut de Biologie du Développement, France

Publication history

  1. Preprint posted: May 25, 2021 (view preprint)
  2. Received: August 27, 2021
  3. Accepted: June 7, 2022
  4. Accepted Manuscript published: June 24, 2022 (version 1)
  5. Version of Record published: July 27, 2022 (version 2)

Copyright

This is an open-access article, free of all copyright, and may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose. The work is made available under the Creative Commons CC0 public domain dedication.

Metrics

  • 1,432
    Page views
  • 545
    Downloads
  • 3
    Citations

Article citation count generated by polling the highest count across the following sources: Crossref, PubMed Central, Scopus.

Download links

A two-part list of links to download the article, or parts of the article, in various formats.

Downloads (link to download the article as PDF)

Open citations (links to open the citations from this article in various online reference manager services)

Cite this article (links to download the citations from this article in formats compatible with various reference manager tools)

  1. Tai-De Li
  2. Peter Bieling
  3. Julian Weichsel
  4. R Dyche Mullins
  5. Daniel A Fletcher
(2022)
The molecular mechanism of load adaptation by branched actin networks
eLife 11:e73145.
https://doi.org/10.7554/eLife.73145
  1. Further reading

Further reading

    1. Cell Biology
    2. Medicine
    Avner Ehrlich, Konstantinos Ioannidis ... Yaakov Nahmias
    Research Article

    Background: Viral infection is associated with a significant rewire of the host metabolic pathways, presenting attractive metabolic targets for intervention.

    Methods: We chart the metabolic response of lung epithelial cells to SARS-CoV-2 infection in primary cultures and COVID-19 patient samples and perform in vitro metabolism-focused drug screen on primary lung epithelial cells infected with different strains of the virus. We perform observational analysis of Israeli patients hospitalized due to COVID-19 and comparative epidemiological analysis from cohorts in Italy and the Veteran's Health Administration in the United States. In addition, we perform a prospective non-randomized interventional open-label study in which 15 patients hospitalized with severe COVID-19 were given 145 mg/day of nanocrystallized fenofibrate added to the standard of care.

    Results: SARS-CoV-2 infection produced transcriptional changes associated with increased glycolysis and lipid accumulation. Metabolism-focused drug screen showed that fenofibrate reversed lipid accumulation and blocked SARS-CoV-2 replication through a PPARa-dependent mechanism in both alpha and delta variants. Analysis of 3,233 Israeli patients hospitalized due to COVID-19 supported in vitro findings. Patients taking fibrates showed significantly lower markers of immunoinflammation and faster recovery. Additional corroboration was received by comparative epidemiological analysis from cohorts in Europe and the United States. A subsequent prospective non-randomized interventional open-label study was carried out on 15 patients hospitalized with severe COVID-19. The patients were treated with 145 mg/day of nanocrystallized fenofibrate in addition to standard-of-care. Patients receiving fenofibrate demonstrated a rapid reduction in inflammation and a significantly faster recovery compared to patients admitted during the same period.

    Conclusions: Taken together, our data suggest that pharmacological modulation of PPARa should be strongly considered as a potential therapeutic approach for SARS-CoV-2 infection and emphasizes the need to complete the study of fenofibrate in large randomized controlled clinical trials.

    Funding: Funding was provided by European Research Council Consolidator Grants OCLD (project no. 681870) and generous gifts from the Nikoh Foundation and the Sam and Rina Frankel Foundation (YN). The interventional study was supported by Abbott (project FENOC0003).

    Clinical trial number: NCT04661930.

    1. Cell Biology
    2. Chromosomes and Gene Expression
    Liangyu Zhang, Weston T Stauffer ... Abby F Dernburg
    Research Article

    Meiotic chromosome segregation relies on synapsis and crossover recombination between homologous chromosomes. These processes require multiple steps that are coordinated by the meiotic cell cycle and monitored by surveillance mechanisms. In diverse species, failures in chromosome synapsis can trigger a cell cycle delay and/or lead to apoptosis. How this key step in 'homolog engagement' is sensed and transduced by meiotic cells is unknown. Here we report that in C. elegans, recruitment of the Polo-like kinase PLK-2 to the synaptonemal complex triggers phosphorylation and inactivation of CHK-2, an early meiotic kinase required for pairing, synapsis, and double-strand break induction. Inactivation of CHK-2 terminates double-strand break formation and enables crossover designation and cell cycle progression. These findings illuminate how meiotic cells ensure crossover formation and accurate chromosome segregation.