Journal of Biological Chemistry
Volume 295, Issue 45, 6 November 2020, Pages 15366-15375
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Cell Biology
Capping protein is dispensable for polarized actin network growth and actin-based motility

https://doi.org/10.1074/jbc.RA120.015009Get rights and content
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Heterodimeric capping protein (CP) binds the rapidly growing barbed ends of actin filaments and prevents the addition (or loss) of subunits. Capping activity is generally considered to be essential for actin-based motility induced by Arp2/3 complex nucleation. By stopping barbed end growth, CP favors nucleation of daughter filaments at the functionalized surface where the Arp2/3 complex is activated, thus creating polarized network growth, which is necessary for movement. However, here using an in vitro assay where Arp2/3 complex-based actin polymerization is induced on bead surfaces in the absence of CP, we produce robust polarized actin growth and motility. This is achieved either by adding the actin polymerase Ena/VASP or by boosting Arp2/3 complex activity at the surface. Another actin polymerase, the formin FMNL2, cannot substitute for CP, showing that polymerase activity alone is not enough to override the need for CP. Interfering with the polymerase activity of Ena/VASP, its surface recruitment or its bundling activity all reduce Ena/VASP's ability to maintain polarized network growth in the absence of CP. Taken together, our findings show that CP is dispensable for polarized actin growth and motility in situations where surface-directed polymerization is favored by whatever means over the growth of barbed ends in the network.

actin
cell motility
Arp2/3 complex
biophysics
cytoskeleton
actin polymerization
capping protein
Ena/VASP proteins
in vitro systems

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Author contributions—M. A.-G., C. S., and J. P. conceptualization; M. A.-G., R. K., S. K., and J. P. formal analysis; M. A.-G. and J. P. validation; M. A.-G, R. K., S. K., J. M., and J. P. investigation; M. A.-G., R. K., and J. P. visualization; M. A.-G., R. K., S. K., J. M., and J. P. methodology; R. K. software; J. M. and J. F. resources; J. F., C. S., and J. P. writing-review and editing; C. S. and J. P. funding acquisition; J. P. supervision; J. P. writing-original draft; J. P. project administration.

Funding and additional information—This work was supported by grants from the program “Investissements d'Avenir” from the French Government and implemented by ANR Grants ANR-10-LABX-0038 and ANR-10-IDEX-0001-02 PSL and a post-Ph.D. grant (to M. A.-G.). J. P. was supported by Fondation pour la Recherche Médicale Grant DEQ20120323737 and Fondation ARC Grants PJA 20151203487 and PJA 20191209604. M. A.-G. was supported by a Ph.D. fellowship from La Ligue Contre le Cancer. S.K. was supported by the ERASMUS+ Student Mobility Placement program. R. K. was supported by the Bettencourt Schueller Foundation long-term partnership and partly by the CRI Research Fellowship program.

Conflict of interest—The authors declare that they have no conflicts of interest with the contents of this article.

Abbreviations—The abbreviations used are:

    CP

    capping protein

    TIRF

    total internal reflection fluorescence

    FAB

    F-actin–binding protein

    GAB

    G-actin–binding domain

    PP

    polyproline

    TET

    tetramerization

    GST

    glutathione S-transferase.