Romet-Lemonne/Jégou – Vimentin promotes actin assembly by stabilizing ATP-actin subunits at the barbed end

The cytoskeleton is composed of three types of filaments: actin, microtubules, and intermediate filaments, which coordinate to control cell shape, mechanics, and movement. Among them, the contribution of vimentin intermediate filaments to these functions has remained elusive. While studies highlighted their influence on actin dynamics, the underlying molecular mechanisms remain to be determined. Using in vitro reconstitution from purified proteins, we show that vimentin directly promotes actin filament assembly by selectively stabilizing ATP-actin subunits at the fast-growing end. This mechanism, distinct from that of canonical actin regulators, reveals a previously unrecognized mode of cytoskeletal regulation. Our findings identify vimentin as an unexpected modulator of actin dynamics, providing a molecular understanding of how intermediate filaments contribute to cytoskeletal organization.

Vimentin intermediate filaments play essential roles in maintaining cell integrity and regulating numerous cellular functions. In particular, vimentin cooperates with the actin cytoskeleton in key cellular processes that rely on actin dynamics, such as migration, division, and mechanosensing. While there is evidence that these two cytoskeletal components interact in cells, the underlying molecular mechanisms are only partially understood. Actin and vimentin can interact through biochemical signaling pathways or via cross-linkers, but whether they engage in a direct protein–protein interaction has remained controversial, in part because such interactions are difficult to isolate and characterize in cells. Using in vitro reconstitution coupled to theoretical modeling, and total internal reflection fluorescence microscopy to monitor the elongation of single actin filaments, we show that vimentin promotes actin elongation by stabilizing actin subunits at the barbed end in a dose-dependent manner. Strikingly, this effect depends on the nucleotide state of actin, as the acceleration is only observed for the elongation from adenosine triphosphate (ATP)-actin, and not adenosine diphosphate (ADP)-actin monomers. We further establish that neither the vimentin tail nor head domains are required for this effect, and both filamentous and nonfilamentous vimentin enhance actin elongation. Finally, we find that vimentin promotes the nucleation of actin filaments. Consistently, magnetic pull-down assays demonstrate a direct interaction between vimentin and ATP-actin monomers. Altogether, these findings identify vimentin as an unexpected new actor in the regulation of actin dynamics at the barbed end and bring new insights into the functional role of vimentin through cytoskeletal crosstalk.

Paty L, Kalvoda L, Varela-Salgado M, Tran QD, Lenz M, Jégou A, Romet-Lemonne G, Leduc C. Vimentin promotes actin assembly by stabilizing ATP-actin subunits at the barbed end. Proc Natl Acad Sci U S A. 2026 Jul 14;123(28):e2531232123. doi: 10.1073/pnas.2531232123. Epub 2026 Jul 6. PMID: 42406954; PMCID: PMC13367874.