A Direct Interaction between Actin and Vimentin Filaments Mediated by the Tail Domain of Vimentin

Osigwe Esue,Ashley A Carson,Yiider Tseng,Denis Wirtz

doi:10.1074/jbc.m605452200

Abstract

The assembly and organization of the three major eukaryotic cytoskeleton proteins, actin, microtubules, and intermediate filaments, are highly interdependent. Through evolution, cells have developed specialized multifunctional proteins that mediate the cross-linking of these cytoskeleton filament networks. Here we test the hypothesis that two of these filamentous proteins, F-actin and vimentin filament, can interact directly, i.e. in the absence of auxiliary proteins. Through quantitative rheological studies, we find that a mixture of vimentin/actin filament network features a significantly higher stiffness than that of networks containing only actin filaments or only vimentin filaments. Maximum inter-filament interaction occurs at a vimentin/actin molar ratio of 3 to 1. Mixed networks of actin and tailless vimentin filaments show low mechanical stiffness and much weaker inter-filament interactions. Together with the fact that cells featuring prominent vimentin and actin networks are much stiffer than their counterparts lacking an organized actin or vimentin network, these results suggest that actin and vimentin filaments can interact directly through the tail domain of vimentin and that these inter-filament interactions may contribute to the overall mechanical integrity of cells and mediate cytoskeletal cross-talk.

Highlights

Growing evidence suggests that cells have evolved specialized multibinding proteins that mediate the cross-linking of two or all three cytoskeleton filament networks
Our results show that a network containing both vimentin and actin filaments at a molar ratio of 3 to 1 displays an elasticity that is significantly higher and less frequency-dependent than the elasticity of networks containing only F-actin or vimentin filaments. ⌬T vimentin, which assembles into filamentous structures of morphology similar to that formed by full-length (FL) vimentin, completely abrogates this synergistic effect
Actin and Vimentin Filaments Interact Directly—We hypothesized that vimentin and actin filaments interact directly, i.e. without auxiliary proteins, forming structures that are stiffer than the two networks they are made of

Summary

Introduction

Growing evidence suggests that cells have evolved specialized multibinding proteins that mediate the cross-linking of two or all three cytoskeleton filament networks These proteins include fimbrin [11], the motor proteins kinesin [12], dynactin and dynein [13, 14], as well as members of the plakin family of large coiled-coil proteins [15, 16], including plectin [17] and BPAG1 [18, 19]. Transfected tailless Xenopus vimentin [36, 37] and human tailless keratin [38] have been shown to migrate into the nucleus of some cell lines, this is not the case for human tailless vimentin, which does not migrate into the nucleus under similar conditions [36] These different cellular processes seem to rely on either direct or indirect interactions between vimentin and actin filament networks [10, 33]. Exploiting this property, actin and vimentin were polymerized simultaneously in the same buffer to form a mixed filamentous network

Methods

Results

Conclusion