A complex containing lysine-acetylated actin inhibits the formin INF2

Abstract

INF2 is a member of the formin family of actin assembly factors. Dominant mis-sense mutations in INF2 link to two diseases: focal segmental glomerulosclerosis (FSGS), a kidney disease; and Charcot-Marie-Tooth disease (CMTD), a neuropathy. All disease mutations map to the autoinhibitory Diaphanous Inhibitory Domain (DID). Curiously, purified INF2 is not autoinhibited, suggesting the existence of additional cellular inhibitors. We purified an INF2 inhibitor from mouse brain, and identified it as a complex between lysine-acetylated actin (KAc-actin) and cyclase-associated protein (CAP). Inhibition of INF2 by CAP/KAc-actin requires INF2 DID. Treatment of CAP/KAc-actin with histone deacetylase 6 (HDAC6) releases INF2 inhibition, while HDAC6 inhibitors block cellular INF2 activation. INF2 disease mutants are poorly inhibited by CAP/KAc-actin, suggesting that FSGS and CMTD result from reduced CAP/KAc-actin binding. These findings reveal a role for lysine-acetylated actin in the regulation of an actin assembly factor by a mechanism which we call facilitated auto-inhibition.

A deregulated stress response underlies distinct INF2 associated disease profiles

“…Indeed, the disease-linked mutations analyzed here also induced intracellular actin polymerization, most prominently manifested by the formation of a perinuclear actin ring ( Figure 1B). Similar actin accumulations have previously been reported for U2OS cells expressing FSGS-linked INF2 variants 11 .…”

“…The CaAR stress response is specifically mediated by the formin INF2 4,14 . Moreover, human osteosarcoma cells (U2OS) expressing disease-linked INF2 variants constitutively exhibit a characteristic reorganization of actin that is reminiscent of that provoked by CaAR 11 . To assess the effects of INF2 mutations on CaAR in physiologically relevant cell types, we first asked whether the stress response can be experimentally induced in primary podocytes.…”

“…Previous studies have identified a range of interaction partners, posttranslational modifications and potential biological functions of INF2 9,[11][12][13] . However, while these reports suggest many 3 intriguing links between INF2 mutations and podocyte pathologies, no systematic analysis of the phenotypic spectrum of known mutations has been performed.…”

CAPt’n of Actin Dynamics: Recent Advances in the Molecular, Developmental and Physiological Functions of Cyclase-Associated Protein (CAP)

“…Specific mutations disrupting G-actin-binding of WH2 caused actin disorganization associated with cell growth and cell morphogenesis defects in yeast (Chaudhry et al, 2010). WH2 domain of human CAP might bind to the ABP INF2, but additional CAP domains or interactions are necessary for this function (Mu et al, 2019(Mu et al, , 2020. The functional relevance of this interaction is discussed below.…”

“…This view has changed drastically in the last decade, because CAP has been implicated in almost all steps relevant for actin dynamics, the spatiotemporally controlled assembly and disassembly of actin filaments (Factin). Specifically, these studies unraveled (i) a cooperation of CAP with key actin regulators such as ADF/Cofilin and Twinfilin in F-actin disassembly including dissociation of actin subunits from filaments' barbed and pointed ends as well as F-actin severing, (ii) a nucleotide exchange activity on G-actin that is required for F-actin assembly, and (iii) an inhibitory function towards the F-actin assembly factor inverted formin 2 (INF2), and they linked each individual actin activity to specific protein domains (Chaudhry et al, 2013;Jansen et al, 2014;Johnston et al, 2015;Kotila et al, 2018Kotila et al, , 2019Mu et al, 2019Mu et al, , 2020Shekhar et al, 2019). In this article, we will summarize and discuss important recent progress in CAP's structure and molecular functions, focusing on those studies that have been published since Shoichiro Ono's excellent review in 2013 (Ono, 2013).…”