Nuclear actin-related proteins take shape

Abstract

T he function of nuclear actin is poorly understood. It is known to be a discrete component of several chromatin-modifying complexes. Nevertheless, filamentous forms of actin are important for various nuclear processes as well. Nuclear actin is often associated with nuclear actin-related protein Arp4 and other actin-related proteins like Arp8 in the INO80 chromatin remodeler. We recently determined the crystal structure of S. cerevisiae Arp4 that explains why Arp4 is unable to form actin like filaments and shows that it is constitutively bound to an ATP nucleotide. More interestingly, in vitro activities of Arp4 and Arp8 seem to be directed towards stabilizing monomeric actin and to integrate it stoichiometrically into the INO80 complex. Based on this activity, we discuss possible roles of nuclear Arps in chromatin modifying complexes and in regulating more general aspects of nuclear actin dynamics.

Nuclear Distribution of the Chromatin-Remodeling Protein ATRX in Mouse Early Embryos during Normal Development and Developmental Arrest In Vitro

“…It has been repeatedly reported that actin can interact with components of chromatin-remodeling complexes, modulating the activity of these complexes as a whole. For example, actin is present in chromatin-remodeling complexes BAF [39,40], INO80 [41,42], and SWR1 [43]. It is assumed that actin can regulate the function of the ATPase subunit in chromatin remodeling complexes and contributes to the recognition of extranucleosomal linker DNAs, forming a subcomplex with actin-related proteins [35].…”

Actin, actin-related proteins and profilin in diatoms: A comparative genomic analysis

“…Arp4 is present in the majority of all phyla and is predominantly a nuclear protein participating in chromatin-remodelling (Meagher et al, 2009;Dion et al, 2010;Fenn et al, 2011;Kast and Dominguez, 2011). Arp4 is also involved in transcription regulation (Harata et al, 2002;Jiang and Stillman, 1996), DNA repair (Van Attikum et al, 2004), histone acetylation (Galarneau et al, 2000) as well as kinetochore-spindle attachment, and gene silencing at centromeres (Minoda et al, 2005).…”

The Actin-Family Protein Arp4 Is a Novel Suppressor for the Formation and Functions of Nuclear F-Actin

“…Two other actin family members, Arp2 and Arp3, are known to facilitate actin polymerization in the cytoplasm and also in the nucleus [10,11]. The basal structures of Arps2/3 and -4 are highly similar to actin, and both bind to actin [6,24]. However, the former binds to the pointed end while the latter binds to the barbed end of an actin molecule [22].…”

“…Nuclear F-actin also plays various roles in the nucleus, including in transcriptional regulation [6]. For example, the formation of nuclear F-actin decreases the nuclear G-actin pool, causing activation of SRF target genes through the retention of MAL in the nucleus [4].…”