title: Nuclear actin filaments recruit cofilin and actin-related protein 3, and their formation is connected with a mitotic block.
abstract: Although actin monomers polymerize into filaments in the cytoplasm, the form of actin in the nucleus remains elusive. We searched for the form and function of β-actin fused to nuclear localization signal and to enhanced yellow fluorescent protein (EN-actin). Our results reveal that EN-actin is either dispersed in the nucleoplasm (homogenous EN-actin) or forms bundled filaments in the nucleus (EN-actin filaments). Formation of such filaments was not connected with increased EN-actin levels. Among numerous actin-binding proteins tested, only cofilin is recruited to the EN-actin filaments. Overexpression of EN-actin causes increase in the nuclear levels of actin-related protein 3 (Arp3). Although Arp3, a member of actin nucleation complex Arp2/3, is responsible for EN-actin filament nucleation and bundling, the way cofilin affects nuclear EN-actin filaments dynamics is not clear. While cells with homogenous EN-actin maintained unaffected mitosis during which EN-actin re-localizes to the plasma membrane, generation of nuclear EN-actin filaments severely decreases cell proliferation and interferes with mitotic progress. The introduction of EN-actin manifests in two mitotic-inborn defects-formation of binucleic cells and generation of micronuclei-suggesting that cells suffer aberrant cytokinesis and/or impaired chromosomal segregation. In interphase, nuclear EN-actin filaments passed through chromatin region, but do not co-localize with either chromatin remodeling complexes or RNA polymerases I and II. Surprisingly presence of EN-actin filaments was connected with increase in the overall transcription levels in the S-phase by yet unknown mechanism. Taken together, EN-actin can form filaments in the nucleus which affect important cellular processes such as transcription and mitosis.
authors.affiliation: Department of Biology of the Cell Nucleus, Institute of Molecular Genetics of the Academy of Sciences of the Czech Republic, v.v.i., Vídeňská 1083, 142 20, Prague, Czech Republic.
authors.forename: Alžběta
authors.initials: A
authors.lastname: Kalendová
authors.forename: Ilona
authors.initials: I
authors.lastname: Kalasová
authors.forename: Shota
authors.initials: S
authors.lastname: Yamazaki
authors.forename: Lívia
authors.initials: L
authors.lastname: Uličná
authors.forename: Masahiko
authors.initials: M
authors.lastname: Harata
authors.forename: Pavel
authors.initials: P
authors.lastname: Hozák
mesh_terms: D008841:Actin Cytoskeleton / Q000378:metabolism*; D051339:Actin Depolymerizing Factors; D051378:Actin-Related Protein 3 / Q000096:biosynthesis / Q000378:metabolism*; D000199:Actins / Q000378:metabolism*; D001426:Bacterial Proteins / Q000378:metabolism*; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism*; D042002:Chromatin Assembly and Disassembly; D057809:HEK293 Cells; D006801:Humans; D008164:Luminescent Proteins / Q000378:metabolism*; D008938:Mitosis / Q000235:genetics; D012318:RNA Polymerase I / Q000235:genetics; D012319:RNA Polymerase II / Q000235:genetics; D014158:Transcription, Genetic
chemical_list: D051339:Actin Depolymerizing Factors; D051378:Actin-Related Protein 3; D000199:Actins; D001426:Bacterial Proteins; D008164:Luminescent Proteins; C054562:yellow fluorescent protein, Bacteria; D012319:RNA Polymerase II; D012318:RNA Polymerase I