Reversible translocation of cytoplasmic actin into the nucleus caused by dimethyl sulfoxide.

Abstract

The addition of 10% dimethyl sulfoxide (Me2SO) to PtK2 and WI-38 cells caused stress fibers to disappear from the cytoplasm and numerous elongated inclusions to appear in the nucleus. When Me2SO was removed, the stress fibers reformed and the nuclear inclusions disappeared. These nuclear inclusions reacted with fluorescent heavy meromyosin, phalloidin, and actin antibody. In the electron microscope, needlelike structures were seqn-to be composed of wavy filaments that bound heavy meromyosin. Antibodies against other components of stress fibers-tropomyosin, a-actinin, and myosin-did not react with the inclusions. When fluorescently labeled actin was microinjected into living PtKX and WI-38 cells, the fluorescent actin was incorporated into stress fibers. Subsequent exposure of the same cells to Me2SO led to breakdown of the fluorescent stress fibers and the appearance of fluorescent inclusions in the nucleus. Removal of Me2SO caused reversion to the normal interphase structure. These results indicate that under the influence of Me2SO, dissolution of stress fiber releases actin in a form which allows it to diffuse into the nucleus where it then becomes organized into filamentous bundles. Evidence that actin is a constituent of the nuclei of a number of different cell types has been accumulating (1-7), although it is still not clear that its occurrence in nuclei is universal (8). The difficulty in identifying actin as an endogenous nuclear component is that the large amount of actin in the cytoplasm is a potential source of contamination of nuclear preparations. The finding by Weber and Osborn that the nucleus is surrounded by a "cage" of detergent-resistant microfilaments (9) emphasizes this problem.Recently, Fukui and Katsumaru (10-12) have shown that under the influence of 10% Me2SO, bundles of actin filaments will form in situ in nuclei of Dictyostelium, amoebae, and HeLa cells. These bundles were believed by these authors to arise from actin normally present in the nucleus. If true, this would indicate that the interphase nuclei of these cells contain a substantial amount of actin, which may play an important role in nuclear functions (10,12). On the other hand, initial studies with Me2SO and PtK2 cells (13) showed that in treated cells, bundles of actin filaments appeared in the nucleus at the same time that actin-containing stress fibers disappeared from the cytoplasm. The present results, which combine immunofluorescence with antibodies against contractile proteins and microinjection of fluorescent actin into living cells, demonstrate that the same actin that participated in the cytoplasmic stress fibers moves into the nucleus under the influence of Me2SO. There it reforms filamentous aggregates that clearly differ in composition from cytoplasmic stress fibers. This translocation of actin is rapid and fully reversible. MATERIALS AND METHODSRat kangaroo cells (PtK2) and WI-38 human fibroblasts were obtained from the American Type Culture Collection and were grown on glass cover slips in Falcon cultu...

Microinjection of actin-binding proteins and actin antibodies demonstrates involvement of nuclear actin in transcription of lampbrush chromosomes

“…However, many observations point to the existence of monomeric or oligomeric actin in the nucleus, and there may be functions of actin that are not dependent on filament formation. Actin microfilaments, the usual form of actin polymers, have not yet been shown to exist in intact nuclei of normal , transcriptionally active cells, although such filaments are clearly demonstrable in the nucleoplasm after treatment of cells with dimethyl sulfoxide (Fukui, 1978;Sanger et al, 1980;Wehland et aI., 1980) or with drugs that inhibit transcription (Lane, 1969) and in isolated nuclei (Cl ark and Rosenbaum , 1979;Gounon and Karsenti , 1981). We have also shown in this study that extended meshworks of actin microfilaments are formed in the vicinity of the lampbrush chromosomes upon inactivation of transcriptional activity.…”

Small nuclear RNA-protein complex anchors on the actin filaments in bovine lymphocyte nuclear matrix.

“…The existence of nuclear actin also has been reported in rat liver (9), Xenopus oocytes (8,22), Physarum polycephalum (17), and dimethylsulfoxide-treated cells (11,34). The function of this nuclear actin, however, has yet to be determined.…”

“…Many reports have described the association of hnRNA with the nuclear matrix (10,11,32,33,34) , and Calvet and Pederson (5) have described the association of snRNA with hnRNA. Pagoulatos and Yaniv (29) found actin in the hnRNP from normal and Simian-Virus-40 infected monkey kidney cells.…”

Exploring Secrets of Nuclear Actin Involvement in the Regulation of Gene Transcription and Genome Organization

“…Sanger and colleagues demonstrated that a disappearance of stress fibers from the cytoplasm and a reversible translocation of cytoplasmic actin into the nucleus occur after treatment of PtK2 and WI-38 cells with 10% DMSO (Sanger et al, 1980a;Sanger et al, 1980b). Courgeon and colleagues showed that heat shock causes actin to accumulate in the nucleus of Drosophila cells (Courgeon et al, 1993).…”

“…However, under certain cellular stress conditions, distinctive actin rods (also called bundles or paracrystals) can be induced in the nucleus in a variety of cell types. These conditions include dimethyl sulfoxide (DMSO) treatment (Sanger et al, 1980a;Sanger et al, 1980b), heat shock (Iida et al, 1986;Welch and Suhan, 1985), Latrunculin B treatment and ATP deletion (Pendleton et al, 2003) as well as viral infection (Charlton and Volkman, 1991;Feierbach et al, 2006). Cellular stress-induced formation of actin filaments seems to be caused by an increased nuclear actin level because nuclear translocation and accumulation of actin are also observed at the same time.…”