title: p90 ribosomal S6 kinase 1 (RSK1) isoenzyme specifically regulates cytokinesis progression.
abstract: The p90 ribosomal S6 kinase family (RSK1-4) of Ser/Thr kinases is a downstream component of the Ras-MAPK cascade responsible for regulating various cellular processes. Here, we examined the potential involvement of RSKs in regulating mitosis by transfecting HeLa cells with siRNAs targeting RSK1 and -2, which are the major isoforms. Depletion of RSK1 but not RSK2 triggered a significant accumulation of binucleated cells compared to control cells (0.5% vs. 10.5%, respectively); this was rescued by expression of exogenous RSK1 but not a kinase-defective mutant. Monitoring of cell division by time-lapse imaging revealed that the observed binucleation mainly stemmed from a failure to form and ingress the cleavage furrow during early cytokinesis. Immunocytochemical analysis of RhoA and anillin, the two principal regulators of cleavage furrow formation and ingression, showed that these proteins were abnormally localized during anaphase in RSK1-depleted cells. Furthermore, RSK1-depleted cells seemed to have impairments in midzone microtubule formation, as suggested by morphological changes and lengthening of the midzone (15.2 ± 1.7 μm vs. 17.4 ± 1.7 μm in control cells). We also observed shortening of the pole-to-polar-cortex distance in RSK1-depleted cells (4.30 ± 1.37 μm vs. 2.80 ± 0.84 μm in control cells) and scanty distribution of microtubules at the periphery of the equatorial region during anaphase, suggesting an aberrant distribution of astral microtubules. Taken together, these results suggest that RSK1 is specifically required for cleavage furrow formation and ingression during cytokinesis. This may occur via the involvement of RSK1 in proper midzone and astral microtubule structure formation during anaphase, which is essential for the correct localization of anillin and RhoA.
authors.affiliation: Department of Biochemistry and Molecular Biology, Ajou University School of Medicine, Suwon 443-721, Republic of Korea.
authors.forename: Hyun-Ja
authors.initials: HJ
authors.lastname: Nam
authors.affiliation: Department of Biochemistry and Molecular Biology, Ajou University School of Medicine, Suwon 443-721, Republic of Korea.
authors.forename: In Jeong
authors.initials: IJ
authors.lastname: Lee
authors.affiliation: Department of Biochemistry and Molecular Biology, Ajou University School of Medicine, Suwon 443-721, Republic of Korea.
authors.forename: Seunghoon
authors.initials: S
authors.lastname: Jang
authors.affiliation: Department of Molecular Cell Biology and Samsung Biomedical Research Institute, Sungkyunkwan University School of Medicine, Suwon 440-746, Republic of Korea.
authors.forename: Chang-Dae
authors.initials: CD
authors.lastname: Bae
authors.affiliation: Department of Biochemistry, College of Medicine, Dankook University, Chonan 330-714, Republic of Korea.
authors.forename: Sahng-June
authors.initials: SJ
authors.lastname: Kwak
authors.affiliation: Department of Biochemistry and Molecular Biology, Ajou University School of Medicine, Suwon 443-721, Republic of Korea. Electronic address: jhlee64@ajou.ac.kr.
authors.forename: Jae-Ho
authors.initials: JH
authors.lastname: Lee
mesh_terms: D000705:Anaphase; D003285:Contractile Proteins / Q000378:metabolism; D048749:Cytokinesis / Q000235:genetics*; D006367:HeLa Cells; D006801:Humans; D008870:Microtubules / Q000378:metabolism; D011123:Polyploidy; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000378:metabolism; D038744:Ribosomal Protein S6 Kinases, 90-kDa / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D059008:Time-Lapse Imaging; D020742:rhoA GTP-Binding Protein / Q000378:metabolism
chemical_list: D003285:Contractile Proteins; D034741:RNA, Small Interfering; C095886:anillin; C069329:RPS6KA1 protein, human; D038744:Ribosomal Protein S6 Kinases, 90-kDa; C069330:ribosomal protein S6 kinase, 90kDa, polypeptide 3; D020742:rhoA GTP-Binding Protein
keywords: Astral microtubule; Cleavage furrow; Cytokinesis; ERK; MAPK; MAPK/ERK kinase; MEK; MTs; RSK1; RSKs; Spindle midzone; extracellular-signal-regulated kinase; microtubules; mitogen-activated protein kinase; p90 ribosomal S6 kinases; siRNA; small interfering RNA