title: Nuclear phospholipase C-beta1b activation during G2/M and late G1 phase in nocodazole-synchronized HL-60 cells.
abstract: In this study, the activity of nuclear phosphatidylinositol-specific phosholipase C (PI-PLC) was investigated in HL-60 cells blocked at G(2)/M phase by the addition of nocodazole, and released into medium as synchronously progressing cells. Two peaks of an increase in the nuclear PI-PLC activities were detected; an early peak reached a maximum at 1 h after release from the nocodazole block, and a second increase was detected at 8.5 h after the release. Immunoprecipitation studies indicated that the increase in the activity was due to the activation of the nuclear PI-PLC-beta(1). Western blot analysis demonstrated no changes in the level of both a and b splicing variants of PI-PLC-beta(1) in the nuclei of cells isolated at either 1 h or 8.5 h after the block. However, an increase in the serine-phosphorylation of PI-PLC-beta(1b) was detected in the nuclei of HL-60 cells isolated at 1 and 8.5 h after the block, and the presence of MEK-inhibitor PD98059 completely inhibited both the serine phosphorylation and the increase in the PI-PLC activities in vitro. The presence of PI-PLC inhibitor prevented the progression of HL-60 cells through the G(1) into S phase of the cell cycle. These results demonstrate that two peaks of nuclear PI-PLC activities, which are due to a PD98059-sensitive phosphorylation of nuclear PLC-beta(1b) on serine, occur at the G(2)/M and late G(1) phase and are necessary for the progression of the cells through the cell cycle.
authors.affiliation: Department of Physiology and Croatian Institute for Brain Research, School of Medicine, University of Zagreb, Croatia.
authors.forename: Vesna
authors.initials: V
authors.lastname: Lukinovic-Skudar
authors.forename: Lana
authors.initials: L
authors.lastname: Donlagic
authors.forename: Hrvoje
authors.initials: H
authors.lastname: Banfíc
authors.forename: Dora
authors.initials: D
authors.lastname: Visnjic
mesh_terms: D002453:Cell Cycle / Q000187:drug effects; D002467:Cell Nucleus / Q000187:drug effects / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D005419:Flavonoids / Q000494:pharmacology; D016193:G1 Phase; D016195:G2 Phase; D018922:HL-60 Cells; D006801:Humans; D007527:Isoenzymes / Q000378:metabolism*; D015739:Nocodazole / Q000494:pharmacology*; D054799:Phospholipase C beta; D010766:Phosphorylation / Q000187:drug effects; D010738:Type C Phospholipases / Q000378:metabolism*
chemical_list: D005419:Flavonoids; D007527:Isoenzymes; D010738:Type C Phospholipases; D054799:Phospholipase C beta; D015739:Nocodazole; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one