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  • Title: [Alterations of protein phosphatases, PP2A and PP1, during retinoic acid-induced differentiation of HL-60 cells].
    Author: Zhu T.
    Journal: Hokkaido Igaku Zasshi; 1996 Mar; 71(2):173-86. PubMed ID: 8641674.
    Abstract:
    Alterations of protein phosphatases, PP2A and PP1, during the retinoic acid-induced differentiation of HL-60 cells have been investigated. The PP2A activity determined with myelin basic protein (MBP) as a substrate showed a sharp transient increase at 18 h of incubation of the cells with retinoic acid, whereas during incubation without retinoic acid, the activity remained at the initial level. On DEAE-Sepharose column chromatography of the extracts preparted from the cells incubated without retinoic acid, the PP2A activities determined with MBP were eluted at 0.13 M or 0.23 m NaCl, respectively. The PP2A activity of the cells incubated for 18 h with retinoic acid was much more greatly activated by protamine compared with the activity of the cells incubated without retinoic acid. These results strongly suggest a conversion of PP2A holoenzyme from PP2A1 to PP2A0 during the initial process of the retinoic acid-induced differentiation. On the other hand PP2A activity determined with phosphorylase alpha as a substrate showed a sharp transient decrease at 24 h of incubation of the cells, irrespective of the presence or the absence of retinoic acid in the incubation mixtures. This decrease may be related to the synchronization of the cells at S phase, which also occurred irrespective of the retinoic acid stimulation. PP1 activity determined with MBP was transiently increased between 27 and 36 h of the incubation of cells without retinoic acid. The increase was strongly suppressed in the cells incubated with retinoic acid, suggesting a role of PP1 in the cell proliferation, the activity of which was also inhibited by retinoic acid.
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