Kakinoki Y, Kitamura K, Matsuzawa S, Mizuno Y, Miyazaki T, Kikuchi K
Section of Biochemistry, Hokkaido University, Japan.
Biochem Biophys Res Commun. 1992 May 29;185(1):291-7. doi: 10.1016/s0006-291x(05)80989-1.
We have examined the levels of gene expressions and activities of protein phosphatases, PP1 and PP2A, in rat regenerating livers. PP1 alpha mRNA started to increase from 6 h after partial hepatectomy (PH) and showed two peaks at 12 and 48 h. PP2A mRNA level showed two peaks at 6 and 10-12 h. Protein phosphatase activities were determined both in non-nuclear fraction and in nuclei. While spontaneous PP1 activity in non-nuclear fraction was nearly constant, potential PP1 activity revealed by Co(2+)-trypsin treatment showed a small peak between 7 and 12 h. In nuclei, both spontaneous and potential PP1 activity began to increase from 4-7 h after PH, reached a maximum (about 2.5-fold over control levels) at 12 h, the time which corresponds to the G1 to S transition in the cell cycle, and then declined back to control levels by 7 days. PP2A activity in non-nuclear fraction was nearly constant in both spontaneous and potential forms. PP2A activity in both forms in nuclei was very low throughout. These results suggest the possibility that PP1 in nuclei plays some role in the G1 to S transition in the cell cycle of hepatocyte proliferation.
我们检测了大鼠再生肝脏中基因表达水平以及蛋白磷酸酶PP1和PP2A的活性。PP1α mRNA在部分肝切除（PH）后6小时开始增加，并在12小时和48小时出现两个峰值。PP2A mRNA水平在6小时以及10 - 12小时出现两个峰值。分别在非核部分和细胞核中测定蛋白磷酸酶活性。非核部分中PP1的自发活性几乎保持恒定，而经Co(2+) - 胰蛋白酶处理后显示的潜在PP1活性在7至12小时之间出现一个小峰值。在细胞核中，PH后4 - 7小时，PP1的自发活性和潜在活性均开始增加，在12小时达到最大值（约为对照水平的2.5倍），此时对应细胞周期中从G1期到S期的转变，然后在7天时下降至对照水平。非核部分中PP2A的自发活性和潜在活性几乎均保持恒定。细胞核中两种形式的PP2A活性在整个过程中都非常低。这些结果表明，细胞核中的PP1可能在肝细胞增殖的细胞周期从G1期到S期的转变中发挥某种作用。
