Gene expressions and activities of protein phosphatases PP1 and PP2A in rat liver regeneration after partial hepatectomy (original) (raw)
1992, Biochemical and Biophysical Research Communications
We have examined the levels of gene expressions and activities of protein phosphatases,PPl and PP2A, in rat regenerating livers. PPI~ 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 PPI activity in non-nuclear fraction was nearly constant, potential PPI activity revealed by Co2+-trypsin treatment showed a small peak between 7 and 12 h. In nuclei, both spontaneous and potential PPI activity began to increase from 447 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 PPI in nuclei plays some role in the G1 to S transition in the cell cycle of hepatocyte proliferation.
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