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TGFβ1 suppresses EGF‐induced increase in nuclear type 1 protein phosphatase activity at the G 1 /S transition of hepatocyte proliferation
Author(s) -
Kakinoki Yasutaka,
Mizuno Yusuke,
Takizawa Norio,
Imai Yoko,
Miyazaki Tamotsu,
Kikuchi Kunimi
Publication year - 1994
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/0014-5793(94)00993-7
Subject(s) - phosphatase , phosphorylation , nuclear localization sequence , protein phosphatase 1 , nuclear protein , biology , chemistry , medicine , endocrinology , microbiology and biotechnology , biochemistry , transcription factor , nucleus , gene
Nuclear type 1 protein phosphatase (PP1) activity in primary culture of EGF‐stimulated hepatocytes was significantly and transiently increased at the G 1 /S transition, being about 2.5‐fold, while that in non‐stimulated hepatocytes showed almost no change. On the other hand, non‐nuclear PP1 activity was gradually increased until the G 1 /S transition, but the activity showed no difference between EGF‐stimulated and non‐stimulated hepatocytes. Under growth‐inhibited conditions in the presence of TGFβ1, the increase in nuclear PP1 activity was completely suppressed, whereas non‐nuclear PP1 activity was little affected. Such close correlation between nuclear PP1 activity and growth factor‐induced positive or negative growth signaling strongly suggests an involvement of PP1 in progression from G 1 to S phase of hepatocytes. On Western immunoblotting using antisera for PP1α, PP1γ1, and PP1δ, no isoform showed any change in amount under these conditions. Mechanism(s) of growth‐associated alterations in nuclear PP1 activity is discussed.