Cell cycle dependent gene expressions and activities of protein phosphatases PP1 and PP2A in mouse NIH3T3 fibroblasts

Nakamura, Koji; Koda, Toshiaki; Kakinuma, Mitsuaki; Matsuzawa, Shu‐ichi; Kitamura, Kazuki; Mizuno, Yusuke; Kikuchi, Kunimi

doi:10.1016/s0006-291x(05)81523-2

Cited by 16 publications

(10 citation statements)

References 21 publications

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“…For example, in various mammalian cells and in fission yeast, it has been shown that the level of PP2A protein remains constant throughout the cell cycle (31)(32)(33). In contrast, analyzing the amount of mRNA, others have demonstrated increased PP2A mRNA levels during the early stages of G 1 in mammalian cells (34,35). Moreover, Kakinoki et al (36) by performing partial hepatectomy, presented evidence of almost constant levels of PP2A protein in regenerating liver, despite a 30-fold increase in PP2A mRNA.…”

Section: Discussionmentioning

confidence: 99%

Autoregulation of Protein Phosphatase Type 2A Expression

Baharians

Schönthal

1998

Journal of Biological Chemistry

138

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Protein phosphatases are involved in many cellular processes. One of the most abundant of these enzymes, the serine/threonine-specific protein phosphatase type 2A (PP2A), is present in most eukaryotic cells and serves a variety of functions. However, the detailed study of its regulation and function has been hampered by the difficulty of manipulating its expression level in cell culture. By using a new mammalian expression vector to forcibly overexpress PP2A in the mouse fibroblast cell line NIH3T3, we now show that the catalytic subunit of PP2A is subject to a potent autoregulatory mechanism that adjusts PP2A protein to constant levels. This control is exerted at the translational level and does not involve regulation of transcription or RNA processing. Thus, our results demonstrate tight control of PP2A expression, and provide an explanation for the difficulty of increasing PP2A expression experimentally.

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Section: Discussionmentioning

confidence: 99%

Autoregulation of Protein Phosphatase Type 2A Expression

Baharians

Schönthal

1998

Journal of Biological Chemistry

138

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“…[2][3][4][5] It has been found in 25% to 60% of cases of acute leukemia and 20% to 50% of cases of lymphoma. 6 Although deletion of the p16 INK4a gene is uncommon in acute myeloid leukemia, messenger RNA expression is frequently undetectable, possibly as a result of DNA hypermethylation or mutations in the p16 INK4a promotor region.…”

Section: Introductionmentioning

confidence: 99%

The influence of INK4 proteins on growth and self-renewal kinetics of hematopoietic progenitor cells

Lewis

Chinswangwatanakul

Zheng

et al. 2001

Blood

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This study investigated the influence of expression of proteins of the INK4 family, particularly p16, on the growth and selfrenewal kinetics of hematopoietic cells. First, retrovirus-mediated gene transfer (RMGT) was used to restore p16 INK4a expression in the p16 INK4a -deficient lymphoid and myeloid cell lines BV173 and K562, and it was confirmed that this inhibited their growth. Second, to sequester p16 INK4a and related INK4 proteins, cyclindependent kinase 4 (CDK4) was retrovirally transduced into normal human CD34 ؉ bone marrow cells and then cultured in myeloid colony-forming cell (CFC) assays. The growth of CDK4-transduced colonies was more rapid; the cell-doubling time was reduced; and, upon replating, the colonies produced greater yields of secondary colonies than mock-untransduced controls. Third, colony formation was compared by marrow cells from p16 INK4a؊/؊ mice and wild-type mice. The results from p16 INK4a؊/؊ marrow were similar to those from CDK4-transduced human CFCs, in terms of growth rate and replating ability, and were partially reversed by RMGT of p16 INK4a IntroductionDeletion of the tumor-suppressor gene p16 INK4a has been implicated in tumorigenesis in general 1 and in leukemogenesis in particular. [2][3][4][5] It has been found in 25% to 60% of cases of acute leukemia and 20% to 50% of cases of lymphoma. 6 Although deletion of the p16 INK4a gene is uncommon in acute myeloid leukemia, messenger RNA expression is frequently undetectable, possibly as a result of DNA hypermethylation or mutations in the p16 INK4a promotor region. 7 These observations raise the possibility that p16 INK4a expression plays an important role in the regulation of normal hematopoiesis. There is ample evidence that restoration of p16 INK4a into p16 INK4a -deficient leukemic cell lines reduces their proliferation rate in liquid culture and some evidence that it suppresses their ability to form colonies in semisolid culture, 8,9 but the effects of p16 INK4a expression on primary normal hematopoietic cell proliferation have not been examined. In particular, it is not known whether p16 INK4a has any effects on the kinetics of progenitor cell renewal and differentiation. This is important because transformation of leukemic target cells must be associated with an increase in self-renewal probability above the steady-state value of 0.5 before the leukemic clone can expand, become established, and eventually predominate over normal hematopoiesis. [10][11][12] The p16 INK4a protein is the prototypic member of the INK4 13 This pathway (the pRB pathway) regulates the transition from G 1 to S phase of the cell cycle. The formation of complexes between cyclin D and CDK4 is inhibited by p16 INK4a through binding to CDK4/6. The cyclin D-CDK4/6 complex phosphorylates pRB, resulting in the release of transcription factors so that the genes necessary for cell cycle progression can be transcribed. 14 The pRB family of pocket proteins consists of pRB itself and the structurally related proteins p107 and p130. They are negative ...

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“…PP1s are known to change their phosphorylation status, their activity, and subcellular localization during the cell cycle. [30][31][32] Although the activities of PP1s during cell-cycle progression were studied, the protein amounts of PP1s were not examined. We demonstrated h. morimoto ET AL.…”

Section: Discussionmentioning

confidence: 99%

Differential expression of protein phosphatase type 1 isotypes and nucleolin during cell cycle arrest

Morimoto

Ozaki

Okamura

et al. 2005

Cell Biochemistry & Function

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In the present study, we examined the expression and cytolocalization of protein phosphatase type 1 (PP1) isoforms and nucleolin in human osteoblastic cell line MG63 cells at two boundaries in the cell cycle. We treated MG63 cells with hydroxyurea and nocodazole to arrest the cells at the G(1)/S and G(2)/M boundaries, respectively. As judged from the results of Western blot analysis, PP1 isoforms were expressed differently at each boundary of the cell cycle. Nucleolin was also shown to have a different expression pattern at each boundary. In the hydroxyurea-treated cells, nucleolus-like bodies were bigger in size and decreased in number compared with those in asynchronized cells. However, the subcellular localization of PP1s and nucleolin was not changed. Anti-nucleolin antibody interacted with 110-kDa and 95-kDa proteins present in asynchronized cells and in the cells treated with hydroxyurea. Treatment of the cells with nocodazole decreased the level of the 95-kDa form of nucleolin. In the nocodazole-treated cells, it was impossible to distinguish the distribution of each protein. The phosphorylation status of nucleolin in the cell cycle arrested samples was examined by 2D-IEF-PAGE followed by Western blot analysis. In the case of asynchronized cells or hydroxyurea-treated ones, nucleolin was located at a basic isoelectric point (dephosphorylated status); whereas in the G(2)/M arrest cells, the isoelectric point of nucleolin shifted to an acidic status, indicating that nucleolin was phosphorylated. The present results indicate that PP1 and nucleolin were differently expressed at G(1)/S and G(2)/M boundaries of the cell cycle and acted in a different fashion during cell-cycle progression.

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Cell cycle dependent gene expressions and activities of protein phosphatases PP1 and PP2A in mouse NIH3T3 fibroblasts

Cited by 16 publications

References 21 publications

Autoregulation of Protein Phosphatase Type 2A Expression

Autoregulation of Protein Phosphatase Type 2A Expression

The influence of INK4 proteins on growth and self-renewal kinetics of hematopoietic progenitor cells

Differential expression of protein phosphatase type 1 isotypes and nucleolin during cell cycle arrest

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