Abstract

The majority of intracellular phosphatase activity is attributed to the serine/threonine protein phosphatases types 1 (PP1) and 2A (PP2A). PP2A is involved in the transcriptional regulation of various growth regulatory genes as well as post-translational control of cell cycle regulatory kinases. The overall objectives of the proposed research are to characterize the mechanisms that control PP2A expression and to determine the role of PP2A function in cellular growth and transformation.
Specific Aim 1 is to characterize regulation of PP2A gene expression at the transcription and post-transcriptional levels and to determine whether autoregulation of PP2A expression occurs. Cloned promoters for both the alpha and beta isoforms will be studied in standard transfection and deletional analyses. The stability of the mRNAs for the alpha and beta isoforms will be examined, and the contributions of the respective 3' untranslated regions (3'-UTR) in controlling mRNA stability will be assessed. The effects of PP2A overexpression and underexpression on promoter activities and mRNA stabilities will be determined to assess autoregulation.
Specific Aim 2 is to evaluate the effects of overexpression and underexpression on cellular phenotype. Strong viral promoters will be utilized to drive overexpression of the two PP2A isoforms, both of which will be tagged at their amino-termini to allow discrimination from the corresponding endogenous proteins. Underexpression of the two PP2A isoforms will be accomplished through use of PP2A-specific ribozymes expressed from an inducible promoter. The effects of overexpression and underexpression of the PP2A isoforms on cell proliferation, the function of cell cycle regulatory kinases and gene expression will be examined.
Specific Aim 3 is to evaluate the role of PP2A in cellular transformation. The relationship between the level of PP2A expression and the ability of okadaic acid, an inhibitor of PP2A, and various oncogenes to transform cells will be evaluated. Transformation will be assessed by examining growth in soft agar.

  Funding Agency

Agency
National Institute of Health (NIH)
Institute
National Cancer Institute (NCI)
Type
First Independent Research Support & Transition (FIRST) Awards (R29)
Project #
5R29CA074278-04
Application #
6173068
Study Section
Metabolic Pathology Study Section (MEP)
Program Officer
Spalholz, Barbara A
Project Start
1997-06-01
Project End
2002-05-31
Budget Start
2000-06-01
Budget End
2001-05-31
Support Year
4
Fiscal Year
2000
Total Cost
$81,750
Indirect Cost

  Institution

Name
University of Southern California
Department
Microbiology/Immun/Virology
Type
Schools of Medicine
DUNS #
041544081
City
Los Angeles
State
CA
Country
United States
Zip Code
90089

  Publications

Blumenthal, Martina; Kardosh, Adel; Dubeau, Louis et al. (2003) Suppression of the transformed phenotype and induction of differentiation-like characteristics in cultured ovarian tumor cells by chronic treatment with progesterone. Mol Carcinog 38:160-9
Chen, Thomas C; Wadsten, Pia; Su, Susan et al. (2002) The type IV phosphodiesterase inhibitor rolipram induces expression of the cell cycle inhibitors p21(Cip1) and p27(Kip1), resulting in growth inhibition, increased differentiation, and subsequent apoptosis of malignant A-172 glioma cells. Cancer Biol Ther 1:268-76
Schonthal, A H (2001) Role of serine/threonine protein phosphatase 2A in cancer. Cancer Lett 170:1-13
Huang, S M; Schonthal, A H; Stallcup, M R (2001) Enhancement of p53-dependent gene activation by the transcriptional coactivator Zac1. Oncogene 20:2134-43
Mueller, S; Cadenas, E; Schonthal, A H (2000) p21WAF1 regulates anchorage-independent growth of HCT116 colon carcinoma cells via E-cadherin expression. Cancer Res 60:156-63
Villalobos Campos, S; Schonthal, A H (2000) Induction of protein phosphatase type 2A in response to disruption of cell-matrix interactions. J Cell Physiol 182:88-96
Wu, R C; Li, X; Schonthal, A H (2000) Transcriptional activation of p21WAF1 by PTEN/MMAC1 tumor suppressor. Mol Cell Biochem 203:59-71
da Costa, S R; Wang, Y; Vilalta, P M et al. (2000) Changes in cytoskeletal organization in polyoma middle T antigen-transformed fibroblasts: involvement of protein phosphatase 2A and src tyrosine kinases. Cell Motil Cytoskeleton 47:253-68
Baharians, Z; Schonthal, A H (1999) Reduction of Ha-ras-induced cellular transformation by elevated expression of protein phosphatase type 2A. Mol Carcinog 24:246-54
Schonthal, A H; Hwang, J J; Stevenson, D et al. (1999) Expression and activity of cell cycle-regulatory proteins in normal and transformed corneal endothelial cells. Exp Eye Res 68:531-9

Showing the most recent 10 out of 12 publications