The major goal of this proposal is to define the role of the nuclear transcription factor, C/EBPalpha in growth inhibition and immortalization. We have shown that C/EBPalpha inhibits cell proliferation in several transformed cell lines in vitro including human hepatoma cells and Saos2, a cell line that lacks p53 and Rb protein. We have further shown that induction of C/EBPalpha expression in stably transformed human fibrosarcoma cells inhibits cell growth and simultaneously elevates p21/SDI-1 mRNA and protein. Because the p21 protein is associated with cellular senescence in fibroblasts, we speculate that C/EBPalpha may be responsible, at least in part, for the resting or quiescent state of the normal hepatocyte in vivo. p21/SDI-1 mRNA is expressed in liver at levels that are easily detectable by Northern blotting. We will examine the role of C/EBPalpha in growth inhibition in three different ways. First, we will clone the target genes of C/EBPalpha that are involved in growth arrest in a novel cell system developed in our laboratory. We will use enzyme degrading subtractive hybridization to identify the genes that are targets of C/EBPalpha and that are responsible for growth arrest. Second, we will determine the biochemical basis for increased expression of p21/SDI-1 in cells that are growth arrested by C/EBPalpha. We will determine whether p21/SDI-1 expression is necessary and/or sufficient for growth arrest by blocking p21/SDI-1 expression using antisense strategies. Preliminary data suggest p53 and Rb are not required for growth arrest by C/EBPalpha; we will establish whether or not either of these tumor suppressor genes is involved in growth inhibition by C/EBPalpha. Finally, we will exploit a C/EBP knock- out mouse model that we have made in our laboratory. Cells derived from these animals will be cultured in vitro in order to test the hypothesis that the loss of C/EBPalpha will alter the growth properties or immortalization frequency of the cells.

Agency
National Institute of Health (NIH)
Institute
National Institute on Aging (NIA)
Type
Research Program Projects (P01)
Project #
5P01AG013663-05
Application #
6299368
Study Section
Project Start
2000-04-15
Project End
2002-03-31
Budget Start
1998-10-01
Budget End
1999-09-30
Support Year
5
Fiscal Year
2000
Total Cost
$423,298
Indirect Cost
Name
Baylor College of Medicine
Department
Type
DUNS #
051113330
City
Houston
State
TX
Country
United States
Zip Code
77030
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Hornsby, Peter J (2002) Cellular senescence and tissue aging in vivo. J Gerontol A Biol Sci Med Sci 57:B251-6
Thomas, Michael; Wang, Xiangdong; Hornsby, Peter J (2002) Human adrenocortical cell xenotransplantation: model of cotransplantation of human adrenocortical cells and 3T3 cells in scid mice to form vascularized functional tissue and prevent adrenal insufficiency. Xenotransplantation 9:58-67
Tominaga, Kaoru; Olgun, Abdullah; Smith, James R et al. (2002) Genetics of cellular senescence. Mech Ageing Dev 123:927-36

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