Opposing roles of C/EBPbeta and AP-1 in the control of fibroblast proliferation and growth arrest-specific gene expression

TY - JOUR

T1 - Opposing roles of C/EBPbeta and AP-1 in the control of fibroblast proliferation and growth arrest-specific gene expression

AU - Gagliardi, Mark

AU - Maynard, Scott

AU - Miyake, Tetsuaki

AU - Rodrigues, Natalie

AU - Tjew, Sie Lung

AU - Cabannes, Eric

AU - Bedard, Pierre-Andre

PY - 2003/10/31

Y1 - 2003/10/31

N2 - Chicken embryo fibroblasts (CEF) express several growth arrest-specific (GAS) gene products in G0. In contact-inhibited cells, the expression of the most abundant of these proteins, the p20K lipocalin, is activated at the transcriptional level by C/EBPbeta. In this report, we describe the role of C/EBPbeta in CEF proliferation. We show that the expression of a dominant negative mutant of C/EBPbeta (designated Delta184-C/EBPbeta) completely inhibited p20K expression at confluence and stimulated the proliferation of CEF without inducing transformation. Mouse embryo fibroblasts nullizygous for C/EBPbeta had a proliferative advantage over cells with one or two functional copies of this gene. C/EBP inhibition enhanced the expression of the three major components of AP-1 in cycling CEF, namely c-Jun, JunD, and Fra-2, and stimulated AP-1 activity. In contrast, the over-expression of C/EBPbeta caused a dramatic reduction in the levels of AP-1 proteins. Therefore, C/EBPbeta is a negative regulator of AP-1 expression and activity in CEF. The expression of cyclin D1 and cell proliferation were stimulated by the dominant negative mutant of C/EBPbeta but not in the presence of TAM67, a dominant negative mutant of c-Jun and AP-1. CEF over-expressing c-Jun, and to a lesser extent JunD and Fra-2, did not growth arrest at high cell density and did not express p20K. Therefore, AP-1 interfered with the action of C/EBPbeta at high cell density, indicating that these factors play opposing roles in the control of GAS gene expression and CEF proliferation.

AB - Chicken embryo fibroblasts (CEF) express several growth arrest-specific (GAS) gene products in G0. In contact-inhibited cells, the expression of the most abundant of these proteins, the p20K lipocalin, is activated at the transcriptional level by C/EBPbeta. In this report, we describe the role of C/EBPbeta in CEF proliferation. We show that the expression of a dominant negative mutant of C/EBPbeta (designated Delta184-C/EBPbeta) completely inhibited p20K expression at confluence and stimulated the proliferation of CEF without inducing transformation. Mouse embryo fibroblasts nullizygous for C/EBPbeta had a proliferative advantage over cells with one or two functional copies of this gene. C/EBP inhibition enhanced the expression of the three major components of AP-1 in cycling CEF, namely c-Jun, JunD, and Fra-2, and stimulated AP-1 activity. In contrast, the over-expression of C/EBPbeta caused a dramatic reduction in the levels of AP-1 proteins. Therefore, C/EBPbeta is a negative regulator of AP-1 expression and activity in CEF. The expression of cyclin D1 and cell proliferation were stimulated by the dominant negative mutant of C/EBPbeta but not in the presence of TAM67, a dominant negative mutant of c-Jun and AP-1. CEF over-expressing c-Jun, and to a lesser extent JunD and Fra-2, did not growth arrest at high cell density and did not express p20K. Therefore, AP-1 interfered with the action of C/EBPbeta at high cell density, indicating that these factors play opposing roles in the control of GAS gene expression and CEF proliferation.

KW - Animals

KW - Avian Proteins

KW - Blood Proteins

KW - Blotting, Western

KW - CCAAT-Enhancer-Binding Protein-beta

KW - Cell Division

KW - Cells, Cultured

KW - Chick Embryo

KW - Cyclin D1

KW - DNA Fragmentation

KW - Fibroblasts

KW - Gene Expression Regulation

KW - Genes, Dominant

KW - Lipocalins

KW - Mutation

KW - Time Factors

KW - Transcription Factor AP-1

U2 - 10.1074/jbc.M304085200

DO - 10.1074/jbc.M304085200

M3 - Journal article

C2 - 12896981

SN - 0021-9258

VL - 278

SP - 43846

EP - 43854

JO - Journal of Biological Chemistry

JF - Journal of Biological Chemistry

IS - 44

ER -