Glucocorticoid-stimulated CCAAT/enhancer-binding protein alpha expression is required for steroid-induced G1 cell cycle arrest of minimal-deviation rat hepatoma cells.

Abstract

By genetic correlation with the growth-suppressible phenotype and direct functional tests, we demonstrate that the glucocorticoid-stimulated expression of the CCAAT/enhancer-binding protein alpha (C/EBP alpha) transcription factor is required for the steroid-mediated G1 cell cycle arrest of minimal-deviation rat hepatoma cells. Comparison of C/EBP alpha transcript and active protein levels induced by the synthetic glucocorticoid dexamethasone in glucocorticoid growth-suppressible (BDS1), nonsuppressible receptor-positive (EDR1) and nonsuppressible receptor-deficient (EDR3) hepatoma cell proliferative variants revealed that the stimulation of C/EBP alpha expression is a rapid, glucocorticoid receptor-mediated response associated with the G1 cell cycle arrest. Consistent with the role of C/EBP alpha as a critical intermediate in the growth suppression response, maximal induction of transcription factor mRNA occurred within 2 h of dexamethasone treatment whereas maximal inhibition of [3H] thymidine incorporation was observed 24 h after steroid treatment. As a direct functional approach, ablation of C/EBP alpha protein expression and DNA-binding activity by transfection of an antisense C/EBP alpha expression vector blocked the dexamethasone-induced G1 cell cycle arrest of hepatoma cells but did not alter general glucocorticoid responsiveness. Transforming growth factor beta induced a G1 cell cycle arrest in C/EBP alpha antisense transfected cells, demonstrating the specific involvement of C/EBP alpha in the glucocorticoid growth suppression response. Constitutive expression of a conditionally activated form of C/EBP alpha caused a G1 cell cycle arrest of BDS1 hepatoma cells in the absence of glucocorticoids. In contrast, overexpression of C/EBP beta or C/EBP delta had no effect on hepatoma cell growth. Taken together, these results demonstrate that the steroid-induced expression of C/EBP alpha is necessary to mediate the glucocorticoid G1 cell cycle arrest of rat hepatoma cells and implicates a role for this transcription factor in the growth control of liver-derived epithelial tumor cells.

• Authors: R A Ramos, Y Nishio, A C Maiyar, K E Simon, C C Ridder, Y Ge, G L Firestone
• Journal: Molecular and cellular biology (Mol Cell Biol) Vol. 16 Issue 10 Pg. 5288-301 (Oct 1996) ISSN: 0270-7306 [Print] United States
• PMID: 8816441 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't, Research Support, U.S. Gov't, P.H.S.)

Chemical References

• CCAAT-Enhancer-Binding Proteins
• DNA Probes
• DNA-Binding Proteins
• Glucocorticoids
• Nuclear Proteins
• Recombinant Proteins
• Transcription Factors
• Dexamethasone

Topics

• Animals
• CCAAT-Enhancer-Binding Proteins
• Cell Cycle (drug effects)
• Cell Division (drug effects)
• Cell Line
• DNA Probes
• DNA Replication
• DNA-Binding Proteins (biosynthesis, physiology)
• Dexamethasone (pharmacology)
• G1 Phase
• Glucocorticoids (pharmacology)
• Humans
• Kinetics
• Liver Neoplasms, Experimental
• Nuclear Proteins (biosynthesis, physiology)
• Phenotype
• Rats
• Recombinant Proteins (biosynthesis)
• Time Factors
• Transcription Factors (biosynthesis)
• Transfection
• Tumor Cells, Cultured