Transforming growth factor β-1 enhances Smad transcriptional activity through activation of p8 gene expression

• Published in: Biochemical journal 2001-07, Vol.357 (1), p.249-253
• Main Authors: GARCÍA-MONTERO, Andrés C., VASSEUR, Sophie, GIONO, Luciana E., CANEPA, Eduardo, MORENO, Silvia, DAGORN, Jean Charles, IOVANNA, Juan Lucio
• Format: Article
• Language: English
• ISSN: 0264-6021; 1470-8728
• DOI: 10.1042/bj3570249

We report that exposure of mouse embryonic fibroblasts to transforming growth factor β-1 (TGFβ-1) (5ng/ml) results in a strong activation of p8 mRNA expression that precedes the induction of cell growth. Involvement of the p8 promoter in the regulation was demonstrated by using a p8–chloramphenicol acetyltransferase construct. We therefore speculated that p8 might be a mediator of TGFβ-1 in these cells. The incorporation of [3H]thymidine on treatment with TGFβ-1 was indeed significantly higher in p8+/+ fibroblasts than in p8−/− fibroblasts. Smad transcriptional activity was used as marker of the TGFβ-1 signalling pathway, to probe the lower p8−/− response to TGFβ-1. Two Smad-binding elements (SBEs)–luciferase constructs were transfected into p8−/− and p8+/+ embryonic fibroblasts before treatment with TGFβ-1. A lower level of Smad transactivation was observed in p8−/− embryonic fibroblasts, under basal conditions and after stimulation with TGFβ-1. To test whether Smad underexpression in p8−/− cells was actually due to p8 depletion, p8−/− embryonic fibroblasts were transfected with a human p8 expression plasmid together with an SBE–luciferase construct. The expression of p8 restored Smad transactivation in unstimulated and TGFβ-1-treated cells to the level found in p8+/+ cells. We concluded that TGFβ-1 activates p8 expression, which in turn enhances the Smad-transactivating function responsible for TGFβ-1 activity.