The transcription factors STAT5a/b negatively regulate cell proliferation through the activation of cdkn2b and cdkn1a expression

Although the cytokine-inducible transcription factors STAT5a/b promote proliferation of a wide range of cell types, there are cell- and context specific cases in which loss of STAT5a/b results in enhanced cell proliferation. Here we report that loss of STAT5a/b from mouse embryonic fibroblasts (MEFs) leads to enhanced proliferation, which was linked to reduced levels of the cell cycle inhibitor p15INK4B and p21CIP1. We further demonstrate that growth hormone through the transcription factor STAT5a/b enhances expression of the cdkn2B gene and that STAT5a binds to GAS sites within the promoter. We have recently demonstrated that ablation of STAT5a/b from liver results in hepatocellular carcinoma upon a CCl4 insult. We also established that in liver tissue, like in MEFs, STAT5a/b activates expression of the cdkn2B gene. Loss of STAT5a/b led to diminished p15INK4B and increased hepatocyte proliferation. This study for the first time demonstrates that cytokines through STAT5a/b can induce the expression of a key cell cycle inhibitor. These experiments therefore shed a light on the context-specific role of STAT5a/b as tumor suppressors.

8

Yu JH, Zhu BM, Wickre M, Riedlinger G, Chen W, Hosui A, Robinson GW, Hennighausen L