Abstract
Forkhead box‐O (FoxO) transcription factors play an important role in tumour suppression by regulating the expression of genes involved in DNA damage repair, apoptosis and cell cycle arrest. We studied the role of extracellular ATP in the modulation of FoxO transcription factors and of cell cycle progression in MCF‐7 breast cancer cells. Western blot analysis showed that 5 μM ATP induced the phosphorylation of FoxO1/3a at threonine 24/32, and also reduced the expression of FoxO1. The use of the phosphatidilinositol 3 kinase (PI3K) inhibitor Ly294002 and of siRNA to reduce the expression of the serine/threonine kinase Akt showed that these effects are mediated by the PI3K/Akt signaling pathway. Immunocytochemistry and subcellular fractionation studies showed that ATP induces the translocation of FoxO3a from the nucleus to the cytoplasm. Flow cytometry analysis revealed that ATP increases the number of cells in the S phase of cell cycle. In addition, analysis by Western blot showed that ATP increases the expression of the cyclins D1 and D3 and diminishes the inhibitory proteins p21Cip1 and p27Kip1. However, these effects were independent of the PI3K/Akt pathway. Taken together, our results suggest that ATP induces the inactivation of FoxO transcription factors in a PI3K dependent manner and also induces changes in the expression of proteins involved in cell cycle regulation in MCF‐7 cells. (PIP‐CONICET Argentina)
Published Version
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