DK009: FOXO target gene CTDSP2 inhibits cell cycle progression through regulation of p21-Cip1/Waf1

Activity of Forkhead box O (FOXO) transcription factors is inhibited by PI3K-PKB/Akt signalling to control a variety of cellular processes including cell cycle progression. Through comparative analysis of a number of microarray datasets, we identified a set of genes commonly regulated by FOXO and PI3K/PKB, which includes Carboxyl-Terminal Domain Small Phosphatase 2 (CTDSP2). We validated CTDSP2 as a genuine FOXO target gene and show that ectopic CTDSP2 can induce cell cycle arrest. We analysed transcriptional regulation after CTDSP2 expression and identified extensive regulation of genes involved in cell cycle progression, which depends on the phosphatase activity of CTDSP2. Most notably regulated genes are p21Cip1/Waf1 and E2F1, both implicated in S-phase entry. We show that p21Cip1/Waf1 is regulated by CTDSP2 in a p53-independent manner and that p21Cip1/Waf1 upregulation results in decreased cyclin/CDK2 and cyclin/CDK6 activity. Thus, we identify FOXO-dependent CTDSP2 regulation as a novel regulatory mechanism for inhibiting proliferation in the absence of growth factor/PI3K signalling. DL23 cells, containing FoxO3.A3-ER, stimulated with 4OHT for 24hrs were compared to unstimulated cells in a common reference design on dual-channel spotted expression microarrays. 4 biological replicates each were used. RNA samples were isolated and dye-swaps were done on half of the samples. As refpool, DLD1 parental cell line was used.