1. ¹Institute of Reproductive and Developmental Biology, Imperial College London, Hammersmith Hospital, London, UK
2. ²Department of Oncology, Imperial College London, Cancer Research-UK Labs and Section of Cancer Cell Biology, Hammersmith Hospital, London, UK
3. ³Section on Endocrinology and Metabolism of Ageing, Department of Pathology, University Clinic Hamburg-Eppendorf, Hamburg, Germany
4. ⁴Department of Morphopathology, University of Bucharest, Bucharest, Romania
5. ⁵Histopathology Department, Imperial College London, Hammersmith Hospital, London, UK
6. ⁶Department of Obstetrics and Gynaecology, Saitama Medical University, Saitama, Japan
7. ⁷Life and Health Science Research Institute (ICVS), Health Science School, University of Minho, Braga, Portugal

Correspondence: Dr JJ Brosens, Institute of Reproductive and Developmental Biology, Imperial College London, Faculty of Medicine, Hammersmith Hospital, London W12 0NN, UK. E-mail: j.brosens@imperial.ac.uk

Received 29 November 2006; Revised 11 April 2007; Accepted 22 May 2007; Published online 25 June 2007.

Abstract

The forkhead transcription factor FOXO1, a downstream target of phosphatidylinositol-3-kinase/Akt signalling pathway, regulates cyclic differentiation and apoptosis in normal endometrium, but its role in endometrial carcinogenesis is unknown. Screening of endometrial cancer cell lines demonstrated that FOXO1 is expressed in HEC-1B cells, but not in Ishikawa cells, which in turn highly express the FOXO1 targeting E3-ubiquitin ligase Skp2. FOXO1 transcript levels were also lower in Ishikawa cells and treatment with the proteasomal inhibitor was insufficient to restore expression. Lack of FOXO1 expression in Ishikawa cells was not accounted for by differential promoter methylation or activity, but correlated with increased messenger RNA (mRNA) turnover. Comparative analysis demonstrated that HEC-1B cells proliferate slower, but are more resistant to paclitaxel-mediated cell death than Ishikawa cells, which were partially reversed upon silencing of FOXO1 in HEC-1B cells or its re-expression in Ishikawa cells. We further show that FOXO1 is required for the expression of the growth arrest- and DNA-damage-inducible gene GADD45. Analysis of biopsy samples demonstrated a marked loss of FOXO1 and GADD45 mRNA and protein expression in endometrioid endometrial cancer compared to normal endometrium. Together, these observations suggest that loss of FOXO1 perturbs endometrial homeostasis, promotes uncontrolled cell proliferation and increases susceptibility to genotoxic insults.