HTLV-1 (human T-cell leukaemia virus type 1) is the causative agent for ATL (adult T-cell leukaemia). HTLV-1 Tax can activate the PI3K (phosphoinositide 3-kinase)/Akt signalling pathway, which is responsible for survival of HTLV-1-infected T-cells. HIFs (hypoxia-inducible factors) are transcriptional regulators that play a central role in the response to hypoxia. Overexpression of HIF-1alpha in many cancers is associated with a poor response to treatment and increased patient mortality. Our objectives in the present study were to investigate whether HIF-1 was activated in HTLV-1-infected T-cells and to elucidate the molecular mechanisms of HIF-1 activation by focusing on the PI3K/Akt signalling pathway. We detected a potent pathway that activated HIF-1 in the HTLV-1-infected T-cells under a normal oxygen concentration. Enhanced HIF-1alpha protein expression and HIF-1 DNA-binding activity were exhibited in HTLV-1-infected T-cell lines. Knockdown of HIF-1alpha by siRNA (small interfering RNA) suppressed the growth and VEGF (vascular endothelial growth factor) expression of the HTLV-1-infected T-cell line. HIF-1 protein accumulation and transcriptional activity were enhanced by Tax, which was inhibited by dominant-negative Akt. Importantly, mutant forms of Tax that are defective in activation of the PI3K/Akt pathway failed to induce HIF-1 transcriptional activity. The PI3K inhibitor LY294002 suppressed HIF-1alpha protein expression, HIF-1 DNA-binding and HIF-1 transcriptional activity in HTLV-1-infected T-cell lines. In primary ATL cells, HIF-1alpha protein levels were strongly correlated with levels of phosphorylated Akt. The results of the present study suggest that PI3K/Akt activation induced by Tax leads to activation of HIF-1. As HIF-1 plays a major role in tumour progression, it may represent a molecular target for the development of novel ATL therapeutics.

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Retraction: The following article has been retracted through agreement between the first author and several coauthors, the journal Editor‐in‐Chief, Peter Lichter, and John Wiley & Sons, Ltd.: Tomita M, Toyota M, Ishikawa C, Nakazato T, Okudaira T, Matsuda T, Uchihara JN, Taira N, Ohshiro K, Senba M, Tanaka Y, Ohshima K, Saya H, Tokino T, Mori N. (2009). Overexpression of Aurora A by loss of CHFR gene expression increases the growth and survival of HTLV‐1‐infected T cells through enhanced NF‐kappaB activity. Int J Cancer; 124 (June (11)): 2607‐2615, published online on 12 JAN 2009 in Wiley Online Library (www.onlinelibrary.wiley.com). After an investigation the retraction has been agreed due to inappropriate duplication of images and overlap with other published work.

Adult T-cell leukemia (ATL), a CD4؉ -T-cell malignancy caused by human T-cell leukemia virus type 1 (HTLV-1), is difficult to cure, and novel treatments are urgently needed. Apo2 ligand (Apo2L; also tumor necrosis factor-related apoptosis-

Following an investigation by the University of the Ryukyus, which revealed that figures that appeared within this paper had also been used in other papers without appropriate attribution or explanation (a pattern repeated over a number of publications in different journals), the Editorial Board of the Biochemical Journal retract this paper. The last author, Naoki Mori, takes full responsibility for the misrepresentation of data in this paper.