1. ¹Laboratory of Molecular Biology, Center for Cancer Research, National Cancer Institute, Bethesda, MD, USA
2. ²Department of Pathology, Wake Forest University, Winston-Salem, NC, USA

Correspondence: Dr S-Y Cheng, Gene regulation section, Laboratory of Molecular Biology, National Cancer Institute, 37 Convent Dr, Room 5128, Bethesda MD 20892-4264, USA. E-mail: chengs@mail.nih.gov

Received 22 May 2008; Revised 8 September 2008; Accepted 23 September 2008; Published online 10 November 2008.

Abstract

Inactivation and silencing of PTEN have been observed in multiple cancers, including follicular thyroid carcinoma. PTEN (phosphatase and tensin homologue deleted from chromosome 10) functions as a tumour suppressor by opposing the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT) signalling pathway. Despite correlative data, how deregulated PTEN signalling leads to thyroid carcinogenesis is not known. Mice harbouring a dominant-negative mutant thyroid hormone receptor (TR^PV/PV mice) spontaneously develop follicular thyroid carcinoma and distant metastases similar to human cancer. To elucidate the role of PTEN in thyroid carcinogenesis, we generated TR^PV/PV mice haploinsufficient for Pten (TR^PV/PVPten^+/- mouse). PTEN deficiency accelerated the progression of thyroid tumour and increased the occurrence of metastasis spread to the lung in TR^PV/PVPten^+/- mice, thereby significantly reducing their survival as compared with TR^PV/PVPten^+/+ mice. AKT activation was further increased by two-fold in TR^PV/PVPten^+/- mice thyroids, leading to increased activity of the downstream mammalian target of rapamycin (mTOR)–p70S6K signalling and decreased activity of the forkhead family member FOXO3a. Consistently, cyclin D1 expression was increased. Apoptosis was decreased as indicated by increased expression of nuclear factor-B (NF-B) and decreased caspase-3 activity in the thyroids of TR^PV/PVPten^+/- mice. Our results indicate that PTEN deficiency resulted in increased cell proliferation and survival in the thyroids of TR^PV/PVPten^+/- mice. Altogether, our study provides direct evidence to indicate that in vivo, PTEN is a critical regulator in the follicular thyroid cancer progression and invasiveness.