title: FOXO1 controls thyroid cell proliferation in response to TSH and IGF-I and is involved in thyroid tumorigenesis.
abstract: TSH and insulin/IGF-I synergistically induce the proliferation of thyroid cells mainly through the cAMP and phosphatidylinositol 3-kinase (PI3K) pathways. However, the events involved in this cooperative induction remain unknown, and molecules that are potentially controlled by both TSH and IGF-I are interesting candidates as integrators of both stimuli. The finding that the PI3K pathway is frequently activated in thyroid malignancies has attracted attention to this pathway in the thyroid field. One of the targets of PI3K is Forkhead box O (FoxO)-1, a widely expressed transcription factor involved in a variety of cellular processes such as differentiation, proliferation, and apoptosis. Here we show that FoxO1 is highly expressed in differentiated rat thyroid cells and human thyroid tissue compared with human thyroid tumor-derived cells and surgically removed thyroid tumors, in which its expression is reduced. In differentiated cells, TSH/cAMP treatment decreases FoxO1 mRNA and protein levels through proteasome activation, whereas both TSH and IGF-I control FoxO1 localization by promoting a rapid exclusion from the nucleus in an Akt-dependent manner. FoxO1 can control p27(KIP1) expression in differentiated and tumor cells of the thyroid. Furthermore, FoxO1 reexpression in tumor cells promotes a decrease in their proliferation rate, whereas FoxO1 interference in differentiated cells increases their proliferation. These data point to an important role of FoxO1 in mediating the effects of TSH and IGF-I on thyroid cell proliferation and provide a link between loss of FoxO1 expression and the uncontrolled proliferation of thyroid tumor cells.
authors.affiliation: Instituto de Investigaciones Biomédicas Alberto Sols, Consejo Superior de Investigaciones Científicas, Universidad Autónoma de Madrid, 28029 Madrid, Spain.
authors.forename: Miguel A
authors.initials: MA
authors.lastname: Zaballos
authors.forename: Pilar
authors.initials: P
authors.lastname: Santisteban
mesh_terms: D021581:Active Transport, Cell Nucleus; D000818:Animals; D002277:Carcinoma / Q000378:metabolism*; D002291:Carcinoma, Papillary; D002460:Cell Line; D049109:Cell Proliferation; D002471:Cell Transformation, Neoplastic / Q000378:metabolism*; D000242:Cyclic AMP / Q000378:metabolism; D050760:Cyclin-Dependent Kinase Inhibitor p27 / Q000378:metabolism; D000071161:Forkhead Box Protein O1; D051858:Forkhead Transcription Factors / Q000235:genetics / Q000378:metabolism*; D015870:Gene Expression; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000502:physiology*; D020935:MAP Kinase Signaling System; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D051057:Proto-Oncogene Proteins c-akt / Q000037:antagonists & inhibitors / Q000378:metabolism; D051381:Rats; D000077273:Thyroid Cancer, Papillary; D013961:Thyroid Gland / Q000473:pathology*; D013964:Thyroid Neoplasms / Q000378:metabolism*; D013972:Thyrotropin / Q000502:physiology*
chemical_list: C493962:Cdkn1b protein, rat; C085126:FOXO1 protein, human; D000071161:Forkhead Box Protein O1; D051858:Forkhead Transcription Factors; D047428:Protein Kinase Inhibitors; D050760:Cyclin-Dependent Kinase Inhibitor p27; D007334:Insulin-Like Growth Factor I; D013972:Thyrotropin; D000242:Cyclic AMP; C494920:Akt1 protein, rat; C494923:Akt2 protein, rat; D051057:Proto-Oncogene Proteins c-akt; D046988:Proteasome Endopeptidase Complex