Targeted Foxe1 Overexpression in Mouse Thyroid Causes the Development of Multinodular Goiter But Does Not Promote Carcinogenesis.

Recent genome-wide association studies have identified several single nucleotide polymorphisms in the forkhead box E1 gene (FOXE1) locus, which are strongly associated with the risk for thyroid cancer. In addition, our recent work has demonstrated FOXE1 overexpression in papillary thyroid carcinomas. To assess possible contribution of Foxe1 to thyroid carcinogenesis, transgenic mice overexpressing Foxe1 in their thyroids under thyroglobulin promoter (Tg-Foxe1) were generated. Additionally, Tg-Foxe1 mice were exposed to x-rays at the age of 5 weeks or crossed with Pten(+/-) mice to examine the combined effect of Foxe1 overexpression with radiation or activated phosphatidylinositol-3-kinase/Akt pathway, respectively. In 5- to 8-week-old Tg-Foxe1 mice, severe hypothyroidism was observed, and mouse thyroids exhibited hypoplasia of the parenchyma. Adult 48-week-old mice were almost recovered from hypothyroidism, their thyroids were enlarged, and featured colloid microcysts and multiple benign nodules of macrofollicular-papilloid growth pattern, but no malignancy was found. Exposure of transgenic mice to 1 or 8 Gy of x-rays and Pten haploinsufficiency promoted hyperplastic nodule formation also without carcinogenic effect. These results indicate that Foxe1 overexpression is not directly involved in the development of thyroid cancer and that proper Foxe1 dosage is essential for achieving normal structure and function of the thyroid.