The thyroid transcription factor Forkhead Box E1 (FOXE1) is part of a network of factors that help maintain thyroid differentiation via transcriptional regulation of thyroid specific genes including thyroglobulin and thyroid peroxidase (1). Germline inactivating mutations in the DNA-binding or forkhead domain (FHD) of FOXE1 result in Bamforth syndrome, characterised by thyroid agenesis, cleft palate and choanal atresia. Population-based studies have demonstrated an association of single nucleotide polymorphisms close to FOXE1 with thyroid cancer (2).
The objective of the study was to identify novel mutations in FOXE1 in papillary thyroid cancer (PTC) and to assess the effect of these mutations on protein expression and transcriptional function on FOXE1 responsive promoters.
Patients and Methods
The coding region of FOXE1 was sequenced in 120 patients with PTC and 110 patients with multinodular goitre (MNG). In vitro studies were performed to examine the protein expression and transcriptional function of wild-type and mutant FOXE1. A molecular model of the FHD of FOXE1 was generated using the SWISS-MODEL online server with the three-dimensional structure of FOXD3 as a template.
Three somatic missense mutations in the FHD of FOXE1 were detected in PTC resulting in the following amino acid substitutions: P54Q, K95Q and L112F. One additional mutation was detected in MNG: G140R. Two of the PTC were clinically recurrent tumours also positive for BRAFV600E mutation while one was a BRAF mutation-negative microPTC. In vitro studies demonstrated significant impairment in transcriptional activation by all four FOXE1 mutants which was not due to differences in protein expression. Molecular modelling localised three of the mutations to highly conserved regions of the FHD.
We have identified novel somatic mutations of FOXE1 in PTC. Mutational inactivation of FOXE1 is an uncommon event in thyroid tumours but may contribute to thyroid carcinogenesis and dedifferentiation in concert with other oncogenic drivers.