Proto-oncogene PBF/PTTG1IP Regulates Thyroid Cell Growth and Represses Radioiodide Treatment

Abstract

Pituitary tumor transforming gene (PTTG)-binding factor (PBF or PTTG1IP) is a little characterized protooncogene that has been implicated in the etiology of breast and thyroid tumors. In this study, we created a murine transgenic model to target PBF expression to the thyroid gland (PBF-Tg mice) and found that these mice exhibited normal thyroid function, but a striking enlargement of the thyroid gland associated with hyperplastic and macrofollicular lesions. Expression of the sodium iodide symporter (NIS), a gene essential to the radioiodine ablation of thyroid hyperplasia, neoplasia, and metastasis, was also potently inhibited in PBF-Tg mice. Critically, iodide uptake was repressed in primary thyroid cultures from PBF-Tg mice, which could be rescued by PBF depletion. PBF-Tg thyroids exhibited upregulation of Akt and the TSH receptor (TSHR), each known regulators of thyrocyte proliferation, along with upregulation of the downstream proliferative marker cyclin D1. We extended and confirmed findings from the mouse model by examining PBF expression in human multinodular goiters (MNG), a hyperproliferative thyroid disorder, where PBF and TSHR was strongly upregulated relative to normal thyroid tissue. Furthermore, we showed that depleting PBF in human primary thyrocytes was sufficient to increase radioiodine uptake. Together, our findings indicate that overexpression of PBF causes thyroid cell proliferation, macrofollicular lesions, and hyperplasia, as well as repression of the critical therapeutic route for radioiodide uptake. Cancer Res; 71(19); 6153-64. Ó2011 AACR.

Regulation of Pituitary Tumor Transforming Gene (PTTG) Expression and Phosphorylation in Thyroid Cells

“…Western blot analyses were performed as we have described previously (3,12,47,48). Blocking was followed by incubation with specific antibodies against hPTTG (2 g/mL) (Invitrogen), CDC-2 (1:1000), SP1 (1:500), phospho-P44/42 ERK1/2 (extracellular signal-regulated kinase 1/2) (1:1000), phospho-AKT (protein kinase B) (1:1000) (Cell Signaling Technology-New England Biolabs), and proliferating cell nuclear antigen (PCNA) (1:1000) (Santa Cruz Biotechnology).…”

“…The generation of the hPTTG-Tg transgenic line (FVB/N strain, both sexes) was performed by microinjection of fertilized mouse oocytes with the Tg-hPTTG-FLAG transgene and subsequent transfer into pseudopregnant females (Transgenic Mouse Facility, University of Birmingham, Birmingham, United Kingdom) (47, 50 -52). Transgene copy number was determined by real-time RT-PCR (53) in relation to the Dscam gene (47). Pttg Ϫ/Ϫ knockout mice (c57BL6 strain, both sexes) were kindly provided by Professor Melmed (Cedars-Sinai Medical Center, University of California, Los Angeles, California), as previously described (13,54).…”

Overexpression of Interleukin-4 in the Thyroid of Transgenic Mice Upregulates the Expression ofDuox1and the Anion Transporter Pendrin

“…However, no significant increase in iodide organification was seen in transgenic thyroid tissues. A thyroid mouse model with overexpression of the proto-oncogene pituitary tumor transforming gene-binding factor also showed modified thyroid architecture that featured enlarged follicles (75), but this phenotype, which was associated with hyperproliferative lesions, was not observed in Thyr-IL-4 mice. As such, the follicular volume may have resulted from a bidirectional transepithelial transport of basal to apical Cl -and an opposite Na + flux (76).…”

Pathological processes and therapeutic advances in radioiodide refractory thyroid cancer

“…Furthermore, global DNA hypomethylation and specific DNA hypermethylation of several gene promoters and enhancers, including those driving expressions of hNIS, TSHR and tumor suppressor genes, have been observed in BRAF V600E-mutant PTCs and are associated with a silenced expression of the corresponding genes, resulting in less-differentiated tumor cells (Hu et al 2006, Lee et al 2008, Hou et al 2011, Rodriguez-Rodero et al 2013, Choi et al 2014. These epigenetic changes could also lead to a dysregulated expression of pituitary tumor transforming gene (PTTG) and PTTG binding factor, factors that are known to repress hNIS expression, impair RAI uptake and to predict poor clinical outcome (Read et al 2011(Read et al , 2017. Moreover, histone deacetylase inhibitors have been demonstrated to elicit beneficial effects on hNIS expression and iodide uptake capacity in vitro, which however was not clinically validated (Hou et al 2010, Cheng et al 2016, Nilubol et al 2017.…”