TTF-1/Nkx2.1 functional connection with mutated EGFR relies on LRIG1 and ß-catenin pathways in lung cancer cells.

In non-small lung cancer, the expression of the transcription factor TTF-1/Nkx2.1 correlates with the presence of EGFR mutations, therefore TTF-1/Nkx2.1 expression is used to optimize an EGFR testing strategy and to guide clinical treatment. We investigate the molecular mechanisms underlying the functional connection between EGFR and TTF-1/Nkx2.1 gene expression in lung adenocarcinoma. Using the H1975 cell line as a non-small cell lung cancer model system and short hairpin RNA, we have selected clones with TTF-1/Nkx2.1 silenced expression. We have found that Leucine-rich immunoglobulin repeats-1 (LRIG1) gene is a direct target of TTF-1/Nkx2.1 and the transcription factor binding to the LRIG1 genomic sequence inhibits its gene expression. In TTF-1/Nkx2.1 depleted clones, we have found high levels of LRIG1 and decreased presence of EGFR protein. Furthermore, in TTF-1/Nkx2.1 depleted clones we detected a reduced ß-catenin level and we provide experimental evidence indicating that TTF-1/Nkx2.1 gene expression is regulated by ß-catenin. Published studies indicate that LRIG1 triggers EGFR degradation and that mutated EGFR induces ß-catenin activity. Hence, with the present study we show that mutated EGFR, enhancing ß-catenin, stimulates TTF-1/Nkx2.1 gene expression and, at the same time, TTF-1/Nkx2.1, down-regulating LRIG1, sustains EGFR pathway. Therefore, LRIG1 and ß-catenin mediate the functional connection between TTF-1/Nkx2.1 and mutated EGFR.

PDGFRα Regulates Follicular Cell Differentiation Driving Treatment Resistance and Disease Recurrence in Papillary Thyroid Cancer.

Dedifferentiation of follicular cells is a central event in resistance to radioactive iodine and patient mortality in papillary thyroid carcinoma (PTC). We reveal that platelet derived growth factor receptor alpha (PDGFRα) specifically drives dedifferentiation in PTC by disrupting the transcriptional activity of thyroid transcription factor-1 (TTF1). PDGFRα activation dephosphorylates TTF1 consequently shifting the localization of this transcription factor from the nucleus to the cytoplasm. TTF1 is required for follicular cell development and disrupting its function abrogates thyroglobulin production and sodium iodide transport. PDGFRα also promotes a more invasive and migratory cell phenotype with a dramatic increase in xenograft tumor formation. In patient tumors we confirm that nuclear TTF1 expression is inversely proportional to PDGFRα levels. Patients exhibiting PDGFRα at time of diagnosis are three times more likely to exhibit nodal metastases and are 18 times more likely to recur within 5years than those patients lacking PDGFRα expression. Moreover, high levels of PDGFRα and low levels of nuclear TTF1 predict resistance to radioactive iodine therapy. We demonstrate in SCID xenografts that focused PDGFRα blockade restores iodide transport and decreases tumor burden by >50%. Focused PDGFRα inhibitors, combined with radioactive iodine, represent an additional avenue for treating patients with aggressive variants of PTC.

Functional characterization of two novel mutations in TTF-1/NKX2.1 homeodomain in patients with benign hereditary chorea.

The thyroid transcription factor 1 (TTF-1) is encoded, on chromosome 14q13, by the gene termed TITF-1/NKX2.1. Mutations in this gene have been associated with chorea, hypothyroidism, and lung disease, all included in the "brain-thyroid-lung syndrome." We here describe two cases of novel missense mutations [NM_003317.3:c.516G>T and c.623G>C resulting in p.(Gln172His) and p.(Trp208Ser), respectively] in TITF-1/NKX2-1 in non-consanguineous patients. We provide a functional study of the role of the two mutations on the TTF-1 ability to bind DNA and to trans-activate both thyroid and lung specific gene promoters. Our results confirm the difficulty to correlate the TTF-1 activity with the clinical phenotype of affected patients and highlight the need to increase the limited knowledge we have on the activity of TTF-1 in neuronal cells.