Identification of targets of Twist1 transcription factor in anaplastic thyroid cancer

Abstract

Thyroid cancer is the most common malignancy of endocrine organs and accounts for about 1% of newly diagnosed cancer cases. Anaplastic thyroid carcinoma (ATC) is one of the most aggressive human tumors; it is characterized by local invasion, distant metastasis, chemoresistance and radioresistance. Effective systemic therapy capable of reversing the aggressive biology of this disease is currently not available. Therefore, there is an urgent need for a better understanding of the molecular mechanisms underlying anaplastic thyroid cancer pathogenesis. Through, a cDNA microarray analysis we have isolated Twist1 as a gene up-regulated in ATC. Twist1 is a basic helix-loop-helix transcription factor that has been shown to contribute to cancer development and progression but its mechanism of action is poorly defined. In this Dissertation we showed that approximately 50% of ATCs up-regulated Twist1 with respect to normal thyroids as well as to poorly and well-differentiated thyroid carcinomas. Silencing of Twist1 by RNA interference in ATC cells reduced cell migration and invasion and increased sensitivity to apoptosis. The ectopic expression of Twist1 in thyroid cancer cells induced resistance to apoptosis and increased cell migration and invasion. To uncover the molecular mechanisms underlying Twist1 biological effects, we have performed a gene expression profile of Twist1 ectopically expressing thyroid cancer TPC cells in comparison to vector control cells. We founded 158 genes up-regulated and 221 genes down-regulated by more than 1.5 fold in TPC-Twist1 cells. We used the Ingenuity Systems Pathway Analysis (IPA) software to classify these genes. Consistent with the biological function of Twist1 in ATC, the top three molecular and cellular functions enriched in TPC-Twist1 cells were: cellular movement, cellular growth and proliferation, cell death and survival. In this dissertation we focused on the up-regulated genes by more than 4 fold. Silencing of the 11 top up-regulated genes reduced cell viability of TPC-Twist1 cells. Silencing of COL1A1, KRT7, PDZK1 induced also apoptosis. Silencing of HS6ST2, THRB, ID4, RHOB, and PDZK1IP, also impaired cell migration and invasion of TPC-Twist1 cells. Thus, our data demonstrate that Twist1 plays a key role in determining malignant features of anaplastic thyroid cancer cells. These effects are mediated by a set of genes whose expression is under Twist1 control. The identified target genes are potential novel molecular determinants of ATC.