Understanding the dosage-dependent role of Dicer1 in thyroid tumorigenesis

Multiple studies suggest Dicer1 as a haploinsufficient tumor suppressor gene: while the loss of one allele promotes tumorigenesis, the complete loss of Dicer1 prevents tumor formation. To study the impact of Dicer1 partial or total loss in papillary thyroid carcinoma cells in vitro, we generated stable Dicer1 (+/-) cell lines by CRISPR-Cas9 from TPC1 cell line. No Dicer1 (-/-) cell lines could be generated. Therefore, siRNA against Dicer1 was transfected into Dicer1 (+/-) cell lines to further decrease its expression. RNA sequencing and transcriptomic analysis revealed alterations in proliferation, cell cycle and cell locomotion. BrdU staining revealed a slow-down of the cell cycle, with lower percentages of cells in S-phase and higher percentages of cells in G0-G1-phase. Furthermore, transwell invasion and migration assays showed a decrease of invasive and migrating cells following transfection of Dicer1 siRNA. These results were confirmed in two supplementary thyroid cell lines, BCPAP and H-Tori3. Additionally, to achieve high protein levels, we performed Dicer1 plasmid transfection and we observed reduced proliferation and invasion as well as increased apoptosis. Globally, our results allow us to better understand the function of Dicer1 in thyroid cancer tumorigenesis and suggest Dicer1 as an attractive target for novel therapeutic strategies.