Endocrine Abstracts

The abnormal expression of miRNAs has been linked to the development of multiple tumors, including thyroid tumors ^1,2. Dicer1 is an essential enzyme for the biogenesis of microRNAs that has been found to be dysregulated in various cancers, notably, its expression is decreased in papillary thyroid carcinoma (PTC) ^3,4. Multiple studies suggest Dicer1 as haploinsufficient tumor suppressor gene: while the loss of one allele promotes tumorigenesis, the complete loss of Dicer1 prevents tumor formation ^5,6,7,8. So far, the impact of partial or total loss of Dicer1 in thyroid cancer has never been addressed. To further understand the consequences of partial or complete inactivation of Dicer1 in thyroid tumorigenesis, we inactivated one (+/-) or two alleles (-/-) of Dicer1 in thyroid cells in a transgenic mice model developing a PTC, following RET/PTC3 oncogene expression exclusively in the thyroid. While homozygous inactivation led to a significant decrease in tumor growth, tumors with hemizygous loss of Dicer1 were larger. Additionally, homozygous inactivation led to a significant increase of vimentin positive cells. All tumors showed normal expression of thyroglobulin and T4. In parallel, the impact of Dicer1 partial or total loss was assessed in vitro. Stable Dicer (+/-) cell lines were generated by Crispr-cas9 from TPC1 cells, a human PTC derived cell line largely characterized. No (-/-) cell lines could be generated, supporting the idea that Dicer1 loss is lethal. 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 following siDicer1 transfection 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, as well as cyclin A, B and E downregulation. Furthermore, transwell invasion and migration assays showed a decrease of invasive and migrating cells following transfection of siRNA against Dicer1. These results were confirmed in another PTC derived cell line, BCPAP and one non tumoral thyroid cell line, HTori3. 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.

References

¹Yong Peng et Carlo M Croce, « The Role of MicroRNAs in Human Cancer», Signal Transduction and Targeted Therapy 1, no 1 (28 janvier 2016): 15004, https://doi.org/10.1038/sigtrans.2015.4.

²Manuel Saiselet et al., « miRNA Expression and Function in Thyroid Carcinomas: A Comparative and Critical Analysis and a Model for Other Cancers», Oncotarget 7, no 32 (9 août 2016): 52475-92, https://doi.org/10.18632/oncotarget.9655.

³Piril Erler et al., « Dicer Expression and microRNA Dysregulation Associate with Aggressive Features in Thyroid Cancer», Surgery 156, no 6 (décembre 2014): 1342-50, https://doi.org/10.1016/j.surg.2014.08.007.

⁴Julia Ramírez-Moya et al., « Impaired microRNA Processing by DICER1 Downregulation Endows Thyroid Cancer with Increased Aggressiveness», Oncogene 38, no 27 (juillet 2019): 5486-99, https://doi.org/10.1038/s41388-019-0804-8.

⁵Vijay Swahari, Ayumi Nakamura, et Mohanish Deshmukh, « The Paradox of Dicer in Cancer», Molecular & Cellular Oncology 3, no 3 (3 mai 2016): e1155006, https://doi.org/10.1080/23723556.2016.1155006.

⁶B Zhang et al., « A Dosage-Dependent Pleiotropic Role of Dicer in Prostate Cancer Growth and Metastasis», Oncogene 33, no 24 (12 juin 2014): 3099-3108, https://doi.org/10.1038/onc.2013.281.

⁷Madhu S. Kumar et al., « Dicer1 Functions as a Haploinsufficient Tumor Suppressor», Genes & Development 23, no 23 (1 décembre 2009): 2700-2704, https://doi.org/10.1101/gad.1848209.

⁸I Lambertz et al., « Monoallelic but Not Biallelic Loss of Dicer1 Promotes Tumorigenesis in vivo», Cell Death & Differentiation 17, no 4 (avril 2010): 633-41, https://doi.org/10.1038/cdd.2009.202.