Endocrine Abstracts

Type 1 deiodinase (D1) catalyses deiodination of tyroxine (T₄), which leads either to synthesis of triiodothyronine or reverse triiodothyronine (rT₃). Triiodothyronine (T₃) regulates the expression of many tumour suppressor genes and oncogenes. We previously revealed that the expression of the whole pool of D1 transcripts was dramatically lowered in ccRCC tissues. One of the mechanism resulting in this aberration could be miRNA-mediated repression of target mRNAs.

The aim of our work was to study the potential regulation of D1 expression by microRNAs in clear cell Renal Cell Carcinoma (ccRCC), which is the most common type of renal cancers (75% of primary renal malignancies). Using semi-quantitative real-time PCR we have analyzed 34 samples of ccRCC tumours (T) and two types of control: the contralateral pole of the same kidney not infiltrated by cancer (C) and samples from patients suffering from other, nonneoplastic kidney abnormalities (N).

Bioinformatic analysis revealed the presence of multiple sites for microRNAs in 3’UTR of D1. We observed statistically significant (P<0.0001) over five fold increase in the expression of miR-224 and three fold increase in the expression of miR-383, in samples T compared to control samples C. In order to evaluate whether D1 was effectively a target of miR-224 and miR-383, the D1 3’UTR was cloned downstream of a luciferase reporter gene vector; the HeLa cell line were then transfected with the over expressing vector and the reporter construct, with the relative luciferase activity showing that miR-224 led to decreased activity of the reporter gene, thus indicating binding with the 3’UTR and destabilization of productive translation of luciferase mRNA.

Conclusions: We identify the miR-224 as a regulator of the D1 mRNA expression.