Endocrine Abstracts

Adrenocortical carcinoma (ACC) is a rare malignancy with dismal prognosis. Deregulated microRNA (miRNA) expression has been implicated in ACC aggressiveness. Nevertheless, the mechanisms underlying such deregulations remain unknown. Aberrant Wnt/β-Catenin signaling has been reported in about 40% of ACC and is associated with poor outcome. In the present work, we aimed to investigate the link between constitutive activation of Wnt/β-Catenin pathway and miRNA expression alterations in ACC. To this end, we used inducible shRNA-mediated gene silencing of β-Catenin (β-Cat) in ACC cells. The miRnome of ACC cells was analyzed using RNA-Sequencing. Selected miRNAs and mRNAs were validated using quantitative PCR and functional experiments. Prognostic values of Wnt/β-Catenin pathway components or mutational status and their correlations with miRNA/mRNA expressions were determined in COMETE-ENSAT and TCGA cohorts. We carried out the first miRnome analysis in β-Catenin-deficient (β-Cat-) ACC cells. Twelve upregulated miRNAs and 42 downregulated miRNAs among which miR-139-5p and miRNAs of the 14q32 locus were identified in β-Cat- cells. Downregulation of selected poor prognosis-associated miRNAs was confirmed using RT-qPCR. Remarkably, the expression of the intronic miR-139-5p was decreased by 90% in β-Cat- cells with a concomitant repression of its host gene phosphodiesterase 2A and upregulation of its target gene N-Myc Downstream-Regulated Gene 4 (NDRG4). In ACC patients, miR-139-5p levels were highly correlated with the levels of PDE2A and anti-correlated with those of NDRG4. MiR-139-5p and PDE2A expressions were higher in patients with mutations in components of Wnt/β-Catenin signaling pathway or high expression of LEF1, with LEF1 proving a better predictor of prognosis than Wnt/β-Catenin signaling pathway mutational status. These findings suggest that in addition to inducing protein-coding target genes in ACC, constitutively active Wnt/β-Catenin signaling upregulates the expression of a subset of miRNAs involved in tumour aggressiveness and poor clinical outcome.