Effects of Dicer Inactivation in the Developing Mouse Adrenal Cortex and Micro-RNAs in Adrenocortical Carcinoma.

Abstract

Adrenocortical carcinoma (ACC) is a rare yet highly aggressive form of cancer with limited treatment options and poor prognosis. Insulin-like growth factor 2 (IGF2) is one of the most highly expressed genes in sporadic ACC, and is an adrenal mitogen. In addition, a microRNA (miRNA), miR-483-3p, is located in an intronic region of IGF2, suggesting co-expression of IGF2 and miR-483-3p in ACC. miRNAs are small, endogenous, non-protein coding RNAs that are an important means of post-transcriptional gene regulation, and have been implicated in numerous physiologic and disease processes. This thesis describes the correlation between IGF2 and miR-483-3p in primary human ACC samples, providing rationale for the development of molecular tools designed to aid in the study of the role of IGF2 and miR-483-3p in ACC. Additionally, we describe the results of genetically deleting Dicer, a key miRNA processing enzyme, in the developing adrenal cortex. Adrenal Dicer knockout (KO) mice did not survive beyond 24-48 hours post-parturition, and were characterized by rapid failure of the adrenal cortex during late gestation at embryonic day 18.5 (E18.5). Specifically, Dicer KO adrenal cortical cells underwent apoptosis and were completely depleted by E18.5. The adrenal medulla, however, remained in E18.5 Dicer KO adrenals, suggesting that initial adrenal cortex formation was unperturbed by Dicer inactivation. To further characterize Dicer KO embryonic adrenals, we subjected purified RNA isolated from control and KO adrenals at both E15.5 and E16.5 to mRNA and miRNA microarray analyses. Intriguingly, Dicer KO adrenals demonstrated significant up-regulation of transcripts belonging to the genes Nr6a1 and Acvr1c, whose functions in adrenocortical development and physiology are currently poorly understood. Finally, several down-regulated miRNAs in Dicer KO adrenals were consistently predicted to target mRNA transcripts from these genes. The increased expression of Nr6a1 and Acvr1c gene transcripts in Dicer KO adrenals may suggest a role for miRNA mediated regulation of these genes, which may in turn be important in normal adrenal development.