Reciprocal interplay of miR-497 and MALAT1 promotes tumourigenesis of adrenocortical cancer.

Adrenocortical carcinoma (ACC) has high recurrence rates and poor prognosis with limited response to conventional cancer therapy. Recent contributions of high throughput transcriptomic profiling identified microRNA-497 (miR-497) as significantly underexpressed; whilst long noncoding RNA (lncRNA) MALAT1 (metastasis-associated lung adenocarcinoma transcript 1) as overexpressed in ACC. miR-497 is located in the chromosomal region 17p13.1, in which there is a high frequency of loss of heterozygosity in ACC. We aim to investigate the interaction of miR-497 and MALAT1 in ACC and its functional roles in the process of tumourigenesis. In this study, we demonstrated miR-497 post-transcriptionally repressed MALAT1 whilst MALAT1 also competes for miR-497 binding to its molecular target, eIF4E (eukaryotic translation initiation factor 4E). We showed that overexpression of miR-497 and silencing of MALAT1 suppressed cellular proliferation and induced cell cycle arrest through downregulation of eIF4E expression. Furthermore, MALAT1 directly binds to SFPQ (Splicing Factor Proline and Glutamine Rich) protein, indicating its multifaceted roles in ACC pathophysiology. This is the first study to identify the feedback axis of miR-497-MALAT1/eIF4E in ACC tumourigenesis, providing novel insights into the molecular functions of noncoding RNAs in ACC.