MDA-7/IL-24 regulates the miRNA processing enzyme DICER through downregulation of MITF.

Abstract

Melanoma differentiation-associated gene-7/interleukin-24 (<i>mda-7/IL-24</i>) is a multifunctional cytokine displaying broad-spectrum anticancer activity in vitro or in vivo in preclinical animal cancer models and in a phase 1/2 clinical trial in patients with advanced cancers. <i>mda-7/IL-24</i> targets specific miRNAs, including miR-221 and miR-320, for down-regulation in a cancer-selective manner. We demonstrate that <i>mda-7/IL-24</i>, administered through a replication incompetent type 5 adenovirus (Ad.<i>mda-7</i>) or with His-MDA-7/IL-24 protein, down-regulates DICER, a critical regulator in miRNA processing. This effect is specific for mature miR-221, as it does not affect Pri-miR-221 expression, and the DICER protein, as no changes occur in other miRNA processing cofactors, including DROSHA, PASHA, or Argonaute. DICER is unchanged by Ad.<i>mda-7/IL-24</i> in normal immortal prostate cells, whereas Ad.<i>mda-7</i> down-regulates DICER in multiple cancer cells including glioblastoma multiforme and prostate, breast, lung, and liver carcinoma cells. MDA-7/IL-24 protein down-regulates DICER expression through canonical IL-20/IL-22 receptors. Gain- and loss-of-function studies confirm that overexpression of DICER rescues deregulation of miRNAs by <i>mda-7/IL-24</i>, partially rescuing cancer cells from <i>mda-7/IL-24-</i>mediated cell death. Stable overexpression of DICER in cancer cells impedes Ad.<i>mda-7</i> or His-MDA-7/IL-24 inhibition of cell growth, colony formation, PARP cleavage, and apoptosis. In addition, stable overexpression of DICER renders cancer cells more resistant to Ad.<i>mda-7</i> inhibition of primary and secondary tumor growth. MDA-7/IL-24-mediated regulation of DICER is reactive oxygen species-dependent and mediated by melanogenesis-associated transcription factor. Our research uncovers a distinct role of <i>mda-7/IL-24</i> in the regulation of miRNA biogenesis through alteration of the MITF-DICER pathway.