miR-181 interacts with signaling adaptor molecule DENN/MADD and enhances TNF-induced cell death

MicroRNAs are small noncoding RNAs, which regulate the expression of protein coding transcripts through mRNA degradation or translational inhibition. Numerous reports have highlighted the role of miRNAs in regulating cell death pathways including the expression of genes involved in the induction of apoptosis. Tumor necrosis factor alpha (TNF-alpha) is a proinflammatory cytokine which can send pro-death signals through its receptor TNFR1. Diverse adaptor molecules including DENN/MADD adaptor protein have been shown to modulate TNF-alpha pro-death signaling via recruitment of MAP kinases to TNFR1 and activation of pro-survival NF kappa B signaling. Herein, we investigated the role of microRNA-181 (miR-181) in regulating DENN/MADD expression levels and its subsequent effects on TNF-alpha-induced cell death. Using bioinformatics analyses followed by luciferase reporter assays we showed that miR-181 interacts with the 3' UTR of DENN/MADD transcripts. miR-181 overexpression also led to decreased endogenous DENN/MADD mRNA levels in L929 murine fibroblasts. Flow cytometric analysis of miR-181 transfected cells showed this miRNA accentuates mitochondrial membrane potential loss caused by TNF-alpha. These findings were associated with enhanced apoptosis of L929 cells following TNF-alpha treatment. Overall, these data point to the potential role of miR-181 in regulating TNF-alpha pro-death signaling, which could be of importance from pathogenesis and therapeutic perspectives in inflammatory disorders associated with tissue degeneration and cell death.