Epigenetic silencing of miR-708 enhances NF-?B signaling in chronic lymphocytic leukemia.

Baer C, Oakes CC, Ruppert AS, Claus R, Kim-Wanner SZ, Mertens D, Zenz T, Stilgenbauer S, Byrd JC, Plass C
Int J Cancer 137 1352-61 09/15/2015

Abstract

MicroRNAs (miRNAs) are post-transcriptional regulators of gene expression and their deregulation is involved in tumor development. Epigenetic gene silencing in cancer by DNA methylation contributes to the silencing of tumor-suppressor genes, including miRNAs. We have recently shown that the promoter of miR-708 is aberrantly methylated in chronic lymphocytic leukemia (CLL). To characterize the molecular signaling networks that are influenced by miR-708, we performed a luciferase-based screen evaluating the effects of ectopic miR-708 expression on leukemia-relevant signaling pathways. We found that miR-708 strongly repressed NF-?B signaling, a pathway known to be deregulated in CLL. Among the predicted miR-708 targets was IKKß (inhibitor of kappa light polypeptide gene enhancer in B cells, kinase-ß/IKBKB), a key kinase facilitating NF-?B signaling. We validated the interaction of miR-708 with the 3'-untranslated region of IKKß and found that miR-708 overexpression represses endogenous IKKß. Phosphorylation of the IKKß target I?Ba and expression of known NF-?B target genes were impaired by miR-708. Furthermore, we identified an enhancer region downstream of the miR-708 promoter that displays a distinct DNA methylation status in CLL. High enhancer methylation is significantly correlated with lower miR-708 expression and is predominantly found in patients with poor prognosis and shorter time to treatment. These results demonstrate that miR-708 regulates the NF-?B pathway by targeting IKKß, and that methylation of a key enhancer region contributes to its suppression in CLL.

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