Abstract 3065: The role of miR-18b in MDM2-p53 pathway signaling and melanoma progression.

Abstract

Abstract MicroRNAs regulate gene expression and are differentially expressed in various tumors. While p53 is inactivated by point mutations in many tumors, melanomas rarely harbor mutations in the p53 gene. Here we report the biological role of miR-18b in melanoma via targeting the MDM2-p53 pathway. Expression of miR-18b was significantly suppressed in melanoma specimens and cell lines by virtue of hypermethylation, and was re-induced in melanoma cell lines following 5-AZA-deoxycytidine treatment. Lower levels of miR-18b expression in primary melanoma were associated with significantly reduced overall survival. MDM2 was identified as a target of miR-18b action, as miR-18b significantly suppressed the luciferase activity of a reporter plasmid containing the 3’UTR sequence of MDM2 complementary to the miR-18b seed sequence. Induction of miR-18b expression in melanoma cells resulted in reduced MDM2 expression, upregulation of p53 as well as PUMA and p21, and suppression of the anti-apoptotic BCL2 and BCL-XL genes, resulting in significant suppression of melanoma cell proliferation. The effects of miR-18b overexpression on the p53 pathway and on melanoma cell growth were reversed by MDM2 overexpression. Stable overexpression of miR-18b produced potent tumor suppressor activity, as evidenced by suppressed melanoma cell proliferation, induction of apoptosis, and reduced tumor cell growth in vivo. In addition, miR-18b overexpression suppressed melanoma cell migration and invasiveness, and reversed epithelial-to-mesenchymal transition in melanoma cell lines. Our results demonstrate a novel role for miR-18b as a tumor suppressor in melanoma, identify the MDM2-p53 pathway as a target of miR-18b action, and suggest miR-18b overexpression as a novel strategy to reactivate the p53 pathway in human tumors. Citation Format: Altaf A. Dar, Shahana Majid, David de Semir, Vladimir Bezrookove, Mehdi Nosrati, Mohammed Kashani-Sabet. The role of miR-18b in MDM2-p53 pathway signaling and melanoma progression. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3065. doi:10.1158/1538-7445.AM2013-3065