Abstract 481: Diminished microRNA-29b results in overexpression of BRD4 and BRD4-regulated oncogenes in cutaneous T-cell lymphoma (2017)

Abstract Cutaneous T-cell lymphoma (CTCL) is a CD4+ T-cell malignancy that affects the skin but may disseminate systemically, and there are no long-term effective therapeutic strategies. Here, we characterized the therapeutic efficacy of manipulating the tumor suppressor microRNA-29b (miR-29b) and its target bromodomain-containing protein 4 (BRD4) in CTCL pathogenesis. Using primary CD4+ T-cells we determined that miR-29b expression is significantly decreased in patients compared to healthy controls (0.007±0.002, n=9 vs 1.008±0.052, n=6, p&amp;lt;0.0001). We utilized miR-29b-/- mice and bortezomib, a proteasome inhibitor known to increase miR-29b levels, to confirm the inverse relationship between miR-29b and BRD4 (Mishra, A. et al. Cancer Cell, 2012). Diminished miR-29b level resulted in increased BRD4 protein expression (1.87±0.29, p=0.014), while increase in miR-29b, as in bortezomib-treated CTCL cell lines, results in nearly undetectable BRD4 protein. We also observed increased genome-wide occupancy of BRD4 at regulatory regions in CTCL patients, an effect that is reversed with BRD4 inhibitor, JQ1, to similar levels as observed in healthy control CD4+ T-cells. Specifically, oncogene loci of NOTCH1 and RBPJ demonstrated enhanced BRD4 binding in CTCL patients, with resultant increases in mRNA in patient vs normal donors (4.16±0.98, p=0.024; 3.02±0.54, p=0.012). Further, in vivo treatment of interleukin-15 (IL-15) transgenic mice (Mishra, A. et al. Cancer Discovery, 2016) with JQ1 prevented CTCL development and decreased lesion severity (3.37±0.49, n=8 vs 6.0±0.45, n=5, p=0.004). Skin from JQ1-treated mice demonstrated decreased protein expression of BRD4, NOTCH1, and RBPJ, consistent with our findings in patients and CTCL cell lines. Bortezomib treatment of CTCL mice yielded similar results to JQ1 in vivo, while miR-29b levels were elevated in treated mice vs control animals. Since IL-15 signals through its receptor complex, we evaluated and observed increased BRD4 binding at IL-15 receptor αβγ gene loci in CTCL patients, which was reversed with both JQ1 and bortezomib treatment. Thus, we conclude that diminished miR-29b results in increased expression and subsequent binding of BRD4 at regulatory regions of known oncogenes in CTCL cells including NOTCH1, RBPJ, and the IL-15 receptor complex. We confirm the potential therapeutic utility of targeting this pathway in vivo, by direct displacement of BRD4 by JQ1, or by rescue of miR-29b expression by bortezomib. We therefore describe a novel targetable oncogenic pathway featuring IL-15, miR-29b, and BRD4 in CTCL. Citation Format: Rebecca Kohnken, Jing Wen, Bethany Mundy-Bosse, Max Yano, Leah Grinshpun, Kathleen McConnell, Ashleigh Keiter, Alex Hartlage, James Bradner, Michael Caligiuri, Pierluigi Porcu, Anjali Mishra. Diminished microRNA-29b results in overexpression of BRD4 and BRD4-regulated oncogenes in cutaneous T-cell lymphoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 481. doi:10.1158/1538-7445.AM2017-481