Abstract 5189: The transcriptional regulation of the long non-coding RNA HOTAIR in ovarian cancer.

Abstract

The Polycomb Group (PcG) Repressive Complexes 1 and 2 (PRC1 and PRC2) maintain gene expression patterns by epigenetically modifying chromatin. PRC2 suppresses transcription by catalyzing the trimethylation of histone H3 at lysine 27 (H3K27me3), a hallmark of repressed chromatin. Although overexpression of PRC2 components has been implicated in cancer initiation, progression and metastasis how PRC2 is recruited to its target genes remains poorly understood. Recent work suggests the interaction of PRC2 with the long-non coding (lnc) RNA HOX transcript antisense intergenic RNA (HOTAIR) could serve as a potential guide to silence target genes, but the mechanism has yet to be defined. In this study, we performed whole transcriptome RNA-seq analysis of isogenic cisplatin- sensitive and -resistant A2780 ovarian cancer (OC) cell lines. Of the lncRNA examined, HOTAIR was markedly induced in the cisplatin resistant cells (5-fold upregulation compared to the cisplatin-sensitve A2780 parental line). shRNA depletion of HOTAIR resensitized the drug-resistant cells to cisplatin. Based on analysis of the HOTAIR promoter using luciferase assays, we identified two putative NF-κB binding sites and three E-box binding sites. To further investigate whether these sites contributed to HOTAIR expression, platinum-sensitive cells were treated with different growth factors and cytokines (0 to 48hrs) and analyzed for changes in HOTAIR expression. Treatment with TNF-α, a well-known inflammatory cytokine and established activator of NF-κB, resulted in 16 fold-induction of HOTAIR. In accord with these results, we observed significant enrichment of both NF-κB and cMYC on the HOTAIR promoter using ChIP assay. Pharmacological inhibition of cMYC and NF-κB reduced HOTAIR expression by 2-fold, and siRNA depletion of the NF-κB p65 subunit or cMYC similarly reduced (P<0.01) HOTAIR expression. Based on these results, we hypothesize a positive feedback loop for HOTAIR transcriptional regulation: HOTAIR inhibits Iκ-Bα (an inhibitor of NF-κB) allowing the lncRNA to enter the nucleus and activate not only its own expression but also cMYC expression to further drive HOTAIR expression as well as cMYC-inducible genes. We are currently testing this hypothesis. We believe this novel pathway, whose components have been implicated in numerous other cancers, may be involved in cisplatin-resistant OC. Citation Format: Ali R. Ozes, Dave Miller, Cong Guo, Anurag Bhattrai, Yunlong Liu, Kenneth P. Nephew. The transcriptional regulation of the long non-coding RNA HOTAIR in ovarian cancer. [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 5189. doi:10.1158/1538-7445.AM2013-5189

Lnc-ing inflammation to disease

“…Increased HOTAIR expression also correlates with the significant reduction in Iκ-Bα protein levels (Figure 2a(v)) in the same cells, which subsequently lead to increased NF-κβ nuclear translocation and activation. Taken together, these findings implicate the HOTAIR-NF-κβ-DDR-positive feedback loop as a causative mechanism of the persistent DNA damage and reduced genomic integrity observed in ovarian cancer [26,27]. Furthermore, this HOTAIR-NF-κβ-DDR loop and the resultant up-regulation of NF-κβ target genes are thought to lead to the acquisition of chemotherapy resistance [28,29].…”

Histones and Their Modifications in Ovarian Cancer – Drivers of Disease and Therapeutic Targets

“…Elevated levels of HOTAIR correlated with worse overall and disease free survival in women with EOC and were also correlated with the presence of lymph node metastasis ( 105 ). Furthermore, HOTAIR is expressed at a fivefold higher level in cisplatin resistant A2780cisR cells compared to parental A2780 cells, and its down-regulation restored cisplatin sensitivity ( 106 ). Levels of HOTAIR have been reported to be fourfold higher in colon and breast cancer stem cell-like cells (CD133 + /CD44 + ) compared to non-stem cell-like cells (CD133 − /CD44 − ), and its down-regulation reduced the number and size of colonies assessed by anchorage-independent growth ( 107 ).…”