Abstract 1450: MicroRNAs in myxoid/round cell liposarcomas: FUS-CHOP regulated miR-497 and miR-30a target the insulin-like growth factor receptor pathway
Authors: Gits Caroline M. , Kuijk Patricia F. van , IJcken Wilfred F. van , Mathijssen Ron HJ , Bakker Michael A. den , Verweij Jaap , Sleijfer Stefan , Wiemer Erik AC 
Published: May 2015

Abstract
Myxoid/round cell liposarcomas (MRCLS) are characterized by a t(12;16)(q13;p11) translocation in 90% of the cases, which gives rise to a FUS-CHOP (FUS-DDIT3) fusion gene. The resulting fusion oncoprotein acts as an abnormal transcription factor, inducing distinct transcriptional programs. However, not much is known about the deregulation of microRNA (miRNA) expression in MRCLS and about the role of FUS-CHOP herein. We examined miRNA expression in MRCLS (n=14) and normal fat (n=9) by LNA™ oligonucleotide microarrays. The 50 most differentially expressed miRNAs (p&lt;0.03) discriminate MRCLS and fat samples in a supervised hierarchical clustering. The miR-23a/27a/24-2 and miR-23b/27b/24-1 cluster members were all significantly downregulated in MRCLS, which was validated by RT-PCR in an extended sample set (MRCLS, n=33; normal fat, n=20). Functional analyses showed that overexpression of miR-24 induced doxorubicin resistance in two myxoid liposarcoma cell lines (MLS 402-91 and MLS 1765-92), while miR-24 inhibitors sensitized a liposarcoma (SW872) and a rhabdomyosarcoma (RH30) cell line to doxorubicin treatment. To identify miRNAs controlled by the fusion gene, FUS-CHOP levels were modulated by expression constructs or siRNA in four sarcoma cell lines. MiR-497, miR-30a and miR-34b expression was found to be inversely correlated with FUS-CHOP expression. Accordingly, their expression was significantly lower in MRCLS compared to normal fat, as determined by RT-PCR analysis. MiR-497 and miR-30a share many predicted target genes of the insulin(-like) growth factor (IGF) pathway. Overexpression of miR-497 and miR-30a considerably downregulated protein expression of IGF1 receptor (IGF1R) and its substrates IRS1 and IRS2. Luciferase reporter constructs containing wild-type and mutated 3′UTR fragments of these genes were used to demonstrate direct regulation of IRS1 by miR-497, IRS2 by miR-30a, and IGF1R by both miRNAs. Surprisingly miR-497 and miR-30a overexpression had little effect on cell proliferation, but significantly sensitized myxoid liposarcoma cell lines to doxorubicin treatment, which is possibly mediated via the IGF1R signaling pathway. In conclusion, the FUS-CHOP oncoprotein in MRCLS mediates differential expression of several miRNAs, which affect the IGF1R pathway and doxorubicin sensitivity. Based on these results, combination therapy of miR-497 / miR-30a overexpression and chemotherapeutic or targeted agents against MRCLS should be further explored.
Citation Format: Caroline MM Gits, Patricia F. van Kuijk, Wilfred F. van IJcken, Ron HJ Mathijssen, Michael A. den Bakker, Jaap Verweij, Stefan Sleijfer, Erik AC Wiemer. MicroRNAs in myxoid/round cell liposarcomas: FUS-CHOP regulated miR-497 and miR-30a target the insulin-like growth factor receptor pathway. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1450. doi:10.1158/1538-7445.AM2014-1450