Abstract 166: Identification of a novel long noncoding RNA as a mediator for CRTC1-MAML2 fusion oncogenic function and a biomarker for CRTC1-MAML2 fusion-positive tumors

Abstract

Abstract Long non-coding RNAs (LncRNA) are non-protein coding transcripts longer than 200 nucleotides and represent a novel class of gene regulators. LncRNA expression is frequently de-regulated in cancer. Specific lncRNAs have been shown to participate in cancer cell proliferation, survival, migration, and invasion, and targeting these cancer-associated lncRNAs inhibits tumor growth and metastasis. Therefore, lncRNAs are implicated as cancer biomarkers and therapeutic targets. The human genome encodes >10,000 lncRNAs; however, only a handful lncRNAs have been well characterized. We revealed through a microarray analysis that a novel lncRNA, lnc473 is a top target for the CRTC1-MAML2 fusion oncogene. CRTC1-MAML2 is generated by a t(11;19)(q21;p13) translocation that is specifically associated with mucoepidermoid carcinoma (MEC). MEC is a distinct type of tumors containing three cellular components, squamous cells, mucus-secreting cells, and intermediate cells. MEC occurs in many glandular tissues and accounts for the most common salivary gland malignancies. The CRTC1-MAML2 functions as a transcriptional co-activator, capable of promoting transcription from CREB and other factors. CRTC1-MAML2 is a major oncogenic driver for MEC initiation and maintenance. Currently, knowledge remains limited regarding how CRTC1-MAML2 mediates its oncogenic activity. In this study, we studied the regulatory mechanism of lnc473 expression and its function in mediating CRTC1-MAML2 oncogenic activity. We observed that lnc473 expression was tightly correlated with CRTC1-MAML2 fusion expression levels in human MEC cell lines and primary tumors using a Nanostring assay that allowed direct digital quantification of RNA molecules, strongly suggesting that lnc473 is a surrogate marker for functional CRTC1-MAML2 fusion. Lentiviral shRNA-mediated depletion of endogenous CRTCT1-MAML2 and its interacting transcription factor CREB resulted in a significant reduction of lnc473 expression. Also, lnc473 contained conserved CREB-binding sites on its proximal promoter, suggesting that CRTC1-MAML2 interacts with CREB in promoting lnc473 transcription. Functionally, depletion of lnc473 significantly reduced human MEC cell proliferation and survival in vitro and blocked the growth of MEC xenograft tumors. Our combined findings indicate that this lnc473 is a biomarker for human CRTC1-MAML2-positive MEC and has a novel regulatory function in mediating CRTC1-MAML2 cancer gene activity. Intriguingly, lnc473 depletion reduced expression of several known CRTC1-MAML2/CREB target genes, suggesting that lnc473 exerts a positive feedback regulation of CRTC1-MAML2-mediated transcription. The molecular mechanisms underlying lnc473 functions in MEC are currently being investigated through analyses of lnc473-regulated targeted gene profiling and lncRNA interacting protein complexes Citation Format: Zirong Chen, Jian-Liang Li, Shuibin Lin, Chunxia Cao, Frederic Kaye, Lizi Wu. Identification of a novel long noncoding RNA as a mediator for CRTC1-MAML2 fusion oncogenic function and a biomarker for CRTC1-MAML2 fusion-positive tumors. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 166. doi:10.1158/1538-7445.AM2015-166