Functional Characterization of lncRNA152 as an Angiogenesis-Inhibiting Tumor Suppressor in Triple-Negative Breast Cancers

Long non-coding RNAs have been implicated in many of the hallmarks of cancer. We previously annotated lncRNA152 (lnc152; a.k.a. DRAIC) and demonstrated its roles in proliferation, cell cycle progression, and regulation of the estrogen signaling pathway in breast cancer cells. Herein, we found that lnc152 is highly upregulated in luminal breast cancers, but is downregulated in triple-negative breast cancers (TNBC). Using a set of complementary experimental approaches, we found that knockdown of lnc152 promotes cell migration and invasion in luminal breast cancer cell lines. In contrast, ectopic expression of lnc152 inhibits growth, migration, invasion, and angiogenesis in TNBC cell lines. In xenograft studies in mice, lnc152 inhibited the growth and metastasis of TNBC cells. Transcriptome analysis of the xenografts indicated that lnc152 downregulates genes regulating cancer-related phenotypes, including angiogenesis. Using RNA-pull down assays coupled with LC-MS/MS analysis, we identified RBM47, a known tumor suppressor protein in breast cancer, as a lnc152-interacting protein. We found that lnc152 suppresses the aggressive phenotypes of TNBC cells by regulating the expression of RBM47. Collectively, our results demonstrate that lnc152 is an angiogenesis-inhibiting tumor suppressor that attenuates the aggressive cancer-related phenotypes found in TNBC. To investigate the in vivo impact of ectopic expression of lnc152 in TNBC, we performed a xenograft experiment using MDA-MB-231 cell line engineered for Dox-inducible overexpression of lnc152 or GFP mRNA as a control. At the end of the experiment, the mice were euthanized to collect the xenograft tissue. Using RNA-seq from xenograft tumor tissue, we evaluated the expression changes of mRNAs after ectopic expression of lnc152 in MDA-MB-231 cells compared to expression of GFP mRNA