Abstract 3198: The RNA-binding protein Musashi-1 stabilizes TAC1 mRNA in breast cancer cells.

Abstract

Abstract Breast cancer (BC) remains a major public health challenge in the United States. Prognosis for metastatic cancer is poor with nearly all deaths from BC due to metastatic disease. Upon discovery in bone, the five year survival rate of BC patients is approximately eight percent. The tachykinin gene, TAC1, has been implicated in facilitating metastasis of BC to the bone marrow. The predominant product of TAC1 is the neuropeptide, substance P (SP). We have previously demonstrated that in non-malignant cells, TAC1 translation is suppressed by miRNAs. Stimulation with specific cytokines decreased these miRNA to allow synthesis of SP. BC cells (BCCs) lack endogenous expression of the TAC1-specific miRNA, which is consistent with the increased levels of SP in these cells. Herein the present study investigated the translational control of TAC1 mRNA in BCCs. Cytoplasmic extracts from BCCs showed an increase in TAC1 translation and stabilization of its mRNA. These findings led us to bioinformatic analyses of the secondary structure of TAC1 mRNA, which predicted candidate interacting sites in Exons 3 and 7. These predictions were further refined by results from an RNA shift assay that indicated an RNA-binding protein specifically targeting Exon 7. Through western blots and proteomic analysis we identified the RNA-binding protein, Musashi-1 (Msi1), as a putative candidate. Identity was confirmed by RNA supershift assay utilizing an antibody specific for Msi1. Gain-of-function and reporter gene assays utilizing the Msi1 expression vector co-transfected with a luciferase reporter gene linked to the 3′UTR of TAC1, including Exon 7, confirmed a stabilizing role for Msi1 in TAC1 mRNA regulation, concomitant with an increase in substance P. In summary, we identified Msi1 as a novel binding protein for the oncogenic TAC1 mRNA. These findings have implications for the identification of novel targets to treat BC. Citation Format: George R. Nahas, Raghav G. Murthy, Steven J. Greco, Pranela Rameshwar. The RNA-binding protein Musashi-1 stabilizes TAC1 mRNA in breast cancer cells. [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 3198. doi:10.1158/1538-7445.AM2013-3198