Abstract 2428: NR4A1 ligands inhibits PSPC1 regulated EMT and stemness markers in breast, lung and liver cancer cells

Abstract

Abstract The orphan nuclear receptor 4A1 (Nur77, TR3, NR4A1) is highly expressed in solid tumors and is a negative prognostic factor for survival of breast, lung, and liver cancer patients (1) and ongoing studies in our laboratory show that NR4A1 is pro-oncogenic in multiple tumor types. We have also identified a series of bis-indole derived compounds including 1,1-bis(3'-indolyl)-1-(p-hydroxyphenyl) methane (DIM-C-pPhOH; CDIM8) that act as NR4A1 antagonists that inhibit pro-oncogenic NR4A1-regulated genes and pathways in multiple cancer cell lines (2). Mechanistic studies show that many of the NR4A1-regulated genes involve interactions of NR4A1 with gene promoter DNA or with Sp-bound to GC-rich sequences and similar mechanisms have previously been observed for steroid hormone and other nuclear receptors. Our studies have identified paraspeckle component 1 (PSPC1) as an NR4A1 regulated gene in breast, lung and liver cancer cells and PSPC1 gene expression and protein levels are suppressed after treatment with C-DIM/NR4A1 antagonists. PSPC1 promotes tumorigenesis, epithelial-to-mesenchymal transition (EMT), stemness and metastasis and is a master activator of pro-metastatic switches and a potential target for anti-metastatic drugs. Knockdown of PSPC1 downregulates EMT and stemness markers in breast, lung and liver cancer cells. The novel buttressed analog of CDIM8 (DIM-C-pPhOH-3-Br-5-OCF3) at a concentration of 10 uM downregulates PSPC1 expression and its downstream targets (Snail, Slug, Nanog, OCT4, SOX2, c-myc). Knockdown of NR4A1 or SP1 inhibits PSPC1 expression in MDA-MB-231, H1299 and SNU449 cell lines respectively. These results identify PSPC1 as a novel gene that regulates EMT and invasion in these cancer cells and NR4A1 is an upstream regulator of PSPC1 gene expression. Thus, NR4A1 ligands act as an antimetastatic mimic by inhibiting PSPC1 and the mechanism of PSPC1 regulation involves ligand induced interactions of NR4A1/SP1 with a GC-rich region of the PSPC1 gene promoter.