Abstract
The orphan nuclear receptor NR4A1 is expressed in tumors from rhabdomyosarcoma (RMS) patients and Rh30 and RD RMS cell lines, and we used RNA interference (RNAi) to investigate the role of this receptor in RMS cells. Knockdown of NR4A1 in Rh30 cells decreased cell proliferation, induced Annexin V staining and induced polyADPribose polymerase (PARP) cleavage and these results were similar to those observed in other solid tumors. Previous studies show that NR4A1 regulates expression of growth promoting/pro-survival genes with GC-rich promoters, activates mTOR through suppression of p53, and maintains low oxidative stress by regulating expression of isocitrate dehydrogenase 1 (IDH1) and thioredoxin domain containing 5 (TXNDC5). Results of RNAi studies demonstrated that NR4A1 also regulates these pathways and associated genes in RMS cells and thereby exhibits pro-oncogenic activity. 1,1-Bis(3-indolyl)-1-(p-substituted phenyl)methane (C-DIM) analogs containing p-hydroxyl (DIM-C-pPhOH) and p-carboxymethyl (DIM-C-pPhCO2Me) substituents are NR4A1 ligands that decreased NR4A1-dependent transactivation in RMS cells and inhibited RMS cell and tumor growth and induced apoptosis. Moreover, the effects of NR4A1 knockdown and the C-DIM/NR4A1 antagonists were comparable as inhibitors of NR4A1-dependent genes/pathways. Both NR4A1 knockdown and treatment with DIM-C-pPhOH and DIM-C-pPhCO2Me also induced ROS which activated stress genes and induced sestrin 2 which activated AMPK and inhibited mTOR in the mutant p53 RMS cells. Since NR4A1 regulates several growth-promoting/pro-survival pathways in RMS, the C-DIM/NR4A1 antagonists represent a novel mechanism-based approach for treating this disease alone or in combination and thereby reducing the adverse effects of current cytotoxic therapies.
Highlights
Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma that is primarily observed in children and adolescents and accounts for 5% of all pediatric cancers and 50% of soft tissue sarcomas in children [1, 2]
This study demonstrates that NR4A1 regulates pro-oncogenic pathways (Figure 1B) in RMS cells and C-DIM/NR4A1 antagonists inhibit these responses, demonstrating that NR4A1 is a potential novel target for RMS chemotherapy
Previous studies show that the C-DIM compounds DIMC-pPhOH and DIM-C-pPhCO2Me bind NR4A1 and act as NR4A1 antagonists for transactivation assays in colon cancer cells [16] and these compounds were used in this study on RMS cells
Summary
Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma that is primarily observed in children and adolescents and accounts for 5% of all pediatric cancers and 50% of soft tissue sarcomas in children [1, 2]. Embryonal RMS (ERMS) and alveolar RMS (ARMS) are the two major classes of RMS in children and adolescents and differ with respect to their histology, genetics, treatment, and prognosis [1,2,3,4]. ERMS accounts for over 60% of RMS patients and is associated with loss of heterozygosity at the 11p15 locus. ERMS patients have a favorable initial prognosis; the overall survival of patients with metastatic ERMS is only 40% [3]. ARMS occurs in a lower percentage of RMS patients and is associated with translocations resulting in formation of pro-oncogenic gene products resulting from the fusion of PAX3 or PAX7 with the Forkhead gene FOXO1A [5, 6]. ARMS patients have a poor diagnosis and patient survival is < 10% for metastatic ARMS
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
