NR4A3 Suppresses Lymphomagenesis In Vitro and In Vivo by Induction of Similar Patterns of Pro-Apoptotic Genes like NR4A1

Abstract

The nuclear orphan receptors NR4A1 and NR4A3 have been demonstrated as cooperating tumour suppressor genes leading to rapid development of acute myeloid leukaemia (AML) in double knock-out mice. In humans, their expression is reduced in leukemic blasts in AML patients. Furthermore, NR4A1 and NR4A3 hypoallelic mice develop preleukemic myelodysplastic/myeloproliferative disorders with progression to AML in some cases. Recently we published a comprehensive study of NR4A nuclear receptor expression levels in lymphoid neoplasms that revealed a marked reduction of NR4A1 and NR4A3 in the majority of patients with B-cell chronic lymphocytic leukaemia, with follicular lymphoma, and with diffuse large B cell lymphoma. Interestingly, functional characterization demonstrated that NR4A1 induces apoptosis of aggressive lymphoma cells in vitro and suppresses tumour growth in a xenograft mouse model.Since the role of NR4A3 in aggressive lymphomas is unknown, we aimed to investigate its etiopathogenic function in these tumors. Low expression of NR4A3 was associated with poor survival in aggressive lymphoma patients. Experimentally, induction of NR4A3 expression by inducible ectopic expression in a variety of lymphoma cell lines led to a significantly higher proportion of apoptotic cells as demonstrated by DNA cleavage, Annexin V staining and increased caspase 3/7 activity. To test the tumor suppressor functions of NR4A3 in vivo, the stably transduced SuDHL4-lymphoma cell line was xenografted in the NOD-SCID-gamma (NSG) mouse model. In this system NR4A3 expression abrogated tumor growth in the NSG mice, whereas vector control and uninduced cells formed massive lymphoid tumors. Pharmacological activation of NR4A3 by Thapsigargin and BF175 resulted in a NR4A3 dependent induction of apoptosis in vitro. To dissect differential transcriptional activity of NR4A3 and NR4A1,both factors were separately over-expressed in four different aggressive lymphoma cell lines followed by semi-quantitative mRNA expression analysis of intrinsic and extrinsic apoptotic genes. NR4A1 or NR4A3 over-expression caused apoptosis by induction of BAK, Puma, BIK, BIM, BID and Trail to the same degree.In summary, our data suggest that NR4A3 possesses tumor suppressive function in aggressive lymphomas by pro-apoptotic transactivation and that NR4A3 is functional redundant to NR4A1 in aggressive lymphomas. DisclosuresNo relevant conflicts of interest to declare.