NF-κB p65 represses microRNA-124 transcription in diffuse large B-cell lymphoma

Background Previous studies have shown that the copy number of microRNA (miR)-124 is decreased in diffuse large B cell lymphoma (DLBCL), and that miR-124 is a tumor suppressor by targeting NF-kappa B p65 in B-cell lymphoma. In turn, miR-124 expression is regulated by transcription factors such as HNF4 alpha, ETS2, and p53. However, whether and how miR-124 transcription is modulated by NF-kappa B transcription factors remain unknown in DLBCL. Objective To investigate whether the activation of NF-kappa B signaling could inhibit the expression of miR-124, possibly contributing to the pathogenesis of DLBCL. Methods Potential transcription factors regulating miR-124 transcription were predicted using the Transfac software. The cellular effects of NF-kappa B p65 on miR-124 were examined by MTS assay, Western blot assay, qPCR, and chromatin immunoprecipitation (ChIP) assays using DLBCL cell lines. Results Inhibition of NF-kappa B signals using Bay11-7085 increased miR-124 expression whereas exposure to TNF-alpha decreased it. Ectopic expression of p65 suppressed miR-124 expression, suggesting that p65 may be a transcriptional repressor of miRNA-124. Pharmacological analyses showed that phosphorylated/activated p65 downregulates miR-124 via two signaling pathways: (1) TAK1/IKK alpha-IKK beta/I kappa B alpha and (2) MAPK/p65. Moreover, ChIP assay demonstrated that p65 directly regulates miR-124 by binding to the NF-kappa B consensus sequence in its promoter region. Finally, we also confirmed that stable ectopic expression of miR-124 suppresses cell proliferation and survival. Conclusion Taken together, our study uncovered a mechanism by which active NF-kappa B signaling disrupts the function of miR-124 as a tumor suppressor in DLBCL.