Expression data from HEK293 cells with or without MIBP1 overexpression

The transcription factor c-MYC intron binding protein 1 (MIBP1) binds to various genomic regulatory regions, including intron 1 of c-MYC. This factor is highly expressed in post-mitotic neurons in the fetal brain and may be involved in various biological steps, such as neurological and immunological processes. In this study, we globally characterized the transcriptional targets of MIBP1 and proteins that interact with MIBP1. Microarray hybridization followed by Gene Set Enrichment Analysis revealed that genes involved in the pathways downstream of MYC, NF-B, and TGF- were downregulated when HEK293 cells stably overexpressed MIBP1. In silico transcription factor binding site analysis of the promoter regions of these downregulated genes showed that the NF-B binding site was the most overrepresented. The upregulation of genes known to be in the NF-B pathway after the knockdown of endogenous MIBP1 in HT1080 cells supports the view that MIBP1 is a downregulator of the NF-B pathway. We also confirmed the binding of the MIBP1 to the NF-B site. By immunoprecipitation and mass spectrometry, we detected O-linked -N-acetylglucosamine (O-GlcNAc) transferase (OGT) as a prominent binding partner of MIBP1. Analyses using deletion mutants revealed that a 154-amino acid region of MIBP1 was necessary for its OGT binding and O-GlcNAcylation. A luciferase reporter assay showed that NF-B-responsive expression was repressed by MIBP1, and stronger repression by MIBP1 lacking the 154-amino acid region was observed. Our results indicate that the primary effect of MIBP1 expression is the downregulation of the NF-B pathway, and that this effect is attenuated by O-GlcNAc signaling.

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Iwashita Y, Fukuchi N, Waki M, Hayashi K, Tahira T