C/EBPβ Activates BCL2 Gene Transcription By Recruiting Co-activator P300 To The Mbr Distal Element In A SATB1 Dependent Manner

Gene expression is regulated by diverse cis-regulatory elements which spread over the whole genome to make sure the cell type specific orchestration of gene activities. It is now becoming increasingly clear that a common mechanism by which distal elements regulate genes involves the formation of direct physical associations between these elements and their target genes. The genome-wide networks of chromosomal interactions may provide new insights into the long-range gene regulation.The BCL2 protein is a key regulator of apoptosis and is additionally involved in DNA repair, cell cycle and differentiation control. Given its fundamental importance for the cellular fate, BCL2 expression is finely tuned by a variety of environmental and endogenous stimuli and regulated at both transcriptional and posttranscriptional levels.BCL2 proto-oncogene was first cloned from the t(14;18) translocation breakpoint in human follicular B-cell lymphoma. It is about 250 kb in length and composed of three exons and two promoters. The 279-bp major breakpoint region (mbr) within the 3’-untranslated region (3’-UTR) of the BCL2 gene is a binding site of special AT-rich sequence binding protein 1 (SATB1) that is well known to participate in the long-range regulation of gene transcription. Our previous studies have revealed that the mbr could up-regulate BCL2 transcription over a 200-kb distance and this regulatory function was closely related to SATB1. The mbr could physically interact with BCL2 promoter through SATB1-mediated chromatin looping, which was required for epigenetic modification of the promoter and high expression of the BCL2 gene. SATB1 not only mediates the special chromosome structure, but also belongs to a class of transcription factors that function as a landing platform for several chromatin remodeling enzymes and transcription factors. In this study, with Chromatin immunoprecipatation assay and Electrophoretic mobility shift assays, we demonstrated that the transcription factor C/EBPβand the co-activator p300 originally bind to the mbr distal element and were brought to the promoter region through SATB1-mediated chromatin looping, which resulted in histones acetylation and the recruitment of RNA polymeraseⅡ. Furthermore, with quantitative analysis of ChIP products, we confirmed that C/EBPβcoordinates with SATB1 to recruite the co-activator p300 at the mbr and activates the BCL2 gene transcription.During early apoptosis. the degradation of SATB1 resulted in the dissociation of the C/EBPβ/p300 protein complex at the mbr and inhibition of RNA polymerase II recruitment as well as histone acetylation on the promoter region. The BCL2 trnascription was finally down regulated. Inhibition of SATB1 cleavage by overexpression of mutant SATB1 restored the BCL2 mRNA level in Jurkat cells. It suggests that the mbr distal regulatory element is involved in apoptotic response of cells through SATB1/C/EBPβ/p300 protein complex.These data revealed a novel mechanism of long-range regulation of gene transcription and mechanistically link the long-range interaction of chromosome with the regulation of a gene controlling apoptosis pathway for the first time.