In Vivo Expression of MHC Class I Genes Depends on the Presence of a Downstream Barrier Element

Regulation of MHC class I gene expression is critical to achieve proper immune surveillance. In this work, we identify elements downstream of the MHC class I promoter that are necessary for appropriate in vivo regulation: a novel barrier element that protects the MHC class I gene from silencing and elements within the first two introns that contribute to tissue specific transcription. The barrier element is located in intergenic sequences 3′ to the polyA addition site. It is necessary for stable expression in vivo, but has no effect in transient transfection assays. Accordingly, in both transgenic mice and stably transfected cell lines, truncation of the barrier resulted in transcriptional gene silencing, increased nucleosomal density and decreased histone H3K9/K14 acetylation and H3K4 di-methylation across the gene. Significantly, distinct sequences within the barrier element govern anti-silencing and chromatin modifications. Thus, this novel barrier element functions to maintain transcriptionally permissive chromatin organization and prevent transcriptional silencing of the MHC class I gene, ensuring it is poised to respond to immune signaling

A Cell Cycle Role for the Epigenetic Factor CTCF-L/BORIS

CTCF is a ubiquitous epigenetic regulator that has been proposed as a master keeper of chromatin organisation. CTCF-like, or BORIS, is thought to antagonise CTCF and has been found in normal testis, ovary and a large variety of tumour cells. The cellular function of BORIS remains intriguing although it might be involved in developmental reprogramming of gene expression patterns. We here unravel the expression of CTCF and BORIS proteins throughout human epidermis. While CTCF is widely distributed within the nucleus, BORIS is confined to the nucleolus and other euchromatin domains. Nascent RNA experiments in primary keratinocytes revealed that endogenous BORIS is present in active transcription sites. Interestingly, BORIS also localises to interphase centrosomes suggesting a role in the cell cycle. Blocking the cell cycle at S phase or mitosis, or causing DNA damage, produced a striking accumulation of BORIS. Consistently, ectopic expression of wild type or GFP- BORIS provoked a higher rate of S phase cells as well as genomic instability by mitosis failure. Furthermore, downregulation of endogenous BORIS by specific shRNAs inhibited both RNA transcription and cell cycle progression. The results altogether suggest a role for BORIS in coordinating S phase events with mitosis

The DNA-binding factor Ctcf critically controls gene expression in macrophages

Macrophages play an important role in immunity and homeostasis. Upon pathogen recognition via specific receptors, they rapidly induce inflammatory responses. This process is tightly controlled at the transcriptional level. The DNA binding zinc-finger protein CCCTC-binding factor (Ctcf) is a crucial regulator of long-range chromatin interactions and coordinates specific communication between transcription factors and gene expression processes. In this study, the Ctcf gene was specifically deleted in myeloid cells by making use of the transgenic Cre-LoxP system. Conditional deletion of the Ctcf gene in myeloid cells induced a mild phenotype in vivo. Ctcf-deficient mice exhibited significantly reduced expression of major histocompatibility complex (MHC) class II in the liver. Ctcf-deficient macrophages demonstrated a normal surface phenotype and phagocytosis capacity. Upon Toll-like receptor (TLR) stimulation, they produced normal levels of the pro-inflammatory cytokines IL-12 and IL-6, but manifested a strongly impaired capacity to produce tumor-necrosis factor (TNF) and IL-10, as well as to express the IL-10 family members IL-19, IL-20 and IL-24. Taken together, our data demonstrate a role of Ctcf that involves fine-tuning of macrophage function

BPTF is required for c-MYC transcriptional activity and in vivo tumorigenesis

c-MYC oncogene is deregulated in most human tumours. Histone marks associated with transcriptionally active genes define high-affinity c-MYC targets. The mechanisms involved in their recognition by c-MYC are unknown. Here we report that c-MYC interacts with BPTF, a core subunit of the NURF chromatin-remodelling complex. BPTF is required for the activation of the full c-MYC transcriptional programme in fibroblasts. BPTF knockdown leads to decreased c-MYC recruitment to DNA and changes in chromatin accessibility. In Bptf-null MEFs, BPTF is necessary for c-MYC-driven proliferation, G1-S progression and replication stress, but not for c-MYC-driven apoptosis. Bioinformatics analyses unveil that BPTF levels correlate positively with c-MYC-driven transcriptional signatures. In vivo, Bptf inactivation in pre-neoplastic pancreatic acinar cells significantly delays tumour development and extends survival. Our findings uncover BPTF as a crucial c-MYC co-factor required for its biological activity and suggest that the BPTF-c-MYC axis is a potential therapeutic target in cancer.This work was supported, in part, by grants from Ministerio de Economía y Competitividad, Madrid, Spain (SAF2007–60860, SAF2011–29530 and ONCOBIO Consolider), Instituto de Salud Carlos III, Madrid, Spain (RTICC RD12/0036/0034), European Union Seventh Framework Programme (grant 256974), and an EIN/Roche-CNIO collaborative grant to F.X.R.; and grants from Instituto de Salud Carlos III (INTRASALUD PI12/00425 and RTICC RD12/0036/0037) to J.C.