YY1 coopère avec AP-2 pour stimuler l'expression du gène ERBB2 dans les cellules de cancer du sein

peer reviewedOverexpression of the ERBB2 oncogene is observed in about 30% of breast cancers and is generally correlated with a poor prognosis. Previous results from our and other laboratories indicated that elevated transcriptional activity contributes significantly to the overexpression of ERBB2 mRNA in mammary adenocarcinoma cell lines. Activator protein 2 (AP-2) transcription factors account for this overexpression through two recognition sequences located 215 and 500 bp upstream from the transcription start site. Furthermore, AP-2 transcription factors are highly expressed in cancer cell lines overexpressing ERBB2. In this report, we examined the cooperative effect of Yin Yang 1 (YY1) on AP-2-induced activation of ERBB2 promoter activity. We detected high levels of YY1 transcription factor in mammary cancer cell lines. Notably, we showed that YY1 enhances AP-2alpha transcriptional activation of the ERBB2 promoter through an AP-2 site both in HepG2 and in HCT116 cells, whereas a carboxyl-terminal-truncated form of YY1 cannot. Moreover, we demonstrated the interaction between endogenous AP-2 and YY1 factors in the BT-474 mammary adenocarcinoma cell line. In addition, inhibition of endogenous YY1 protein by an antisense decreased the transcription of an AP-2-responsive ERBB2 reporter plasmid in BT-474 breast cancer cells. Finally, we detected in vivo AP-2 and YY1 occupancy of the ERBB2 proximal promoter in chromatin immunoprecipitation assays. Our data thus provide evidence that YY1 cooperates with AP-2 to stimulate ERBB2 promoter activity through the AP-2 binding sites

CpG binding protein (CFP1) occupies open chromatin regions of active genes, including enhancers and non-CpG islands.

Funding This work was supported by a University of Edinburgh Chancellor’s Fellowship to Douglas Vernimmen and by Institute Strategic Grant funding to the Roslin Institute from the BBSRC [BB/J004235/1] and [BB/P013732/1]. Louie N. van de Lagemaat was supported by Roslin Institute funding to Douglas Vernimmen. We are very grateful to Zhanyun Tang and Bob Roeder for the CFP1 antibody. We would like to thank our colleagues Alan Archibald, Philipp Voigt and Duncan Sproul for critically reading the manuscript. We also thank Jim Hughes for curating data sets obtained in Oxford. High-throughput sequencing was provided by the Oxford Genomics Centre (http://www.well.ox.ac.uk/ogc/ home/) and Edinburgh Genomics (http://genomics.ed.ac.uk).Peer reviewe

Chromosome looping at the human alpha-globin locus is mediated via the major upstream regulatory element (HS-40)

Previous studies in the mouse have shown that high levels of alpha-globin gene expression in late erythropoiesis depend on long-range, physical interactions between remote upstream regulatory elements and the globin promoters. Using quantitative chromosome conformation capture (q3C), we have now analyzed all interactions between 4 such elements lying 10 to 50 kb upstream of the human alpha cluster and their interactions with the alpha-globin promoter. All of these elements interact with the alpha-globin gene in an erythroid-specific manner. These results were confirmed in a mouse model of human alpha globin expression in which the human cluster replaces the mouse cluster in situ (humanized mouse). We have also shown that expression and all of the long-range interactions depend largely on just one of these elements; removal of the previously characterized major regulatory element (called HS -40) results in loss of all the interactions and alpha-globin expression. Reinsertion of this element at an ectopic location restores both expression and the intralocus interactions. In contrast to other more complex systems involving multiple upstream elements and promoters, analysis of the human alpha-globin cluster during erythropoiesis provides a simple and tractable model to understand the mechanisms underlying long-range gene regulation

Analysis of neonatal brain lacking ATRX or MeCP2 reveals changes in nucleosome density, CTCF binding and chromatin looping

ATRX and MeCP2 belong to an expanding group of chromatin-associated proteins implicated in human neurodevelopmental disorders, although their gene-regulatory activities are not fully resolved. Loss of ATRX prevents full repression of an imprinted gene network in the postnatal brain and in this study we address the mechanistic aspects of this regulation. We show that ATRX binds many imprinted domains individually but that transient co-localization between imprinted domains in the nuclei of neurons does not require ATRX. We demonstrate that MeCP2 is required for ATRX recruitment and that deficiency of either ATRX or MeCP2 causes decreased frequency of long-range chromatin interactions associated with altered nucleosome density at CTCF-binding sites and reduced CTCF occupancy. These findings indicate that MeCP2 and ATRX regulate gene expression at a subset of imprinted domains by maintaining a nucleosome configuration conducive to CTCF binding and to the maintenance of higher order chromatin structure