Subject(s)
DNA Methylation , DNA-Binding Proteins/metabolism , Gene Silencing , Repressor Proteins/metabolism , Transcription Factors/metabolism , DNA (Cytosine-5-)-Methyltransferases/metabolism , Enhancer of Zeste Homolog 2 Protein , Epigenesis, Genetic , Humans , Polycomb Repressive Complex 2 , Polycomb-Group Proteins , Promoter Regions, Genetic/geneticsABSTRACT
Polycomb group (PcG) proteins are epigenetic chromatin modifiers involved in heritable gene repression. Two main PcG complexes have been characterized. Polycomb repressive complex 2 (PRC2) is thought to be involved in the initiation of gene silencing, whereas Polycomb repressive complex 1 (PRC1) is implicated in the stable maintenance of gene repression. Here, we investigate the kinetic properties of the binding of one of the PRC1 core components, BMI1, with PcG bodies. PcG bodies are unique nuclear structures located on regions of pericentric heterochromatin, found to be the site of accumulation of PcG complexes in different cell lines. We report the presence of at least two kinetically different pools of BMI1, a highly dynamic and a less dynamic fraction, which may reflect BMI1 pools with different binding capacities to these stable heterochromatin domains. Interestingly, PRC2 members EED and EZH2 appear to be essential for BMI1 recruitment to the PcG bodies. Furthermore, we demonstrate that the maintenance DNA methyltransferase DNMT1 is necessary for proper PcG body assembly independent of DNMT-associated histone deacetylase activity. Together, these results provide new insights in the mechanism for regulation of chromatin silencing by PcG proteins and suggest a highly regulated recruitment of PRC1 to chromatin.
Subject(s)
DNA (Cytosine-5-)-Methyltransferases/metabolism , DNA-Binding Proteins/metabolism , Gene Silencing , Heterochromatin/metabolism , Nuclear Proteins/metabolism , Proto-Oncogene Proteins/metabolism , Repressor Proteins/metabolism , Transcription Factors/metabolism , Cells, Cultured , DNA/metabolism , DNA (Cytosine-5-)-Methyltransferase 1 , DNA Methylation , Enhancer of Zeste Homolog 2 Protein , Heterochromatin/chemistry , Humans , Nuclear Proteins/analysis , Polycomb Repressive Complex 1 , Polycomb Repressive Complex 2 , Proto-Oncogene Proteins/analysis , Repressor Proteins/analysis , S Phase/geneticsABSTRACT
Hypoxia-inducible factor 1 (HIF-1) transactivates genes the products of which mediate tumor angiogenesis and glycolytic metabolism. Overexpression of the HIF-1 alpha subunit, resulting from intratumoral hypoxia and genetic alterations, has been demonstrated in common human cancers and is correlated with tumor angiogenesis and patient mortality. Here we demonstrate that hypoxia or HIF-1 alpha overexpression stimulates Matrigel invasion by HCT116 human colon carcinoma cells, whereas this process is inhibited by a small interfering RNA directed against HIF-1 alpha. We show that HIF-1 regulates the expression of genes encoding cathepsin D; matrix metalloproteinase 2; urokinase plasminogen activator receptor (uPAR); fibronectin 1; keratins 14, 18, and 19; vimentin; transforming growth factor alpha; and autocrine motility factor, which are proteins that play established roles in the pathophysiology of invasion. Neutralizing antibodies against uPAR block tumor cell invasion induced by hypoxia or HIF-1 alpha overexpression. These results provide a molecular basis for promotion of the invasive cancer phenotype by hypoxia and/or HIF-1 alpha overexpression.
