The Polycomb-repressive complex 2 (PRC2) is important for maintenance of stem cell pluripotency and suppression of cell differentiation by promoting histone H3 lysine 27 trimethylation (H3K27me3) and transcriptional repression of differentiation genes. Here we show that the tumoursuppressor protein BRCA1 interacts with the Polycomb protein EZH2 in mouse embryonic stem (ES) and human breast cancer cells. The BRCA1-binding region in EZH2 overlaps with the noncoding RNA (ncRNA)-binding domain, and BRCA1 expression inhibits the binding of EZH2 to the HOTAIR ncRNA. Decreased expression of BRCA1 causes genome-wide EZH2 re-targeting and elevates H3K27me3 levels at PRC2 target loci in both mouse ES and human breast cancer cells. BRCA1 deficiency blocks ES cell differentiation and enhances breast cancer migration and invasion in an EZH2-dependent manner. These results reveal that BRCA1 is a key negative modulator of PRC2 and that loss of BRCA1 inhibits ES cell differentiation and enhances an aggressive breast cancer phenotype by affecting PRC2 function.

Histone H3 lysine 27 trimethylation (H3K27me3) catalyzed by the enzymatic subunit EZH2 in the Polycomb repressive complex 2 (PRC2) is essential for cells to 'memorize' gene expression patterns through cell divisions and plays an important role in establishing and maintaining cell identity during development. However, how the epigenetic mark is inherited through cell generations remains poorly understood. Recently, we and others demonstrate that CDK1 and CDK2 phosphorylate EZH2 at threonine 350 (T350) and that T350 phosphorylation is important for the binding of EZH2 to PRC2 recruiters, such as noncoding RNAs (ncRNAs) HOTAIR and XIST, and for the effective recruitment of PRC2 to EZH2 target loci in cells. These findings imply that phosphorylation of EZH2 by CDK1 and CDK2 may provide cells a mechanism that enhances EZH2 function during S and G 2 phases of the cell cycle, thereby ensuring K27me3 on de novo synthesized H3 incorporated in nascent nucleosomes before sister chromosomes are divided into two daughter cells. Additionally, a potential role of T350 phosphorylation of EZH2 in differing EZH2 from its homolog EZH1 in catalyzing H3K27me3 as well as the interplay between phosphorylation at T350 and other residues [e.g., phosphorylation by p38 at threonine 372 (T372)] in governing EZH2 activity in proliferating versus non-dividing cells are also discussed. Together, CDK phosphorylation of EZH2 at T350 may represent a key regulatory mechanism of EZH2 function that is essential for

Cyclophilin A (CypA) is a member of peptidyl prolyl isomerases (PPIases), which catalyze the cis/trans isomerization of prolyl peptide bonds on the NH-terminal side of Pro residues in peptide chains. Altered expression of CypA has been reported in hepatocellular carcinoma (HCC), but the biological functions of CypA in HCC remain unknown. We found that the level of CypA expression correlated with the metastatic capability of two HCC cell lines, MHCC97-L and MHCC97-H. Stable expression of ectopic CypA in SK-Hep1 cells promotes cell adhesion, motility, chemotaxis, and in vivo lung metastasis, without affecting cell proliferation. We further analyzed microarray results to identify target genes controlled by CypA. Twenty-one genes related to metastasis were altered by CypA over-expression. A member of matrix metalloproteinase, MMP3, was identified by microarray analysis. The regulation of MMP3 and its homologue MMP9 by CypA were further confirmed by quantitative real-time RT-PCR and zymography assay. Taken together, our data suggest that CypA promotes HCC cell metastasis at least partially through up-regulation of MMP3 and MMP9.

Cyclophilin A acts as protein folding chaperones and intracellular transports in many cellular processes. Previous studies have shown that cyclophilin A can interact with HIV-1 (human immunodeficiency virus type 1) gag protein and enhance viral infectivity. Many cyclophilin A inhibitors such as cyclosporin A can inhibit HIV-1 replication in vitro. Here, we report a structure-based identification of novel non-peptidic cyclophilin A inhibitors as anti-HIV lead compounds. Following a computer-aided virtual screening and subsequent surface plasmon resonance (SPR) analysis, 12 low molecular weight cyclophilin A ligands were selected for further evaluation of their in vitro inhibition of peptidyl-prolyl cis-trans isomerase (PPIase) activity of cyclophilin A and HIV-1 replication. Five of these compounds (FD5, FD8, FD9, FD10 and FD12) exhibited inhibition against both PPIase activity and HIV-1 infection. These active compounds will be used as leads for structure and activity relationship (SAR) and optimization studies in order to design more effective anti-HIV-1 therapeutics, and as probes for investigating the effect of cyclophilins on HIV-1 replication.