SUMMARY While chromosomal rearrangements fusing the androgen-regulated gene TMPRSS2 to the oncogenic ETS transcription factor ERG occur in approximately 50% of prostate cancers, how the fusion products regulate prostate cancer remains unclear. Using chromatin immunoprecipitation coupled with massively parallel sequencing (ChIP-Seq), we found that ERG disrupts androgen receptor (AR) signaling by inhibiting AR expression, binding to and inhibiting AR activity at gene-specific loci, and inducing repressive epigenetic programs via direct activation of the H3K27 methyltransferase EZH2, a Polycomb group protein. These findings provide a working model in which TMPRSS2-ERG plays a critical role in cancer progression by disrupting lineage-specific differentiation of the prostate and potentiating the EZH2-mediated de-differentiation program.

FIG. 3. LPDs: Sharply contoured lateralized periodic discharges. In this case, PDs are bilateral asymmetric. Although some discharges are on the border of sharp, most are sharply contoured. FIG. 4. LPDs: 0.5 per second spiky lateralized periodic discharges.FIG. 5. LPDs: 0.5-1 per second spiky lateralized periodic discharges. Despite their spike-and-wave morphology, the discharges are periodic (as there is a quantifiable inter-discharge interval between consecutive waveforms and recurrence of the waveform at nearly regular intervals). FIG. 6. LPDs1F: 0.5 to 1 per second spiky LPDs with superimposed burst of low amplitude fast activity (highlighted in boxes). Hirsch LJ et al FIG. 7. LPDs1R: Irregular (in morphology and repetition rate) 0.5-1 per second quasi-periodic discharges with superimposed quasi-rhythmic delta activity in the right hemisphere with occasional spread to the left. Less "stable" pattern and more ictalappearing than LPDs alone; compare with Figure 1. FIG. 8. Fluctuating LPDs: Lateralized periodic discharges that fluctuate in frequency between 0.5 and 1 per second.

Enhancer of zeste homolog 2 (EZH2) is a mammalian histone methyltransferase that contributes to the epigenetic silencing of target genes and that regulates the survival and metastasis of cancer cells. EZH2 is overexpressed in aggressive solid tumors by mechanisms that remain unclear. Here, we show that the expression and function of EZH2 in cancer cell lines is inhibited by microRNA-101 (miR-101). Analysis of human prostate tumors revealed that miR-101 expression decreases during cancer progression, paralleling an increase in EZH2 expression. One or both of the two genomic loci encoding miR-101 were somatically lost in 37.5% of clinically localized prostate cancers (6/16) and 66.7% of metastatic disease (22/33). We propose that genomic loss of miR-101 in cancer leads to overexpression of EZH2 and concomitant dysregulation of epigenetic pathways, resulting in cancer progression.Polycomb Group Proteins, including EZH2, play a master regulatory role in controlling important cellular process such as maintaining stem cell pluripotency (1-3), cell proliferation (4,5), early embryogenesis (6), and X chromosome inactivation (7). EZH2 functions in a multiprotein complex called Polycomb Repressive Complex 2 (PRC2) which includes SUZ12 (Suppressor of Zeste 12) and EED (Embryonic Ectoderm Development) (8,9). The primary activity of the EZH2 protein complex is to tri-methylate histone H3 lysine 27 (H3K27) at target gene promoters, leading to epigenetic silencing (10,11). Mounting evidence suggests that #Address correspondence and requests for reprints to:

Enhancer of zeste homolog 2 (EZH2) is a critical component of the polycomb-repressive complex 2 (PRC2), which is involved in gene silencing and histone H3 lysine 27 methylation. EZH2 has a master regulatory function in controlling such processes as stem cell differentiation, cell proliferation, early embryogenesis and X chromosome inactivation. Although benign epithelial cells express very low levels of EZH2, increased levels of EZH2 have been observed in aggressive solid tumors such as those of the prostate, breast and bladder. The mechanism by which EZH2 mediates tumor aggressiveness is unclear. Here, we demonstrate that EZH2 mediates transcriptional silencing of the tumor suppressor gene E-cadherin by trimethylation of H3 lysine 27. Histone deacetylase inhibitors can prevent EZH2-mediated repression of E-cadherin and attenuate cell invasion, suggesting a possible mechanism that may be useful for the development of therapeutic treatments. Taken together, these observations provide a novel mechanism of E-cadherin regulation and establish a functional link between dysregulation of EZH2 and repression of E-cadherin during cancer progression.

Gene fusions have a critical role in cancer progression. Mechanisms associated with the genesis and cell type specificity of these fusions are not well understood. A prototypical gene fusion, TMPRSS2-ERG, involves the 5' untranslated region of the androgen-regulated gene TMPRSS2 with the ERG gene, and is the most common gene fusion associated with prostate cancer. We demonstrate that androgen signaling induces chromosomal proximity between TMPRSS2 and ERG loci, and facilitates the formation of the TMPRSS2-ERG gene fusion when subjected to an agent that causes DNA double strand breaks. These results provide a conceptual framework for the genesis of gene fusions and may provide suggestions as to the general etiology of human prostate cancer.Gene fusions are a hallmark of cancer development (1), but the mechanisms underlying their genesis and cell type specificities are unclear (2).Fusions of the TMPRSS2 and ERG genes, which are located 3 Mb apart on human chromosome 21q22.2, are found in about 50% of prostate cancers and consist of the 5' untranslated region of TMPRSS2, an androgen-regulated gene, fused to the protein-coding sequence of ERG, which encodes an erythroblast transformation-specific (ETS) transcription factor (2). Recently, estrogen was shown to induce rapid chromosomal movements that bring together estrogen receptor α-bound genes on different chromosomes (3). Given the broad similarities between estrogen and androgen signaling, we hypothesized that androgen might likewise induce chromosomal movements and bring together the TMPRSS2 and ERG genes, thereby facilitating the formation of gene fusions.To examine the effects of androgen signaling on the formation of TMPRSS2-ERG, we studied LNCaP prostate cancer cells, which are androgen sensitive but lack this fusion gene (4) (fig.

Summary Polycomb Repressive Complexes (PRC1 and PRC2) mediated epigenetic regulation is critical for maintaining cellular homeostasis. Members of Polycomb Group (PcG) proteins including EZH2, a PRC2 component, are up-regulated in various cancer types, implicating their role in tumorigenesis. Here, we have identified several microRNAs (miRNAs) that are repressed by EZH2. These miRNAs in turn regulate the expression of PRC1 proteins, BMI1 and RING2. We found that ectopic overexpression of EZH2-regulated miRNAs attenuated cancer cell growth and invasiveness, and abrogated cancer stem cell properties. Importantly, expression analysis revealed an inverse correlation between miRNA and PRC protein levels in cell culture and prostate cancer tissues. Taken together, our data has uncovered a coordinate regulation of PRC1 and PRC2 activities that is mediated by miRNAs.

Head and neck cancer (SCCHN) is a common, aggressive, treatment-resistant cancer with a high recurrence rate and mortality, but the mechanism of treatment-resistance remains unclear. Here we describe a mechanism where the AAA-ATPase TRIP13 promotes treatment-resistance. Overexpression of TRIP13 in non-malignant cells results in malignant transformation. High expression of TRIP13 in SCCHN leads to aggressive, treatment-resistant tumors and enhanced repair of DNA damage. Using mass spectrometry, we identify DNA-PKcs complex proteins that mediate non homologous end joining (NHEJ), as TRIP13 binding partners. Using repair-deficient reporter systems, we show that TRIP13 promotes NHEJ, even when homologous recombination is intact. Importantly, overexpression of TRIP13 sensitizes SCCHN to an inhibitor of DNA-PKcs. Thus, this study defines a new mechanism of treatment resistance in SCCHN and underscores the importance of targeting NHEJ to overcome treatment failure in SCCHN and potentially in other cancers that overexpress TRIP13.

Genomic rearrangements are associated with many human genomic disorders, including cancers. It was previously thought that most genomic rearrangements formed randomly but emerging data suggest that many are nonrandom, cell type-, cell stage- and locus-specific events. Recent studies have revealed novel cellular mechanisms and environmental cues that influence genomic rearrangements. In this Review, we consider the multitude of influences on genomic rearrangements by grouping these influences into four categories: proximity of chromosomal regions in the nucleus, cellular stress, inappropriate DNA repair or recombination, and DNA sequence and chromatin features. The synergy of these triggers can poise a cell for rearrangements and here we aim to provide a conceptual framework for understanding the genesis of genomic rearrangements.