SUMMARY High Gleason grade prostate carcinomas are aggressive, poorly differentiated tumors that exhibit diminished estrogen receptor β (ERβ) expression. We report that a key function of ERβ and its specific ligand 5α-androstane-3β,17β-diol (3β-adiol) is to maintain an epithelial phenotype and repress mesenchymal characteristics in prostate carcinoma. Stimuli (TGF-β and hypoxia) that induce an epithelial-mesenchymal transition (EMT) diminish ERβ expression, and loss of ERβ is sufficient to promote an EMT. The mechanism involves ERβ-mediated destabilization of HIF-1α and transcriptional repression of VEGF-A. The VEGF-A receptor neuropilin-1 drives the EMT by promoting Snail1 nuclear localization. Importantly, this mechanism is manifested in high Gleason grade cancers, which exhibit significantly more HIF-1α and VEGF expression, and Snail1 nuclear localization compared to low Gleason grade cancers.

Recent work with mouse models and human leukemic samples has shown that gain-of-function mutation(s) in Notch1 is a common genetic event in T-cell acute lymphoblastic leukemia (T-ALL). The Notch1 receptor signals through a γ-secretase-dependent process that releases intracellular Notch1 from the membrane to the nucleus, where it forms part of a transcriptional activator complex. To identify Notch1 target genes in leukemia, we developed mouse T-cell leukemic lines that express intracellular Notch1 in a doxycycline-dependent manner. Using gene expression profiling and chromatin immunoprecipitation, we identified c-myc as a novel, direct, and critical Notch1 target gene in T-cell leukemia. c-myc mRNA levels are increased in primary mouse T-cell tumors that harbor Notch1 mutations, and Notch1 inhibition decreases c-myc mRNA levels and inhibits leukemic cell growth. Retroviral expression of c-myc, like intracellular Notch1, rescues the growth arrest and apoptosis associated with γ-secretase inhibitor treatment or Notch1 inhibition. Consistent with these findings, retroviral insertional mutagenesis screening of our T-cell leukemia mouse model revealed common insertions in either notch1 or c-myc genes. These studies define the Notch1 molecular signature in mouse T-ALL and importantly provide mechanistic insight as to how Notch1 contributes to human T-ALL.

Mutations in NOTCH1 are frequently detected in patients with T-cell acute lymphoblastic leukemia (T-ALL) and in mouse T-ALL models. Treatment of mouse or human T-ALL cell lines in vitro with ␥-secretase inhibitors (GSIs) results in growth arrest and/or apoptosis. These studies suggest GSIs as potential therapeutic agents in the treatment of T-ALL. To determine whether GSIs have antileukemic activity in vivo, we treated near-endstage Tal1/Ink4a/Arf ϩ/Ϫ leukemic mice with vehicle or with a GSI developed by Merck (MRK-003). We found that GSI treatment significantly extended the survival of leukemic mice compared with vehicle-treated mice. Notch1 target gene expression was repressed and increased numbers of apoptotic cells were observed in the GSItreated mice, demonstrating that Notch1 inhibition in vivo induces apoptosis. T-ALL cell lines also exhibit PI3K/mTOR pathway activation, indicating that rapamycin may also have therapeutic benefit. When GSIs are administered in combination with rapamycin, mTOR kinase activity is ablated and apoptosis induced. Moreover, GSI and rapamycin treatment inhibits human T-ALL growth and extends survival in a mouse xenograft model. This work supports the idea of targeting NOTCH1 in T IntroductionT-cell acute lymphoblastic leukemia (T-ALL) is associated with the misexpression of the basic helix-loop-helix protein TAL1/SCL and LIM-domain only proteins LMO1 and LMO2. [1][2][3][4][5][6][7][8] These oncogenes are found misexpressed in greater than 60% of human T-ALL patients. 3,9 Mouse models of T-ALL recapitulate the disease through ectopic expression of Tal1 in the thymus. [10][11][12] These mice develop respiratory distress due to the presence of large thymic masses and have detectable T-cell blasts in peripheral blood lymphocytes (PBLs), spleen, liver, and kidney. 10 Misexpression of Tal1 results in perturbed thymocyte development by interfering with the basic-helix-loop-helix (bHLH) heterodimer E47/HEB that regulates the expression of genes critical for thymocyte differentiation including Rag1/2, CD4, CD3, and TCR␣/␤. 13,14 Consistent with this finding, loss of the E2A gene that encodes the E47 and E12 bHLH protein is associated with human B-progenitor ALL. 15 Mutations in the Notch1 receptor have been frequently detected in mouse T-ALL models [16][17][18][19] and importantly in 54% of T-ALL patients. 20 These mutations cluster in the heterodimerization domain (HD) 20 and the juxtamembrane (JME) region, 21 or result in truncation of PEST regulatory sequences. 18,20 Mutations in the HD domain result in increased susceptibility to cleavage by the gamma-secretase complex; JME mutations may facilitate metalloprotease cleavage, whereas deletion of PEST regulatory sequences is thought to result in increased Notch1 stability. [21][22][23] Treatment of mouse Tal1 leukemic cell lines in vitro with ␥-secretase inhibitors (GSIs) results in cell cycle arrest and apoptosis, revealing that Notch1 signaling is required for leukemic growth/survival. 18Notch1-mediated leukemic growth in mouse and ...

Gene expression requires the recruitment of chromatin remodeling activities and general transcription factors (GTFs) to promoters. Whereas the role of activators in recruiting chromatin remodeling activities has been clearly demonstrated, the contributions of the transcription machinery have not been firmly established. Here we demonstrate that the remodeling of the RNR3 promoter requires a number of GTFs, mediator and RNA polymerase II. We also show that remodeling is dependent upon the SWI/SNF complex, and that TFIID and RNA polymerase II are required for its recruitment to the promoter. In contrast, Gcn5p-dependent histone acetylation occurs independently of TFIID and RNA polymerase II function, and we provide evidence that acetylation increases the extent of nucleosome remodeling, but is not required for SWI/SNF recruitment. Thus, the general transcription machinery can contribute to nucleosome remodeling by mediating the association of SWI/SNF with promoters, thereby revealing a novel pathway for the recruitment of chromatin remodeling activities.[Keywords: Chromatin remodeling; SWI/SNF; TAFs; RNR3; SAGA; TFIID] Supplemental material is available at http://www.genesdev.org.

Background: FSP27 depletion increases both basal and stimulated lipolysis. Results: FSP27 interacts with ATGL via amino acids 120 -220 to regulate lipolysis and triglyceride storage in human adipocytes. Conclusion: FSP27 inhibits ATGL-mediated lipolysis and protects adipocytes against free fatty acid-impaired insulin signaling. Significance: The novel lipolytic regulation shown here may lead to new treatments for insulin resistance.