The Sin3-histone deacetylase (HDAC) corepressor complex is conserved from yeast to humans. Mammals possess two highly related Sin3 proteins, mSin3A and mSin3B, which serve as scaffolds tethering HDAC enzymatic activity, and numerous sequence-specific transcription factors to enable local chromatin regulation at specific gene targets. Despite broad overlapping expression of mSin3A and mSin3B, mSin3A is cell-essential and vital for early embryonic development. Here, genetic disruption of mSin3B reveals a very different phenotype characterized by the survival of cultured cells and lethality at late stages of embryonic development with defective differentiation of multiple lineages-phenotypes that are strikingly reminiscent of those associated with loss of retinoblastoma family members or E2F transcriptional repressors. Additionally, we observe that, whereas mSin3B ؊/؊ cells cycle normally under standard growth conditions, they show an impaired ability to exit the cell cycle with limiting growth factors. Correspondingly, mSin3B interacts physically with the promoters of known E2F target genes, and its deficiency is associated with derepression of these gene targets in vivo. Together, these results reveal a critical role for mSin3B in the control of cell cycle exit and terminal differentiation in mammals and establish contrasting roles for the mSin3 proteins in the growth and development of specific lineages.E2F ͉ histone deacetylase ͉ knockout ͉ quiescence T he Sin3-histone deacetylase (HDAC) corepressor has been physically and functionally linked to diverse transcriptional complexes governing many physiological processes (1, 2). The two highly related mammalian Sin3 proteins, mSin3A and mSin3B, use their multiple interaction domains to direct chromatin-modifying activities to specific sites in the genome, most typically via sequence-specific transcription factors and their cognate binding elements. Class I HDACs, HDAC1 and HDAC2, are the principal enzymatic activities of the mSin3 complex. In addition, there are several other mSin3-associated proteins, including mSds3, p33 ING1 ,.mSin3A has been shown to be essential for early embryonic development and for the growth and survival of cultured cells that may relate to its requirement for the regulation of multiple transcriptional programs (7). Of relevance to the current study, mSin3B is expressed in cells deleted for mSin3A, suggesting that, despite their structural relatedness, mSin3B is not functionally equivalent to mSin3A. Both yeast and mammalian Sds3 are required for the maintenance of Sin3-associated HDAC enzymatic activity (3,8). Nullizygosity for mammalian Sds3 results in early embryonic lethality and engenders marked chromosome segregation defects due to a failure in pericentric heterochromatin formation (9). mSin3A-null fibroblasts exhibited normal karyotypes (7).In mammalian cell cycle, the G 0 /G 1 -to-S transition is a highly regulated event whose disruption represents a prerequisite for essentially all human cancers. This critical phase of the cell cy...

The stability of a lineage program (cellular memory) is dependent on mechanisms that epigenetically maintain active or repressed states of gene expression (transcriptional memory). Although epigenetic silencing of genes has been clearly demonstrated from yeast to mammals, heritable maintenance of active transcription has been less clearly defined. To investigate the potential role of active transcriptional memory during lineage diversification, we employed targeted mutation of a positive-acting cis element in the Cd4 locus to determine the impact on CD4 expression and the differentiation of CD4+ helper T cells in mice. We show that the proximal enhancer (E4 P ) of Cd4 is essential for CD4 expression in immature CD4+ 8 + thymocytes. Futhermore, its loss resulted in reduced and unstable expression of CD4 in mature T cells. However, if the enhancer was deleted after cells had already committed to the helper T-cell lineage, CD4 expression remained high and was stable upon cell division. ''Active'' histone modifications, once initiated by E4 P , were also propagated independently of the enhancer. Thus, E4 P is responsible for establishing an epigenetically inherited active Cd4 locus in the helper T-cell lineage. To our knowledge, this is the first genetic demonstration of active transcriptional memory in mammalian cells. The formation of diverse tissues and organ systems during development requires the heritable propagation of distinct programs of gene expression in each type of differentiated cell. These programs are generated and maintained by epigenetic mechanisms that are only partially understood. The differentiation from multipotent thymic progenitors of T lymphocytes with distinct phenotypes and immune system functions has provided a valuable developmental system for studying how heritable gene expression is initiated and maintained. CD4 + helper T cells and CD8 + cytotoxic T cells are each derived from progenitors that express both the CD4 and CD8 coreceptors (termed ''double-positive'' or DP cells). Investigation of coreceptor expression, which is tightly linked to the functional program of the mature cells, has provided valuable insight into transcriptional mechanisms involved in the lineage bifurcation. Because of the convenient phenotypic characterization of T-cell subsets, they have also proved to be ideal to study mechanisms of heritability of transcription states, or transcriptional memory, during cell lineage diversification. The most immature thymocytes, double-negative (DN) cells, express neither CD4 nor CD8. Rearrangement of the Tcrb locus that results in expression of the b subunit of the T-cell antigen receptor (TCR) is followed by upregulation of both CD4 and CD8 at the DP stage, during which the Tcra locus is rearranged (Berg and Kang 2001). The few DP thymocytes that express an ab TCR of appropriate avidity for self-peptide-major histocompatibility complexes (MHC) undergo positive selection, whereupon they down-regulate CD8 expression to exhibit the CD4 + 8 lo phenotype. These transitional cel...

On July 23, 2014, the FDA granted accelerated approval to idelalisib (Zydelig tablets; Gilead Sciences, Inc.) for the treatment of patients with relapsed follicular B-cell non-Hodgkin lymphoma or relapsed small lymphocytic lymphoma (SLL) who have received at least two prior systemic therapies. In a multicenter, single-arm trial, 123 patients with relapsed indolent non-Hodgkin lymphomas received idelalisib, 150 mg orally twice daily. In patients with follicular lymphoma, the overall response rate (ORR) was 54%, and the median duration of response (DOR) was not evaluable; median follow-up was 8.1 months. In patients with SLL, the ORR was 58% and the median DOR was 11.9 months. One-half of patients experienced a serious adverse reaction of pneumonia, pyrexia, sepsis, febrile neutropenia, diarrhea, or pneumonitis. Other common adverse reactions were abdominal pain, nausea, fatigue, cough, dyspnea, and rash. Common treatment-emergent laboratory abnormalities were elevations in alanine aminotransferase, aspartate aminotransferase, gamma-glutamyltransferase, absolute lymphocytes, and triglycerides. Continued approval may be contingent upon verification of clinical benefit in confirmatory trials.

Abstractp23 is a heat shock protein 90 (Hsp90) cochaperone located in both the cytoplasm and nucleus that stabilizes unliganded steroid receptors, controls the catalytic activity of certain kinases, regulates protein-DNA dynamics, and is upregulated in several cancers. We had previously shown that p23-overexpressing MCF-7 cells (MCF-7+p23) exhibit increased invasion without affecting the estrogen-dependent proliferative response, which suggests that p23 differentially regulates genes controlling processes linked to breast tumor metastasis. To gain a comprehensive view of the effects of p23 on estrogen receptor (ER)-dependent and -independent gene expression, we profiled mRNA expression from control versus MCF-7+p23 cells in the absence and presence of estrogen. A number of p23-sensitive target genes involved in metastasis and drug resistance were identified. Most striking is that many of these genes are also misregulated in invasive breast cancers, including PMP22, ABCC3, AGR2, Sox3, TM4SF1, and p8 (NUPR1). Upregulation of the ATP-dependent transporter ABCC3 by p23 conferred resistance to the chemotherapeutic agents etoposide and doxorubicin in MCF-7+p23 cells. MCF-7+p23 cells also displayed higher levels of activated Akt and an expanded phosphoproteome relative to control cells, suggesting that elevated p23 also enhances cytoplasmic signaling pathways. For breast cancer patients, tumor stage together with high cytoplasmic p23 expression more accurately predicted disease recurrence and mortality than did stage alone. High nuclear p23 was found to be associated with high cytoplasmic p23, therefore both may promote tumor progression and poor prognosis by increasing metastatic potential and drug resistance in breast cancer patients. Cancer Res; 70(21); 8446-56. ©2010 AACR.