Calorie restriction extends lifespan in organisms ranging from yeast to mammals. In yeast, the SIR2 gene mediates the life-extending effects of calorie restriction. Here we show that the mammalian SIR2 orthologue, Sirt1 (sirtuin 1), activates a critical component of calorie restriction in mammals; that is, fat mobilization in white adipocytes. Upon food withdrawal Sirt1 protein binds to and represses genes controlled by the fat regulator PPAR-gamma (peroxisome proliferator-activated receptor-gamma), including genes mediating fat storage. Sirt1 represses PPAR-gamma by docking with its cofactors NCoR (nuclear receptor co-repressor) and SMRT (silencing mediator of retinoid and thyroid hormone receptors). Mobilization of fatty acids from white adipocytes upon fasting is compromised in Sirt1+/- mice. Repression of PPAR-gamma by Sirt1 is also evident in 3T3-L1 adipocytes, where overexpression of Sirt1 attenuates adipogenesis, and RNA interference of Sirt1 enhances it. In differentiated fat cells, upregulation of Sirt1 triggers lipolysis and loss of fat. As a reduction in fat is sufficient to extend murine lifespan, our results provide a possible molecular pathway connecting calorie restriction to life extension in mammals.

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Chicken ovalbumin upstream promoter transcription factor (COUP-TF)-interacting proteins 1 and 2 [CTIP1/Evi9/B cell leukaemia (Bcl) l1a and CTIP2/Bcl11b respectively] are highly related C(2)H(2) zinc finger proteins that are abundantly expressed in brain and the immune system, and are associated with immune system malignancies. A selection procedure was employed to isolate high-affinity DNA binding sites for CTIP1. The core binding site on DNA identified in these studies, 5'-GGCCGG-3' (upper strand), is highly related to the canonical GC box and was bound by a CTIP1 oligomeric complex(es) in vitro. Furthermore, both CTIP1 and CTIP2 repressed transcription of a reporter gene harbouring a multimerized CTIP binding site, and this repression was neither reversed by trichostatin A (an inhibitor of known class I and II histone deacetylases) nor stimulated by co-transfection of a COUP-TF family member. These results demonstrate that CTIP1 is a sequence-specific DNA binding protein and a bona fide transcriptional repressor that is capable of functioning independently of COUP-TF family members. These findings may be relevant to the physiological and/or pathological action(s) of CTIPs in cells that do not express COUP-TF family members, such as cells of the haematopoietic and immune systems.

Bcl11b is a transcription factor that, within the hematopoietic system, is expressed specifically in T cells. Although Bcl11b is required for T-cell differentiation in newborn Bcl11b-null mice, and for positive selection in the adult thymus of mice bearing a T-celltargeted deletion, the gene network regulated by Bcl11b in T cells is unclear. We report herein that Bcl11b is a bifunctional transcriptional regulator, which is required for the correct expression of approximately 1000 genes in CD4 1 CD8 1 CD3 lo double-positive (DP) thymocytes. Bcl11b-deficient DP cells displayed a gene expression program associated with mature CD4 1 CD8 À and CD4 À CD8 1 single-positive (SP) thymocytes, including upregulation of key transcriptional regulators, such as Zbtb7b and Runx3. Bcl11b interacted with regulatory regions of many dysregulated genes, suggesting a direct role in the transcriptional regulation of these genes. However, inappropriate expression of lineageassociated genes did not result in enhanced differentiation, as deletion of Bcl11b in DP cells prevented development of SP thymocytes, and that of canonical NKT cells. These data establish Bcl11b as a crucial transcriptional regulator in thymocytes, in which Bcl11b functions to prevent the premature expression of genes fundamental to the SP and NKT cell differentiation programs.Key words: Mouse . T-cell differentiation . Transcription factor Supporting Information available online Introduction T-cell differentiation is a complex and dynamic process that leads to the production of functionally distinct populations within the thymus -gd and ab T-cell subsets, the latter of which include helper CD4 1 T cells, cytotoxic CD8 1 T cells, Treg cells, and NKT cells. Hematopoietic progenitor cells enter the thymus as CD4 À CD8 À double-negative (DN) cells and proceed through successive steps of maturation. DN thymocytes are further divided into at least four developmental stages based on the differential expression of CD44 and CD25: CD44 1 CD25 À (DN1), CD44 1 CD25 1 (DN2), CD44 À CD25 1 (DN3), and CD44 À CD25 À Ã Joint senior authors; additional correspondence, Dr. Mark Leid Eur. J. Immunol. 2010. 40: 2143-2154 DOI 10.1002 HIGHLIGHTS 2143Frontline (DN4). gd T cells differentiate from DN3 thymocytes, following rearrangement of the b, g, and d TCR chains. ab T cells develop from DN4 thymocytes that further differentiate into CD4 1 CD8 1 double-positive (DP) CD3 lo abTCR lo thymocytes. Positive selection events between the TCR expressed by DP cells and MHC molecules expressed by thymic stromal cells lead to the appearance of mature CD4 1 and CD8 1 single-positive (SP) CD3 hi /TCR hi thymocytes, and NKT cells, all presumably resulting from large-scale changes in gene expression programs.Transcription factors essential for the ab T-cell developmental programs have been identified [1][2][3]. In particular, Zbtb7b (also known as ThPok) is required for CD4 1 T-cell differentiation [4,5]. Zbtb7b is not expressed in DP thymocytes, but is activated downstream of TCR signaling by TOX [...

Chicken ovalbumin upstream promoter transcription factor (COUP-TF)-interacting protein 2 (CTIP2), also known as Bcl11b, is a transcriptional repressor that functions by direct, sequence-specific DNA binding activity or by recruitment to the promoter template by interaction with COUP-TF family members. CTIP2 is essential for both T cell development and axonal projections of corticospinal motor neurons in the central nervous system. However, little is known regarding the molecular mechanism(s) by which CTIP2 contributes to either process. CTIP2 complexes that were isolated from SK-N-MC neuroblastoma cells were found to harbor substantial histone deacetylase activity, which was likely conferred by the nucleosome remodeling and deacetylation (NuRD) complex. CTIP2 was found to associate with the NuRD complex through direct interaction with both RbAp46 and RbAp48, and components of the NuRD complex were found to be recruited to an artificial promoter template in a CTIP2-dependent manner in transfected cells. Finally, the NuRD complex and CTIP2 were found to co-occupy the promoter template of p57KIP2, a gene encoding a cyclin-dependent kinase inhibitor, and identified herein as a novel transcriptional target of CTIP2 in SK-N-MC cells. Therefore, it seems likely that the NuRD complex may be involved in transcriptional repression of CTIP2 target genes and contribute to the function(s) of CTIP2 within a neuronal context.