BCL11B is a general transcriptional repressor of the HIV-1 long terminal repeat in T lymphocytes through recruitment of the NuRD complex

AbstractIn this study we provide evidence that the transcription factor BCL11B represses expression from the HIV-1 long terminal repeat (LTR) in T lymphocytes through direct association with the HIV-1 LTR. We also demonstrate that the NuRD corepressor complex mediates BCL11B transcriptional repression of the HIV-1 LTR. In addition, BCL11B and the NuRD complex repressed TAT-mediated transactivation of the HIV-1 LTR in T lymphocytes, pointing to a potential role in initiation of silencing. In support of all the above results, we demonstrate that BCL11B affects HIV-1 replication and virus production, most likely by blocking LTR transcriptional activity. BCL11B showed specific repression for the HIV-1 LTR sequences isolated from seven different HIV-1 subtypes, demonstrating that it is a general transcriptional repressor for all LTRs

CTIP2 Expression in Human Head and Neck Squamous Cell Carcinoma Is Linked to Poorly Differentiated Tumor Status

We have demonstrated earlier that CTIP2 is highly expressed in mouse skin during embryogenesis and in adulthood. CTIP2 mutant mice die at birth with epidermal differentiation defects and a compromised epidermal permeability barrier suggesting its role in skin development and/or homeostasis. CTIP2 has also been suggested to function as tumor suppressor in cells, and several reports have described a link between chromosomal rearrangements of CTIP2 and human T cell acute lymphoblast leukemia (T-ALL). The aim of the present study was to look into the pattern of CTIP2 expression in Head and Neck Squamous Cell Carcinoma (HNSCC).In the present study, we analyzed CTIP2 expression in human HNSCC cell lines by western blotting, in paraffin embedded archival specimens by immunohistochemistry (IHC), and in cDNA samples of human HNSCC by qRT-PCR. Elevated levels of CTIP2 protein was detected in several HNSCC cell lines. CTIP2 staining was mainly detected in the basal layer of the head and neck normal epithelium. CTIP2 expression was found to be significantly elevated in HNSCC (p<0.01), and increase in CTIP2 expression was associated with poorly differentiated tumor status. Nuclear co-localization of CTIP2 protein and cancer stem cell (CSC) marker BMI1 was observed in most, if not all of the cells expressing BMI1 in moderately and poorly differentiated tumors.We report for the first time expression of transcriptional regulator CTIP2 in normal human head and neck epithelia. A statistically significant increase in the expression of CTIP2 was detected in the poorly differentiated samples of the human head and neck tumors. Actual CTIP2, rather than the long form of CTIP2 (CTIP2(L)) was found to be more relevant to the differentiation state of the tumors. Results demonstrated existence of distinct subsets of cancer cells, which express CTIP2 and underscores the use of CTIP2 and BMI1 co-labeling to distinguish tumor initiating cells or cancer stem cells (CSCs) from surrounding cancer cells

Retroviral insertions in the VISION database identify molecular pathways in mouse lymphoid leukemia and lymphoma

AKXD recombinant inbred (RI) strains develop a variety of leukemias and lymphomas due to somatically acquired insertions of retroviral DNA into the genome of hematopoetic cells that can mutate cellular proto-oncogenes and tumor suppressor genes. We generated a new set of tumors from nine AKXD RI strains selected for their propensity to develop B-cell tumors, the most common type of human hematopoietic cancers. We employed a PCR technique called viral insertion site amplification (VISA) to rapidly isolate genomic sequence at the site of provirus insertion. Here we describe 550 VISA sequence tags (VSTs) that identify 74 common insertion sites (CISs), of which 21 have not been identified previously. Several suspected proto-oncogenes and tumor suppressor genes lie near CISs, providing supportive evidence for their roles in cancer. Furthermore, numerous previously uncharacterized genes lie near CISs, providing a pool of candidate disease genes for future research. Pathway analysis of candidate genes identified several signaling pathways as common and powerful routes to blood cancer, including Notch, E-protein, NFκB, and Ras signaling. Misregulation of several Notch signaling genes was confirmed by quantitative RT-PCR. Our data suggest that analyses of insertional mutagenesis on a single genetic background are biased toward the identification of cooperating mutations. This tumor collection represents the most comprehensive study of the genetics of B-cell leukemia and lymphoma development in mice. We have deposited the VST sequences, CISs in a genome viewer, histopathology, and molecular tumor typing data in a public web database called VISION (Viral Insertion Sites Identifying Oncogenes), which is located at http://www.mouse-genome.bcm.tmc.edu/vision

Cardiac telocytes — their junctions and functional implications

Telocytes (TCs) form a cardiac network of interstitial cells. Our previous studies have shown that TCs are involved in heterocellular contacts with cardiomyocytes and cardiac stem/progenitor cells. In addition, TCs frequently establish ‘stromal synapses’ with several types of immunoreactive cells in various organs (www.telocytes.com). Using electron microscopy (EM) and electron microscope tomography (ET), we further investigated the interstitial cell network of TCs and found that TCs form ‘atypical’ junctions with virtually all types of cells in the human heart. EM and ET showed different junction types connecting TCs in a network (puncta adhaerentia minima, processus adhaerentes and manubria adhaerentia). The connections between TCs and cardiomyocytes are ‘dot’ junctions with nanocontacts or asymmetric junctions. Junctions between stem cells and TCs are either ‘stromal synapses’ or adhaerens junctions. An unexpected finding was that TCs have direct cell–cell (nano)contacts with Schwann cells, endothelial cells and pericytes. Therefore, ultrastructural analysis proved that the cardiac TC network could integrate the overall ‘information’ from vascular system (endothelial cells and pericytes), nervous system (Schwann cells), immune system (macrophages, mast cells), interstitium (fibroblasts, extracellular matrix), stem cells/progenitors and working cardiomyocytes. Generally, heterocellular contacts occur by means of minute junctions (point contacts, nanocontacts and planar contacts) and the mean intermembrane distance is within the macromolecular interaction range (10–30 nm). In conclusion, TCs make a network in the myocardial interstitium, which is involved in the long-distance intercellular signaling coordination. This integrated interstitial system appears to be composed of large homotropic zones (TC–TC junctions) and limited (distinct) heterotropic zones (heterocellular junctions of TCs)

Bcl11b sets pro-T cell fate by site-specific cofactor recruitment and by repressing Id2 and Zbtb16

Multipotent progenitor cells confirm their T cell–lineage identity in the CD4^–CD8^– double-negative (DN) pro-T cell DN2 stages, when expression of the essential transcription factor Bcl11b begins. In vivo and in vitro stage-specific deletions globally identified Bcl11b-controlled target genes in pro-T cells. Proteomics analysis revealed that Bcl11b associated with multiple cofactors and that its direct action was needed to recruit those cofactors to selective target sites. Regions near functionally regulated target genes showed enrichment for those sites of Bcl11b-dependent recruitment of cofactors, and deletion of individual cofactors relieved the repression of many genes normally repressed by Bcl11b. Runx1 collaborated with Bcl11b most frequently for both activation and repression. In parallel, Bcl11b indirectly regulated a subset of target genes by a gene network circuit via the transcription inhibitor Id2 (encoded by Id2) and transcription factor PLZF (encoded by Zbtb16); Id2 and Zbtb16 were directly repressed by Bcl11b, and Id2 and PLZF controlled distinct alternative programs. Thus, our study defines the molecular basis of direct and indirect Bcl11b actions that promote T cell identity and block alternative potentials

Repressive LTR Nucleosome Positioning by the BAF Complex Is Required for HIV Latency

The SWI/SNF BAF chromatin remodeling complex generates a repressive nucleosome structure at the HIV LTR conducive to establishment and maintenance of HIV latency, while PBAF augments HIV transcription

Telocytes and putative stem cells in the lungs: electron microscopy, electron tomography and laser scanning microscopy

This study describes a novel type of interstitial (stromal) cell — telocytes (TCs) — in the human and mouse respiratory tree (terminal and respiratory bronchioles, as well as alveolar ducts). TCs have recently been described in pleura, epicardium, myocardium, endocardium, intestine, uterus, pancreas, mammary gland, etc. (see www.telocytes.com). TCs are cells with specific prolongations called telopodes (Tp), frequently two to three per cell. Tp are very long prolongations (tens up to hundreds of μm) built of alternating thin segments known as podomers (≤ 200 nm, below the resolving power of light microscope) and dilated segments called podoms, which accommodate mitochondria, rough endoplasmic reticulum and caveolae. Tp ramify dichotomously, making a 3-dimensional network with complex homo- and heterocellular junctions. Confocal microscopy reveals that TCs are c-kit- and CD34-positive. Tp release shed vesicles or exosomes, sending macromolecular signals to neighboring cells and eventually modifying their transcriptional activity. At bronchoalveolar junctions, TCs have been observed in close association with putative stem cells (SCs) in the subepithelial stroma. SCs are recognized by their ultrastructure and Sca-1 positivity. Tp surround SCs, forming complex TC-SC niches (TC-SCNs). Electron tomography allows the identification of bridging nanostructures, which connect Tp with SCs. In conclusion, this study shows the presence of TCs in lungs and identifies a TC-SC tandem in subepithelial niches of the bronchiolar tree. In TC-SCNs, the synergy of TCs and SCs may be based on nanocontacts and shed vesicles

In vitro nuclear interactome of the HIV-1 Tat protein

<p>Abstract</p> <p>Background</p> <p>One facet of the complexity underlying the biology of HIV-1 resides not only in its limited number of viral proteins, but in the extensive repertoire of cellular proteins they interact with and their higher-order assembly. HIV-1 encodes the regulatory protein Tat (86–101aa), which is essential for HIV-1 replication and primarily orchestrates HIV-1 provirus transcriptional regulation. Previous studies have demonstrated that Tat function is highly dependent on specific interactions with a range of cellular proteins. However they can only partially account for the intricate molecular mechanisms underlying the dynamics of proviral gene expression. To obtain a comprehensive nuclear interaction map of Tat in T-cells, we have designed a proteomic strategy based on affinity chromatography coupled with mass spectrometry.</p> <p>Results</p> <p>Our approach resulted in the identification of a total of 183 candidates as Tat nuclear partners, 90% of which have not been previously characterised. Subsequently we applied <it>in silico </it>analysis, to validate and characterise our dataset which revealed that the Tat nuclear interactome exhibits unique signature(s). First, motif composition analysis highlighted that our dataset is enriched for domains mediating protein, RNA and DNA interactions, and helicase and ATPase activities. Secondly, functional classification and network reconstruction clearly depicted Tat as a polyvalent protein adaptor and positioned Tat at the nexus of a densely interconnected interaction network involved in a range of biological processes which included gene expression regulation, RNA biogenesis, chromatin structure, chromosome organisation, DNA replication and nuclear architecture.</p> <p>Conclusion</p> <p>We have completed the <it>in vitro </it>Tat nuclear interactome and have highlighted its modular network properties and particularly those involved in the coordination of gene expression by Tat. Ultimately, the highly specialised set of molecular interactions identified will provide a framework to further advance our understanding of the mechanisms of HIV-1 proviral gene silencing and activation.</p