The histone variant mH2A is believed to be involved in transcriptional repression, but how it exerts its function remains elusive. By using chromatin immunoprecipitation and tandem affinity immunopurification of the mH2A1.1 nucleosome complex, we identified numerous genes with promoters containing mH2A1.1 nucleosomes. In particular, the promoters of the inducible Hsp70.1 and Hsp70.2 genes, but not that of the constitutively expressed Hsp70.8, were highly enriched in mH2A1.1. PARP-1 was identified as a part of the mH2A1.1 nucleosome complex and was found to be associated with the Hsp70.1 promoter. A specific interaction between mH2A1.1 and PARP-1 was demonstrated and found to be associated with inactivation of PARP-1 enzymatic activity. Heat shock released both mH2A1.1 and PARP-1 from the Hsp70.1 promoter and activated PARP-1 automodification activity. The data we present point to a novel mechanism for control of Hsp70.1 gene transcription. mH2A1.1 recruits PARP-1 to the promoter, thereby inactivating it. Upon heat shock, the Hsp70.1 promoter-bound PARP-1 is released to activate transcription through ADP-ribosylation of other Hsp70.1 promoter-bound proteins.[Keywords: Histone variant; mH2A; PARP-1; ADP-ribosylation; transcription] Supplemental material is available at http://www.genesdev.org.

Timely negative regulation of the immune system is critical to allow it to perform its duty while maintaining it under tight control to avoid overactivation. We previously reported that the neuronal receptor neuropilin-1 (NP-1) is expressed in human lymph nodes. However, the role of NP-1 interaction with its physiological ligand semaphorin-3A (Sema-3A) on immune cells remains elusive. Here we show that Sema-3A is expressed by activated DC and T cells, and that its secretion in DC/T cell cocultures is delayed. Sema-3A/NP-1 interaction down-modulated T cell activation since addition of Sema-3A in DC/T cell cocultures dramatically inhibited allogeneic T cell proliferation. More importantly, neutralization by blocking antibodies or by antagonist peptide of endogenous Sema-3A produced by DC/T cell cocultures resulted in a 130% increase in T cell proliferation. Sema-3A acted directly on T cells, since it could block anti-CD3/ CD28-stimulated proliferation of T cells. Finally, immunomodulatory functions of Sema-3A relied on the blockage of actin cytoskeleton reorganization, affecting TCR polarization and interfering with early TCR signal transduction events such as ZAP-70 or focal adhesion kinase phosphorylation. Therefore, we propose that Sema-3A secretion and the resulting NP-1/Sema-3A interaction are involved in a late negative feedback loop controlling DC-induced T cell proliferation.

It is largely established that molecules first discovered in the nervous system are also found in the immune system. Neuropilin-1 (NP-1) was initially identified to mediate semaphorin-induced chemorepulsion during brain development and is also involved in peripheral T cell/dendritic cell interactions. Herein, we studied NP-1 during T cell development in the human thymus. NP-1 is expressed in both cortex and medulla of thymic lobules, being found in distinct CD4/CD8-defined thymocyte subsets. NP-1 is also found in thymic epithelial cells (TEC) in situ and in vitro, and is recruited at the site of TEC-thymocyte contact. Moreover, NP-1 was rapidly up-regulated during thymocyte stimulation by T cell receptor (TCR) and IL-7 or after adhesion to TEC. Semaphorin-3A (Sema-3A), a natural ligand of NP-1, is also present in human thymus, both in TEC and thymocytes, being up-regulated in thymocytes after TCR engagement. Functionally, Sema-3A decreases the adhesion capacity of NP-1 ؉ thymocytes and induces their migration by a repulsive effect. In conclusion, we show here that NP-1/Sema-3A-mediated interactions participate in the control of human thymocyte development. extracellular matrix ͉ integrins ͉ thymocyte adhesion and migration

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Type I interferon (IFN) enhances the transcription of the tumor suppressor gene p53. To elucidate the molecular mechanism mediating IFN-induced apoptosis, we analysed programmed cell death in response to type I (IFNa) or type II (IFNc) treatment in relation to p53 status. In two cell lines (MCF-7, SKNSH), IFNa, but not IFNc, enhanced apoptosis in a p53-dependent manner. Furthermore, only IFNa upregulated p53 as well as p53 target genes (Noxa, Mdm2 and CD95). The apoptotic response to IFNa decreased in the presence of ZB4, an anti-CD95 antibody, suggesting that CD95 is involved in this process. When p53 was inactivated by the E6 viral protein or the expression of a p53 mutant, IFNa-induced apoptosis and p53 target genes upregulation were abrogated. Altogether these results demonstrate that p53 plays a pivotal role in the IFNa-induced apoptotic response. IFNa-induced PML was unable to recruit p53 into nuclear bodies and its downregulation by siRNA did not alter CD95 expression. In contrast, IFNc-induced apoptosis is p53-independent. CD95 and IFN-regulatory factor 1 (IRF1) are directly upregulated by this cytokine. Apoptotic response to IFNc is decreased in the presence of ZB4 and strongly diminished by IRF1 siRNA, implicating both CD95 and IRF1 in IFNc-induced apoptotic response. Taken together, these results show that in two different cell lines, IFNa and IFNc, induce p53-dependent -independent apoptosis, respectively. Oncogene (2005) 24, 605-615.

A recent report demonstrated that free human T-cell leukemia virus 1 (HTLV-1) could infect plasmacytoid dendritic cells (pDCs). The major role of pDCs is to secrete massive levels of interferon-␣ (IFN-␣) upon virus exposure; however, the induction of IFN-␣ by HTLV-1 remains unknown. We demonstrate here that cellfree HTLV-1 generated a pDC innate immune response by producing massive levels of IFN-␣ that were inhibited by anti-HTLV-1 antibodies. HTLV-1 induced costimulatory molecules and rapid expression of the apoptotic ligand tumor necrosis factor-related apoptosis-inducing ligand (TRAIL). Furthermore, HTLV-1 stimulated pDC-induced apoptosis of CD4 ؉ T cells expressing DR5, transforming pDCs into IFN-producing killer pDCs. We also observed that an endosomal acidification inhibitor and a Toll-like receptor-7 (TLR7)-specific blocker drastically inhibited pDC response to HTLV-1. Three-dimensional microscopy analysis revealed that unstimulated pDCs were "dormant" IFNproducing killer pDCs with high levels of intracellular TRAIL that could be rapidly mobilized to the surface in response to TLR7 activation. Inhibition of viral degradation in endosomes by chloroquine maintained viral integrity, allowing virus detection by 3-dimensional microscopy. We demonstrate that pDCs respond to cell-free HTLV-1 by producing high levels of IFN-␣ and by mobilizing TRAIL on cell surface after TLR7 triggering. This is the first demonstration of an innate immune response induced by free HTLV-1. (Blood. 2010;115:2177-2185) IntroductionHuman T-cell leukemia virus 1 (HTLV-1), the first characterized human retrovirus, 1 has been identified as the causative agent for adult T-cell leukemia/lymphoma (ATLL) 2,3 and HTLV-1-associated myelopathy/tropical spastic paraparesis, 4 uveitis, and infective dermatitis in children. 5 HTLV-1 virions infect CD4 ϩ T cells, which represent the main target for HTLV-1 infection in peripheral blood. HTLV-1-associated diseases occur after long periods of virus latency. 6 For years it has been thought that unlike other retroviruses, free virions were poorly infectious. 7 However, Jones et al 8 recently reported that freshly isolated myeloid dendritic cells (mDCs) and plasmacytoid dendritic cells (pDCs) are efficiently and productively infected by cell-free HTLV-1. Furthermore, infected mDCs and pDCs were able to transfer virions to autologous CD4 ϩ T cells, clearly demonstrating that cell-free HTLV-1 can be infectious and target DCs. 8 pDCs participate in innate and adaptive immunity, 9,10 are located in blood and lymphoid organs, 10,11 and produce up to 1000-fold more interferon-␣ (IFN-␣) than other cell types in response to virus exposure. 12 Three molecules have been characterized for HTLV-1 entry into cells, heparan sulfate proteoglycans 13 and BDCA-4 (also called neuropilin-1) 14 for the initial virus binding to target cells 15 and glucose transporter 1 for the postattachment and the viral fusion. 16,17 Interestingly, BDCA-4 is expressed by mDC and T cells 18,19 but cells expressing the greatest level of BDCA...

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