Constitutive NF-κB activation has causative roles in adult T cell leukemia (ATL) caused by HTLV-1 and other cancers. Here, we report a pathway involving Polycomb-mediated miRNA silencing and NF-κB activation. We determine the miRNA signatures and reveal miR-31 loss in primary ATL cells. MiR-31 negatively regulates the noncanonical NF-κB pathway by targeting NF-κB inducing kinase (NIK). Loss of miR-31 therefore triggers oncogenic signaling. In ATL cells, miR-31 level is epigenetically regulated, and aberrant upregulation of Polycomb proteins contribute to miR-31 downregulation in an epigenetic fashion, leading to activation of NF-κB and apoptosis resistance. Furthermore, this emerging circuit operates in other cancers and receptor-initiated NF-κB cascade. Our findings provide a perspective involving the epigenetic program, inflammatory responses, and oncogenic signaling.

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Group X secretory phospholipase A 2 (sPLA 2 -X) possesses several structural features characteristic of both group IB and IIA sPLA 2 s (sPLA 2 -IB and -IIA) and is postulated to be involved in inflammatory responses owing to its restricted expression in the spleen and thymus. Here, we report the purification of human recombinant COOH-terminal His-tagged sPLA 2 -X, the preparation of its antibody, and the purification of native sPLA 2 -X. The affinity-purified sPLA 2 -X protein migrated as various molecular species of 13-18 kDa on SDS-polyacrylamide gels, and N-glycosidase F treatment caused shifts to the 13-and 14-kDa bands. NH 2 -terminal amino acid sequencing analysis revealed that the 13-kDa form is a putative mature sPLA 2 -X and the 14-kDa protein possesses a propeptide of 11 amino acid residues attached at the NH 2 termini of the mature protein. Separation with reverse-phase high performance liquid chromatography revealed that N-linked carbohydrates are not required for the enzymatic activity and prosPLA 2 -X has a relatively weak potency compared with the mature protein. The mature sPLA 2 -X induced the release of arachidonic acid from phosphatidylcholine more efficiently than other human sPLA 2 groups (IB, IIA, IID, and V) and elicited a prompt and marked release of arachidonic acid from human monocytic THP-1 cells compared with sPLA 2 -IB and -IIA with concomitant production of prostaglandin E 2 . A prominent release of arachidonic acid was also observed in sPLA 2 -X-treated human U937 and HL60 cells. Immunohistochemical analysis of human lung preparations revealed its expression in alveolar epithelial cells. These results indicate that human sPLA 2 -X is a unique N-glycosylated sPLA 2 that releases arachidonic acid from human myeloid leukemia cells more efficiently than sPLA 2 -IB and -IIA.Phospholipase A 2 (PLA 2 ) 1 comprises a diverse family of lipolytic enzymes that hydrolyze the sn-2 fatty acid ester bond of glycerophospholipids to produce free fatty acid and lysophospholipids (1, 2). PLA 2 s participate in pathophysiological processes by releasing arachidonic acid from membrane phospholipids, leading to the production of various types of proinflammatory lipid mediators, such as prostaglandins (PGs) and leukotrienes (LTs) (3). Over the past two decades, a number of PLA 2 s have been identified and characterized. From their biochemical features, these PLA 2 s are classified into several families (4), including secretory PLA 2 (sPLA 2 ) (5-11), arachidonoyl-specific cytosolic PLA 2 (cPLA 2 ) (12, 13), and Ca 2ϩ -independent PLA 2 (14).Low molecular mass sPLA 2 s (13-18 kDa) have several features including a high disulfide bond content, a requirement for millimolar concentrations of Ca 2ϩ for catalysis, and a broad specificity for phospholipids with different polar head groups and fatty acyl chains (15, 16). Mammalian sPLA 2 s are classified into different groups depending on the primary structure characterized by the number and positions of cysteine residues. At present, five types of functional sPL...

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BackgroundRecent evidence proposes a novel concept that mammalian natural antisense RNAs play important roles in cellular homeostasis by regulating the expression of several genes. Identification and characterization of retroviral antisense RNA would provide new insights into mechanisms of replication and pathogenesis. HIV-1 encoded-antisense RNAs have been reported, although their structures and functions remain to be studied. We have tried to identify and characterize antisense RNAs of HIV-1 and their function in viral infection.ResultsCharacterization of transcripts of HEK293T cells that were transiently transfected with an expression plasmid with HIV-1NL4–3 DNA in the antisense orientation showed that various antisense transcripts can be expressed. By screening and characterizing antisense RNAs in HIV-1NL4–3-infected cells, we defined the primary structure of a major form of HIV-1 antisense RNAs, which corresponds to a variant of previously reported ASP mRNA. This 2.6 kb RNA was transcribed from the U3 region of the 3′ LTR and terminated at the env region in acutely or chronically infected cell lines and acutely infected human peripheral blood mononuclear cells. Reporter assays clearly demonstrated that the HIV-1 LTR harbours promoter activity in the reverse orientation. Mutation analyses suggested the involvement of NF-κΒ binding sites in the regulation of antisense transcription. The antisense RNA was localized in the nuclei of the infected cells. The expression of this antisense RNA suppressed HIV-1 replication for more than one month. Furthermore, the specific knockdown of this antisense RNA enhanced HIV-1 gene expression and replication.ConclusionsThe results of the present study identified an accurate structure of the major form of antisense RNAs expressed from the HIV-1NL4–3 provirus and demonstrated its nuclear localization. Functional studies collectively demonstrated a new role of the antisense RNA in viral replication. Thus, we suggest a novel viral mechanism that self-limits HIV-1 replication and provides new insight into the viral life cycle.

Key Points ATL involves genome-wide reprogramming of the H3K27me3 pattern that is distinct from other cell types. Druggable epigenetic mechanisms are associated with ATL cell development and HTLV-1–mediated transformation.

Recognition of acetylated chromatin by the bromodomains and extra-terminal domain (BET) family proteins is a hallmark for transcriptional activation and anchoring viral genomes to mitotic chromosomes of the host. One of the BET family proteins BRD2 interacts with acetylated chromatin during mitosis and leads to transcriptional activation in culture cells. Here, we report the crystal structures of the N-terminal bromodomain of human BRD2 (BRD2-BD1; residues 74 -194) in complex with each of three different Lys-12-acetylated H4 peptides. The BRD2-BD1 recognizes the H4 tail acetylated at Lys-12 (H4K12ac), whereas the side chain of hypoacetylated Lys-8 of H4 binds at the cavity of the dimer interface of BRD2-BD1. From binding studies, we identified the BRD2-BD1 residues that are responsible for recognition of the Lys-12-acetylated H4 tail. In addition, mutation to Lys-8 in the Lys-12-acetylated H4 tail decreased the binding to BRD2-BD1, implicating the critical role of Lys-8 in the Lys-12-acetylated H4 tail for the recognition by BRD2-BD1. Our findings provide a structural basis for deciphering the histone code by the BET bromodomain through the binding with a long segment of the histone H4 tail, which presumably prevents erasure of the histone code during the cell cycle.In eukaryotes, genomic DNA is complexed with core histones, consisting of two H2A-H2B dimers and one H3-H4 tetramer, to form a nucleoprotein architecture called the nucleosome (1, 2). These four core histones include a central core domain, and N-and C-terminal tail regions. The N-terminal histone tails, especially that of histone H4, are rich in lysine residues, onto which several different acetyltransferases and methyltransferases covalently add post-translational modifications (3, 4). The histone codes defined by combinations of such a histone tail modification are considered as a key regulatory mechanism for DNA metabolisms that trigger alteration of the chromatin structure and/or association of several different trans-acting factors (5-7). Among these post-translational modifications, acetylation of the histone tails and its recognition are typical hallmarks for activation of chromatin DNA (4, 7, 8, 10). The acetylated N-terminal tails of the histones are selectively recognized by the bromodomain, an ϳ110-amino acid-long domain found in several chromatin-associated factors, including nuclear histone acetyltransferases, ATP-dependent chromatin-remodeling factors, and the bromodomain and extra-terminal domain (BET) 6 family of nuclear proteins (11, 12). The human BET family, including BRD2, BRD3, BRD4, and BRDT, has a unique architecture with two tandem bromodomains and a conserved extra-terminal domain (13-15). In the intact nuclei, the BET protein BRD2 associates through its bromodomains mainly with the acetylated lysine 12 (K12ac) of H4, one of the active marks of chromatin, and activates transcription (16). Another study indicates that BRD2 binds chromatin containing Lys-12-or Lys-5-acetylated histone H4, although it scarcely bound to those con...

Purpose: Cell adhesion molecule 1 (CADM1), initially identified as a tumor suppressor gene, has recently been reported to be ectopically expressed in primary adult T-cell leukemia–lymphoma (ATL) cells. We incorporated CADM1 into flow-cytometric analysis to reveal oncogenic mechanisms in human T-cell lymphotrophic virus type I (HTLV-I) infection by purifying cells from the intermediate stages of ATL development. Experimental Design: We isolated CADM1- and CD7-expressing peripheral blood mononuclear cells of asymptomatic carriers and ATLs using multicolor flow cytometry. Fluorescence-activated cell sorted (FACS) subpopulations were subjected to clonal expansion and gene expression analysis. Results: HTLV-I–infected cells were efficiently enriched in CADM1+ subpopulations (D, CADM1posCD7dim and N, CADM1posCD7neg). Clonally expanding cells were detected exclusively in these subpopulations in asymptomatic carriers with high proviral load, suggesting that the appearance of D and N could be a surrogate marker of progression from asymptomatic carrier to early ATL. Further disease progression was accompanied by an increase in N with a reciprocal decrease in D, indicating clonal evolution from D to N. The gene expression profiles of D and N in asymptomatic carriers showed similarities to those of indolent ATLs, suggesting that these subpopulations represent premalignant cells. This is further supported by the molecular hallmarks of ATL, that is, drastic downregulation of miR-31 and upregulation of abnormal Helios transcripts. Conclusion: The CADM1 versus CD7 plot accurately reflects disease progression in HTLV-I infection, and CADM1+ cells with downregulated CD7 in asymptomatic carriers have common properties with those in indolent ATLs. Clin Cancer Res; 20(11); 2851–61. ©2014 AACR.