Epigenetic silencing in cancer cells is mediated by at least two distinct histone modifications, polycomb-based histone H3 lysine 27 trimethylation (H3K27triM) and H3K9 dimethylation. The relationship between DNA hypermethylation and these histone modifications is not completely understood. Using chromatin immunoprecipitation microarrays (ChIP-chip) in prostate cancer cells compared to normal prostate, we found that up to 5% of promoters (16% CpG islands and 84% non-CpG islands) were enriched with H3K27triM. These genes were silenced specifically in prostate cancer, and those CpG islands affected showed low levels of DNA methylation. Downregulation of the EZH2 histone methyltransferase restored expression of the H3K27triM target genes alone or in synergy with histone deacetylase inhibition, without affecting promoter DNA methylation, and with no effect on the expression of genes silenced by DNA hypermethylation. These data establish EZH2-mediated H3K27triM as a mechanism of tumor-suppressor gene silencing in cancer that is potentially independent of promoter DNA methylation.

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.

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.

CD26 is a T cell costimulatory molecule with dipeptidyl peptidase IV activity in its extracellular region. We previously reported that recombinant soluble CD26 enhanced T cell proliferation induced by the recall antigen tetanus toxoid (TT). However, the mechanism involved in this enhancement is not yet elucidated. We now demonstrate that CD26 binds Caveolin-1 on antigen-presenting cells, and that residues 201-211 of CD26 along with the serine catalytic site at residue 630 contribute to binding to caveolin-1 scaffolding domain. In addition, after CD26 -caveolin-1 interaction on TT-loaded monocytes, caveolin-1 is phosphorylated, which links to activate NF-B, followed by up-regulation of CD86. Finally, reduced caveolin-1 expression on monocytes inhibits CD26-mediated CD86 up-regulation and abrogates CD26 effect on TT-induced T cell proliferation. Taken together, these results strongly suggest that CD26 -caveolin-1 interaction plays a role in the up-regulation of CD86 on TT-loaded monocytes and subsequent engagement with CD28 on T cells, leading to antigen-specific T cell activation. C D26 is a widely distributed, 110-kDa cell-surface glycoprotein with known dipeptidyl peptidase IV (DPPIV) (EC 3.4.14.5) activity in its extracellular domain (1, 2), capable of cleaving amino-terminal dipeptides with either L-proline or L-alanine at the penultimate position. The CD4 ϩ CD26 high T cells respond maximally to recall antigens, such as tetanus toxoid (TT) (3). Crosslinking of CD26 and CD3 with solid-phase immobilized mAbs induces T cell costimulation and IL-2 production by either human CD4 ϩ T cells or CD26 Jurkat transfectants (4, 5, 6). Importantly, DPPIV enzyme activity is required for CD26-mediated T cell costimulation (7). More recently, we have shown that internalization of CD26 after crosslinking is mediated in part by the mannose-6-phosphate͞ insulin-like growth factor II receptor (M6P͞IGF-IIR), and that CD26-M6P͞IGFIIR interaction plays a role in CD26-induced T cell costimulation (8).Caveolin-1 was first identified as a major tyrosine phosphorylated protein in v-Src-transformed chicken embryo fibroblasts (9). Multiple lines of evidence suggest that caveolin-1 acts as a scaffolding protein capable of directly interacting with and modulating the activity of caveolin-bound signaling molecules. In support of this hypothesis, caveolin-1 binding can functionally modulate the activity of G protein-coupled proteins, membrane proteins, nonreceptor tyrosine and serine͞threonine kinases, protein kinase C isoforms, epidermal growth factor receptor, and endothelial nitric oxide synthetase (10, 11). In immune cells, caveolin-1 on monocytes͞ macrophages regulates metabolism of scavenged lipids (12). However, it is unknown whether caveolin-1 also plays a role in signal transduction in antigen-presenting cells (APC).Maximal T cell activation requires both an antigen-specific stimulus provided by an MHC peptide complex and a costimulatory signal (13). Engagement of CD28 on T cell surface by B7-1 (CD80) or B7-2 (CD86) expressed on AP...

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.