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.

Post-translational modification and degradation of proteins by the ubiquitin-proteasome system are key regulatory mechanisms in cellular responses to various stimuli. The NF-jB signaling pathway is controlled by the ubiquitin-mediated proteolysis. RelA/p65, which is a main subunit of NF-jB, is ubiquitinated for degradation by SOCS-1, but the functional mechanism of its ubiquitination remains poorly understood. In this study we show that phosphorylation of RelA/p65 at Ser276 prevents its degradation by ubiquitin-mediated proteolysis. In contrast, impairment of Ser276 phosphorylation affects constitutive degradation of RelA/p65. Importantly, we identify Pim-1 as a further kinase responsible for the phosphorylation of RelA/p65 at Ser276. Depletion of Pim-1 hinders not only Ser276 phosphorylation but also transactivation of RelA/p65 target genes. We also show that Pim-1 contributes to recruitment of RelA/p65 to jB-elements to activate NF-jB signalling after TNF-a stimulation. In concert with these results, the knockdown of Pim-1 impairs IL-6 production and augments apoptosis by interfering RelA/p65 activation. These findings provide a model in which Pim-1 phosphorylation of RelA/p65 at Ser276 allows defense against ubiquitin-mediated degradation and whereby exerts activation of NF-jB signalling. NF-kB is an inducible transcription factor that controls the expression of a number of proteins involved in the regulation of cell survival and immune response. 1 It is a dimmer formed from a multisubset family consisting of RelA/p65, RelB, c-Rel, p105/p50 (NF-kB1), and p100/p52 (NF-kB2). It is activated by a bewildering array of stimuli and its activation is regulated by multiple distinct signalling cascades, including inhibitors of the NF-kB (IkB) kinase (IKK) signalosome. IKK phosphorylates IkB-a at Ser32 and Ser36 in response to a variety of stimuli, resulting in its ubiquitination and subsequent proteasomal degradation. The released NF-kB targets to the nucleus and thereby induces the expression of specific target genes. In addition to nuclear translocation of the NF-kB complex, previous studies have shown that a subunit of NF-kB, RelA/ p65, is post-translationally modified, such as phosphorylation, ubiquitination, or acetylation, and these changes influence its transcriptional activity. In particular, phosphorylation of RelA/ p65 at Ser276, Ser529, or Ser536 could be indispensable for its ability to function as an activator of gene expression. 2 However, recent findings showing a role for Ser529/536 phosphorylation on RelA/p65 activation in response to TNF-a arise conflicting evidences. [3][4][5] In contrast, accumulating evidences have revealed that Ser276 phosphorylation is critical for transactivation of RelA/p65 at least in response to TNF-a. Moreover, Ser276 is the major phosphorylation site of RelA/p65 induced by TNF-a. Phospho-RelA/p65 at Ser276 forms a stable complex with co-activator CBP/p300, a modification apparently required for assembly of a functional enhanceosome on the responsive promoters. 6,7 As nucle...

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Ulva compressa L. is a heterothallic macroalga considered to be in the early evolutionary stage between isogamy and anisogamy. Two genetic lines of this species, each consisting of gametophytes with opposite mating types, were collected on the coasts of Ehime and Iwate prefectures: MGEC-1 (mt(+) ) and MGEC-2 (mt(-) ) from Ehime, and MGEC-5 (mt(+) ) and MGEC-6 (mt(-) ) from Iwate. Their relative gamete sizes (i.e., cell volumes) do not correspond to their mating types: MGEC-6 (19.8 μm(3) ) > MGEC-1 (18.6 μm(3) ) > MGEC-5 (17.0 μm(3) ) > MGEC-2 (10.1 μm(3) ). The pattern of organelle inheritance is an important sexual characteristic in many eukaryotes. We therefore investigated the relationship between gamete size and the inheritance of chloroplast DNA (cpDNA). Polymorphisms between the cpDNA of the two lines were used as markers. We found a 24 bp insertion between psbF and psbL, and the substitution of a StyI site (from CCAAGG to TCAAGG) in the intergenic region between petD and accD. Two interline crosses (MGEC-1 × MGEC-6 and MGEC-2 × MGEC-5) produced 42 and 38 zygotes, respectively. PCR and PCR-RFLP analyses showed that the cpDNA of the mt(+) gametes was consistently inherited in both crosses. The cpDNA is inherited from one parent only, and it depends not on gamete size but on being mt(+) . The cpDNA was observed during crossing and in the zygotes 6 h after mating. In 6% of the zygotes, the cpDNA derived from the mt(-) gametes disappeared 3-4 h after mating. Preferential digestion of the cpDNA in the zygote's mt(-) gamete may form the basis for uniparental inheritance of cpDNA.

Gametes of the marine green alga Ulva compressa L. are biflagellate and pear shaped, with one eyespot at the posterior end of the cell. The species is at an early evolutionary stage between isogamy and anisogamy. In the past, zygote formation of green algae was categorized solely by the relative sizes of gametes produced by two mating types (+ and -). Recently, however, locations of cell fusion sites and/or mating structures of gametes have been observed to differ between mating types in several green algae (asymmetry of cell fusion site and/or mating structure positions). To use this asymmetry for determining gamete mating type, we explored a new method, field emission scanning electron microscopy (FE-SEM), for visualizing the mating structure of U. compressa. When gametes were subjected to drying stress in the process of a conventional critical-point-drying method, a round structure was observed on the cell surfaces. In the mating type MGEC-1 (mt(+) ), this structure was located on the same side of the cell as the eyespot, whereas it was on the side opposite the eyespot in the mating type MGEC-2 (mt(-) ). The gametes fuse at the round structures. TEM showed an alignment of vesicles inside the cytoplasm directly below the round structures, which are indeed the mating structures. Serial sectioning and three-dimensional construction of TEM micrographs confirmed the association of the mating structure with flagellar roots. The mating structure was associated with 1d root in the MGEC-1 gamete but with 2d root in the MGEC-2 gamete.