Signal transducing adaptor protein‐2 (STAP‐2) is a recently identified adaptor protein, that contains pleckstrin and Src homology 2 (SH2)‐like domains as well as a YXXQ motif in its C‐terminal region. Our previous studies have demonstrated that STAP‐2 binds to STAT3 and STAT5, and regulates their signaling pathways. In the present study, STAP‐2 was found to positively regulate LPS/TLR4‐mediated signals in macrophages. Disruption of STAP‐2 resulted in impaired LPS/TLR4‐induced cytokine production and NF‐κB activation. Conversely, overexpression of STAP‐2 enhanced these LPS/TLR4‐induced biological activities. STAP‐2, particularly its SH2‐like domain, bound to both MyD88 and IKK‐α/β, but not TRAF6 or IRAK1, and formed a functional complex composed of MyD88‐STAP‐2‐IKK‐α/β. These interactions augmented MyD88‐ and/or IKK‐α/β‐dependent signals, leading to enhancement of the NF‐κB activity. These results demonstrate that STAP‐2 may constitute an alternative LPS/TLR4 pathway for NF‐κB activation instead of the TRAF6‐IRAK1pathway.

Smads proteins play a key role in the intracellular signaling of the transforming growth factor (TGF)-␤ family of growth factors, which exhibits a diverse set of cellular responses, including cell proliferation and differentiation. In particular, Smad7 acts as an antagonist of TGF-␤ signaling, which could determine the intensity or duration of its signaling cascade. In this study we identified a protein inhibitor of activated STAT (signal transducers and activators of transcription), PIASy, as a novel interaction partner of Smad7 by yeast two-hybrid screening using the MH2 domain of Smad7 as bait. The association of Smad7 and PIASy was confirmed using co-expressed tagged proteins in 293T cells. Moreover, we found that other Smads including Smad3 also associated with PIASy through its MH2 domain, and PIASy suppressed TGF-␤-mediated activation of Smad3. PIASy also stimulated the sumoylation of Smad3 in vivo. Furthermore, endogenous PIASy expression was induced by TGF-␤ in Hep3B cells. These findings provide the first evidence that a PIAS family protein, PIASy, associates with Smads and involves the regulation of TGF-␤ signaling using the negative feedback loop.

Daxx has been shown to play an essential role in type I IFN-αβ-mediated suppression of B cell development and apoptosis. Recently, we demonstrated that Tyk2 is directly involved in IFN signaling for the induction and translocation of Daxx, which may result in growth arrest and/or apoptosis of B lymphocyte progenitors. To clarify how Daxx regulates B cell development, we examined Daxx interacting partners by yeast two-hybrid screening. DNA methyltransferase 1 (DNMT1)-associated protein (DMAP1) was identified and demonstrated to interact with Daxx. The interaction regions in both proteins were mapped, and the cellular localization of the interaction was examined. Both Daxx and DMAP1 formed a complex with DNMT1 and colocalized in the nucleus. DMAP1 enhanced Daxx-mediated repression of glucocorticoid receptor transcriptional activity. Furthermore, Daxx protected protein degradation of DMAP1 in vivo. These results provide the novel molecular link between Daxx and DNMT1, which establishes a repressive transcription complex in the nucleus.

In the previous study, we demonstrated the involvement of dual specificity phosphatase 22 (DUSP22/LMW-DSP2) in regulating the leukemia inhibitory factor/interleukin-6/ signal transducer and activator of transcription 3-mediated signaling pathway. In this study, we show b-estradiol (E2)-induced DUSP22 mRNA expression in estrogen receptor a (ERa)-positive breast cancer cells, whereas E2-induced phosphorylation and activation of ERa was suppressed by overexpression of DUSP22 but not catalytically inactive mutants. Furthermore, small-interfering RNA-mediated reduction of DUSP22 expression enhanced ERa-mediated transcription and endogenous gene expression. In fact, DUSP22 associated with ERa in vivo and both endogenous proteins interacted in ERa-positive breast cancer T47D cells. These results strongly suggest that DUSP22 acts as a negative regulator of the ERamediated signaling pathway.

No abstract