The POU transcription factor Oct-4 is a master regulator affecting the fate of pluripotent embryonic stem cells. However, the precise mechanisms by which the activation and expression of Oct-4 are regulated still remain to be elucidated. We describe here a novel murine ubiquitin ligase, Wwp2, that specifically interacts with Oct-4 and promotes its ubiquitination both in vivo and in vitro.

Transcription factor Oct4 plays critical roles in maintaining pluripotency and controlling lineage commitment of embryonic stem cells (ESCs). Our previous study indicates that Wwp2, a mouse HECT-type E3 ubiquitin ligase, ubiquitinates Oct4 and promotes its degradation in a heterologous system. However, roles of Wwp2 in regulating endogenous Oct4 protein levels as well as molecular characteristics of the function of Wwp2 have not been determined. Here, we report that Wwp2 plays an important role in Oct4 ubiquitination and degradation during differentiation of embryonal carcinoma cells (ECCs), although it does not appear to affect Oct4 protein levels in the undifferentiated ECCs and ESCs. Importantly, inhibition of Wwp2 expression by specific RNA interference elevates the Oct4 protein level, leading to attenuation in retinoid acid-induced activation of differentiation-related marker genes. Mechanistically, Wwp2 catalyzes Oct4 poly-ubiquitination via the lysine 63 linkage in a dosage-dependent manner. Interestingly, Wwp2 also regulates its own ligase activity in a similar manner. Moreover, auto-ubiquitination of Wwp2 occurs through an intra-molecular mechanism. Taken together, these results demonstrate a crucial role of Wwp2 in controlling endogenous Oct4 protein levels during differentiation processes of ECCs and suggest an interesting dosagedependent mechanism for regulating the catalytic activity of the E3 ubiquitin ligase, Wwp2.

Recognition of viral double-stranded RNA by Toll-like receptor 3 (TLR3) triggers activation of the transcription factors NF-κB and interferon regulated factor 3, leading to induction of type I interferons and proinflammatory cytokines. TIR-domain-containing adapter-inducing interferon-β (TRIF) is an adapter protein required for TLR3-mediated signaling. Here we identified the E3 ubiquitin ligase WW domaincontaining protein 2 (WWP2) as a TRIF-associated protein by biochemical purification. WWP2 mediated K48-linked ubiquitination and degradation of TRIF upon TLR3 activation. Overexpression of WWP2 inhibited TLR3-mediated NF-κB and interferon regulated factor 3 activation, whereas knockdown of WWP2 had opposite effects. We generated Wwp2-deficient mice to further investigate the roles of Wwp2 in innate immune responses. Consistently, production of IFN-β, CCL5, TNFα, and IL-6 in response to the TLR3 ligand poly(I:C) was elevated in Wwp2 −/− macrophages and Wwp2-deficient mice exhibited increased susceptibility to poly(I:C)-induced death than the control littermates. Our findings suggest that WWP2 negatively regulates TLR3-mediated innate immune and inflammatory responses by targeting TRIF for ubiquitination and degradation.T oll-like receptors (TLRs) are evolutionarily conserved pattern recognition receptors (PRRs) that are critically involved in host defense from plants to humans. So far, 13 TLRs (named TLR1 to TLR13) have been identified in humans and mice, each of which recognizes a distinct set of pathogen-associated molecular patterns (PAMPs) (1). TLRs contain an extracellular domain consisting of leucine rich repeats which is responsible for PAMP recognition, a transmembrane domain, and a conserved cytoplasmic toll/IL-1 receptor (TIR) domain which is able to mediate homotypic protein-protein interactions (2). The TIR domains of TLRs are responsible for their homo-or hetero-dimerization, and upon ligand stimulation, they also act as platforms to recruit downstream TIR domain-containing adaptor proteins and signaling molecules, leading to the activation of transcription factors such as NF-κB and interferon regulated factor 3 (IRF3) (1, 3, 4). These transcription factors act alone or in collaboration to induce transcription of proinflammatory cytokines and/or type I interferons (IFNs).Among the TLRs, TLR3 has been reported to recognize viral dsRNA as well as its analog poly(I:C). Recognition of these ligands by TLR3 activates signaling pathways leading to the activation of NF-κB and IRF3 and subsequent production of type I IFNs and proinflammatory cytokines (5). TLR3-mediated signaling critically depends on the TIR domain-containing adapter TIRdomain-containing adapter-inducing interferon-β (TRIF; also called TICAM-1) (6). It has been shown that Trif −/− lung fibroblasts are defective in poly(I:C)-induced activation of NF-κB and IRF3 as well as production of type I IFNs, demonstrating that TRIF is indispensable for TLR3-mediated signaling (7). In addition, the TLR4 ligand LPS has been shown to signal through TRIF-...