Summary Stringent control of the NF-κB and type I interferon pathways is critical to effective host immune responses, yet the molecular mechanisms that negatively regulate these pathways are poorly understood. Here we show that NLRC5, a member of the NOD-like protein family, can inhibit the IKK complex and RIG-I/MDA5 function. NLRC5 strongly inhibited NF-κB-dependent responses by interacting with IKKα/IKKβ and blocking their phosphorylation. It also interacted with RIG-I and MDA5, but not with MAVS, to potently inhibit RIG-I-like receptor-mediated type I interferon responses. Consistent with these observations, NLRC5-specific siRNA knockdown not only enhanced the activation of NF-κB and its responsive genes, TNF-α and IL-6, but also promoted type I interferon signaling and antiviral immunity. Our findings identify NLRC5 as a key negative regulator that blocks two central components of the NF-κB and type I interferon pathways, and hence is a pivotal element in the homeostatic control of the innate immune system.

Circulating tumor cells (CTCs) are tumor cells that have sloughed off the primary tumor and extravasate into and circulate in the blood. Understanding of the metastatic cascade of CTCs has tremendous potential for the identification of targets against cancer metastasis. Detecting these very rare CTCs among the massive blood cells is challenging. However, emerging technologies for CTCs detection have profoundly contributed to deepening investigation into the biology of CTCs and have facilitated their clinical application. Current technologies for the detection of CTCs are summarized herein, together with their advantages and disadvantages. The detection of CTCs is usually dependent on molecular markers, with the epithelial cell adhesion molecule being the most widely used, although molecular markers vary between different types of cancer. Properties associated with epithelial-to-mesenchymal transition and stemness have been identified in CTCs, indicating their increased metastatic capacity. Only a small proportion of CTCs can survive and eventually initiate metastases, suggesting that an interaction and modulation between CTCs and the hostile blood microenvironment is essential for CTC metastasis. Single-cell sequencing of CTCs has been extensively investigated, and has enabled researchers to reveal the genome and transcriptome of CTCs. Herein, we also review the clinical applications of CTCs, especially for monitoring response to cancer treatment and in evaluating prognosis. Hence, CTCs have and will continue to contribute to providing significant insights into metastatic processes and will open new avenues for useful clinical applications.

Cullin-Ring E3 ubiquitin ligases target substrates for ubiquitindependent, proteasome-mediated degradation and regulate critical cellular processes. These cullins assemble with cellular substrate receptor proteins through specific adaptor molecules. F-box-and BC-box-containing receptors use Skp1, ElonginB, and ElonginC as adaptors to recruit Cul1͞Cul7 and Cul2͞Cul5, respectively. At present, the determinants of Cul2 vs. Cul5 specificity for the BC-box-containing receptors are poorly defined. Here, we demonstrate that primate lentiviral Vif (virion infectivity factor) proteins represent previously uncharacterized substrate receptor proteins that contain divergent BC-box motifs. These molecules selectively assemble with a Cul5-E3 ligase to suppress the antiviral activity of autologous cytidine deaminase APOBEC3G. A previously unrecognized Hx 5Cx17-18Cx3-5H motif that is highly conserved among all primate lentiviral Vif proteins was found to be critical for the selective assembly and activity of Vif-Cul5-E3 ligase. Non-primate lentiviral Vif proteins, which lack this HCCH motif, displayed reduced interaction with Cul5. These data suggest that in addition to target protein specificity, substrate receptor proteins play important roles in cullin selection and functional assembly of cullinRing E3 ligases. The discovery of these viral substrate receptor molecules that recruit Cul5 through distinct mechanisms from cellular proteins may facilitate the identification of additional cellular factors that regulate cellular functions through Cul5-E3 ligase. Motifs in Vif that are absent from cellular proteins could also be targets for the development of innovative therapeutics. cullin-E3 ubiquitin ligase ͉ HIV-simian immunodeficiency virus virion infectivity factorT argeted protein degradation is one mechanism by which critical processes such as mitosis and the cell cycle are regulated (1). The specificity of protein degradation is mediated by members of the E3 ubiquitin ligase family, including the cullin-based E3 ligases. Cullins form a scaffold on which other components of the E3 ligase organize to bring the substrate into close proximity with the E2 ubiquitin-conjugating enzyme (2-5). E3 ligases are substratespecific, and cullin-based E3 ligases display striking similarities. In SCF (Skp1-Cul1-F-box) complexes, the adaptor protein Skp1 bridges the interaction between the Cul1 and substrate receptor proteins through specific interaction with an F-box (2-5). These substrate receptor proteins bind substrates through distinct protein-protein interaction domains (e.g

Lung cancer is the leading cause of cancer death. However, the mechanism of lung cancer relapse and metastasis has been poorly elucidated. Recent researches have addressed the role of MicroRNAs (miRNAs) in mediating tumor metastasis. In the present study, we identified microRNA-183 (miR-183) as a potential metastasis-inhibitor. Expression level of miR-183 was reversely correlated with the metastatic potential of lung cancer cells. Furthermore, over-expression of miR-183 inhibited migration and invasion of lung cancer cells. Mechanistically, we identified VIL2-coding-protein Ezrin as a bona fide target of miR-183. We also found that miR-183 could regulate the expression of other genes involved in migration and invasion. Taken together, our findings demonstrated a new role and regulatory mechanism of miR-183 in controlling cancer metastasis.

The emergence of SARS-CoV-2 has resulted in the COVID-19 pandemic, leading to millions of infections and hundreds of thousands of human deaths. The efficient replication and population spread of SARS-CoV-2 indicates an effective evasion of human innate immune responses, although the viral proteins responsible for this immune evasion are not clear. In this study, we identified SARS-CoV-2 structural proteins, accessory proteins, and the main viral protease as potent inhibitors of host innate immune responses of distinct pathways. In particular, the main viral protease was a potent inhibitor of both the RLR and cGAS-STING pathways. Viral accessory protein ORF3a had the unique ability to inhibit STING, but not the RLR response. On the other hand, structural protein N was a unique RLR inhibitor. ORF3a bound STING in a unique fashion and blocked the nuclear accumulation of p65 to inhibit nuclear factor-κB signaling. 3CL of SARS-CoV-2 inhibited K63-ubiquitin modification of STING to disrupt the assembly of the STING functional complex and downstream signaling. Diverse vertebrate STINGs, including those from humans, mice, and chickens, could be inhibited by ORF3a and 3CL of SARS-CoV-2. The existence of more effective innate immune suppressors in pathogenic coronaviruses may allow them to replicate more efficiently in vivo. Since evasion of host innate immune responses is essential for the survival of all viruses, our study provides insights into the design of therapeutic agents against SARS-CoV-2.

Membrane disruption has been proposed to be a key event in plant senescence, and phospholipase D (PLD; EC 3.1.4.4) has been thought to play an important role in membrane deterioration. We recently cloned and biochemically characterized three different PLDs from Arabidopsis. In this study, we investigated the role of the most prevalent phospholipidhydrolyzing enzyme, PLDa, in membrane degradation and senescence in Arabidopsis. The expression of PLDa was suppressed by introducing a PLDa antisense cDNA fragment into Arabidopsis. When incubated with abscisic acid and ethylene, leaves detached from the PLDa-deficient transgenic plants showed a slower rate of senescence than did those from wild-type and transgenic control plants. The retardation of senescence was demonstrated by delayed leaf yellowing, lower ion leakage, greater photosynthetic activity, and higher content of chlorophyll and phospholipids in the PLDa antisense leaves than in those of the wild type. Treatment of detached leaves with abscisic acid and ethylene stimulated PLDa expression, as indicated by increases in PLDa mRNA, protein, and activity. In the absence of abscisic acid and ethylene, however, detached leaves from the PLDa-deficient and wild-type plants showed a similar rate of senescence. In addition, the suppression of PLDa did not alter natural plant growth and development. These data suggest that PLDa is an important mediator in phytohormone-promoted senescence in detached leaves but is n o t a direct promoter of natural senescence. The physiological relevance of these findings is discussed. INTRODUCTIONSenescence in plants is characterized by degradation of cellular components, leading to the loss of cellular compartmentalization and tissue structure and ultimately to plant death. Disruption of membrane integrity has been hypothesized to be a major contributing factor to senescence (Beutelman and Kender, 1977; Thompson, 1988; Paliyath and Droilard, 1992; Borochov et al., 1997). One of the most characteristic features in membrane deterioration is a progressive decline of phospholipid levels with a relative enrichment of free fatty acids and sterols in the membranes (Draper, 1969;Liljenberg and Kates, 1985;Manoharan et al., 1990; Paliyath and Droilard, 1992). The change in lipid composition may cause the localized transformation of a membrane lipid bilayer into destabilized bilayer and nonbilayer structures, such as gel, micellar, and hexagonal phases (Lafleur et al., 1990), leading to the loss of membrane integrity and functions of membrane-associated proteins during senescence.How does the loss of membrane phospholipids occur during senescence? One model suggests that the breakdown of phospholipids results from a membrane lipid degradation pathway (Thompson, 1988;Paliyath and Droillard, 1992; Both authors contributed equally to this work. 'To whom correspondence should be addressed. E-mail wangs@ ksu.edu; fax 785-532-7278. Samama and Pearce, 1993;Voisine et al., 1993). In this process, phospholipase D (PLD) initiates the first reacti...

SummaryPhospholipase D (PLD) has been implicated in various processes, including signal transduction, membrane traf®cking, and membrane degradation. Multiple forms of PLD with distinct biochemical properties have been described in the cell. In Arabidopsis, PLDa and PLDg, but not PLDb, were detected in guard cells, and antisense suppression resulted in a speci®c loss of PLDa. The abrogation of PLDa rendered plants less sensitive to abscisic acid and impaired stomatal closure induced by water de®cits. PLDa-depleted plants exhibited accelerated transpirational water loss and a decreased ability to tolerate drought stress. Overexpression of PLDa enhanced the leaf's sensitivity to abscisic acid. These ®ndings provide molecular and physiological evidence that PLDa plays a crucial role in regulating stomatal movement and plant-water status.

HERV-K (human endogenous retrovirus type K) type 1-encoded Np9 is a tumor-specific biomarker, but its oncogenic role and targets in human leukemia remain elusive. We first identified Np9 as a potent viral oncogene in human leukemia. Silencing of Np9 inhibited the growth of myeloid and lymphoblastic leukemic cells, whereas expression of Np9 significantly promoted the growth of leukemia cells in vitro and in vivo. Np9 not only activated ERK, AKT and Notch1 pathways but also upregulated β-catenin essential for survival of leukemia stem cells. In human leukemia, Np9 protein level in leukemia patients was substantially higher than that in normal donors (56% vs 4.5%). Moreover, Np9 protein level was correlated with the number of leukemia stem/progenitor cells but not detected in normal CD34(+) hematopoietic stem cells. In addition, Np9-positive samples highly expressed leukemia-specific pol-env polyprotein, env and transmembrane proteins as well as viral particles. Thus, the viral oncogene Np9 is a critical molecular switch of multiple signaling pathways regulating the growth of leukemia stem/progenitor cells. These findings open a new perspective to understand the etiology of human common leukemia and provide a novel target for treating leukemia.