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The influenza A virus (IAV) consists of 8 single-stranded, negative-sense viral RNA (vRNA) segments. After infection, vRNA is transcribed, replicated, and wrapped by viral nucleoprotein (NP) to form viral ribonucleoprotein (vRNP). The transcription, replication, and nuclear export of the viral genome are regulated by the IAV protein, NS2, which is translated from spliced mRNA transcribed from viral NS vRNA. This splicing is inefficient, explaining why NS2 is present in low abundance after IAV infection. The levels of NS2 and its subsequent accumulation are thought to influence viral RNA replication and vRNP nuclear export. Here we show that NS2 is ubiquitinated at the K64 and K88 residues by K48-linked and K63-linked polyubiquitin (polyUb) chains, leading to the degradation of NS2 by the proteasome. Additionally, we show that a host deubiquitinase, OTUB1, can remove polyUb chains conjugated to NS2, thereby stabilizing NS2. Accordingly, knock down of OTUB1 by siRNA reduces the nuclear export of vRNP, and reduces the overall production of IAV. These results collectively demonstrate that the levels of NS2 in IAV-infected cells are regulated by a ubiquitination-deubiquitination system involving OTUB1 that is necessary for optimal IAV replication. Author summary: The influenza A virus (IAV) protein, NS2, plays a critical role in virus replication, as the abundance of NS2 influences viral transcription, viral RNA (vRNA) synthesis, and viral ribonucleoprotein (vRNP) export from the nucleus. Interestingly, high levels of NS2 are known to inhibit IAV transcription yet promote vRNA synthesis. In this study, we found that ubiquitination destabilizes NS2, and a host deubiquitinase, OTUB1, was shown to deubiquitinate and stabilize NS2, thus contributing to NS2 accumulation. OTUB1 has previously been reported to be a negative regulator of host cellular antiviral defense, and its upregulation enhances virion production. Our study sheds additional light on the role of OTUB1 during IAV infection which can now be considered for the development of anti-influenza strategies. [ABSTRACT FROM AUTHOR]

In this study, a marine medicinal brown alga Sargassum cristaefolium-derived fungal strain Xylaria acuta SC1019 was isolated and identified. Column chromatography of the extracts from liquid- and solid-fermented products of the fungal strain was carried out, and led to the isolation of twenty-one compounds. Their structures were characterized by spectroscopic analysis, and the absolute configurations were further established by single X-ray diffraction analysis or modified Mosher's method as nine previously undescribed compounds, namely xylarilactones A-C (1-3), ent-gedebic acid 8-O-α-D-glucopyranoside (4), 5R-hydroxylmethylmellein 11-O-α-D-glucopyranoside (5), ent-hymatoxin E 16-O-α-D-mannopyranoside (6), 19,20-epoxycytochalasin S (7), 19,20-epoxycytochalasin T (8), and (2R)-butylitaconic acid (9), along with twelve known compounds 10-21. All the isolates were subjected to anti-inflammatory and anti-angiogenic assays. Compounds 1, 5, 7, 10, and 17 showed moderate nitric oxide production inhibitory activities in lipopolysaccharide-activated BV-2 microglial cells with IC 50 values of 19.55 ± 0.35, 16.10 ± 0.57, 15.20 ± 0.87, 11.76 ± 0.49, and 11.30 ± 0.32 μM, respectively, as compared to curcumin (IC 50 = 2.69 ± 0.34 μM) without any significant cytotoxicity. Compounds 7, 8, and 21 displayed potent anti-angiogenic activities by suppressing the growth of human endothelial progenitor cells with IC 50 values of 0.44 ± 0.01, 0.47 ± 0.03, and 0.53 ± 0.01 μM, respectively, as compared to sorafenib (IC 50 = 5.50 ± 1.50 μM).