Zika virus (ZIKV), a recently emerged member of the flavivirus family, forms replication compartments at the ER during its lifecycle. The proteins that are responsible for the biogenesis of replication compartments are not well defined. Here, we show that Zika nonstructural protein 1 (NS1)–induced ER remodeling is essential for viral replication. NS1 expressed in the ER lumen induced ER perinuclear aggregation with an ultrastructure resembling that of the replication compartment. Data from model membrane system indicated that the membrane-binding and membrane-remodeling properties of NS1 depend on its hydrophobic insertion into the membrane. These findings demonstrate that NS1 plays a crucial role in flavivirus replication compartment formation by remodeling the ER structure.

Supranutritional selenite has anti-cancer therapeutic effects in vivo; however, the detailed mechanisms underlying these effects are not clearly understood. Further studies would broaden our understanding of the anti-cancer effects of this compound and provide a theoretical basis for its clinical application. In this study, we primarily found that selenite exposure inhibited phosphorylation of cyclic adenosine monophosphate (cAMP)-response element binding protein (CREB), leading to suppression of Bcl-2 in HCT116 and SW480 colorectal cancer (CRC) cells. Moreover, the selenite-induced inhibitory effect on PKD1 activation was involved in suppression of the CREB signalling pathway. Additionally, we discovered that selenite treatment can upregulate p38 MAPK phosphorylation, which results in inhibition of the PKD1/CREB/Bcl-2 survival pathway and triggers apoptosis. Finally, we established a colorectal cancer xenograft model and found that selenite treatment markedly inhibits tumour growth through the MAPK/PKD1/CREB/Bcl-2 pathway in vivo. Our results demonstrated that a supranutritional dose of selenite induced CRC cell apoptosis through inhibition of the PKD1/CREB/Bcl-2 axis both in vitro and in vivo.

Zika virus is a positive single-strand RNA virus whose replication involved RNA unwinding and synthesis. ZIKV NS3 contains a helicase domain, but its enzymatic activity is not fully characterized. Here, we established a dsRNA unwinding assay based on the FRET effect to study the helicase activity of ZIKV NS3, which provided kinetic information in real time. We found that ZIKV NS3 specifically unwound dsRNA/dsDNA with a 3′ overhang in the 3′ to 5′ direction. The RNA unwinding ability of NS3 significantly decreased when the duplex was longer than 18 base pairs. The helicase activity of NS3 depends on ATP hydrolysis and binding to RNA. Mutations in the ATP binding region or the RNA binding region of NS3 impair its helicase activity, thus blocking viral replication in the cell. Furthermore, we showed that ZIKV NS5 interacted with NS3 and stimulated its helicase activity. Disrupting NS3-NS5 interaction resulted in a defect in viral replication, revealing the tight coupling of RNA unwinding and synthesis. We suggest that NS3 helicase activity is stimulated by NS5; thus, viral replication can be carried out efficiently. Our work provides a molecular mechanism of ZIKV NS3 unwinding and novel insights into ZIKV replication.

It has previously been shown that selenite can act as an antitumor agent and inhibit cancer cell growth, although the mechanism responsible for this effect is not well understood. In this study, we have shown that selenite can induce cell cycle arrest and apoptosis in NB4 cells. Selenite treatment of these cells also inhibited the JNK/ATF2 axis. Further experiments demonstrated that selenite-induced production of reactive oxygen species (ROS) worked as an upstream of the JNK/ATF2 axis, cell cycle arrest and apoptosis. Inactivation of ATF2 resulted in decreased affinity of this transcription factor for the promoters of cyclin A, cyclin D3 and CDK4, which led to the arrest of the NB4 cells in the G0/G1 phase. Finally, in vivo experiments confirmed the antitumor activity of selenite and the mechanisms that were described in vitro. Taken together, our results indicate that selenite-induced ROS arrest NB4 cells at G0/G1 phase through inhibiting the JNK/ATF2 axis in vitro and in vivo.

Reactive oxygen species (ROS) have an important role in regulating various cellular processes. Our previous study confirmed that selenite, an anti-tumour agent, triggered apoptosis through the production of ROS in multiple types of cancer cells. In this study, we discovered that ROS also inhibited protective autophagy by decreasing the expression of ULK1, an initiator of autophagy, in selenite-treated NB4 cells. Further experiments demonstrated that p-p53 (S392), a phosphorylation event promoted by p70S6K, bound to the promoter of ULK1 and modulated its expression. Experiments in a mouse tumour model with NB4 cells provided in vivo confirmation of the alterations in the p70S6K/p53/ULK1 axis. Collectively, our results show that ROS inhibited autophagy by downregulating the p70S6K/p53/ULK1 axis in selenite-treated NB4 cells.