Viral mediated tethering to SEL1L facilitates ER-associated degradation of IRE1

The battle between host antiviral innate immunity and immune evasion by cytomegalovirus

Cytomegalovirus (CMV) has successfully established a long-lasting latent infection in humans due to its ability to counteract the host antiviral innate immune response. During coevolution with the host, the virus has evolved various evasion techniques to evade the host's innate immune surveillance. At present, there is still no vaccine available for the prevention and treatment of CMV infection, and the interaction between CMV infection and host antiviral innate immunity is still not well understood. However, ongoing studies will offer new insights into how to treat and prevent CMV infection and its related diseases. Here, we update recent studies on how CMV evades antiviral innate immunity, with a focus on how CMV proteins target and disrupt critical adaptors of antiviral innate immune signaling pathways. This review also discusses some classic intrinsic cellular defences that are crucial to the fight against viral invasion. A comprehensive review of the evasion mechanisms of antiviral innate immunity by CMV will help investigators identify new therapeutic targets and develop vaccines against CMV infection.

Mitochondria-associated endoplasmic reticulum membrane as a mediator of vanadium-induced endoplasmic reticulum quality control in duck brains

Vanadium (V) plays a crucial role in normal cells, but excess V causes multi-organ toxicity, including neurotoxicity. Mitochondria-associated endoplasmic reticulum membrane (MAM) is a dynamic structure between endoplasmic reticulum (ER) and mitochondria that mediates ER quality control (ERQC). To explore the effects of excess V on MAM and ERQC in the brain, 72 ducks were randomly divided into two groups: the control group (basal diet) and the V group (30 mg V/kg basal diet). On days 22 and 44, brain tissues were collected for histomorphological observation and determination of trace element contents. In addition, the mRNA and protein levels of MAM and ERQC-related factors in the brain were analyzed. Results show that excessive V causes the imbalance of trace elements, the integrity disruption of MAM, rupture of ER and autophagosomes formation. Moreover, it inhibits IP3R and VDAC1 co-localization, down-regulates the expression levels of MAM-related factors, but up-regulates the expression levels of ERQC and autophagy related factors. Together, results indicate that V exposure causes disruption of MAM and activates ERQC, which is further causing autophagy.

The functional importance of VCP to maintaining cellular protein homeostasis

The AAA-ATPase (ATPases associated with diverse cellular activities) valosin-containing protein (VCP), is essential for many cellular pathways including but not limited to endoplasmic reticulum-associated degradation (ERAD), DNA damage responses, and cell cycle regulation. VCP primarily identifies ubiquitylated proteins in these pathways and mediates their unfolding and degradation by the 26S proteasome. This review summarizes recent research on VCP that has uncovered surprising new ways that this ATPase is regulated, new aspects of recognition of substrates and novel pathways and substrates that utilize its activity.

ATF6-mediated unfolded protein response facilitates AAV2 transduction by releasing the suppression of AAV receptor on ER stress

Adeno-associated virus (AAV) is extensively used as a viral vector to deliver therapeutic genes during human gene therapy. A high affinity cellular receptor (AAVR) for most serotypes was recently identified, however, its biological function as a gene product remains unclear. In this study, we used AAVR knockdown cell models to show that AAVR depletion significantly attenuated cells to activate unfolded protein response (UPR) pathways, when exposed to the endoplasmic reticulum (ER) stress inducer, tunicamycin. By analyzing three major UPR pathways, we found that ATF6 signaling was most affected in an AAVR-dependent fashion, distinct to CHOP and XBP1 branches. AAVR capacity in UPR regulation required the full native AAVR protein, and AAV2 capsid binding to the receptor altered ATF6 dynamics. Conversely, the transduction efficiency of AAV2 was associated with changes in ATF6 signaling in host cells following treatment with different small molecules. Thus, AAVR served as an inhibitory molecule to repress UPR responses via a specificity for ATF6 signaling, and the AAV2 infection route involved the release from AAVR-mediated ATF6 repression, thereby facilitating viral intracellular trafficking and transduction. Importance The native function of the AAVR as an ER-Golgi localized protein is largely unknown. We showed that AAVR acted as a functional molecule to regulate UPR signaling under induced ER stress. AAVR inhibited the activation of the transcription factor, ATF6, whereas receptor binding to AAV2 released the suppression effects. This finding has expanded our understanding of AAV infection biology in terms of the physiological properties of AAVR in host cells. Importantly, our research provides a possible strategy which may improve the efficiency of AAV mediated gene delivery during gene therapy.

CHOP Pro-Apoptotic Transcriptional Program in Response to ER Stress Is Hacked by Zika Virus

Zika virus (ZIKV) is an emerging mosquito-borne flavivirus considered as a threat to human health due to large epidemics and serious clinical outcomes such as microcephaly in new-borns. Like all flaviviruses, ZIKV relies on the cellular machinery to complete its viral cycle, with the endoplasmic reticulum (ER) being the critical site of viral replication factories. The sudden high protein load in the ER induces an ER stress to which the cell responds with an appropriate unfolded protein response (UPR) in an attempt to restore its disturbed homeostasis. When the restoration fails, the cell signalling leads to a programmed cell death by apoptosis with the upregulation of the UPR-induced C/EBP homologous protein (CHOP) which acts as the main trigger for this fatal outcome. Our previous studies have shown the ability of ZIKV to manipulate various cellular responses in order to optimize virus production. ZIKV is able to delay apoptosis to its benefit and although ER stress is induced, the UPR is not complete. Here we discovered that ZIKV impairs the expression of CHOP/DDIT3, the main factor responsible of ER-stress driven apoptosis. Surprisingly, the mechanism does not take place at the transcriptional level but at the translational level.