Stressful life event is closely associated with depression, thus strategies that blunt or prevent the negative effect stress on the brain might benefits for the treatment of depression. Although previous study showed the role of protein kinase R (PKR)-like ER kinase (PERK) in inflammation related depression, its involvement in the neuropathology of chronic stress induced depression is still unknown. We tried to explore whether block the PERK pathway would alleviate the animals\' depression-like behavior induced by chronic restraint stress (CRS) and investigate the underlying mechanism. The CRS-exposed mice exhibited depression-like behavior, including anhedonia in the sucrose preference test (SPT), and increased immobility time in tail suspension test (TST) and forced swim test (FST). ISRIB administration for 2 weeks significantly improved the depression-like behavior in male mice exposed to CRS, which was manifested by markedly increasing the sucrose preference and reducing the immobility time in the FST and TST. However, we observed that exposure to the same dose of ISRIB in CRS female mice only showed improved anhedonia-like deficits,leaving unaltered improvement in the FST and TST. Mechanically, we found that ISRIB reversed the hypothalamic-pituitary-adrenal (HPA) axis hyperactivity, indicating decreased levels of serum corticosterone, reduced hippocampal glucocorticoidreceptor (GR) expression and expression of FosB in hypothalamic paraventricularnucleus (PVN), which was accompanied by preserved hippocampal neurogenesis. The present findings further expand the potential role of ER stress in depression and provide important details for a therapeutic path forward for PERK inhibitors in mood disorders.

Enteroviruses are single-stranded, positive-sense RNA viruses causing endoplasmic reticulum (ER) stress to induce or modulate downstream signaling pathways known as the unfolded protein responses (UPR). However, viral and host factors involved in the UPR related to viral pathogenesis remain unclear. In the present study, we aimed to identify the major regulator of enterovirus-induced UPR and elucidate the underlying molecular mechanisms. We showed that host Golgi-specific brefeldin A-resistant guanine nucleotide exchange factor 1 (GBF1), which supports enteroviruses replication, was a major regulator of the UPR caused by infection with enteroviruses. In addition, we found that severe UPR was induced by the expression of 3A proteins encoded in human pathogenic enteroviruses, such as enterovirus A71, coxsackievirus B3, poliovirus, and enterovirus D68. The N-terminal-conserved residues of 3A protein interact with the GBF1 and induce UPR through inhibition of ADP-ribosylation factor 1 (ARF1) activation via GBF1 sequestration. Remodeling and expansion of ER and accumulation of ER-resident proteins were observed in cells infected with enteroviruses. Finally, 3A induced apoptosis in cells infected with enteroviruses via activation of the protein kinase RNA-like endoplasmic reticulum kinase (PERK)/C/EBP homologous protein (CHOP) pathway of UPR. Pharmaceutical inhibition of PERK suppressed the cell death caused by infection with enteroviruses, suggesting the UPR pathway is a therapeutic target for treating diseases caused by infection with enteroviruses.IMPORTANCEInfection caused by several plus-stranded RNA viruses leads to dysregulated ER homeostasis in the host cells. The mechanisms underlying the disruption and impairment of ER homeostasis and its significance in pathogenesis upon enteroviral infection remain unclear. Our findings suggested that the 3A protein encoded in human pathogenic enteroviruses disrupts ER homeostasis by interacting with GBF1, a major regulator of UPR. Enterovirus-mediated infections drive ER into pathogenic conditions, where ER-resident proteins are accumulated. Furthermore, in such scenarios, the PERK/CHOP signaling pathway induced by an unresolved imbalance of ER homeostasis essentially drives apoptosis. Therefore, elucidating the mechanisms underlying the virus-induced disruption of ER homeostasis might be a potential target to mitigate the pathogenesis of enteroviruses.

MicroRNA and mitofusin-2 (Mfn2) play an important role in the myocardial apoptosis induced by acute myocardial infarction (AMI). However, the target relationship and underlying mechanism associated with interorganelle interaction between endoplasmic reticulum (ER) and mitochondria under ischemic condition is not completely clear. MI-induced injury, Mfn2 expression, Mfn2-mediated mitochondrial function and ER stress, and target regulation by miRNA-15b (miR-15b) were evaluated by animal MI and cellular hypoxic models with advanced molecular techniques. The results confirmed that Mfn2 was down-regulated and miR-15b was up-regulated upon the target binding profile under ischemic/hypoxic condition. Our data showed that miR-15b caused cardiac apoptotic injury that was reversed by rAAV9-anti-miR-15b or AMO-15b. The damage effect of miR-15b on Mfn2 expression and mitochondrial function was observed and rescued by rAAV9-anti-miR-15b or AMO-15b. The targeted regulation of miR-15b on Mfn2 was verified by luciferase reporter and microRNA-masking. Importantly, miR-15b-mediated Mfn2 suppression activated PERK/CHOP pathway, by which leads to ER stress and mitochondrial dysfunction, and cardiac apoptosis eventually. In conclusion, our research, for the first time, revealed the missing molecular link in Mfn2 and apoptosis and elucidated that pro-apoptotic miR-15b plays crucial roles during the pathogenesis of AMI through down-regulation of Mfn2 and activation of PERK-mediated ER stress. These findings may provide an opportunity to develop new therapies for prophylaxis and treatment of ischemic heart disease.

Despite the consensus that accumulation of unfolded proteins in the endoplasmic reticulum (ER) lumen, i.e. ER stress, activates the unfolded protein response (UPR), studies under physiological and pathophysiological conditions suggest that ER stress may not always trigger the UPR, and the UPR can be activated in an ER stress-independent way. To better understand how the UPR is regulated and its relationship with ER stress requires direct detection of unfolded proteins in the ER, a method that is still lacking. Here, we report a strategy of visualizing unfolded protein accumulation in the ER lumen in living cells by employing an engineered ER stress sensor, PERK, which forms fluorescence puncta upon unfolded protein binding, in a fast and reversible way. Our reporter enables us to clarify the involvement of unfolded proteins in UPR activation under several physiological conditions and suggests that persistent unfolded protein accumulation in the ER despite UPR attenuation predicts cell death.

Colorectal cancer (CRC) is the second most deadly cancer worldwide. Although various treatments for CRC have made progress, they have limitations. Therefore, the search for new effective molecular targets is important for the treatment of CRC. p20BAP31 induces apoptosis through diverse pathways and exhibits greater sensitivity in CRC. Therefore, a comprehensive exploration of the molecular functions of p20BAP31 is important for its application in anti-tumor therapy. In this study, we showed that exogenous p20BAP31 was still located in the ER and significantly activated the unfolded protein response (UPR) through the PERK pathway. The activation of the PERK pathway is prominent in p20BAP31-induced reactive oxygen species (ROS) accumulation and apoptosis. We found, for the first time, that p20BAP31 leads to ER stress and markedly attenuates tumor cell growth in vivo. Importantly, mechanistic investigations indicated that p20BAP31 competitively binds to GRP78 from PERK and causes hyperactivation of the UPR. Furthermore, p20BAP31 upregulates the expression of GRP78 by promoting HSF1 nuclear translocation and enhancing its binding to the GRP78 promoter. These findings reveal p20BAP31 as a regulator of ER stress and a potential target for tumor therapy, and elucidate the underlying mechanism by which p20BAP31 mediates signal transduction between ER and mitochondria.

Background: Alternol is a small molecular compound isolated from the fermentation of a mutant fungus obtained from Taxus brevifolia bark. Our previous studies showed that Alternol treatment induced reactive oxygen species (ROS)-dependent immunogenic cell death. This study conducted a comprehensive investigation to explore the mechanisms involved in Alternol-induced immunogenic cell death. Methods: Prostate cancer PC-3, C4-2, and 22RV1 were used in this study. Alternol interaction with heat shock proteins (HSP) was determined using CETSA assay. Alternol-regulated ER stress proteins were assessed with Western blot assay. Extracellular adenosine triphosphate (ATP) was measured using ATPlite Luminescence Assay System. Results: Our results showed that Alternol interacted with multiple cellular chaperone proteins and increased their expression levels, including endoplasmic reticulum (ER) chaperone hypoxia up-regulated 1 (HYOU1) and heat shock protein 90 alpha family class B member 1 (HSP90AB1), as well as cytosolic chaperone heat shock protein family A member 8 (HSPA8). These data represented a potential cause of unfolded protein response (UPR) after Alternol treatment. Further investigation revealed that Alternol treatment triggered ROS-dependent (ER) stress responses via R-like ER kinase (PERK), inositol-requiring enzyme 1α (IRE1α). The double-stranded RNA-dependent protein kinase (PKR) but not activating transcription factor 6 (ATF6) cascades, leading to ATF-3/ATF-4 activation, C/EBP-homologous protein (CHOP) overexpression, and X-box binding protein XBP1 splicing induction. In addition, inhibition of these ER stress responses cascades blunted Alternol-induced extracellular adenosine triphosphate (ATP) release, one of the classical hallmarks of immunogenic cell death. Conclusion: Taken together, our data demonstrate that Alternol treatment triggered multiple ER stress cascades, leading to immunogenic cell death.

Coronaviruses represent a significant class of viruses that affect both animals and humans. Their replication cycle is strongly associated with the endoplasmic reticulum (ER), which, upon virus invasion, triggers ER stress responses. The activation of the unfolded protein response (UPR) within infected cells is performed from three transmembrane receptors, IRE1, PERK, and ATF6, and results in a reduction in protein production, a boost in the ER\'s ability to fold proteins properly, and the initiation of ER-associated degradation (ERAD) to remove misfolded or unfolded proteins. However, in cases of prolonged and severe ER stress, the UPR can also instigate apoptotic cell death and inflammation. Herein, we discuss the ER-triggered host responses after coronavirus infection, as well as the pharmaceutical targeting of the UPR as a potential antiviral strategy.

Autophagy and Unfolded Protein Response (UPR) can be regarded as the safe keepers of cells exposed to intense stress. Autophagy maintains cellular homeostasis, ensuring the removal of foreign particles and misfolded macromolecules from the cytoplasm and facilitating the return of the building blocks into the system. On the other hand, UPR serves as a shock response to prolonged stress, especially Endoplasmic Reticulum Stress (ERS), which also includes the accumulation of misfolded proteins in the ER. Since one of the many effects of viral infection on the host cell machinery is the hijacking of the host translational system, which leaves in its wake a plethora of misfolded proteins in the ER, it is perhaps not surprising that UPR and autophagy are common occurrences in infected cells, tissues, and patient samples. In this book chapter, we try to emphasize how UPR, and autophagy are significant in infections caused by six major oncolytic viruses-Epstein-Barr (EBV), Human Papilloma Virus (HPV), Human Immunodeficiency Virus (HIV), Human Herpesvirus-8 (HHV-8), Human T-cell Lymphotropic Virus (HTLV-1), and Hepatitis B Virus (HBV). Here, we document how whole-virus infection or overexpression of individual viral proteins in vitro and in vivo models can regulate the different branches of UPR and the various stages of macro autophagy. As is true with other viral infections, the relationship is complicated because the same virus (or the viral protein) exerts different effects on UPR and Autophagy. The nature of this response is determined by the cell types, or in some cases, the presence of diverse extracellular stimuli. The vice versa is equally valid, i.e., UPR and autophagy exhibit both anti-tumor and pro-tumor properties based on the cell type and other factors like concentrations of different metabolites. Thus, we have tried to coherently summarize the existing knowledge, the crux of which can hopefully be harnessed to design vaccines and therapies targeted at viral carcinogenesis.

Immunosuppressive macrophages restrict anti-cancer immunity in glioblastoma (GBM). Here, we studied the contribution of microglia (MGs) and monocyte-derived macrophages (MDMs) to immunosuppression and mechanisms underlying their regulatory function. MDMs outnumbered MGs at late tumor stages and suppressed T cell activity. Molecular and functional analysis identified a population of glycolytic MDM expressing GLUT1 with potent immunosuppressive activity. GBM-derived factors promoted high glycolysis, lactate, and interleukin-10 (IL-10) production in MDMs. Inhibition of glycolysis or lactate production in MDMs impaired IL-10 expression and T cell suppression. Mechanistically, intracellular lactate-driven histone lactylation promoted IL-10 expression, which was required to suppress T cell activity. GLUT1 expression on MDMs was induced downstream of tumor-derived factors that activated the PERK-ATF4 axis. PERK deletion in MDM abrogated histone lactylation, led to the accumulation of intratumoral T cells and tumor growth delay, and, in combination with immunotherapy, blocked GBM progression. Thus, PERK-driven glucose metabolism promotes MDM immunosuppressive activity via histone lactylation.

Ambient air temperature is a key factor affecting human health. Female reproductive disorders are representative health risk events under low temperature. However, the mechanism involving in cold-induced female reproductive disorders remains largely unknown. Female mice were intermittently exposed to cold conditions (4 °C) to address the health risk of low temperature on female reproductive system. Primary granulosa cells (GCs) were prepared and cultured under low temperature (35 °C) or exposed to β3-adrenoreceptor agonist, isoproterenol, to mimic the condition of cold exposure. Western-blot, RT-PCR, co-IP, ELISA, pharmacological inhibition or siRNA-mediated knockdown of target gene were performed to investigate the possible role of hormones, gap conjunction proteins, and ER stress sensor protein in regulating female reproductive disorders under cold exposure. Cold exposure induced estrous cycle disorder and follicular dysplasia in female mice, accompanying with abnormal upregulation of progesterone and its synthetic rate-limiting enzyme, StAR, in the ovarian granulosa cells. Under the same conditions, an increase in connexin 43 (CX43) expressions in the GCs was also observed, which contributed to elevated progesterone levels in the ovary. Moreover, ER stress sensor protein, PERK, was activated in the ovarian GCs after cold exposure, leading to the upregulation of downstream NRF2-dependent CX43 transcription and aberrant increase in progesterone synthesis. Most importantly, blocking PERK expression in vivo significantly inhibited NRF2/CX43/StAR/progesterone pathway activation in the ovary and efficiently rescued the prolongation of estrous cycle and the increase in follicular atresia of the female mice induced by cold stress. We have elucidated the mechanism of ovarian PERK/NRF2/CX43/StAR/progesterone pathway activation in mediating female reproductive disorder under cold exposure. Targeting PERK might be helpful for maintaining female reproductive health under cold conditions.