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 newborns. 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 signaling 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.

The imipramine ONC201 exerts a novel anti-proliferative activity over a wide spectrum of cancer cell types. ONC201 activates integrated stress response pathway that is associated with induction of Damage Inducible Transcript 3 (DDIT3, also known as C/EBP homologous protein or CHOP). We questioned whether the ONC201/CHOP crosstalk is regulated by diverse signaling pathways in non-metastatic versus metastatic cancer cell lines. Therefore, the Dukes' type B colorectal adenocarcinoma non-metastatic (SW480) and metastatic (LS-174T) cell lines were treated with ONC201. Cell proliferation and apoptosis were evaluated by MTT assay, flow cytometry analysis, gene expression was assessed by Affymetrix microarray, and key regulatory proteins were validated by Western blot assays. Unlike LS-174T cells, SW480 cells were resistant to ONC201 treatment. Gene ontology pathway enrichment analysis of differentially expressed genes revealed substantial differences between LS-174T and SW480 responsiveness to ONC201 treatment. In both cell lines, CHOP expression was upregulated in response to ONC201 treatment, however, its upstream regulatory mechanisms were not identical. Although, PERK, ATF6 and IRE1 ER-stress pathways were found to upregulated CHOP in both cell types, the BAK/BAX pathway was a notable regulator of CHOP in the metastatic LS-174T cells alone. In addition, CHOP RNA splicing profiles were varied between the two cell lines, which was further modified in response to ONC201 treatments. In conclusion, we delineated the signaling mechanisms regulating the expression of CHOP in non-metastatic versus metastatic colorectal cells in response to ONC201 treatment. The observed differences were related to cellular plasticity and metabolic reprogramming.

Obesity and metabolic syndrome involve chronic low-grade inflammation called metabolic inflammation as well as metabolic derangements from increased endotoxin and free fatty acids. It is debated whether the endoplasmic reticulum (ER) stress in monocytic cells can contribute to amplify metabolic inflammation; if so, by which mechanism(s). To test this, metabolic stress was induced in THP-1 monocytic cells by treatments with lipopolysaccharide (LPS), palmitic acid (PA), or oleic acid (OA), in the presence or absence of ER stressor thapsigargin (TG). Gene expression of tumor necrosis factor (TNF)-α and markers of ER/oxidative stress was determined by qRT-PCR, TNF-α protein by ELISA, ROS by DCFH-DA assay, HIF-1α/p38/ERK-1,2/NF-κB phosphorylation by immunoblotting, and insulin sensitivity by glucose-uptake assay. Regarding clinical analyses, adipose TNF-α was assessed by qRT-PCR/IHC and plasma TNF-α/hs-CRP/MDA/OX-LDL by ELISA. We found that the cooperative interaction between metabolic and ER stresses promoted TNF-α, ROS, CHOP, ATF6, SOD2, and NRF2 expression (P≤0.0183),. However, glucose uptake was not impaired. TNF-α amplification was dependent on HIF-1α/p38/NF-κB phosphorylation, while MAPK/NF-κB inhibitors and antioxidants/ROS scavengers attenuated TNF-α production (P≤0.05). Individuals with obesity displayed increased adipose TNF-α gene/protein expression as well as elevated plasma levels of TNF-α, CRP, MDA, and OX-LDL (P≤0.05). Our findings support a cooperative interaction between metabolic and ER stresses, favoring inflammation by triggering TNF-α production via the ROS/CHOP/HIF-1α and MAPK/NF-κB dependent mechanisms. This study also shows the therapeutic potential of ROS scavengers/anti-oxidants in inflammatory conditions involving metabolic/ER stresses.