Cyclosporine A binding to COX-2 reveals a novel signaling pathway that activates the IRE1α unfolded protein response sensor

Abstract

Cyclosporine, a widely used immunosuppressant in organ transplantation and in treatment of various autoimmune diseases, activates the unfolded protein response (UPR), an ER stress coping response. In this study we discovered a new and unanticipated cyclosporine-dependent signaling pathway, with cyclosporine triggering direct activation of the UPR. COX-2 binds to and activates IRE1α, leading to IRE1α splicing of XBP1 mRNA. Molecular interaction and modeling analyses identified a novel interaction site for cyclosporine with COX-2 which caused enhancement of COX-2 enzymatic activity required for activation of the IRE1α branch of the UPR. Cyclosporine-dependent activation of COX-2 and IRE1α in mice indicated that cyclosporine-COX-2-IRE1α signaling pathway was functional in vivo. These findings identify COX-2 as a new IRE1α binding partner and regulator of the IRE1α branch of the UPR pathway, and establishes the mechanism underlying cytotoxicity associated with chronic cyclosporine exposure.

Endoplasmic reticulum and the microRNA environment in the cardiovascular system

“…Silencing of COX-2 resulted in significant decreases in XBP1 splicing, implying a direct role for COX-2 in the ER stress response, similar to what we have seen previously (Fig. 5D) (Groenendyk et al 2018). COX-2 is a novel regulator of ER stress (Groenendyk et al 2018) that is downregulated during ER stress conditions by miR-101b.…”

“…5D) (Groenendyk et al 2018). COX-2 is a novel regulator of ER stress (Groenendyk et al 2018) that is downregulated during ER stress conditions by miR-101b. COX-2 is involved in the conversion of arachidonic acid to prostaglandin endoperoxide H2.…”

“…COX-2 inhibitors increase the risk of heart disease in patients that have been using coxibs for a long period of time (Streicher and Wang 2008). COX-2 is linked to ER stress responses and may be responsible for the UPR seen during conditions that induce oxidative stress (Choo-Wing et al 2013;Groenendyk et al 2018).…”

“…The pRL-IXFL XBP1 contains an internal Renilla control and the nucleotide sequence encoding XBP1 followed by firefly luciferase separated by an internal ribosomal entry site (IRES) initiation region (Back et al 2006b;Groenendyk et al 2014a). (D) HEK-293 cells were transfected with siRNA specific for COX-2 (Groenendyk et al 2018), treated for 24 hours with 0.5 µM thapsigargin (Groenendyk et al 2014b). (E) HEK-293 cells were transfected with hsa-miR-101b mimic, treated for 24 hours with 0.5 µM thapsigargin and mRNA harvested.…”

Cyclophilin inhibition as a potential treatment for nonalcoholic steatohepatitis (NASH)

“…These findings were often observed with cancer cells which may be more susceptible to ER stress due to the need for cyclophilins to support high metabolic demands. Another caveat is that the concentrations of CsA that generated UPR in many of the studies exceeded the CsA half-maximal cytotoxicity concentration (CC 50 ≈ 12 µM) [43,[166][167][168][169][170][171]. Therefore, ER stress may indeed be a mechanism of highdose CsA cytotoxicity, but most studies do not show that cyclophilin inhibitors at therapeutic concentrations induce ER stress.…”