A redox state-dictated signalling pathway deciphers the malignant cell specificity of CD40-mediated apoptosis

Abstract

CD40, a member of the tumour necrosis factor receptor (TNFR) superfamily, has the capacity to cause extensive apoptosis in carcinoma cells, while sparing normal epithelial cells. Yet, apoptosis is only achieved by membrane-presented CD40 ligand (mCD40L), as soluble receptor agonists are but weakly pro-apoptotic. Here, for the first time we have identified the precise signalling cascade underpinning mCD40L-mediated death as involving sequential TRAF3 stabilisation, ASK1 phosphorylation, MKK4 (but not MKK7) activation and JNK/AP-1 induction, leading to a Bak- and Bax-dependent mitochondrial apoptosis pathway. TRAF3 is central in the activation of the NADPH oxidase (Nox)-2 component p40phox and the elevation of reactive oxygen species (ROS) is essential in apoptosis. Strikingly, CD40 activation resulted in down-regulation of Thioredoxin (Trx)-1 to permit ASK1 activation and apoptosis. Although soluble receptor agonist alone could not induce death, combinatorial treatment incorporating soluble CD40 agonist and pharmacological inhibition of Trx-1 was functionally equivalent to the signal triggered by mCD40L. Finally, we demonstrate using normal, ‘para-malignant' and tumour-derived cells that progression to malignant transformation is associated with increase in oxidative stress in epithelial cells, which coincides with increased susceptibility to CD40 killing, while in normal cells CD40 signalling is cytoprotective. Our studies have revealed the molecular nature of the tumour specificity of CD40 signalling and explained the differences in pro-apoptotic potential between soluble and membrane-bound CD40 agonists. Equally importantly, by exploiting a unique epithelial culture system that allowed us to monitor alterations in the redox-state of epithelial cells at different stages of malignant transformation, our study reveals how pro-apoptotic signals can elevate ROS past a previously hypothesised ‘lethal pro-apoptotic threshold' to induce death; an observation that is both of fundamental importance and carries implications for cancer therapy.

Hydrogen Sulfide Alleviates Lipopolysaccharide‐Induced Diaphragm Dysfunction in Rats by Reducing Apoptosis and Inflammation through ROS/MAPK and TLR4/NF‐κB Signaling Pathways

“…High levels of ROS could lead to an imbalance of the cellular redox state and oxidative stress, as well as induce cell apoptosis or necrosis in a number of physiological and pathological conditions [ 59 , 60 ]. Our results demonstrated that LPS increased the levels of ROS and decreased the activities of SOD, GSH-Px, and CAT, which were similar to a previous study [ 61 ].…”

Genetic Alterations of TRAF Proteins in Human Cancers

“…In addition to the above TRAF3-dependent tumor suppressive pathways verified in both human cancers and in vivo mouse models, several additional tumor suppressive pathways involving TRAF3 have been suggested by studies of cultured human cancer cells or xenograft models. These include: (1) TRAF3-mediated inhibition of the oncogenic RelB-SMAD4 association that represses TGFβ-SMAD target gene expression to promote the tumorigenesis of lung cancer, in which TRAF3 is targeted by RAS-NDP52-mediated autophagic degradation via the NDP52-TRAF3 interaction ( 183 ); (2) LIGHT-LTβR-TRAF3/TRAF5-ROS-ASK1-Caspase3 in the apoptosis of human colon cancer and hepatoma cells ( 184 ); (3) membrane-bound CD40L-CD40-TRAF3-p40phox-ROS-ASK1-MKK4-JNK-AP1-caspase 9/3/Bax/Bak in the apoptosis of human bladder and CRC cells but not normal epithelial cells ( 185 – 187 ); and (4) TRAF3-mediated inhibition of the oncogenic RIP2-NF-κB1/NF-κB2/p38-Bcl-xL pathway in the survival and proliferation of glioblastoma cells ( 188 ). Taken together, available evidence supports that TRAF3 acts as a tumor suppressor in a variety of cell types, but we cannot rule out that TRAF3 upregulation might also alter normal cell homeostasis in the same or other cell types and therefore contribute to transformation, as it has been observed in B cells and T cells.…”

Biomimetic artificial organelles with in vitro and in vivo activity triggered by reduction in microenvironment

“…Another essential factor for tuning AO functionality is a triggered response to its environment, as, for example, the redox state of the cell, which regulates various processes involved in cellular signalling pathways 33 , 34 . While there are a few reported examples of polymersomes with a stimuli-responsive permeable membrane based on the incorporation of genetically or chemically modified membrane proteins 35 , only two of them have served for the design of catalytic nanocompartments 36 , 37 , and none has been used to control reactions inside AOs.…”