Pirin Inhibits FAS‐Mediated Apoptosis to Support Colorectal Cancer Survival

Resistance to immunotherapy in colorectal cancer (CRC) is associated with obstruction of FAS (Apo‐1 or CD95)‐dependent apoptosis, a hallmark of cancer. Here it is demonstrated that the upregulation of pirin (PIR) protein in colon cancers promotes tumorigenesis. Knockout or inhibition of PIR dramatically increases FAS expression, FAS‐dependent apoptosis and attenuates colorectal tumor formation in mice. Specifically, NFκB2 is a direct transcriptional activator of FAS and robustly suppressed by PIR in dual mechanisms. One is the disruption of NFκB2 complex (p52‐RELB) association with FAS promoter, the other is the inhibition of NIK‐mediated NFκB2 activation and nuclear translocation, leading to the inability of active NFκB2 complex toward the transcription of FAS. Furthermore, PIR interacts with FAS and recruits it in cytosol, preventing its membrane translocation and assembling. Importantly, knockdown or knockout of PIR dramatically sensitizes cells to FAS mAb‐ or active CD8+ T cells‐triggered cell death. Taken together, a PIR‐NIK‐NFκB2‐FAS survival pathway is established, which plays a key role in supporting CRC survival. Upregulated pirin (PIR) facilitates colorectal cancer (CRC) survival by suppressing Fas‐mediated apoptosis in two ways, namely, the disruption of NFκB2‐driven FAS transcription and the attenuation of FAS membrane translocation and assembling. Downregulation or inhibition of PIR dramatically sensitizes CRC cells to killing activity of CD8+ T cell and promotes FAS‐dependent apoptosis, suggesting the potential of PIR as an anti‐CRC target.