Alternative splicing of GSDMB modulates killer lymphocyte–triggered pyroptosis

Abstract

Granzyme A from killer lymphocytes cleaves gasdermin B (GSDMB) and triggers pyroptosis in targeted human tumor cells, eliciting antitumor immunity. However, GSDMB has a controversial role in pyroptosis and has been linked to both anti- and protumor functions. Here, we found that GSDMB splicing variants are functionally distinct. Cleaved N-terminal (NT) fragments of GSDMB isoforms 3 and 4 caused pyroptosis, but isoforms 1, 2, and 5 did not. The nonfunctional isoforms have a deleted or modified exon 6 and therefore lack a stable belt motif. The belt likely contributes to the insertion of oligomeric GSDMB-NTs into the membrane. Consistently, noncytotoxic GSDMB-NTs blocked pyroptosis caused by cytotoxic GSDMB-NTs in a dominant-negative manner. Upon natural killer (NK) cell attack, GSDMB3-expressing cells died by pyroptosis, whereas GSDMB4-expressing cells died by mixed pyroptosis and apoptosis, and GSDMB1/2-expressing cells died only by apoptosis. GSDMB4 partially resisted NK cell-triggered cleavage, suggesting that only GSDMB3 is fully functional. GSDMB1-3 were the most abundant isoforms in the tested tumor cell lines and were similarly induced by interferon-γ and the chemotherapy drug methotrexate. Expression of cytotoxic GSDMB3/4 isoforms, but not GSDMB1/2 isoforms that are frequently up-regulated in tumors, was associated with better outcomes in bladder and cervical cancers, suggesting that GSDMB3/4-mediated pyroptosis was protective in those tumors. Our study indicates that tumors may block and evade killer cell-triggered pyroptosis by generating noncytotoxic GSDMB isoforms. Therefore, therapeutics that favor the production of cytotoxic GSDMB isoforms by alternative splicing may improve antitumor immunity.

The gasdermin family: emerging therapeutic targets in diseases

“… 163 However, two other studies point out that GSDMB3, like GSDMB4, also has pro-pyroptosis activity, as GSDMB3 also has a stable band motif encoded by exon 6. 37 , 164 These research discrepancies warrant further investigation. However, these findings hold significant value in elucidating the intricate roles of GSDMB isoforms in disease pathogenesis and in informing the future design of targeted GSDMB therapies.…”

“…It is worth pointing out that the cleavage products of GSDMs do not always result in cell death. Specifically, NT domains of GSDMB isoforms 3 and 4 are able to cause pyroptosis, whereas isoforms 1, 2, and 5 are not, 37 suggesting that cells may inhibit and evade pyroptosis by generating noncytotoxic isoforms of GSDMB. Ongoing studies of the GSDM family have delved into the mechanisms of PCD and inflammation, highlighting the necessity for comprehensive inquiries into the roles and operational mechanisms of these molecules in both health and disease states.…”

Emerging roles of type 1 innate lymphoid cells in tumour pathogenesis and cancer immunotherapy

“…While classically thought to be non-cytotoxic, IL-15 increases expression of granzyme (Gzm)A, B and C and may promote ILC1s towards a cytotoxic phenotype against tumours [ 78 – 82 ]. Mechanistically, GzmA causes lytic granule-mediated noncanonical apoptosis and pyroptosis [ 83 , 84 ]. Intriguingly, comparison of chromophobe renal cell carcinoma (RCC; chRCC) to clear cell RCC (ccRCC) in human patients revealed that chRCC tumours express higher levels of IL-15, and this is reflected by the higher expression of GzmA in ILC1s compared to NK cells in chRCC, while the opposite is observed in ccRCC which express minimal levels of IL-15 [ 78 ].…”

Stress/cell death pathways, neuroinflammation, and neuropathic pain

“…Nevertheless, GSDMB has a controversial role in pyroptosis. Kong et al reported that GSDMB splicing variants present functional distinction: Cleaved N‐GSDMB isoforms 3/4 can cause pyroptotic cell death, but isoforms 1/2/5 cannot 40 . Streptococcal pyrogenic exotoxin B enables to cleave GSDMA and evoke pyroptosis 41 .…”