Alternative Splicing of GSDMB Modulates Pyroptosis in Cancer Cells

Killer lymphocytes can eliminate tumor cells via pyroptosis, a mode of programmed cell death in which lymphocytes release granules containing serine proteases known as granzymes, in addition to other cytotoxic molecules. Upon tumor cell entry, granzymes cleave cytosolic gasdermins (GSDM) and release GSDM N-terminal (NT) domains from autoinhibition, enabling NT domains to bind membrane lipids, oligomerize, and create plasma membrane pores that lead to pyroptotic cell death. Granzyme A can cleave GSDMB to drive pyroptosis, but previous studies have both supported and challenged the pore-forming activity of GSDMB. Given that alternative splicing of GSDMB gives rise to multiple distinct isoforms, Kong, Xia, and colleagues explored whether GSDMB isoforms differed in function by ectopically expressing the NT domain of each of five isoforms in human embryonic kidney cells and demonstrated that GSDMB isoforms differed in pore-forming activity, as only GSDMB3 and, to a lesser extent, GSDMB4 induced pyroptosis. The NT domains of GSDMB isoforms differ only within the belt motif, and structural models predicted that the belt motif was uniquely stabilized within the cytotoxic GSDMB3 and GSDMB4 isoforms, suggesting that this motif contributed to differential isoform functions. While the NT domains of all GSDMB isoforms could bind lipids and oligomerize, coexpression of noncytotoxic NT domains from isoforms lacking the belt motif hindered the induction of pyroptosis by cytotoxic NT domains in a dominant-negative manner, implicating a role of the belt motif in the final stage of membrane insertion and pore formation and suggesting that noncytotoxic GSDMB isoforms are negative regulators of pyroptosis. Analysis of GSDMB isoform expression in tumor and normal samples within the Cancer DEIso and The Cancer Genome Atlas databases indicated that cytotoxic isoforms GSDMB3 and GSDMB4 were often suppressed in tumors, while noncytotoxic isoforms GSDMB1 and GSDMB2 were more often upregulated. Moreover, high levels of cytotoxic GSDMB3 were associated with better survival in patients with bladder cancer. In summary, these findings outline functional differences between GSDMB isoforms and reveal alternative splicing as a mechanism by which tumors may evade antitumor immunity.

Kong Q, Xia S, Pan X, Ye K, Li Z, Li H, et al. Alternative splicing of GSDMB modulates killer lymphocyte—triggered pyroptosis. Sci Immunol 2023;8:eadg3196.

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