Granzyme B (GZMB) belongs to a family of serine proteases stored in the cytotoxic granules of natural killer (NK) cells and cytotoxic T lymphocytes. GZMB weakly cleaves recombinant gasdermin E (GSDME) in vitro and in lysates from GSDME‑overexpressing human embryonic kidney 293T (HEK293T) cells (Zhang Z et al. 2020). Mutational analysis suggests that GZMB activates GSDME at the same site (D270) as caspase‑3 (CASP3). In the presence of perforin (PFN), GZMB cleaved GSDME in human neuroblastoma SH‑SY5Y cells inducing pyroptotic cell death. Despite that direct targeting of GSDME by GZMB is not efficient, GSDME can be cleaved by CASP3. Activation of CASP3 by GZMB was also detected in GZMB +PFN ‑treated SH‑Y5Y cells (Zhang Z et al. 2020). In addition, human NK line YT or NK‑92 triggered pyroptosis in GSDME‑overexpressing HeLa cells in both CASP3‑dependent and ‑independent manners. The data suggest that GZMB released from killer cytotoxic lymphocytes may induce GSDME‑dependent lytic cell death in tumor targets via GZMB/CASP3‑mediated cleavage of GSDME (Zhang Z et al. 2020). Similar findings were reported for chimeric antigen receptor (CAR) T cells that release a large amount of PFN and GZMB and result in the activation of GSDME in B leukemic cells leading to cell pyroptosis (Liu Y et al. 2020).

NOTCH2 coactivator complex together with CREB1 and EP300 stimulates transcription of GZMB (granzyme B), which is important for the cytotoxic function of CD8+ T-cells (Maekawa et al. 2008).

ALK+ anaplastic large cell lymphomas (ALCL) contain cytotoxic granules that express high levels of the serine protease Granzyme B (GZMB) and the pore-forming protein Perforin (PFR1) (Foss et al, 1996; d'Amore et al, 2007). Expression of GZMB is activated downstream of NPM1-ALK through the binding of AP-1 transcription factor JUNB to its cognate site in the promoter, as assessed by electrophoretic mobililty shift assay (Pearson et al, 2011). Consistent with this, mutation of the JUNB-B binding sites or knockdown of JUNB or NPM1-ALK abrogate expression of GZMB RNA or a GZMB reporter gene in ALCL cell lines (Pearson et al, 2011).

Granzyme B (GZMB) is a member of a family of 5 cytotoxic GZMB protein that contribute to cell death in response to cancer and infection (reviewed in Arias et al, 2017; Tibbs and Cao, 2022). GZMB is expressed in NPM1-ALK cells in a manner that depends on JUNB binding to cognate sites in its promoter (Pearson et al, 2011).

GZMB (granzyme B) promoter contains several RBPJ binding elements (RBEs). NOTCH2 coactivator complex occupies the proximal RBE and at the same time interacts with phosphorylated CREB1, bound to an adjacent CRE site. EP300 transcriptional coactivator is also recruited to this complex through association with CREB1 (Maekawa et al. 2008).

GZMB (granzyme B) cleaves BID to produce a p15 truncated form of BID (tBID) (Alimonti et al. 2001).

In the nucleus, NICD2 forms a complex with RBPJ (CBF1, CSL) and MAML (mastermind). NICD2:RBPJ:MAML complex activates transcription from RBPJ-binding promoter elements (RBEs) (Wu et al. 2000). Besides NICD2, RBPJ and MAML, NOTCH2 coactivator complex likely includes other proteins, shown as components of the NOTCH1 coactivator complex.

NOTCH2 coactivator complex directly stimulates transcription of HES1 and HES5 genes (Shimizu et al. 2002), both of which are known NOTCH1 targets.

The promoter of FCER2 (CD23A) contains several RBEs that are occupied by NOTCH2 but not NOTCH1 coactivator complexes, and NOTCH2 activation stimulates FCER2 transcription. Overexpression of FCER2 (CD23A) is a hallmark of B-cell chronic lymphocytic leukemia (B-CLL) and correlates with the malfunction of apoptosis, which is thought be an underlying mechanism of B-CLL development. The Epstein-Barr virus protein EBNA2 can also activate FCER2 transcription through RBEs, possibly by mimicking NOTCH2 signaling (Hubmann et al. 2002).

NOTCH2 coactivator complex occupies the proximal RBE of the GZMB (granzyme B) promoter and at the same time interacts with phosphorylated CREB1, bound to an adjacent CRE site. EP300 transcriptional coactivator is also recruited to this complex through association with CREB1 (Maekawa et al. 2008). NOTCH2 coactivator complex together with CREBP1 and EP300 stimulates transcription of GZMB (granzyme B), which is important for the cytotoxic function of CD8+ T-cells (Maekawa et al. 2008).

There are indications that NOTCH2 genetically interacts with hepatocyte nuclear factor 1-beta (HNF1B) in kidney development (Massa et al. 2013, Heliot et al. 2013) and with hepatocyte nuclear factor 6 (HNF6) in bile duct formation (Vanderpool et al. 2012), but the exact nature of these genetic interactions has not been defined.

NOTCH2 is activated by binding Delta-like and Jagged ligands (DLL/JAG) expressed in trans on neighboring cells (Shimizu et al. 1999, Shimizu et al. 2000, Hicks et al. 2000, Ji et al. 2004). In trans ligand-receptor binding is followed by ADAM10 mediated (Gibb et al. 2010, Shimizu et al. 2000) and gamma secretase complex mediated cleavage of NOTCH2 (Saxena et al. 2001, De Strooper et al. 1999), resulting in the release of the intracellular domain of NOTCH2, NICD2, into the cytosol. NICD2 traffics to the nucleus where it acts as a transcriptional regulator. For a recent review of the cannonical NOTCH signaling, please refer to Kopan and Ilagan 2009, D'Souza et al. 2010, Kovall and Blacklow 2010. CNTN1 (contactin 1), a protein involved in oligodendrocyte maturation (Hu et al. 2003) and MDK (midkine) (Huang et al. 2008, Gungor et al. 2011), which plays an important role in epithelial-to-mesenchymal transition, can also bind NOTCH2 and activate NOTCH2 signaling.

In the nucleus, NICD2 forms a complex with RBPJ (CBF1, CSL) and MAML (mastermind). The NICD2:RBPJ:MAML complex activates transcription from RBPJ binding promoter elements (RBEs) (Wu et al. 2000). NOTCH2 coactivator complexes directly stimulate transcription of HES1 and HES5 genes (Shimizu et al. 2002), both of which are known NOTCH1 targets. NOTCH2 but not NOTCH1 coactivator complexes, stimulate FCER2 transcription. Overexpression of FCER2 (CD23A) is a hallmark of B-cell chronic lymphocytic leukemia (B-CLL) and correlates with the malfunction of apoptosis, which is thought be an underlying mechanism of B-CLL development (Hubmann et al. 2002). NOTCH2 coactivator complexes together with CREBP1 and EP300 stimulate transcription of GZMB (granzyme B), which is important for the cytotoxic function of CD8+ T cells (Maekawa et al. 2008).

NOTCH2 gene expression is differentially regulated during human B-cell development, with NOTCH2 transcripts appearing at late developmental stages (Bertrand et al. 2000).

NOTCH2 mutations are a rare cause of Alagille syndrome (AGS). AGS is a dominant congenital multisystem disorder characterized mainly by hepatic bile duct abnormalities. Craniofacial, heart and kidney abnormalities are also frequently observed in the Alagille spectrum (Alagille et al. 1975). AGS is predominantly caused by mutations in JAG1, a NOTCH2 ligand (Oda et al. 1997, Li et al. 1997), but it can also be caused by mutations in NOTCH2 (McDaniell et al. 2006).


Hajdu-Cheney syndrome, an autosomal dominant disorder characterized by severe and progressive bone loss, is caused by NOTCH2 mutations that result in premature C-terminal NOTCH2 truncation, probably leading to increased NOTCH2 signaling (Simpson et al. 2011, Isidor et al. 2011, Majewski et al. 2011).

Pyroptosis is a form of lytic inflammatory programmed cell death that is triggered by microbial infection or pathological stimuli, such as stroke or cancer (reviewed in Shi J et al. 2017; Man SM et al. 2017; Tang D et al. 2019; Zheng Z & Li G 2020). The process of pyroptosis protects the host from microbial infection but can also lead to pathological inflammation if overactivated. The morphologic characteristics of pyroptosis include cell swelling, rupture of the cell membrane and release of intracellular contents into the extracellular environment. Pyroptosis is also characterized by chromatin condensation, however this is not the key or universal feature of pyroptosis (reviewed in Man SM et al. 2017; Tang D et al. 2019). Pyroptosis is executed by proteins of the gasdermin family, which mediate formation of membrane pores (Liu X et al. 2016; Ding J et al. 2016; Mulvihill E et al. 2018; Broz P et al. 2020). Pyroptosis can be defined as gasdermin-mediated programmed necrotic cell death (Shi J et al. 2017; Galluzzi L et al. 2018). The gasdermin (GSDM) superfamily includes GSDMA, GSDMB, GSDMC, GSDMD, GSDME (or DFNA5) and PJVK (DFNB59) (Kovacs SB & Miao EA 2018). Each protein contains an N-terminal domain with intrinsic necrotic pore-forming activity and a C‑terminal domain reported to inhibit cell death through intramolecular domain association (Liu X et al. 2016; Ding J et al. 2016; Liu Z et al. 2018, 2019; Kuang S et al. 2017). Proteolytic cleavage in the linker connecting the N‑ and C‑terminal domains of gasdermins releases the C‑terminus, allowing the gasdermin N‑terminus to translocate to the cell membrane and oligomerize to form pores (Shi J et al. 2015; Ding J et al. 2016; Sborgi L et al. 2016; Feng S et al. 2018; Yang J et al. 2018; Mulvihill E et al. 2018). Although PJVK (DFNB59) is included to the gasdermin family, it is not known whether PJVK is cleaved and whether the full length or the N-terminal portion of PJVK is responsible for forming membrane pores. The N‑terminal fragments of GSDMs strongly bind to phosphatidylinositol phosphates and weakly to phosphatidylserine, found on the inner leaflet of the plasma membrane (Liu X et al. 2016; Ding J et al. 2016; Mulvihill E et al. 2018). Gasdermins are also able to target cardiolipin, which is often found in mitochondrial membranes and membranes of bacteria (Liu X et al. 2016; Rogers C et al. 2019). The size of the GSDMD pore is estimated to be 10–20 nm (Ding J et al. 2016; Sborgi L et al. 2016). The pore‑forming activity of GSDMs in the cell membrane facilitates the release of inflammatory molecules such as interleukin (IL)‑1β and IL‑18 (mainly in GSDMD-mediated pyroptosis), and eventually leads to cytolysis in mammalian cells, releasing additional proinflammatory cellular contents including danger signals such as high mobility group box‑1 (HMGB1) (Shi J et al. 2015; He W et al. 2015; Evavold CL et al. 2017; Semino C et al. 2018; Volchuk A et al. 2020). Pyroptosis can occur in immune cells such as macrophages, monocytes and dendritic cells and non‑immune cell types such as intestinal epithelial cells, trophoblasts and hepatocytes (Taabazuing CY et al. 2017; Li H et al. 2019; Jia C et al. 2019). GSDME can be cleaved by caspase‑3 (CASP3) to induce pyroptosis downstream of the “apoptotic” machinery (Wang Y et al. 2017; Rogers C et al. 2017), whereas GSDMD is cleaved by inflammatory CASP1, CASP4 and CASP5 in humans, and CASP1, CASP11 in mice to induce pyroptosis associated with inflammasome activation (Shi J et al. 2015; Kayagaki N et al. 2015). CASP3 cleavage of GSDMD results in its inactivation (Taabazuing et al. 2017). In mouse macrophages, CASP8 can also cleave GSDMD and cause pyroptosis when TAK1 is inhibited (Malireddi R et al. 2018; Orning P et al. 2018; Sarhan J et al. 2018), and TAK1 inhibition also leads to GSDME cleavage (Sarhan J et al. 2018). Furthermore, activated CASP8 can drive inflammasome-independent cleavage of both pro-IL-1β and GSDMD downstream of the extrinsic cell death receptor signaling pathway switching apoptotic signaling to GSDMD-dependent pyroptotic-like cell death (Donado CA et al. 2020). The cleavage and activation of GSDMD in neutrophils is mediated by neutrophil elastase (NE or ELANE), which is released from azurophil granules into the cytosol during neutrophil extracellular trap (NET) formation (Kambara H et al. 2018). Further, granzyme A (GZMA) released from cytotoxic T lymphocytes and natural killer (NK) cells specifically target GSDMB for interdomain cleavage to activate GSDMB-dependent pyroptosis in target tumor cells (Zhou Z et al. 2020). Similarly, granzyme B (GZMB) released from cytotoxic T lymphocytes and natural killer (NK) cells, can induce GSDME‑dependent lytic cell death in tumor targets via the CASP3‑mediated cleavage of GSDME (Zhang Z et al. 2020).

This Reactome module describes pyroptotic activities of GSDMD and GSDME. While the N‑terminal domains of mammalian GSDMA, GSDMB, and GSDMC also have the ability to form pores (Feng S et al. 2018; Ruan J et al. 2018), their functions in the induction of pyroptosis, secretion of proinflammatory cytokines or in bactericidal activity in host remain to be studied and are not covered by this Reactome module.