Caspase-3 activation during apoptosis can trigger caspase-3 cleavage of gasdermin E (GSDME). The gasdermins (GSDM) are afamilyofproteins, whose cleavage activates inflammatorydeath, calledpyroptosis. N-terminalGSDMfragmentsformporesinthecellmembranethatcauserapidcelldeathinwhichthecellswells, activatesandreleasesinflammatorycytokinesandotherinflammatorymediators,andeventuallybursts.GSDME cleavageconvertsnoninflammatoryapoptoticdeathtomorerapidinflammatorypyroptoticdeath.GSDMEisnot expressedinmostcancercelllines,isepigeneticallyinactivatedingastric,colorectalandbreastcancer,relative tonormal tissue,and mutated in someothers. GSDME expression suppresses colony formation ingastric and colorectal cancer and invasivity of breast cancer. Worse 5-year survival and an increase in lymph node metastases areassociated with reduced GSDME in breast cancer. Moreover, lack ofGSDMEpromotesdrug resistanceinmelanomaandlungcancercelllines.WehypothesizethatGSDMEactslikeatumorsuppressor, thatsometumorcellsavoidpyroptosisbydownregulatingormutatingGSDMEandthattheswitchfrom apoptosis to pyroptosis profoundly affects tumor cell survival, anti-tumor immunity and response to chemotherapy and radiation. In preliminary data, cancer-associated GSDME mutations are shown to be primarily loss of function mutations. Gsdme knockout in cancer lines promoted tumor growth while ectopic GSDMEexpressionstronglyinhibitedtumorgrowthinimmunecompetentmice.Thetumorsuppressiveroleof GSDME was lost in immunodeficient NOD.scid.Il2rg-/- (NSG) and Prf1-/- mice deficient in perforin and strongly inhibitedbyNKorCD8Tcelldepletion.GSMDEexpressionbythetumorincreasedinfiltrating,functionalCD8 T cells and NK cells. Based on these data, we hypothesize that GSDME suppresses tumor growth by recruiting and activating anti-tumor killer lymphocytes. We also found that granzymes B and M, death- inducingproteasesofkillerlymphocytes,directlycleaveGSDMEduringkillercellattacktoactivatepyroptosisin a caspase-independent manner, which is amplified by caspase activation. We also hypothesize that direct granzyme cleavage of GSDME in cancer cells triggers pyroptosis and enhances their anti-tumor immunity.Killerlymphocytemediateddeathhaspreviouslybeenthoughttobenon-inflammatory.Ourgoalis to test these hypotheses and develop mechanistic insights to understand whether and how suppression of GSDME activation ofpyroptosis in cancer cells impactsoncogenesis, drug sensitivity and protective immunity.
Our specificaims aretoinvestigatetheeffectofGSDMEmutationandexpressiononGSDMEactivation,lipid binding, oligomerization and pore formation, on whether cell death by apoptotic stimuli or killer cells is inflammatoryandimmunogenic,andwhetherandhowGSDMEaffectstumorgrowth,immunityandresponses totherapyinvitroandintransplantedmousetumormodels.
Thisproposalisbasedonthehypothesisthatcancercellsavoidtriggeringinflammatorydeathbypyroptosis,by down-regulating or mutating GSDME, which suppresses effective anti-tumor immunity. A corollary is that inducing pyroptosis in cancer cells will enhance immune control and responsiveness to chemotherapy drugs. TherapeuticstrategiesthatinduceGSDMEand/ormakecancercellssusceptibletopyroptosismaybeeffective atactivatinganti-tumorimmunity,controllingtumorgrowthandimprovingresponsestoconventionalortargeted drugs,radiationorimmunotherapy.
