Sphingosine analogue drug FTY720 targets I2PP2A/SET and mediates lung tumour suppression via activation of PP2A-RIPK1-dependent necroptosis.
Bottom Line: Mechanistically, targeting I2PP2A/SET by FTY720 mediated PP2A/RIPK1-dependent programmed necrosis (necroptosis), but not by apoptosis.The RIPK1 inhibitor necrostatin and knockdown or genetic loss of RIPK1 prevented growth inhibition by FTY720.Expression of WT- or death-domain-deleted (DDD)-RIPK1, but not the kinase-domain-deleted (KDD)-RIPK1, restored FTY720-mediated necroptosis in RIPK1(-/-) MEFs.
Affiliation: Department of Biochemistry and Molecular Biology, Medical University of South Carolina, Charleston, SC, USA.Show MeSH
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Mentions: To delineate the downstream mechanism by which targeting I2PP2A/SET by FTY720 results in cell death [as confirmed by increased Annexin V/7-aminoactinomycin D (7-AAD) positive A549 populations compared to controls using flow cytometry; Supporting Information Fig S11A], we examined the effects of FTY720 on apoptotis- or autophagy-dependent cell death using MEFs obtained from caspase3/7−/− DKO, Bax/Bak−/− DKO or ATG5−/− KO mice. The data showed that genetic loss of caspases3/7, Bax/Bak, or ATG5 had no protective effect on FTY720-induced cell death in these immortalized MEFs (Fig 8A–C), which express endogenous I2PP2A/SET (Supporting Information Fig S11B). Consistent with these data, treatment with a pan-caspase inhibitor Z-VAD had no effect on A549 cell death in response to FTY720 (Fig 8D). Accordingly, ATG5−/− MEFs were more sensitive to taxol-induced apoptosis (80 nM and 24 h) as measured by increased caspase 3 activity compared to WT MEFs and used as an additional control to confirm their expected response to chemotherapy-induced apoptosis (Supporting Information Fig S11C). Overall, these data suggest that FTY720 induces cell death independently of caspase/Bax/Bak-mediated apoptosis or ATG5-mediated autophagy.
Affiliation: Department of Biochemistry and Molecular Biology, Medical University of South Carolina, Charleston, SC, USA.