Insulin Regulates Cleavage of Procaspase-9 via Binding of X Chromosome-Linked Inhibitor of Apoptosis Protein in HT-29 Cells

Abstract

Insulin significantly reduced tumor necrosis factor (TNF)-␣-induced cleavage of procaspase-8, -9, and -3 and poly(ADP-ribose) polymerase when observed for up to 24 hours in a dose-dependent manner. Signaling pathways responsible for the inhibitory effects of insulin were investigated by using protein kinase inhibitors. Both phosphatidylinositol 3-kinase (PI3K) and mitogen-activated protein kinase kinase pathways mediate the ability of insulin to decrease the TNF-␣-induced cleavage of procaspase-8. In contrast, only the PI3K inhibitor reversed the effect of insulin on the TNF-␣-induced cleavage of procaspase-9. Moreover, insulin decreased the apoptotic level induced by TNF-␣, whereas the PI3K inhibitor enhanced it. The protein level of Apaf-1, an activator of procaspase-9, remained constant with the application of agents affecting the cleavage of procaspase-9. In examining another regulator of cleaved caspase-9, X chromosome-linked inhibitor of apoptosis protein (XIAP), we observed that TNF-␣ treatment induced fragmentation of XIAP, which was also enhanced by the PI3K inhibitor. In addition, XIAP was coimmunoprecipitated with procaspase-9. The treatment with TNF-␣ reduced the level of XIAP precipitated with procaspase-9, whereas insulin reversed this effect. Moreover, PI3K and Akt inhibitors, but not mammalian target of rapamycin inhibitor, inhibited the effect of insulin on the coprecipitation of procaspase-9 and XIAP. Our data suggest that insulin decreases the TNF-␣-induced cleavage of procaspase-9 and subsequent apoptosis by regulating XIAP via the PI3K/Akt pathway.

Pseudomonas aeruginosa Delays Kupffer Cell Death via Stabilization of the X-Chromosome-Linked Inhibitor of Apoptosis Protein

“…TNF-␣ and its counterpart, TRAIL, are known to induce cleavage and degradation of XIAP although the exact mechanism remains unclear (9,41,42). XIAP is regulated by several proteins.…”

“…XIAP is the most potent IAP, blocking caspase activity with nanomolar affinity (7). TNF-␣ induces cleavage of XIAP to an inactive fragment (9). Recently, XIAP was found to be phosphorylated by Akt, a kinase downstream of PI3K, rendering it resistant to cleavage (10).…”

NRF2-Dependent Glutamate-L-Cysteine Ligase Catalytic Subunit Expression Mediates Insulin Protection Against Hyperglycemia-Induced Brain Endothelial Cell Apoptosis

“…That insulin can confer cytoprotection of endothelial cells against oxidative stress has been demonstrated (Hermann et al 2000); however, whether insulin exerts anti-apoptotic effect on cerebral endothelial cells, and its mechanism of cytoprotection is unknown. An important pathway by which insulin promotes endothelial cells survival is the suppression of the mitochondrial pathway of apoptosis through phosphorylation of Bad and procaspase-9 via phosphatidylinositol 3-kinase (PI3K)/Akt signaling (Hermann et al 2000;Kim & Tannenbaum 2004). More recently, a novel pathway of insulin protection has been demonstrated in hepatocytes; insulin was shown to increase GSH through the induction of glutamate-L-cysteine ligase (GCL) expression via PI3K/Akt/mTOR pathway ).…”

Procaspase-9 induces its cleavage by transnitrosylating XIAP via the Thioredoxin system during cerebral ischemia-reperfusion in rats

“…Whether XIAP can directly interact with procaspase-9 remain elusive, as earlier literature suggested a possibility 35 36 , but recent studies emphasize that XIAP can only interact directly with processed capase-9 in either human U-937 myeloid leukemia cells stably overexpressing XIAP or reconstituted caspase-9-Apaf-1 holoenzyme complexes containing fully processed caspase-9 or unprocessed procaspase-9 27 37 . However, Kim and Tannenbaum found that XIAP was able to bind the precursor of caspase-9 38 . In this study, we demonstrated that cerebral ischemia-reperfusion enhanced the interaction between procaspase-9 and XIAP, and pretreatment with TAT-AVPY [which can competitively bind the third baculoviral IAP repeat (BIR3) domain of XIAP] significantly inhibited this interaction ( Fig.…”