Calpain small-1 modulates Akt/FoxO3A signaling and apoptosis through PP2A.
Here, we show that FoxO3A transcription factor is upregulated upon calpain small-1 (CAPNS1) depletion both in mouse embryonic fibroblasts (MEFs) and in the human mammary carcinoma cell line MCF-7. On starvation, CAPNS1 depletion is associated with a higher rate of FoxO3A dephosphorylation and translocation to the nucleus and to a sharper increase in the levels of p27Kip1 and Bim, the products of two FoxO target genes. Notably, FoxO3A depletion in CAPNS1-/- MEFs reduces both the induction of Bim and apoptosis. Both okadaic acid treatment and silencing of the protein phosphatase 2A (PP2A) catalytic subunit can partially reduce starvation-induced FoxO3A activation and apoptosis in CAPNS1-/- fibroblasts. PP2A associates more tightly with Akt in CAPNS1 knockout cells, indicating that PP2A is involved in calpain-mediated FoxO regulation. Finally, we show that PP2A regulatory subunits B56 alpha and gamma are in vitro substrates of calpain, and calpain regulates B56 alpha stability in vivo, suggesting a direct role of calpain in the regulation of PP2A function. In conclusion, for the first time we report that CAPNS1 interferes with PP2A-Akt interaction consequently affecting FoxO3A-dependent cell death. Calpain inhibition might therefore be exploited as a tool to induce apoptosis in tumors sensitive to FoxO activation.
Bertoli
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C
Laboratorio Nazionale Consorzio Interuniversitario Biotecnologie (LNCIB), Trieste, Italy.
Copetti
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T
Lam
E W-F
EW
Demarchi
F
F
Schneider
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C
D000818:Animals; D017209:Apoptosis / Q000235:genetics; D002154:Calpain / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*; D002467:Cell Nucleus / Q000378:metabolism; D002478:Cells, Cultured; D000071316:Forkhead Box Protein O3; D051858:Forkhead Transcription Factors / Q000378:metabolism*; D055785:Gene Knockdown Techniques; D006801:Humans; D051379:Mice; D051058:Oncogene Protein v-akt / Q000378:metabolism*; D010766:Phosphorylation; D054648:Protein Phosphatase 2 / Q000378:metabolism / Q000502:physiology*; D021381:Protein Transport; D015398:Signal Transduction / Q000235:genetics / Q000502:physiology; D013217:Starvation / Q000235:genetics / Q000503:physiopathology
D000071316:Forkhead Box Protein O3; D051858:Forkhead Transcription Factors; C474033:FoxO3 protein, mouse; D051058:Oncogene Protein v-akt; D054648:Protein Phosphatase 2; D002154:Calpain; C410233:Capns1 protein, mouse