title: Autophagy induced by deficiency of sphingosine-1-phosphate phosphohydrolase 1 is switched to apoptosis by calpain-mediated autophagy-related gene 5 (Atg5) cleavage.
abstract: Sphingosine 1-phosphate (S1P) and ceramide have been implicated in both autophagy and apoptosis. However, the roles of these sphingolipid metabolites in the links between these two processes are not completely understood. Depletion of S1P phosphohydrolase-1 (SPP1), which degrades intracellular S1P, induces the unfolded protein response and endoplasmic reticulum stress-induced autophagy (Lépine, S., Allegood, J. C., Park, M., Dent, P., Milstien, S., and Spiegel, S. (2011) Cell Death Differ. 18, 350-361). Surprisingly, however, treatment with doxorubicin, which by itself also induced autophagy, markedly reduced the extent of autophagy mediated by depletion of SPP1. Concomitantly, doxorubicin-induced apoptosis was greatly enhanced by down-regulation of SPP1. Autophagy and apoptosis seemed to be sequentially linked because inhibiting autophagy with 3-methyladenine also markedly attenuated apoptosis. Moreover, silencing Atg5 or the three sensors of the unfolded protein response, IRE1α, ATF6, and PKR-like eIF2α kinase (PERK), significantly decreased both autophagy and apoptosis. Doxorubicin stimulated calpain activity and Atg5 cleavage, which were significantly enhanced in SPP1-depleted cells. Inhibition or depletion of calpain not only suppressed Atg5 cleavage, it also markedly decreased the robust apoptosis induced by doxorubicin in SPP1-deficient cells. Importantly, doxorubicin also increased de novo synthesis of the pro-apoptotic sphingolipid metabolite ceramide. Elevation of ceramide in turn stimulated calpain; conversely, inhibiting ceramide formation suppressed Atg5 cleavage and apoptosis. Hence, doxorubicin switches protective autophagy in SPP1-depleted cells to apoptosis by calpain-mediated Atg5 cleavage.
authors: Department of Biochemistry and Molecular Biology and the Massey Cancer Center, Virginia Commonwealth University School of Medicine, Richmond, Virginia 23298, USA.
authors: Sandrine
authors: S
authors: Lépine
authors: Jeremy C
authors: JC
authors: Allegood
authors: Yvette
authors: Y
authors: Edmonds
authors: Sheldon
authors: S
authors: Milstien
authors: Sarah
authors: S
authors: Spiegel
mesh_terms: D051702:Activating Transcription Factor 6 / Q000235:genetics / Q000378:metabolism; D000225:Adenine / Q000031:analogs & derivatives / Q000494:pharmacology; D000903:Antibiotics, Antineoplastic / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D001343:Autophagy / Q000187:drug effects / Q000502:physiology*; D000071187:Autophagy-Related Protein 5; D002154:Calpain / Q000235:genetics / Q000378:metabolism*; D045744:Cell Line, Tumor; D002518:Ceramides / Q000096:biosynthesis / Q000235:genetics; D015536:Down-Regulation / Q000187:drug effects / Q000502:physiology; D004317:Doxorubicin / Q000494:pharmacology; D004722:Endoribonucleases / Q000235:genetics / Q000378:metabolism; D005260:Female; D020868:Gene Silencing; D006801:Humans; D008246:Lysophospholipids / Q000235:genetics / Q000378:metabolism; D008565:Membrane Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D008869:Microtubule-Associated Proteins / Q000235:genetics / Q000378:metabolism*; D010744:Phosphoric Monoester Hydrolases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D059748:Proteolysis; D013110:Sphingosine / Q000031:analogs & derivatives / Q000235:genetics / Q000378:metabolism; D019892:eIF-2 Kinase / Q000235:genetics / Q000378:metabolism
chemical_list: D051702:Activating Transcription Factor 6; D000225:Adenine; D000903:Antibiotics, Antineoplastic; D000071187:Autophagy-Related Protein 5; D002154:Calpain; D002518:Ceramides; D004317:Doxorubicin; D004722:Endoribonucleases; D008246:Lysophospholipids; D008565:Membrane Proteins; D008869:Microtubule-Associated Proteins; D010744:Phosphoric Monoester Hydrolases; D017346:Protein Serine-Threonine Kinases; D013110:Sphingosine; D019892:eIF-2 Kinase; C497111:ATF6 protein, human; C502778:ATG5 protein, human; C060506:sphingosine 1-phosphate; C025946:3-methyladenine; C528229:ERN1 protein, human; C401298:sphingosine-1-phosphate phosphatase