Ceramide induces Bcl2 dephosphorylation via a mechanism involving mitochondrial PP2A.
Phosphorylation of Bcl2 at serine 70 is required for its potent anti-apoptotic function. We have recently shown that Bcl2 phosphorylation is a dynamic process that involves the protein kinase C alpha and protein phosphatase 2A (PP2A) (Ruvolo, P. P., Deng, X., Carr, B. K., and May, W. S. (1998) J. Biol. Chem. 273, 25436-25442; and Deng, X., Ito, T., Carr, B. K., Mumby, M. C., and May, W. S. (1998) J. Biol. Chem. 273, 34157-34163). The potent apoptotic agent ceramide can activate a PP2A, suggesting that one potential component of the ceramide-induced death signal may involve the inactivation of Bcl2. Results indicate that C2-ceramide but not inactive C2-dihydroceramide, was found to specifically activate a mitochondrial PP2A, which rapidly and completely induced Bcl2 dephosphorylation and correlated closely with ceramide-induced cell death. Using a genetic approach, the gain-of-function S70E Bcl2 mutation, which mimics phosphorylation, fails to undergo apoptosis even with the addition of high doses of ceramide (IC50 > 50 microM). In contrast, cells overexpressing exogenous wild-type Bcl2 were sensitive to ceramide at dosages where PP2A is fully active and Bcl2 would be expected to be dephosphorylated (IC50 = 14 microM). These findings indicate that in cells expressing functional Bcl2, the mechanism of death action for ceramide may involve, at least in part, a mitochondrial PP2A that dephosphorylates and inactivates Bcl2.
Sealy Center for Oncology and Hematology and Department of Internal Medicine, The University of Texas Medical Branch, Galveston, Texas 77555-1048, USA.
P P
PP
Ruvolo
X
X
Deng
T
T
Ito
B K
BK
Carr
W S
WS
May
D000818:Animals; D002518:Ceramides / Q000494:pharmacology*; D006801:Humans; D051379:Mice; D008928:Mitochondria / Q000201:enzymology*; D010749:Phosphoprotein Phosphatases / Q000378:metabolism*; D010766:Phosphorylation; D054648:Protein Phosphatase 2; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism*; D014407:Tumor Cells, Cultured
D002518:Ceramides; D019253:Proto-Oncogene Proteins c-bcl-2; D010749:Phosphoprotein Phosphatases; D054648:Protein Phosphatase 2