Ceramide Induces Bcl2 Dephosphorylation via a Mechanism Involving Mitochondrial PP2A*
- From the Sealy Center for Oncology and Hematology and Department of Internal Medicine, The University of Texas Medical Branch, Galveston, Texas 77555-1048
Abstract
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 α 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 μm). 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 μm). 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.
Footnotes
-
↵* This work was supported by National Institutes of Health Grants CA44649 and CA47993 and Leukemia Society of America Grant 6089-99.The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
-
↵‡ To whom correspondence should be addressed: Sealy Center for Oncology and Hematology and Dept. of Internal Medicine, The University of Texas Medical Branch, 301 University Blvd., Galveston, TX 77555-1048. Tel: 409-747-1935; Fax: 409-747-1938.
- Abbreviations:
- DAG
-
diacylglycerol
- PP2A
-
protein phosphatase 2A
- PP1
-
protein phosphatase 1
- CAPP
-
ceramide-activated protein phosphatase
- PKC
-
protein kinase C
- PMSF
-
phenylmethylsulfonyl fluoride
- FACS
-
fluorescence-activated cell sorter
- WT
-
wild type
- Hepes
-
4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid
-
- Received March 31, 1999.
- Revision received May 14, 1999.
- The American Society for Biochemistry and Molecular Biology, Inc.
