title: A mechanism for suppression of the CDP-choline pathway during apoptosis.
abstract: Inhibition of the CDP-choline pathway during apoptosis restricts the availability of phosphatidylcholine (PtdCho) for assembly of membranes and synthesis of signaling factors. The N-terminal nuclear localization signal (NLS) in CTP:phosphocholine cytidylyltransferase (CCT)α is removed during apoptosis but the caspase(s) involved and the contribution to suppression of the CDP-choline pathway is unresolved. In this study we utilized siRNA silencing of caspases in HEK293 cells and caspase 3-deficient MCF7 cells to show that caspase 3 is required for CCTα proteolysis and release from the nucleus during apoptosis. CCTα-Δ28 (a caspase-cleaved mimic) expressed in CCTα-deficient Chinese hamster ovary cells was cytosolic and had increased in vitro activity. However, [³H]choline labeling experiments in camptothecin-treated MCF7 cells and MCF7 cells expressing caspase 3 (MCF7-C3) revealed a global suppression of the CDP-choline pathway that was consistent with inhibition of a step prior to CCTα. In camptothecin-treated MCF7 and MCF7-C3 cells, choline kinase activity was unaffected; however, choline transport into cells was reduced by 30 and 60%, respectively. We conclude that caspase 3-mediated removal of the CCTα NLS contributes minimally to the inhibition of PtdCho synthesis during DNA damage-induced apoptosis. Rather, the CDP-choline pathway is inhibited by caspase 3-independent and -dependent suppression of choline transport into cells.
authors.affiliation: Departments of Pediatrics and Biochemistry and Molecular Biology, Atlantic Research Centre, Dalhousie University, Halifax, Nova Scotia, Canada B3H 4R2.
authors.forename: Craig C
authors.initials: CC
authors.lastname: Morton
authors.forename: Adam J
authors.initials: AJ
authors.lastname: Aitchison
authors.forename: Karsten
authors.initials: K
authors.lastname: Gehrig
authors.forename: Neale D
authors.initials: ND
authors.lastname: Ridgway
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D016466:CHO Cells; D002166:Camptothecin / Q000494:pharmacology; D053148:Caspase 3 / Q000378:metabolism; D002797:Choline Kinase / Q000378:metabolism; D019916:Choline-Phosphate Cytidylyltransferase / Q000378:metabolism; D006224:Cricetinae; D003412:Cricetulus; D003566:Cytidine Diphosphate Choline / Q000378:metabolism*; D057809:HEK293 Cells; D006801:Humans; D010446:Peptide Fragments / Q000378:metabolism; D059748:Proteolysis / Q000187:drug effects
chemical_list: D010446:Peptide Fragments; D003566:Cytidine Diphosphate Choline; D002797:Choline Kinase; D019916:Choline-Phosphate Cytidylyltransferase; D053148:Caspase 3; D002166:Camptothecin
keywords: CTP:phosphocholine cytidylyltransferase; RNA interference; caspase 3; choline transporter; phosphatidylcholine