| dc.contributor.author | Yu, Anan. | en_US |
| dc.date.accessioned | 2014-10-21T12:37:26Z | |
| dc.date.available | 2002 | |
| dc.date.issued | 2002 | en_US |
| dc.identifier.other | AAINQ75713 | en_US |
| dc.identifier.uri | http://hdl.handle.net/10222/55866 | |
| dc.description | Externalization of phosphatidylserine (PtdSer) plays important roles in signaling the recognition and removal of apoptotic cells. We hypothesized that PtdSer exposed during apoptosis is newly formed and that biosynthesis of PtdSer correlates with its externalization. In this study, U937 and CHO-K1 cells were induced with various apoptotic stimuli and metabolism of serine-derived phospholipids was studied. In U937 cells, PtdSer synthesis was stimulated and newly synthesized PtdSer was transferred preferentially to apoptotic bodies when apoptosis was induced with camptothecin. Stimulation of PtdSer synthesis and transport to apoptotic bodies were abolished by a caspase inhibitor, z-VAD-fmk. In contrast, changes in synthesis and transport of other phospholipids were minor. Even greater effects on PtdSer synthesis, movement to vesicles and inhibition by z-VAD-fmk were observed in apoptotic cells induced by UV irradiation or tumor necrosis factor-alpha. In CHO-K1 cells UV-induced apoptosis resulted in a 2-fold increase in PtdSer biosynthesis but this was not reversed by z-VAD-fink and was less specific for PtdSer as similar levels of stimulation were observed for sphingomyelin biosynthesis. Thus, increased PtdSer biosynthesis may be a general phenomenon during apoptosis but the stimulation of PtdSer synthesis may involve distinct regulatory pathways depending on the type of cell involved. In U937 cells, this event is specific for PtdSer and depends on caspase activation whereas in CHO-K1 cells, stimulation of PtdSer synthesis seems to be less specific and independent of caspase activities. | en_US |
| dc.description | PtdSer formation in mammalian cells is catalyzed by PtdSer synthases (PSS) that convert existing phospholipids to PtdSer. Members of the phospholipid scramblase (PLSCR) family contribute to exposure of PtdSer in the outer leaflet of the plasma membrane during apoptosis. CHO-K1 cells over-expressing isoforms of PSS or PLSCR were established to determine whether PtdSer biosynthesis associated with apoptosis is altered by their activities. PSS I- and PSS II-expressing cells showed resistance to UV-induced apoptosis based on a lack of caspase-3 activation or morphology and nuclear changes. When exposed to UV light, PtdSer biosynthesis was further stimulated approximately 2-fold in PSS I cells and 3-fold in PSS II cells compared to treated control cells. Caspase activation was not required as z-VAD-fmk did not change PtdSer metabolism in PSS I or PSS II-expressing cells. Cells over-expressing PLSCR1 showed significant morphological changes and cell death. Following UV irradiation, these cells had earlier and enhanced PtdSer exposure, and increased caspase-3 activation, PARP cleavage and nuclear changes. UV-irradiated cells expressing PLSCR1 had a 6-fold stimulation of PtdSer synthesis relative to untreated PLSCR1 cells whereas UV-irradiated vector control cells increased only 2-fold. No differences in these responses were observed in PLSCR2-expressing cells. PtdSer synthesis and apoptosis stimulated by PLSCR1 over-expression were blocked by z-VAD-fmk. | en_US |
| dc.description | In conclusion, PSS I and II appear to be involved in the formation of PtdSer following UV irradiation through caspase-independent mechanisms. Cells over-expressing PSS I and II are resistant to UV-induced apoptosis, indicating potential anti-apoptotic effects when these synthetic enzymes are over-expressed. Over-expression of PLSCR1 in CHO cells increased PtdSer synthesis and externalization and enhanced the rate of apoptosis in a caspase-dependent manner following UV irradiation. Thus, stimulation of PtdSer biosynthesis seems to be directly related to PtdSer externalization and this could be a point of regulation or intervention during programmed cell death. | en_US |
| dc.description | Thesis (Ph.D.)--Dalhousie University (Canada), 2002. | en_US |
| dc.language | eng | en_US |
| dc.publisher | Dalhousie University | en_US |
| dc.publisher | | en_US |
| dc.subject | Biology, Cell. | en_US |
| dc.subject | Chemistry, Biochemistry. | en_US |
| dc.title | Metabolism and externalization of phosphatidylserine during apoptosis in cultured cells with and without over-expression of metabolic enzymes. | en_US |
| dc.type | text | en_US |
| dc.contributor.degree | Ph.D. | en_US |
