title: De novo ceramide accumulation due to inhibition of its conversion to complex sphingolipids in apoptotic photosensitized cells.
abstract: The oxidative stress induced by photodynamic therapy (PDT) with the photosensitizer phthalocyanine 4 is accompanied by increases in ceramide mass. To assess the regulation of de novo sphingolipid metabolism during PDT-induced apoptosis, Jurkat human T lymphoma and Chinese hamster ovary cells were labeled with [14C]serine, a substrate of serine palmitoyltransferase (SPT), the enzyme catalyzing the initial step in the sphingolipid biosynthesis. A substantial elevation in [14C]ceramide with a concomitant decrease in [14C]sphingomyelin was detected. The labeling of [14C]ceramide was completely abrogated by the SPT inhibitor ISP-1. In addition, ISP-1 partly suppressed PDT-induced apoptosis. Pulse-chase experiments showed that the contribution of sphingomyelin degradation to PDT-initiated increase in de novo ceramide was absent or minor. PDT had no effect on either mRNA amounts of the SPT subunits LCB1 and LCB2, LCB1 protein expression, or SPT activity in Jurkat cells. Moreover in Chinese hamster ovary cells LCB1 protein underwent substantial photodestruction, and SPT activity was profoundly inhibited after treatment. We next examined whether PDT affects conversion of ceramide to complex sphingolipids. Sphingomyelin synthase, as well as glucosylceramide synthase, was inactivated by PDT in both cell lines in a dose-dependent manner. These results are the first to show that in the absence of SPT up-regulation PDT induces accumulation of de novo ceramide by inhibiting its conversion to complex sphingolipids.
authors.affiliation: Occupational and Environmental Health Sciences, The Department of Fundamental and Applied Sciences, Eugene Applebaum College of Pharmacy and Health Sciences, Detroit, Michigan 48201, USA.
authors.forename: Vladislav
authors.initials: V
authors.lastname: Dolgachev
authors.forename: M Sharjeel
authors.initials: MS
authors.lastname: Farooqui
authors.forename: Olga I
authors.initials: OI
authors.lastname: Kulaeva
authors.forename: Michael A
authors.initials: MA
authors.lastname: Tainsky
authors.forename: Biserka
authors.initials: B
authors.lastname: Nagy
authors.forename: Kentaro
authors.initials: K
authors.lastname: Hanada
authors.forename: Duska
authors.initials: D
authors.lastname: Separovic
mesh_terms: D000217:Acyltransferases / Q000378:metabolism; D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000528:radiation effects; D016466:CHO Cells; D002518:Ceramides / Q000378:metabolism*; D006224:Cricetinae; D006801:Humans; D007211:Indoles / Q000008:administration & dosage; D019169:Jurkat Cells; D010789:Phototherapy; D011838:Radiation-Sensitizing Agents / Q000008:administration & dosage; D051102:Serine C-Palmitoyltransferase; D013107:Sphingolipids / Q000378:metabolism*; D013601:T-Lymphocytes / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology / Q000528:radiation effects; D015854:Up-Regulation
chemical_list: D002518:Ceramides; D007211:Indoles; D011838:Radiation-Sensitizing Agents; D013107:Sphingolipids; C107448:phthalocyanine Pc 4; D000217:Acyltransferases; C495089:SPTLC2 protein, human; D051102:Serine C-Palmitoyltransferase