title: Suppression of sphingomyelin synthase 1 by small interference RNA is associated with enhanced ceramide production and apoptosis after photodamage.
abstract: We have shown that overexpression of SMS1, an enzyme that converts de novo ceramide into sphingomyelin, is accompanied by attenuated ceramide response and apoptotic resistance after photodamage with the photosensitizer Pc 4 (photodynamic therapy; PDT). To test whether SMS1 overexpression-related effects after PDT can be reversed, in this study SMS1 was downregulated in Jurkat T lymphoma/leukemia cells using small inhibitory RNA (siRNA) for SMS1. Compared to scrambled (control) siRNA-transfectants, in SMS1 siRNA-transfected cells the activity of SMS at rest was downregulated with concomitant decrease in sphingomyelin mass. In SMS1 siRNA-transfected cells increases in ceramides were higher than in control siRNA-transfectants after PDT. Similar findings were obtained for dihydroceramides suggesting the involvement of de novo ceramide pathway. PDT-induced DEVDase (caspase-3-like) activation was enhanced in SMS1 siRNA-transfected cells compared to their control counterparts. The data show that RNA interference-dependent downregulation of SMS1 is associated with increased accumulation of ceramide and dihydroceramide with concomitant sensitization of cells to apoptosis after photodamage. Similarly, in SMS2 siRNA-transfected cells, downregulation of SMS activity was accompanied by potentiated DEVDase activation post-photodamage. These findings suggest that SMS is a potential novel molecular target that can augment therapeutic efficacy of PDT.
authors: Department of Pharmaceutical Sciences, Eugene Applebaum College of Pharmacy and Health Sciences, Wayne State University, Detroit, MI 48201, USA. dseparovic@wayne.edu <dseparovic@wayne.edu>
authors: Duska
authors: D
authors: Separovic
authors: Louie
authors: L
authors: Semaan
authors: Adi L
authors: AL
authors: Tarca
authors: Ma'In Yehya
authors: MY
authors: Awad Maitah
authors: Kentaro
authors: K
authors: Hanada
authors: Jacek
authors: J
authors: Bielawski
authors: Maristella
authors: M
authors: Villani
authors: Chiara
authors: C
authors: Luberto
mesh_terms: D017209:Apoptosis; D053148:Caspase 3 / Q000378:metabolism; D002518:Ceramides / Q000096:biosynthesis* / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D007211:Indoles / Q000633:toxicity*; D019169:Jurkat Cells; D008565:Membrane Proteins / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D009419:Nerve Tissue Proteins / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D017319:Photosensitizing Agents / Q000633:toxicity*; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000378:metabolism; D021241:Spectrometry, Mass, Electrospray Ionization; D013109:Sphingomyelins / Q000737:chemistry / Q000378:metabolism; D017855:Transferases (Other Substituted Phosphate Groups) / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism
chemical_list: D002518:Ceramides; D007211:Indoles; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D017319:Photosensitizing Agents; D034741:RNA, Small Interfering; D013109:Sphingomyelins; C109343:dihydroceramide; C107448:phthalocyanine Pc 4; C455440:SGMS1 protein, human; D017855:Transferases (Other Substituted Phosphate Groups); D053148:Caspase 3