Suppression of sphingomyelin synthase 1 by small interference RNA is associated with enhanced ceramide production and apoptosis after photodamage.
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.
Separovic
Duska
D
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>
Semaan
Louie
L
Tarca
Adi L
AL
Awad Maitah
Ma'In Yehya
MY
Hanada
Kentaro
K
Bielawski
Jacek
J
Villani
Maristella
M
Luberto
Chiara
C
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
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