title: Curcumin induces apoptosis of multidrug-resistant human leukemia HL60 cells by complex pathways leading to ceramide accumulation.
abstract: Most anti-cancer agents induce apoptosis, however, a development of multidrug resistance in cancer cells and defects in apoptosis contribute often to treatment failure. Here, the mechanism of curcumin-induced apoptosis was investigated in human leukemia HL60 cells and their HL60/VCR multidrug-resistant counterparts. In both cell lines curcumin induced a bi-phasic ceramide generation with a slow phase until 6 h followed by a more rapid one. The level of the ceramide accumulation correlated inversely with the cell viability. We found that the ceramide elevation resulted from multifarious changes of the activity of sphingolipid-modifying enzymes. In both cell lines curcumin induced relatively fast activation of neutral sphingomyelinase (nSMase), which peaked at 3 h, and was followed by inhibition of sphingomyelin synthase activity. In addition, in HL60/VCR cells the glucosylceramide synthase activity was diminished by curcumin. This process was probably due to curcumin-induced down-regulation of P-gp drug transporter, since cyclosporine A, a P-gp blocker, also inhibited the glucosylceramide synthase activity. Inhibition of nSMase activity with GW4869 or silencing ofSMPD3 gene encoding nSMase2 reversed the curcumin-induced inhibition of sphingomyelin synthase without affecting the glucosylceramide synthase activity. The early ceramide generation by nSMase was indispensable for the later lipid accumulation, modulation of Bax, Bcl-2 and caspase 3 levels, and for reduction of cell viability in curcumin-treated cells, as all these events were inhibited by GW4869 or nSMase2 depletion. These data indicate that the early ceramide generation by nSMase2 induced by curcumin intensifies the later ceramide accumulation via inhibition of sphingomyelin synthase, and controls pro-apoptotic signaling.
authors.forename: Abo Bakr Abdel
authors.initials: AB
authors.lastname: Shakor
authors.forename: Mona
authors.initials: M
authors.lastname: Atia
authors.forename: Ismail Ahmed
authors.initials: IA
authors.lastname: Ismail
authors.forename: Ali
authors.initials: A
authors.lastname: Alshehri
authors.forename: Hesham
authors.initials: H
authors.lastname: El-Refaey
authors.forename: Katarzyna
authors.initials: K
authors.lastname: Kwiatkowska
authors.forename: Andrzej
authors.initials: A
authors.lastname: Sobota
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000378:metabolism; D017209:Apoptosis / Q000187:drug effects*; D002470:Cell Survival / Q000187:drug effects; D002518:Ceramides / Q000378:metabolism*; D003474:Curcumin / Q000494:pharmacology* / Q000627:therapeutic use; D015536:Down-Regulation / Q000187:drug effects; D018432:Drug Resistance, Multiple / Q000187:drug effects*; D019008:Drug Resistance, Neoplasm / Q000187:drug effects*; D004789:Enzyme Activation / Q000187:drug effects; D005964:Glucosyltransferases / Q000378:metabolism; D018922:HL-60 Cells; D006801:Humans; D007938:Leukemia / Q000188:drug therapy / Q000201:enzymology / Q000473:pathology*; D008954:Models, Biological; D015398:Signal Transduction / Q000187:drug effects*; D013108:Sphingomyelin Phosphodiesterase / Q000378:metabolism; D014750:Vincristine / Q000494:pharmacology / Q000627:therapeutic use
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D002518:Ceramides; D014750:Vincristine; D005964:Glucosyltransferases; C023246:ceramide glucosyltransferase; D013108:Sphingomyelin Phosphodiesterase; D003474:Curcumin