Involvement of sphingolipids in apoptin-induced cell killing.
The potential anti-tumor agent Apoptin activates apoptosis in many human cancers and transformed cell lines, but is believed to be less potent in primary cells. Although caspase 3 is activated during apoptin-induced apoptosis, the mechanism of tumor cell killing remains elusive. We now show that apoptin-mediated cell death involves modulation of the sphingomyelin-ceramide pathway. Treating cells with Ad-GFPApoptin resulted in increased ceramide accumulation and enhanced expression of acid sphingomyelinase (ASMase) with a concomitant increase in ASMase activity and decreased sphingomyelin. Using confocal microscopy, ASMase, normally present in the endosomal/lysosomal compartment, was observed to translocate to the cell's periphery. Cotreatment of Ad-GFPApoptin-infected cells with the ASMase inhibitor desipramine (2.5 muM) attenuated (30%; P<0.01) apoptin-induced cell death. Apoptin was also able to induce a significant decline in sphingosine content by inhibition of ceramide deacylation through down-regulation of acid ceramidase at the protein level. Supporting the role of ceramide in apoptin action, treatment of cells with the combination of an exogenous cell-permeable ceramide analog (C6-ceramide) and Ad-GFPApoptin infection yielded a significant increase (P<0.01) in apoptosis over either treatment modality alone. Together, these data suggest that apoptin modulates ceramide/sphingolipid metabolism as part of its mechanism of action.
Liu
Xiang
X
Department of Microbiology and Immunology, Medical University of South Carolina, P.O. Box 250504, 173 Ashley Avenue, Charleston, SC 29425, USA.
Zeidan
Youssef H
YH
Elojeimy
Saeed
S
Holman
David H
DH
El-Zawahry
Ahmed M
AM
Guo
Gui-Wen
GW
Bielawska
Alicja
A
Bielawski
Jacek
J
Szulc
Zdzislaw
Z
Rubinchik
Semyon
S
Dong
Jian-Yun
JY
Keane
Thomas E
TE
Tavassoli
Mahvash
M
Hannun
Yusuf A
YA
Norris
James S
JS
D000256:Adenoviridae / Q000235:genetics; D017209:Apoptosis / Q000187:drug effects; D036022:Capsid Proteins / Q000235:genetics / Q000378:metabolism*; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000378:metabolism; D002518:Ceramides / Q000096:biosynthesis; D003891:Desipramine / Q000494:pharmacology; D015536:Down-Regulation; D011992:Endosomes / Q000378:metabolism; D002517:Galactosylgalactosylglucosylceramidase / Q000378:metabolism; D015870:Gene Expression; D017930:Genes, Reporter / Q000235:genetics; D006801:Humans; D008247:Lysosomes / Q000378:metabolism; D008297:Male; D011471:Prostatic Neoplasms / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D021381:Protein Transport; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D013107:Sphingolipids / Q000378:metabolism*; D013108:Sphingomyelin Phosphodiesterase / Q000378:metabolism; D015854:Up-Regulation
D036022:Capsid Proteins; D002518:Ceramides; D011993:Recombinant Fusion Proteins; D013107:Sphingolipids; C091717:VP3 protein, Chicken anemia virus; D013108:Sphingomyelin Phosphodiesterase; D002517:Galactosylgalactosylglucosylceramidase; D003891:Desipramine