Flavopiridol synergizes TRAIL cytotoxicity by downregulation of FLIPL.
OBJECTIVE
Flavopiridol is known to modulate the transcription of genes. We investigated the effect of flavopiridol pretreatment on TRAIL cytotoxicity and on the expression of FLIP(L) in different TRAIL-resistant cell lines, because FLIP expression is known to confer TRAIL-resistance.


METHODS
Apoptosis was assessed by PI staining and protein expression by Western blotting. RT-PCR was used for mRNA quantitation. siRNA gene silencing was used to knock down FLIP(L).


RESULTS
Flavopiridol pretreatment synergized TRAIL-induced apoptosis in human myeloma and breast cancer cells. Flavopiridol treatment repressed the transcription of FLIP(L) and downregulated its expression in both myeloma and breast cancer cells. Silencing of FLIP(L) gene by siRNA sensitized myeloma cells to TRAIL. Flavopiridol treatment downregulated the expression of the proapoptotic members of the Bcl-2 family proteins (Bak, Bax and PUMA-alpha). The expression of the antiapoptotic Bcl-2 members (Bcl-2 and Bcl-X(L)) was not altered by flavopiridol treatment in myeloma cells.


CONCLUSIONS
Our data indicate that flavopiridol synergizes TRAIL cytotoxicity by downregulation of FLIP(L) and this synergistic effect is Bcl-2 family independent.
Fandy
Tamer E
TE
School of Pharmacy, Department of Pharmaceutical Sciences, University of Maryland, Baltimore, MD 21201, USA. tfandy@jhu.edu
Ross
Douglas D
DD
Gore
Steven D
SD
Srivastava
Rakesh K
RK
D000970:Antineoplastic Agents / Q000633:toxicity; D017209:Apoptosis / Q000187:drug effects; D001943:Breast Neoplasms / Q000473:pathology; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein / Q000235:genetics*; D045744:Cell Line, Tumor; D004396:Coloring Agents; D015536:Down-Regulation; D004357:Drug Synergism; D005260:Female; D005419:Flavonoids / Q000633:toxicity*; D015972:Gene Expression Regulation, Neoplastic; D020868:Gene Silencing / Q000187:drug effects; D006801:Humans; D009101:Multiple Myeloma / Q000235:genetics; D010880:Piperidines / Q000633:toxicity*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D053221:TNF-Related Apoptosis-Inducing Ligand / Q000633:toxicity*
D000970:Antineoplastic Agents; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; D004396:Coloring Agents; D005419:Flavonoids; D010880:Piperidines; D019253:Proto-Oncogene Proteins c-bcl-2; D053221:TNF-Related Apoptosis-Inducing Ligand; C505653:TNFSF10 protein, human; C077990:alvocidib