Downregulation of Bid is associated with PKCepsilon-mediated TRAIL resistance.
Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a promising anticancer agent as it selectively kills tumor cells but spares normal cells. Resistance to TRAIL by tumor cells limits its therapeutic use. We have previously shown that protein kinase C-epsilon (PKCepsilon) acts as an antiapoptotic protein in MCF-7 breast cancer cells. In the present study, we have investigated the mechanism(s) by which PKCepsilon contributes to TRAIL resistance. Overexpression of PKCepsilon inhibited caspase-8 and -9 activation, release of mitochondrial cytochrome c and cell death induced by TRAIL, but did not interfere with the recruitment of caspase-8 to the death-inducing signaling complex. Knockdown/inhibition of PKCepsilon resulted in enhanced sensitivity to TRAIL. The level of Bcl-2 was increased and Bid was decreased by PKCepsilon at both the protein and mRNA level but PKCepsilon had no effect on Bax. Knockdown of Bcl-2 by siRNA reversed TRAIL resistance in PKCepsilon-overexpressing cells, whereas depletion of Bid contributed to TRAIL resistance in MCF-7 cells. A decrease in Bid content was also associated with inhibition of TRAIL-induced caspase-8 activation. Furthermore, PKCepsilon depletion or overexpression of DN-PKCepsilon was associated with a decrease in Bcl-2 protein level. Thus, our results suggest that PKCepsilon acts upstream of mitochondria and mediates TRAIL resistance via both Bcl-2 and Bid in MCF-7 cells.
Sivaprasad
U
U
Department of Molecular Biology and Immunology, University of North Texas Health Science Center, Fort Worth, TX 76107, USA.
Shankar
E
E
Basu
A
A
D017209:Apoptosis / Q000502:physiology*; D051023:BH3 Interacting Domain Death Agonist Protein / Q000235:genetics / Q000378:metabolism*; D001943:Breast Neoplasms / Q000378:metabolism; D020169:Caspases / Q000378:metabolism; D045744:Cell Line, Tumor; D015536:Down-Regulation / Q000235:genetics; D005260:Female; D005434:Flow Cytometry; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism; D051744:Protein Kinase C-epsilon / Q000235:genetics / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000235:genetics; D053221:TNF-Related Apoptosis-Inducing Ligand / Q000378:metabolism*; D014162:Transfection; D014407:Tumor Cells, Cultured
D051023:BH3 Interacting Domain Death Agonist Protein; D047908:Intracellular Signaling Peptides and Proteins; D034741:RNA, Small Interfering; D053221:TNF-Related Apoptosis-Inducing Ligand; D051744:Protein Kinase C-epsilon; D020169:Caspases