TY - JOUR
T1 - Downregulation of Bid is associated with PKCε-mediated TRAIL resistance
AU - Sivaprasad, U.
AU - Shankar, E.
AU - Basu, A.
N1 - Funding Information:
Acknowledgements. This work was supported by the grant CA71727 (AB) from the NCI. We thank Dr Sandra Zinkel for providing us Bid plasmid and Jose Mireles for technical assistance.
PY - 2007/4
Y1 - 2007/4
N2 - 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-ε (PKCε) acts as an antiapoptotic protein in MCF-7 breast cancer cells. In the present study, we have investigated the mechanism(s) by which PKCε contributes to TRAIL resistance. Overexpression of PKCε 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 PKCε resulted in enhanced sensitivity to TRAIL. The level of Bcl-2 was increased and Bid was decreased by PKCε at both the protein and mRNA level but PKCε had no effect on Bax. Knockdown of Bcl-2 by siRNA reversed TRAIL resistance in PKCε-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, PKCε depletion or overexpression of DN-PKCε was associated with a decrease in Bcl-2 protein level. Thus, our results suggest that PKCε acts upstream of mitochondria and mediates TRAIL resistance via both Bcl-2 and Bid in MCF-7 cells.
AB - 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-ε (PKCε) acts as an antiapoptotic protein in MCF-7 breast cancer cells. In the present study, we have investigated the mechanism(s) by which PKCε contributes to TRAIL resistance. Overexpression of PKCε 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 PKCε resulted in enhanced sensitivity to TRAIL. The level of Bcl-2 was increased and Bid was decreased by PKCε at both the protein and mRNA level but PKCε had no effect on Bax. Knockdown of Bcl-2 by siRNA reversed TRAIL resistance in PKCε-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, PKCε depletion or overexpression of DN-PKCε was associated with a decrease in Bcl-2 protein level. Thus, our results suggest that PKCε acts upstream of mitochondria and mediates TRAIL resistance via both Bcl-2 and Bid in MCF-7 cells.
UR - http://www.scopus.com/inward/record.url?scp=33947418962&partnerID=8YFLogxK
U2 - 10.1038/sj.cdd.4402077
DO - 10.1038/sj.cdd.4402077
M3 - Article
C2 - 17186022
AN - SCOPUS:33947418962
SN - 1350-9047
VL - 14
SP - 851
EP - 860
JO - Cell Death and Differentiation
JF - Cell Death and Differentiation
IS - 4
ER -