title: Protein kinase Cδ and caspase-3 modulate TRAIL-induced apoptosis in breast tumor cells.
abstract: This report describes that protein kinase C delta (PKCδ) overexpression prevents TRAIL-induced apoptosis in breast tumor cells; however, the regulatory mechanism(s) involved in this phenomenon is(are) incompletely understood. In this study, we have shown that TRAIL-induced apoptosis was significantly inhibited in PKCδ overexpressing MCF-7 (MCF7/PKCδ) cells. Our data reveal that PKCδ inhibits caspase-8 activation, a first step in TRAIL-induced apoptosis, thus preventing TRAIL-induced apoptosis. Inhibition of PKCδ using rottlerin or PKCδ siRNA reverses the inhibitory effect of PKCδ on caspase-8 activation leading to TRAIL-induced apoptosis. To determine if caspase-3-induced PKCδ cleavage reverses its inhibition on caspase-8, we developed stable cell lines that either expresses wild-type PKCδ (MCF-7/cas-3/PKCδ) or caspase-3 cleavage-resistant PKCδ mutant (MCF-7/cas-3/PKCδ mut) utilizing MCF-7 cells expressing caspase-3. Cells that overexpress caspase-3 cleavage-resistant PKCδ mutant (MCF-7/cas-3/PKCδmut) significantly inhibited TRAIL-induced apoptosis when compared to wild-type PKCδ (MCF-7/cas-3/PKCδ) expressing cells. In MCF-7/cas-3/PKCδmut cells, TRAIL-induced caspase-8 activation was blocked leading to inhibition of apoptosis when compared to wild-type PKCδ (MCF-7/cas-3/PKCδ) expressing cells. Together, these results strongly suggest that overexpression of PKCδ inhibits caspase-8 activation leading to inhibition of TRAIL-induced apoptosis and its inhibition by rottlerin, siRNA, or cleavage by caspase-3 sensitizes cells to TRAIL-induced apoptosis. Clinically, PKCδ overexpressing tumors can be treated with a combination of PKCδ inhibitor(s) and TRAIL as a new treatment strategy.
authors.affiliation: Department of Pathology, Wayne State University School of Medicine, 540 E. Canfield, Detroit, Michigan 48201, USA.
authors.forename: Shuping
authors.initials: S
authors.lastname: Yin
authors.forename: Seema
authors.initials: S
authors.lastname: Sethi
authors.forename: Kaladhar B
authors.initials: KB
authors.lastname: Reddy
mesh_terms: D017209:Apoptosis / Q000187:drug effects*; D001943:Breast Neoplasms / Q000201:enzymology* / Q000473:pathology*; D053148:Caspase 3 / Q000378:metabolism*; D045744:Cell Line, Tumor; D019610:Cytoprotection / Q000187:drug effects; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D051745:Protein Kinase C-delta / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000378:metabolism; D053221:TNF-Related Apoptosis-Inducing Ligand / Q000494:pharmacology*
chemical_list: D034741:RNA, Small Interfering; D053221:TNF-Related Apoptosis-Inducing Ligand; C497258:PRKCD protein, human; D051745:Protein Kinase C-delta; C505407:CASP3 protein, human; D053148:Caspase 3