title: Protein kinase C epsilon confers resistance of MCF-7 cells to TRAIL by Akt-dependent activation of Hdm2 and downregulation of p53.
abstract: Protein kinase C epsilon (PKC epsilon ) acts as an antiapoptotic protein and inhibits tumor necrosis factor-alpha (TNF)-related apoptosis-inducing ligand (TRAIL)-induced apoptosis in MCF-7 breast cancer cells. Members of the TNF receptor superfamily trigger apoptosis independent of the tumor suppressor protein p53, which primarily affects DNA damage-induced apoptosis. We have previously shown that PKC epsilon acts upstream of Akt to inhibit receptor-initiated cell death. Since Akt can regulate p53, we have examined the involvement of p53 in PKC epsilon-mediated TRAIL resistance. Overexpression of PKC epsilon in MCF-7 cells (MCF-7/PKC epsilon ) caused a decrease in p53 and an increase in human homolog of murine double minute 2 (Hdm2) and phospho-Hdm2. Depletion of p53 by siRNA attenuated, whereas depletion of Hdm2 enhanced TRAIL-mediated apoptosis. Knockdown of Akt decreased Hdm2 phosphorylation, increased p53 level and potentiated TRAIL-induced cell death. Depletion of epsilon from MCF-7 cells caused an increase in p53, whereas knockdown of p53 caused a decrease in Bid mRNA. Depletion of Akt from MCF-7/PKC epsilon cells resulted in an increase in p53 and Bid. These results suggest that PKC epsilon mediates TRAIL resistance by Akt-mediated phosphorylation of Hdm2 resulting in suppression of p53 expression and downregulation of Bid in MCF-7 breast cancer cells.
authors.affiliation: Department of Molecular Biology and Immunology, University of North Texas Health Science Center, Fort Worth, TX 76107, USA.
authors.forename: E
authors.initials: E
authors.lastname: Shankar
authors.forename: U
authors.initials: U
authors.lastname: Sivaprasad
authors.forename: A
authors.initials: A
authors.lastname: Basu
mesh_terms: D000818:Animals; D017209:Apoptosis; D051023:BH3 Interacting Domain Death Agonist Protein / Q000378:metabolism*; D045744:Cell Line, Tumor; D019008:Drug Resistance, Neoplasm; D015972:Gene Expression Regulation, Neoplastic; D016158:Genes, p53; D006801:Humans; D051379:Mice; D051744:Protein Kinase C-epsilon / Q000378:metabolism / Q000502:physiology*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D051736:Proto-Oncogene Proteins c-mdm2 / Q000378:metabolism*; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism / Q000502:physiology*
chemical_list: D051023:BH3 Interacting Domain Death Agonist Protein; C495901:TP53 protein, human; D016159:Tumor Suppressor Protein p53; C497206:MDM2 protein, human; C497207:Mdm2 protein, mouse; D051736:Proto-Oncogene Proteins c-mdm2; D051057:Proto-Oncogene Proteins c-akt; D051744:Protein Kinase C-epsilon