title: Green tea polyphenol (-) -epigallocatechin-3-gallate promotes the rapid protein kinase C- and proteasome-mediated degradation of Bad: implications for neuroprotection.
abstract: The aim of the present study was to gain a deeper insight into the cell signaling pathways involved in the neuroprotection/neurorescue activity of the major green tea polyphenol (-)-epigallocatechin-3-gallate (EGCG). EGCG (1 micro m) caused an immediate (30 min) down-regulation (approximately 40%) of Bad protein levels, and a more pronounced reduction after 24 h (55%) in the human neuroblastoma cell line SH-SY5Y. Co-treatment with EGCG and the protein synthesis inhibitor cycloheximide prominently shortened Bad half-life, with as little as 30% of the Bad protein content remaining after 2 h, suggesting an effect of EGCG on Bad protein degradation. Accordingly, the proteasome inhibitors MG-132 and lactacystin damped Bad down-regulation by EGCG. The general protein kinase C (PKC) inhibitor GF109203X, or the down-regulation of conventional and novel PKC isoforms, abolished EGCG-induced Bad decline. However, no inhibition was seen with the cell-permeable myristoylated pseudosubstrate inhibitor of the atypical PKCzeta isoform. The enforced expression of Bad for up to 72 h rendered the cells more susceptible to serum deprivation-induced cell death, whereas EGCG treatment significantly improved cell viability (up to 1.6-fold). The present study reveals a novel pathway in the neuroprotective mechanism of the action of EGCG, which involves a rapid PKC-mediated degradation of Bad by the proteasome.
authors.affiliation: Eve Topf Center for Neurodegenerative Diseases, and Department of Pharmacology, Faculty of Medicine, Technion, Haifa, Israel.
authors.forename: Limor
authors.initials: L
authors.lastname: Kalfon
authors.forename: Moussa B H
authors.initials: MB
authors.lastname: Youdim
authors.forename: Silvia A
authors.initials: SA
authors.lastname: Mandel
mesh_terms: D015153:Blotting, Western; D002392:Catechin / Q000031:analogs & derivatives* / Q000494:pharmacology; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D002918:Chymotrypsin / Q000494:pharmacology; D004347:Drug Interactions; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005786:Gene Expression Regulation / Q000187:drug effects*; D006801:Humans; D008954:Models, Biological; D009447:Neuroblastoma; D018696:Neuroprotective Agents / Q000494:pharmacology*; D046988:Proteasome Endopeptidase Complex / Q000494:pharmacology*; D011493:Protein Kinase C / Q000502:physiology*; D013997:Time Factors; D014162:Transfection; D051025:bcl-Associated Death Protein / Q000378:metabolism*
chemical_list: D004791:Enzyme Inhibitors; D018696:Neuroprotective Agents; D051025:bcl-Associated Death Protein; D002392:Catechin; C045651:epigallocatechin gallate; D011493:Protein Kinase C; D002918:Chymotrypsin; D046988:Proteasome Endopeptidase Complex