title: Etoposide induces protein kinase Cdelta- and caspase-3-dependent apoptosis in neuroblastoma cancer cells.
abstract: In this report, we reveal that etoposide inhibits the proliferation of SK-N-AS neuroblastoma cancer cells and promotes protein kinase Cdelta (PKCdelta)- and caspase-dependent apoptosis. Etoposide induces the caspase-3-dependent cleavage of PKCdelta to its active p40 fragment, and active PKCdelta triggers the processing of caspase-3 by a positive-feedback mechanism. Treatment of cells with the caspase-3-specific inhibitor N-benzyloxycarbonyl-Asp-Glu-Val-Asp-fluoromethyl ketone or caspase-3-specific small interacting RNA (siRNA) prevented the etoposide-induced activation of caspase-8 and inhibited apoptosis. The silencing of the caspase-2 or caspase-8 genes using siRNAs did not affect the etoposide-induced processing of caspase-3, indicating that these caspases lie downstream of caspase-3 in this signaling pathway. Furthermore, the etoposide-induced processing of caspase-2 required the expression of caspase-8, and the etoposide-mediated processing of caspase-8 required the expression of caspase-2, indicating that these two caspases activate each other after etoposide treatment. We also observed that etoposide-mediated apoptosis was decreased by treating the cells with the caspase-6-specific inhibitor benzyloxycarbonyl-Val-Glu(OMe)-Ile-Asp-(OMe)-fluoromethyl ketone and that caspase-6 was activated by a caspase-8-dependent mechanism. Finally, we show that rottlerin blocks etoposide-induced apoptosis by inhibiting the PKCdelta-mediated activation of caspase-3 and by degrading caspase-2, which prevents caspase-8 activation. Our results add important insights into how etoposide mediates apoptotic signaling and how targeting these pathways may lead to the development of novel therapeutics for the treatment of neuroblastomas.
authors: Department of Pharmacology and Toxicology and Indiana University Simon Cancer Center, Indiana University School of Medicine, Indianapolis, Indiana 46202, USA.
authors: Travis W
authors: TW
authors: Day
authors: Ching-Huang
authors: CH
authors: Wu
authors: Ahmad R
authors: AR
authors: Safa
mesh_terms: D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology*; D017209:Apoptosis; D053148:Caspase 3 / Q000378:metabolism*; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D005047:Etoposide / Q000494:pharmacology*; D006801:Humans; D009447:Neuroblastoma / Q000201:enzymology*; D051745:Protein Kinase C-delta / Q000378:metabolism*
chemical_list: D000972:Antineoplastic Agents, Phytogenic; D005047:Etoposide; D051745:Protein Kinase C-delta; D053148:Caspase 3