Abstract
The novel protein kinase C-beta inhibitor enzastaurin (ENZA) induced apoptosis in LNT-229 and T98G cells whereas A172 cells were resistant. Further, ENZA reduced proliferation in glioblastoma-initiating cells T 269 and T 323 but did not induce apoptosis. ENZA-induced apoptosis involved cleavage of caspases 3, 8, and 9 and led to mitochondrial cytochrome c release and was strongly suppressed by the broad spectrum caspase inhibitor zVAD-fmk but only slightly by the expression of the viral caspase 1/8 inhibitor cytokine response modifier-A. ENZA did not reduce the phosphorylation of protein kinase B (Akt), but of p70 S6 kinase and of its substrate S6 protein in T98G cells. Inhibition of the phosphatidylinositol 3 kinase signaling pathway did not restore sensitivity of A172 cells towards ENZA, and constitutively active Akt did not protect LNT-229 and T98G cells from ENZA-induced apoptosis. Dephosphorylation of glycogen synthase kinase 3beta, a biomarker of ENZA action, and cell death induction by ENZA were separately regulated. Inhibition or activation of Akt only weakly modulated ENZA-induced dephosphorylation of glycogen synthase kinase 3beta. In ENZA-resistant A172 cells, apoptosis ligand 2 (Apo2L.0)-induced cleavage of caspases 3, 8, and 9 was increased by ENZA, resulting in synergistic activity of ENZA and Apo2L.0.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Adult
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Amino Acid Chloromethyl Ketones / pharmacology
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Antineoplastic Agents / pharmacology
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Apoptosis / drug effects*
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Apoptosis / physiology
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Brain Neoplasms / drug therapy*
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Brain Neoplasms / enzymology
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Caspases / drug effects*
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Caspases / metabolism
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Cell Line, Tumor
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Cytochromes c / drug effects
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Cytochromes c / metabolism
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Drug Resistance, Neoplasm
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Enzyme Inhibitors / pharmacology
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Glioma / drug therapy*
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Glioma / enzymology
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Glycogen Synthase Kinase 3 / drug effects
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Glycogen Synthase Kinase 3 / metabolism
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Glycogen Synthase Kinase 3 beta
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Humans
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Indoles / pharmacology*
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Mitochondria / drug effects
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Mitochondria / enzymology
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Protein Kinase C / antagonists & inhibitors
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Protein Kinase C / metabolism
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Proto-Oncogene Proteins c-akt / drug effects
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Proto-Oncogene Proteins c-akt / metabolism
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Receptors, TNF-Related Apoptosis-Inducing Ligand / drug effects
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Receptors, TNF-Related Apoptosis-Inducing Ligand / metabolism
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bcl-X Protein / metabolism*
Substances
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Amino Acid Chloromethyl Ketones
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Antineoplastic Agents
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BCL2L1 protein, human
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Enzyme Inhibitors
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Indoles
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Receptors, TNF-Related Apoptosis-Inducing Ligand
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bcl-X Protein
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benzyloxycarbonylvalyl-alanyl-aspartyl fluoromethyl ketone
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Cytochromes c
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GSK3B protein, human
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Glycogen Synthase Kinase 3 beta
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Proto-Oncogene Proteins c-akt
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Protein Kinase C
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Glycogen Synthase Kinase 3
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Caspases
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enzastaurin