title: Targeting the actin cytoskeleton: selective antitumor action via trapping PKCɛ.
abstract: Targeting the actin cytoskeleton (CSK) of cancer cells offers a valuable strategy in cancer therapy. There are a number of natural compounds that interfere with the actin CSK, but the mode of their cytotoxic action and, moreover, their tumor-specific mechanisms are quite elusive. We used the myxobacterial compound Chondramide as a tool to first elucidate the mechanisms of cytotoxicity of actin targeting in breast cancer cells (MCF7, MDA-MB-231). Chondramide inhibits cellular actin filament dynamics shown by a fluorescence-based analysis (fluorescence recovery after photobleaching (FRAP)) and leads to apoptosis characterized by phosphatidylserine exposure, release of cytochrome C from mitochondria and finally activation of caspases. Chondramide enhances the occurrence of mitochondrial permeability transition (MPT) by affecting known MPT modulators: Hexokinase II bound to the voltage-dependent anion channel (VDAC) translocated from the outer mitochondrial membrane to the cytosol and the proapoptotic protein Bad were recruited to the mitochondria. Importantly, protein kinase C-ɛ (PKCɛ), a prosurvival kinase possessing an actin-binding site and known to regulate the hexokinase/VDAC interaction as well as Bad phosphorylation was identified as the link between actin CSK and apoptosis induction. PKCɛ, which was found overexpressed in breast cancer cells, accumulated in actin bundles induced by Chondramide and lost its activity. Our second goal was to characterize the potential tumor-specific action of actin-binding agents. As the nontumor breast epithelial cell line MCF-10A in fact shows resistance to Chondramide-induced apoptosis and notably express low level of PKCɛ, we suggest that trapping PKCɛ via Chondramide-induced actin hyperpolymerization displays tumor cell specificity. Our work provides a link between targeting the ubiquitously occurring actin CSK and selective inhibition of pro-tumorigenic PKCɛ, thus setting the stage for actin-stabilizing agents as innovative cancer drugs. This is moreover supported by the in vivo efficacy of Chondramide triggered by abrogation of PKCɛ signaling shown in a xenograft breast cancer model.
authors.affiliation: Department of Pharmacy, Pharmaceutical Biology, University of Munich, Munich, Germany.
authors.forename: F
authors.initials: F
authors.lastname: Foerster
authors.affiliation: Department of Pharmacy, Pharmaceutical Biology, University of Munich, Munich, Germany.
authors.forename: S
authors.initials: S
authors.lastname: Braig
authors.affiliation: Department of Pharmacy, Pharmaceutical Biology, University of Munich, Munich, Germany.
authors.forename: C
authors.initials: C
authors.lastname: Moser
authors.affiliation: Department of Pharmacy, Pharmaceutical Biology, University of Munich, Munich, Germany.
authors.forename: R
authors.initials: R
authors.lastname: Kubisch
authors.affiliation: Department of Pharmacy, Pharmaceutical Biotechnology, University of Munich, Munich, Germany.
authors.forename: J
authors.initials: J
authors.lastname: Busse
authors.affiliation: Department of Pharmacy, Pharmaceutical Biotechnology, University of Munich, Munich, Germany.
authors.forename: E
authors.initials: E
authors.lastname: Wagner
authors.affiliation: Institute of Pathology, University of Munich, Munich, Germany.
authors.forename: E
authors.initials: E
authors.lastname: Schmoeckel
authors.affiliation: Institute of Pathology, University of Munich, Munich, Germany.
authors.forename: D
authors.initials: D
authors.lastname: Mayr
authors.affiliation: Institute for Molecular Toxicology and Pharmacology, Helmholtz Centre Munich, German Research Center for Environmental Health, Neuherberg, Germany.
authors.forename: S
authors.initials: S
authors.lastname: Schmitt
authors.affiliation: Institute of Pathology, University of Munich, Munich, Germany.
authors.forename: S
authors.initials: S
authors.lastname: Huettel
authors.affiliation: Institute for Molecular Toxicology and Pharmacology, Helmholtz Centre Munich, German Research Center for Environmental Health, Neuherberg, Germany.
authors.forename: H
authors.initials: H
authors.lastname: Zischka
authors.affiliation: Helmholtz Institute for Pharmaceutical Research Saarland, Helmholtz Centre for Infection Research and Department of Pharmaceutical Biotechnology, Saarland University, Saarbrücken, Germany.
authors.forename: R
authors.initials: R
authors.lastname: Mueller
authors.affiliation: Department of Pharmacy, Pharmaceutical Biology, University of Munich, Munich, Germany.
authors.forename: A M
authors.initials: AM
authors.lastname: Vollmar
mesh_terms: D008841:Actin Cytoskeleton / Q000187:drug effects / Q000378:metabolism*; D000199:Actins / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D000970:Antineoplastic Agents / Q000627:therapeutic use / Q000633:toxicity; D017209:Apoptosis / Q000187:drug effects; D001665:Binding Sites; D001943:Breast Neoplasms / Q000188:drug therapy / Q000473:pathology; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D045304:Cytochromes c / Q000378:metabolism; D047630:Depsipeptides / Q000627:therapeutic use / Q000633:toxicity; D005260:Female; D036681:Fluorescence Recovery After Photobleaching; D006593:Hexokinase / Q000378:metabolism; D006801:Humans; D061986:MCF-7 Cells; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects; D051379:Mice; D016513:Mice, SCID; D008928:Mitochondria / Q000378:metabolism; D010718:Phosphatidylserines / Q000494:pharmacology; D011493:Protein Kinase C / Q000378:metabolism*; D015398:Signal Transduction; D014183:Transplantation, Heterologous; D050994:Voltage-Dependent Anion Channels / Q000378:metabolism; D051025:bcl-Associated Death Protein / Q000378:metabolism
chemical_list: D000199:Actins; D000970:Antineoplastic Agents; D047630:Depsipeptides; D010718:Phosphatidylserines; D050994:Voltage-Dependent Anion Channels; D051025:bcl-Associated Death Protein; C097819:chondramide A; D045304:Cytochromes c; D006593:Hexokinase; D011493:Protein Kinase C