Targeting oncogenic Ras by the Clostridium perfringens toxin TpeL
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Björn Schorch1, Hannah Heni1, Nour-Imene Zahaf1, Tilman Brummer2,3,4, Marina Mione5,6, Gudula Schmidt1, Panagiotis Papatheodorou1,7,8 and Klaus Aktories1,4
1Institut für Experimentelle und Klinische Pharmakologie und Toxikologie, Medizinische Fakultät, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
2Institut für Molekulare Medizin und Zellforschung, Medizinische Fakultät, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
3German Cancer Consortium (DKTK), Partner Site Freiburg, Germany, and German Cancer Research Center (DKFZ), Heidelberg, Germany
4Centre for Biological Signalling Studies (BIOSS), Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
5Institute of Toxicology and Genetics, Karlsruhe Institute of Technology, Eggestein-Leopoldshafen, Germany
6Present Address: Center for Integrative Biology, University of Trento, Trento, Italy
7Present Address: Institute of Pharmaceutical Biotechnology, University of Ulm, Ulm, Germany
8Present Address: Institute of Pharmacology and Toxicology, University of Ulm Medical Center, Ulm, Germany
Klaus Aktories, email: email@example.com
Keywords: Clostridium perfringens toxin; glycosylation; immunotoxins; paradoxical activation; Ras
Received: April 04, 2017 Accepted: March 02, 2018 Published: March 27, 2018
Clostridium perfringens toxin TpeL belongs to the family of large clostridial glycosylating toxins. The toxin causes N-acetylglucosaminylation of Ras proteins at threonine35 thereby inactivating the small GTPases. Here, we show that all main types of oncogenic Ras proteins (H-Ras, K-Ras and N-Ras) are modified by the toxin in vitro and in vivo. Toxin-catalyzed modification of Ras was accompanied by inhibition of the MAP kinase pathway. Importantly, TpeL inhibited the paradoxical activation of the MAP kinase pathway induced by the BRAF inhibitor Vemurafenib in the human melanoma cell line SBCL2. The toxin also blocked Ras signaling in a zebrafish embryo model expressing oncogenic H-RasG12V, resulting in a reduction of melanocyte number. By using the binding and translocation component of anthrax toxin (protective antigen), the glucosyltransferase domain of TpeL was effectively introduced into target cells that were not sensitive to native TpeL toxin. To reach a higher specificity towards cancer cells, a chimeric TpeL toxin was engineered that possessed the knob region of adenovirus serotype 35 fiber, which interacts with CD46 of target cells frequently overexpressed in cancer cells. The chimeric TpeL fusion toxin efficiently inhibited Ras and MAP kinases in human pancreatic cancer Capan-2 cells, which were insensitive to the wild-type toxin. The data reveal that TpeL and TpeL-related immunotoxins provide a new toolset as Ras-inactivating agents.
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