Effects of RAF inhibitors on PI3K/AKT signalling depend on mutational status of the RAS/RAF signalling axis
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Raphaela Fritsche-Guenther1, Franziska Witzel2,3, Stefan Kempa1, Tilman Brummer4, Christine Sers2, Nils Blüthgen2,3,5
1Max-Delbrück-Center for Molecular Medicin (MDC) Berlin Buch, The Berlin Institute for Medical Systems Biology (BIMSB), 13125 Berlin, Germany
2Institute of Pathology, Molecular Tumor Pathology, Charité - Universitätsmedizin Berlin, 10117 Berlin, Germany
3Institute for Theoretical Biology, Charité - Universitätsmedizin Berlin, 10115 Berlin, Germany
4Institute of Molecular Medicine and Cell Research and Centre for Biological Signalling Studies BIOSS, Albert-Ludwigs University Freiburg, 79104 Freiburg, Germany
5Integrative Research Institute for the Life Sciences, Humboldt University Berlin, 10099 Berlin, Germany
Nils Blüthgen, e-mail: firstname.lastname@example.org
Keywords: sorafenib, signal transduction networks, BRAF, KRAS, colon cancer
Received: August 11, 2015 Accepted: December 23, 2015 Published: January 20, 2016
Targeted therapies within the RAS/RAF/MEK/ERK signalling axis become increasingly popular, yet cross-talk and feedbacks in the signalling network lead to unexpected effects. Here we look systematically into how inhibiting RAF and MEK with clinically relevant inhibitors result in changes in PI3K/AKT activation. We measure the signalling response using a bead-based ELISA, and use a panel of three cell lines, and isogenic cell lines that express mutant forms of the oncogenes KRAS and BRAF to interrogate the effects of the MEK and RAF inhibitors on signalling. We find that treatment with the RAF inhibitors have opposing effects on AKT phosphorylation depending on the mutational status of two important oncogenes, KRAS and BRAF. If these two genes are in wildtype configuration, RAF inhibitors reduce AKT phosphorylation. In contrast, if BRAF or KRAS are mutant, RAF inhibitors will leave AKT phosphorylation unaffected or lead to an increase of AKT phosphorylation. Down-regulation of phospho-AKT by RAF inhibitors also extends to downstream transcription factors, and correlates with apoptosis induction. Our results show that oncogenes rewire signalling such that targeted therapies can have opposing effects on parallel pathways, which depend on the mutational status of the cell.
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