BRAF Fusion Confers Resistance to c-Met Inhibitor Figure 6. Higher ERK activity coincides with highly expressed SND1-BRAF fusion proteins in GTL16R1 and GTL16R3. (A) Western immunoblot of GTL16, GTL16R1 and GTL16R3 treated with inhibitors as single agent or combinations for 4 hr. (B) Densitometry measurement of the relative intensity of phospho ERK normalized to total ERK within each sample. (C) Densitometry measurement of the relative intensity of phospho AKT S473 normalized to total AKT within each sample. doi:10.1371/journal.pone.0039653.g006 upon the MAPK pathway using MEKi alone. Single agent MEKi was able to completely inhibit ERK phosphorylation in all cells. Consistent with BRAF activation, these data indicate that METi inhibition is bypassed downstream of c-Met and upstream of MEK. Discussion In some cancers, dysregulated c-Met signaling results in oncogene addiction, a dependence on the pathway to maintain cancer cell growth and survival [46]. The MET locus is amplified or mutated in selected tumor types, and these patients are predicted to be responsive to treatment with c-Met inhibitors [8,47]. Unfortunately, acquired resistance is a significant concern for single agent therapy based on precedence with agents like imatinib in CML and erlotinib in lung adenocarcinoma [48]. Here we describe a GTL16 cell line model of METi resistance. We identify an activated SND1-BRAF fusion protein which confers resistance to METi. BRAF promotes cell growth and proliferation by transducing signals from growth factor receptors as part of the MAP kinase pathway via MEK and ERK. Our findings are consistent with a model of resistance where the fusion PLoS ONE | www.plosone.org 9 June 2012 | Volume 7 | Issue 6 | e39653