MEKi-induced RTK changes are consistent with decreased proteolytic receptor shedding. MEKi-induced RTK changes are consistent with decreased proteolytic receptor shedding. A, top bar graph, differentially detected supernatant proteins from MDA-MB-231 treated with MEKi (PD325901) for 24 hours, measured by Ab microarray (n= 4). Middle, enrichment score trace for top-ranked gene set of proteins depleted with MEKi; vertical bars below trace indicate location of proteins in the top-ranked gene set. B, diverse kinase inhibitors (labeled as drug target followed by drug name) affect supernatant (supe.) concentrations in MDA-MB-231 (n≥ 2; ELISA), after normalizing to cell count. C, Venn diagram of differentially expressed genes (DEG) from RNA microarray analysis of MDA-MB-231 treated with PD325901 (PD) or BB94 for 24 hours (q= FDR-corrected P value; n≥ 2). D, surface level changes of sheddase substrates following MPi or MEKi in two TNBC cell lines (live-cell immunostaining; n= 3). E and F, intact lysate AXL from LOX-IMVI (E) and MDA-MB-231 cells (F), as detected using Abs probing N-term or C-term epitopes (n= 4). G, full-length exosomal AXL and exosome markers CD63 and HSP70, in isolated MDA-MB-231 supernatant (n= 6). H, the immunoprecipitated shed AXL fragment from supernatant of MDA-MB-231 cells decreases in abundance with BB94 (BB) or PD320951 treatment (n= 3). For E to H, *, P < 0.05, two-tailed t test. I, supernatant, lysate total, and pRTK levels following MPi; each dot represents one of 19 cell lines tested (see Supplementary Fig. S4K and S4L). Miles A. Miller et al. Cancer Discov 2016;6:382-399 ©2016 by American Association for Cancer Research