Supplementary Figure S7 - MAP17 levels determine the sensitivity to bortezomib regulating autophagy. Cells were treated with the indicated drug concentrations and performed western blot as described (see Supplementary Methods). (A) levels of proteins of the autophagosomal markers LC3B (LC3-II), in T47D and MDA-MB-231 cells overexpressing MAP17 or expressing only empty vector. (B) Quantification of proteins from A, measured as the fold increase (from control untreated cells) of protein referred to a-tubulin. Supplementary Figure S8 - MAP17 overrexpression increases endogenous ROS. Quantification of intracellular ROS leves in T47D and MDA-MB-231 cell lines. Average and SD of three independent experiments are shown. ***, P<0.001 (Student's t-test).
ARTICLE ABSTRACT
MAP17 is a small nonglycosylated membrane protein that is overexpressed in a high percentage of carcinomas. High levels of MAP17 enhance the tumorigenic properties of tumor cells by increasing oxidative stress, which is dependent on Na+-coupled cotransport. Here, we show that MAP17 is associated with proteins involved in protein degradation and that proteasome inhibition induces autophagy. To analyze whether MAP17 could also alter this process, we used the proteasome inhibitor bortezomib (Velcade, PS-341), which is approved for the treatment of multiple myeloma and mantle cell lymphoma, although it has a high rate of resistance emergence and poor efficacy in solid tumors. We provide evidence that bortezomib induces a cytoprotective effect by activating autophagy and NFκB nuclear translocation, responses that are repressed in the presence of high levels of MAP17 both in vitro and in vivo. Indeed, patients with multiple myeloma treated with bortezomib showed higher response rates and a longer time to progression associated with increased levels of MAP17 expression. The MAP17-induced sensitivity to bortezomib is dependent on the oxidative status of the cells and the activity of Na+-coupled transporters because treatment with antioxidants or the inhibitor furosemide restores the cytoprotective activity induced by bortezomib. Therefore, bortezomib induces a prosurvival response through cytoprotective autophagy and NFκB nuclear translocation, which is repressed by high levels of MAP17. We propose that the levels of MAP17 could be used as a prognostic marker to predict the response to bortezomib in hematologic malignancies and in other tissues that are not commonly responsive to the drug. Mol Cancer Ther; 14(6); 1454–65. ©2015 AACR.
