Abstract 4597: Stroma-derived Basigin controls survival of leukemia cells through regulation of their redox state.
Authors: Bornhauser Beat C. , Boutter Jeannette , Horvath Peter , Stanulla Martin , Bourquin Jean-Pierre 
Published: August 2014

Abstract
Leukemia cells critically depend on interactions with the microenvironment in bone marrow and at extramedullary sanctuary sites, which provides protection to escape chemotherapy. Co-culture of primary leukemia cells on mesenchymal stroma cells (MSCs) derived from human bone marrow supports leukemia cell survival. We have developed an automated microscopy-based approach to identify stroma-derived pro-survival signals by RNA interference of candidate genes in MSCs enabling functional profiles of primary leukemia cells with respect to support from the microenvironment. We took advantage of our leukemia xenograft system of well characterized primary ALL samples, including cases with refractory disease. Based on gene expression and cell surface proteomic data from both cellular compartments, we generated a customized siRNA library of 110 genes with a potential function in stromal support. Primary ALL cells were seeded on reversely transfected MSC cells, and ALL cell viability was assessed with a fluorescent viability dye after 6 days. Image analysis and machine learning algorithms were developed for specific quantification of surviving ALL cells on top of MSCs.
As proof of concept, we could show that down-regulation of VCAM1 or the VEGF pathway in MSCs decreased ALL survival in a subgroup of cases. Inhibitors of VEGF signalling recapitulated a decrease of ALL cell viability for the same samples. One of the strongest effects on ALL survival was achieved by down-regulation of the membrane protein Basigin (CD147). Specifically, 13 out of 17 ALL cases analysed in validation experiments were affected by modulation of Basigin on MSC level. Basigin has been implicated in cell signalling, in interactions with extracellular matrix, and serves as chaperone to different membrane carrier proteins. Among putative Basigin interactors we identified the heteromeric amino acid transporter SLC3A2 (CD98) to be required for ALL survival in the same 13 ALL cases. Down-regulation of Basigin or SLC3A2 in MSCs induced a decrease of GSH levels and increased ROS levels in leukemia cells, enhancing oxidative stress. Downregulation of Basigin/SLC3A2 also increased the sensitivity of leukemia cells to oxidative stress by H2O2. Depletion of cysteine in co-culture conditions mimicked the effect of Basigin downregulation, and addition of cysteine restored ALL cell viability despite downregulation of Basigin in MSCs, identifying stroma-dependent cysteine metabolism as important regulatory mechanism to maintain GSH levels in ALL cells.
Taken together, we have established a robust platform for functional investigation of primary ALL cell survival in a model of the leukemia microenvironment and obtained evidence for dependence of ALL cell survival on Basigin/SLC3A2 activity in stroma. Our data indicate that Basigin/SLC3A2 function is important for the regulation of the redox state of ALL cells in this model of the leukemia niche.
Citation Format: Beat C. Bornhauser, Jeannette Boutter, Peter Horvath, Martin Stanulla, Jean-Pierre Bourquin. Stroma-derived Basigin controls survival of leukemia cells through regulation of their redox state. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4597. doi:10.1158/1538-7445.AM2013-4597