Analysis of exosome RNA from co-culture of cancer cell and stroma cell

How stroma communicates with cancer to influence treatment response is poorly understood. We show that stromal fibroblasts protect breast cancer (BrCa) against radiation and chemotherapy through an exosome-mediated anti-viral pathway and NOTCH3. Stroma increases RAB27B and transfers exosomes to BrCa. RNA within exosomes, comprised largely of non-coding transcripts and transposable elements, stimulates the pattern recognition receptor RIG-I through a 5'-triphosphate motif to activate STAT1. BrCa NOTCH3 is activated in parallel by stromal JAG1 and cooperates with STAT1 to enhance transcriptional responses of NOTCH target genes and to expand therapy resistant tumor-initiating cells. Computational modeling using primary human and mouse BrCa supports the interaction of anti-viral/NOTCH3 pathways in controlling NOTCH target genes and treatment resistance, particularly in basal subtype tumors. Gamma secretase inhibitors reverse stromal protection and abrogate radiation resistance in vivo. Thus, stroma orchestrates an intricate cross-talk with BrCa by utilizing exosomes to coax anti-viral signaling that expands therapy resistant cells through druggable pathways. Overall design: RNA profile of ceullar RNA and exosome of co-culture of breast caner cell line 1833 and stroma cell line MRC5.