Figure 6: Recurrent NRG1 rearrangements in lung cancer.

(a) Recurrent fusions involving NRG1 as a 3′-partner were detected in lung adenocarcinoma and lung squamous carcinoma in the three cohorts included in this study. Schematic representation of functional domains present in the NRG1 fusion proteins namely CD74-NRG1; RBPMS-NRG1 (LUAD), WRN-NRG1 (LUSC), SDC4-NRG1 (LUSC) and RAB2IL1-NRG1 (ovarian cancer from TCGA) compared with the wild-type NRG1 (top). The receptor-binding EGF domain is preserved in all fusions. TM, transmembrane domain; RRM domain; IGc2 domain; SEC2P domain. (b) Analysis of RNASeq expression values revealed outlier NRG1 mRNA expression in all index cases (large blue dots) within each cohort. (c) High NRG1 mRNA expression driven by the fusion event in the index tumour tissue compared with matched normal, in both an LUAD patient in the University of Michigan and Seoul cohorts. (d) Box plot showing outlier expression of NRG1 in H1793 in the University of Michigan lung cell line cohort. (e) Two independent small interfering RNA-mediated knockdown of NRG1 in H1793 cells as assessed by quantitative PCR. (f) Knockdown of NRG1 decreased cell proliferation as monitored by IncuCyte confluence analysis. (g) Overexpression of NRG1 induces cell proliferation and migration. Cell proliferation by WST-1 assay (left panel) and cell counting (middle panel) on BEAS-2B cells stably transfected with Lac-Z or CD74-NRG1 fusion. Both assays demonstrated that cells expressing the CD74-NRG1 fusion had significantly higher proliferation rate at day 3 and 5 (Student’s t-test P<0.001 for both time points) as compared with Lac-Z. The right panel represents a cell migration assay after 24 h. BEAS-2B cells expressing CD74-NRG1 fusion showed a higher migration rate as compared with Lac-Z (Student’s t-test P=0.0014).