Figure 4. Notch is a tumour suppressor and a key regulator of neuroendocrine differentiation in SCLC.

a, Unsupervised expression analysis of human SCLC tumours. Tumour samples are arranged in columns and grouped by the expression of differentially expressed genes (rows). Expression values are represented as a heatmap; yellow and blue indicate high and low expression, respectively. b, Schematic representation of NOTCH1 and NOTCH2. Somatic mutations are mapped to the respective protein domains. Damaging and missense mutations are highlighted in red and black, respectively. c, Representative H&E images of lungs from Trp53;Rb1;Rbl2 triple-knockout (TKO) or TKO;N2ICD (Notch2) mice collected 3 months after Ad-Cre instillation. Scale bar, 1 mm. Tumours were quantified for each genotype (n = 8). Statistical significance was determined by two-tailed unpaired Student’s t-test. d, Survival analysis of TKO (n = 7, median survival = 210 days) and TKO;N2ICD (n = 8, median survival = 274 days) mice. Statistical significance was determined by log-rank test. e, Cell viability assay of the murine SCLC cell line KP1 transfected with a N1ICD (Notch1) expression plasmid or empty vector control (Ctrl) (3 independent biological replicas with 3 technical replicas each). Fold growth is normalized to day 0; representative images were taken on day 8. Scale bar, 50 µm. Statistical significance was determined by two-tailed paired Student’s t-test. f, Mouse SCLC cells were transfected with control or N1ICD and analysed 48 h after transfection by gene expression microarrays. The heatmap describes differentially expressed genes in control or N1ICD-transfected cells (n = 3, each); red and green indicate high and low expression, respectively. *P < 0.05; **P < 0.01; ***P < 0.001. Data are represented as mean ± s.d.