To test whether RB1 and TP53 regulate YAP expression, we stably expressed RB1 or TP53 in SCLC lines H209, H69, and H526, which have mutations in both TP53 and RB1. Re-expression of RB1, but not TP53, increased YAP and YAP target genes CCN1/2 (Supplementary Fig. S3a–d), indicating that loss of RB1 is responsible for YAP repression. Here, CCN1 is linked to small cell lung carcinoma.