To understand the molecular mechanisms by which loss of function of Smad4 promotes lung cancer cell metastasis, we compared gene expression profiles between SPK and PK model cells by RNA-sequencing (RNA-seq) analysis (Fig. 3a) which disclosed 3777 differentially expressed genes (DEGs) (Supplementary Data 1), including an increased SNAIL1 mRNA expression. Here, SMAD4 is linked to lung cancer.