Canonical BMP signaling executes epithelial-mesenchymal transition downstream of SNAIL1

Epithelial-mesenchymal transition (EMT) is a pivotal process in development and disease. In carcinogenesis, various signaling pathways are known to trigger EMT by inducing the expression of EMT transcription factors (EMT-TFs) like SNAIL1, ultimately promoting invasion, metastasis and chemoresistance. However, how EMT is executed downstream of EMT-TFs is incompletely understood. Here, using human colorectal cancer (CRC) and mammary cell line models of EMT, we demonstrate that SNAIL1 critically relies on bone morphogenetic protein (BMP) signaling for EMT execution. This activity requires the transcription factor SMAD4 common to BMP/TGFβ pathways, but is TGFβ signaling-independent. Further, we define a signature of BMP-dependent genes in the EMT-transcriptome which orchestrate EMT-induced invasiveness, and are found to be regulated in human CRC transcriptomes and during EMT in vivo. Collectively, our findings substantially augment the knowledge of mechanistic routes whereby EMT can be effectuated, which is relevant for the conceptual understanding and therapeutic targeting of EMT processes. To identify BMP-dependent genes regulated during EMT, LS174T cells overexpressing Snail1-HA in a doxycycline (Dox)-inducible manner were treated with Dox and inhibitors of BMP signaling (LDN193189/mNoggin) or DMSO as control for different periods of time. 36 samples of total RNA from LS174T-Snail1-HA cells treated with six different combinations of Dox and BMP inhibitors or DMSO for three different periods of time (6 h, 24 h, 72 h) in two biological replicates.