The SMAD2/3 interactome reveals that TGFβ controls m6A mRNA methylation in pluripotency.

Abstract

The TGFβ pathway plays an essential role in embryonic development, organ 22 homeostasis, tissue repair, and disease1,2. This diversity of tasks is achieved through the 23 intracellular effector SMAD2/3, whose canonical function is to control activity of target 24 genes by interacting with transcriptional regulators3. Nevertheless, a complete 25 description of the factors interacting with SMAD2/3 in any given cell type is still lacking. 26 Here we address this limitation by describing the interactome of SMAD2/3 in human 27 pluripotent stem cells (hPSCs). This analysis reveals that SMAD2/3 is involved in 28 multiple molecular processes in addition to its role in transcription. In particular, we 29 identify a functional interaction with the METTL3-METTL14-WTAP complex, which 30 deposits N6-methyladenosine (m6A)4. We uncover that SMAD2/3 promotes binding of 31 the m6A methyltransferase complex onto a subset of transcripts involved in early cell 32 fate decisions. This mechanism destabilizes specific SMAD2/3 transcriptional targets, 33 including the pluripotency factor NANOG, thereby poising them for rapid 34 downregulation upon differentiation to enable timely exit from pluripotency. 35 Collectively, these findings reveal the mechanism by which extracellular signalling can 36 induce rapid cellular responses through regulations of the epitranscriptome. These novel 37 aspects of TGFβ signalling could have far-reaching implications in many other cell types 38 and in diseases such as cancer5