Targeted dephosphorylation of SMAD3 as an approach to impede TGF- β signaling

TGF- 0 (transforming growth factor- 0 ) signaling is involved in a myriad of cellular processes and its dysregulation has been implicated in many human diseases, including fibrosis and cancer. TGF- 0 transcriptional responses are controlled by tail phosphorylation of transcription factors SMAD2 and SMAD3 (mothers against decapentaplegic homolog 2/3). Therefore, targeted dephosphorylation of phospho-SMAD3 could provide an innovative mechanism to block some TGF- 0- induced transcriptional responses, such as the transcription of SERPINE-1 , which encodes plasminogen activator inhibitor 1 (PAI-1). Here, by developing and employing a bifunctional molecule, BDPIC (bromoTAG-dTAG proximity-inducing chimera), we redirected multiple phosphatases, tagged with bromoTAG, to dephosphorylate phosphoSMAD3, tagged with dTAG. Using CRISPR-Cas9 technology, we generated homozygous double knockin A549 bromoTAG/bromoTAG PPM1H/ dTAG/dTAG SMAD3 cells, in which the BDPIC-induced proximity between bromoTAG-PPM1H and dTAG-SMAD3 led to a robust dephosphorylation of dTAG-SMAD3 and a significant decrease in SERPINE-1 transcription. Our work demonstrates targeted dephosphorylation of phospho-proteins as an exciting modality for rewiring cell signaling.