Reprogramming of cellular identity using exogenous expression of transcription factors (TFs) is a powerful and exciting tool for tissue engineering, disease modeling, and regenerative medicine. However, generation of desired cell types using this approach is often plagued by inefficiency, slow conversion, and an inability to produce mature functional cells. Here, we show that expression of constitutively active SMAD2/3 significantly improves the efficiency of induced pluripotent stem cell (iPSC) generation by the Yamanaka factors. Mechanistically, SMAD3 interacts with reprogramming factors and co-activators and co-occupies OCT4 target loci during reprogramming. Unexpectedly, active SMAD2/3 also markedly enhances three other TF-mediated direct reprogramming conversions, from B cells to macrophages, myoblasts to adipocytes, and human fibroblasts to neurons, highlighting broad and general roles for SMAD2/3 as cell-reprogramming potentiators. Our results suggest that co-expression of active SMAD2/3 could enhance multiple types of TF-based cell identity conversion and therefore be a powerful tool for cellular engineering.

This work was supported by the ERC (grants ROADTOIPS 261075 to K.K. and BRAINCELL 261063 to S.L. and iN-Brain 309712 to M.P.), the BBSRC (project grant BB/L023474/1 to K.K.), the Anne Rowling Regenerative Neurology Clinic (K.K.), the Swedish Research Council (grant STARGET to S.L. and grants 521-2012-5624 and 521-2013-3347 to M.P.), and the Wellcome Trust (grant WT098051 to K.Y.). T.R., L.T., J.A., and D.F.K. are funded by a Darwin Trust scholarship, a CMVM scholarship, and Principal's Career Development scholarship from the University of Edinburgh, respectively. D.F.K. is supported by the BBSRC (EASTBIO doctoral training partnership). T.V.T. is supported by a Juan de la Cierva postdoctoral fellowship (MINECO, FJCI-2014-22946). B.D.S. was supported by an EMBO long-term fellowship (ALTF 1143-2015). K.K. is an MRC senior non-clinical fellow (MR/N008715/1). M.P. is a New York Stem Cell Foundation Robertson Investigator.