TGFBR1 and breast cancer: A functional loss study showed that ppGalNAc-T4 modulates TGF-β1 signaling by catalyzing the O-GalNAcylation of TGF-β type II receptor (TβRII) at the Ser31 site and TGF-β type I receptor (TβRI), which in turn inhibits the dimerization of TβRI and TβRII, ultimately suppressing TGF-β1 signaling and epithelial-mesenchymal transition (EMT) in human breast cancer cells.90