After TGF-beta stimulation, TGFBR2 binds TGFBR1 anchored to tight junctions through association with PARD6A (Ozdamar et al. 2005). FKBP1A (FKBP12) prevents phosphorylation of TGFBR1 by TGFBR2 in the absence of ligand. FKBP1A dissociates from TGFBR1 after it forms a complex with ligand-activated TGFBR2 (Chen et al. 1997). This was inferred from experiments in which a recombinant mouse Pard6a and recombinant human TGFBR1 and TGFBR2 were studied in the context of endogenous mouse tight junctions.