Secretion of PAI-1 by PC-3 cells was quantified by ELISAs. TGF-β2 alone (-) stimulated secretion of PAI-1 significantly compared to the control (Ctrl). Antibody perturbation experiments with antibodies specific for the extracellular domains of TβRII (RII), the alternative exons of TβRIIB (RIIB) and TβRIIC (RIIC), demonstrated a significant decrease in the amount of PAI-1 only for TβRII compared to the stimulation with TGF-β2 (-) or the unspecific antibody (ctrl-R). For the sake of clarity, we have not indicated that the antibody perturbation experiments were also significantly different to the control (Ctrl) without any TGF-β2 treatment. An unspecific antibody (ctrl-R) did not inhibit PAI-1 secretion stimulated by TGF-β2. Each experiment was independently repeated five times (n = 5) in duplicate, with each value given as the mean ± SEM. Statistically significant differences are indicated (*, P < 0.05; ***, P < 0.001).