Expression, purification and characterization of BG_ERII: A novel pan-TGFβ inhibitor

Transforming growth factor beta (TGFβ) isoforms are known to be upregulated during the progression of some diseases. They have been shown to stimulate invasion and metastasis during carcinogenesis and promote many pathological fibrotic diseases when overstimulated. This involvement in late-stage carcinoma and pathological fibrosis makes TGFβ isoforms prime targets for therapeutic intervention. Although soluble ectodomains of TGFβ type II (RII) and betaglycan (BG) have been utilized as TGFβ inhibitors, their antagonistic potency against different TGFβ isoforms varies considerably because RII does not appreciably bind to TGFβ2 whereas BG binds weakly to TGFβ1 and TGFβ3. In this study, we have successfully constructed and expressed a recombinant fusion protein containing the endoglin domain of BG (BG_E) and the extracellular domain of RII. The fusion protein (named BG_ERII) was purified from bacterial inclusion bodies by immobilized metal ion chromatography, refolded and characterized. It bound with higher affinity to TGFβ1 and TGFβ3 than a commercially available soluble RII and to TGFβ2 than a commercially available soluble BG. More significantly, whereas BG_E or RII alone showed no antagonistic activity towards TGFβ2, BG_ERII inhibited the signaling of both TGFβ1 and TGFβ2 in cell-based assays including TGFβ-induced phosphorylation of Smad2 and Smad3, and transcription from a TGFβ-responsive promoter more effectively than equimolar concentrations of either RII or BG. After further purification by gel filtration chromatography, BG_ERII was found to have greater activity than other potent TGFβ inhibitors in blocking the signaling of TGFβ1 and TGFβ3. Thus, BG_ERII is a potent pan-TGFβ inhibitor in vitro and has potential for blocking TGFβ-induced pathogenesis in vivo.