A Novel Splice Variant of Human TGF-β Type II Receptor Encodes a Soluble Protein and Its Fc-Tagged Version Prevents Liver Fibrosis in vivo .

We describe, for the first time, a new splice variant of the human TGF-β type II receptor (TβRII). The new transcript lacks 149 nucleotides, resulting in a frameshift and the emergence of an early stop codon, rendering a truncated mature protein of 57 amino acids. The predicted protein, lacking the transmembrane domain and with a distinctive 13-amino-acid stretch at its C-terminus, was named TβRII-Soluble Endogenous (TβRII-SE). Binding predictions indicate that the novel 13-amino-acid stretch interacts with all three TGF-β cognate ligands and generates a more extensive protein-protein interface than TβRII. TβRII-SE and human IgG1 Fc domain were fused in frame in a lentiviral vector (Lv) for further characterization. With this vector, we transduced 293T cells and purified TβRII-SE/Fc by A/G protein chromatography from conditioned medium. Immunoblotting revealed homogeneous bands of approximately 37 kDa (reduced) and 75 kDa (non-reduced), indicating that TβRII-SE/Fc is secreted as a disulfide-linked homodimer. Moreover, high-affinity binding of TβRII-SE to the three TGF-β isoforms was confirmed by surface plasmon resonance (SPR) analysis. Also, intrahepatic delivery of Lv.TβRII-SE/Fc in a carbon tetrachloride-induced liver fibrosis model revealed amelioration of liver injury and fibrosis. Our results indicate that TβRII-SE is a novel member of the TGF-β signaling pathway with distinctive characteristics. This novel protein offers an alternative for the prevention and treatment of pathologies caused by the overproduction of TGF-β ligands.
Competing Interests: AC, TMR, ANC, and RAD are co-inventors of the patent family “Isoform of the TGF-beta receptor II,” US10233227B2 (granted in United States), EP3082846B1 (granted by the European Patent Office), ES2749615T3 (granted in Spain), and AR098827A1 (pending in Argentina). TMR, ANC, ALC, MSB, AR, and RAD are co-inventors of the patent application “TGF-β receptor II isoform, fusion peptide, methods of treatment and methods in vitro,” US11072647B2 (granted in United States). Patents are owned by CONICET and Fundación Articular, and were licensed to RAD BIO S.A.S. by Intellectual property license agreement 2019-890-APN-DIR#CONICET. AR has shareholder equity of RAD BIO S.A.S. RAD is the co-founder and shareholder of RAD BIO S.A.S. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
(Copyright © 2021 Bertolio, La Colla, Carrea, Romo, Canziani, Echarte, Campisano, Barletta, Monzon, Rodríguez, Chisari and Dewey.)