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.

Abstract

We describe, for the first time, a new splice variant of the human TGF-{beta} type II receptor (T{beta}RII). The new transcript lacks 149 nucleotides, causing a frameshift with the appearance 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 in the C-terminus, was named T{beta}RII-Soluble Endogenous (T{beta}RII-SE). Binding predictions indicated that the novel 13 amino acid stretch interacts with all three TGF-{beta} cognate ligands and generate a more extensive protein-protein interface than T{beta}RII. T{beta}RII-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 T{beta}RII-SE/Fc by A/G protein chromatography from conditioned medium. Immunoblotting revealed homogeneous bands of approximately 37 kDa (reduced) and 75 kD (non-reduced), indicating that T{beta}RII-SE/Fc is secreted as a disulphide-linked homodimer. Moreover, high affinity binding of T{beta}RII-SE to the three TGF-{beta} isoforms was confirmed by Surface Plasmon Resonance (SPR) analysis. Also, intrahepatic delivery of Lv.T{beta}RII-SE/Fc in a carbon tetrachloride-induced liver fibrosis model revealed amelioration of liver injury and fibrosis. Our results indicate that T{beta}RII-SE is a novel member of the TGF-{beta} signaling pathway with distinctive characteristics. This novel protein offers an alternative for the prevention and treatment of pathologies caused by the overproduction of TGF-{beta} ligands.