ABSTRACT
Transforming growth factor beta (TGF-ß) is a multi-functional cytokine that plays a significant role in multiple diseases, including fibrosis and tumor progression. Whilst the biologic effects of TGF-ß are well characterized, it is unclear how TGF-ß signaling is regulated to impart specific responses within certain cell types. One mechanism of regulation may be through TGF-ß activation, since TGF-ß is always expressed in a latent form (L-TGF-ß). Campbell et al.(2020) recently presented a new structural model to demonstrate how the integrin αvß8 might specifically control TGF-ß activation and signaling. In this model, αvß8 binds to cell surface L-TGF-ß1 to induce a conformational change, which exposes mature TGF-ß peptide to TGF-ß receptors (TGF-ßRs), allowing initiation of TGF-ß signaling from within the latent complex. This model also predicts that TGF-ß signaling would be directed specifically towards the TGF-ß expressing cell surface. We sought to test the validity of the new structural model by creating a cell-based assay which utilizes luciferase TGF-ß reporter cells (TMLC). TMLC cells express high levels of TGF-ßRs, but do not express cell surface L-TGF-ß. We modified TMLC reporter cells to express cell surface L-TGF-ß1 in a mutant form, which prevents the release of mature TGF-ß from the latent complex. The newly generated cell lines were then used in a novel functional assay to investigate whether integrin αvß8 could potentiate cell intrinsic TGF-ß signaling from within the latent complex in vitro.