Cryo-EM Reveals Integrin-Mediated TGF-β Activation without Release from Latent TGF-β

Cell. 2020 Feb 6;180(3):490-501.e16. doi: 10.1016/j.cell.2019.12.030. Epub 2020 Jan 16.

Abstract

Integrin αvβ8 binds with exquisite specificity to latent transforming growth factor-β (L-TGF-β). This binding is essential for activating L-TGF-β presented by a variety of cell types. Inhibiting αvβ8-mediated TGF-β activation blocks immunosuppressive regulatory T cell differentiation, which is a potential therapeutic strategy in cancer. Using cryo-electron microscopy, structure-guided mutagenesis, and cell-based assays, we reveal the binding interactions between the entire αvβ8 ectodomain and its intact natural ligand, L-TGF-β, as well as two different inhibitory antibody fragments to understand the structural underpinnings of αvβ8 binding specificity and TGF-β activation. Our studies reveal a mechanism of TGF-β activation where mature TGF-β signals within the confines of L-TGF-β and the release and diffusion of TGF-β are not required. The structural details of this mechanism provide a rational basis for therapeutic strategies to inhibit αvβ8-mediated L-TGF-β activation.

Keywords: GARP; TGF-b signaling; TGF-beta; TGF-beta activation; cryo-electron microscopy; integrin; integrin conformation; structural biology.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Antibodies / immunology
  • Binding Sites
  • Bronchi / cytology
  • CHO Cells
  • Cricetulus
  • Cryoelectron Microscopy / methods*
  • Female
  • Humans
  • Immunoglobulin Fab Fragments / immunology
  • Integrins / chemistry*
  • Integrins / immunology
  • Integrins / metabolism*
  • Latent TGF-beta Binding Proteins / chemistry*
  • Latent TGF-beta Binding Proteins / metabolism*
  • Lymphocyte Activation
  • Male
  • Mink
  • Protein Binding
  • Protein Conformation, alpha-Helical
  • Protein Interaction Domains and Motifs
  • T-Lymphocytes, Regulatory / immunology
  • Transforming Growth Factor beta1 / chemistry*
  • Transforming Growth Factor beta1 / metabolism*

Substances

  • Antibodies
  • Immunoglobulin Fab Fragments
  • Integrins
  • Latent TGF-beta Binding Proteins
  • TGFB1 protein, human
  • Transforming Growth Factor beta1
  • integrin alphavbeta8