title: The single-molecule mechanics of the latent TGF-β1 complex.
abstract: BACKGROUND
  TGF-β1 controls many pathophysiological processes including tissue homeostasis, fibrosis, and cancer progression. Together with its latency-associated peptide (LAP), TGF-β1 binds to the latent TGF-β1-binding protein-1 (LTBP-1), which is part of the extracellular matrix (ECM). Transmission of cell force via integrins is one major mechanism to activate latent TGF-β1 from ECM stores. Latent TGF-β1 mechanical activation is more efficient with higher cell forces and ECM stiffening. However, little is known about the molecular events involved in this mechanical activation mechanism.
  
  
  RESULTS
  By using single-molecule force spectroscopy and magnetic microbeads, we analyzed how forces exerted on the LAP lead to conformational changes in the latent complex that can ultimately result in TGF-β1 release. We demonstrate the unfolding of two LAP key domains for mechanical TGF-β1 activation: the α1 helix and the latency lasso, which together have been referred to as the "straitjacket" that keeps TGF-β1 associated with LAP. The simultaneous unfolding of both domains, leading to full opening of the straitjacket at a force of ~40 pN, was achieved only when TGF-β1 was bound to the LTBP-1 in the ECM.
  
  
  CONCLUSIONS
  Our results directly demonstrate opening of the TGF-β1 straitjacket by application of mechanical force in the order of magnitude of what can be transmitted by single integrins. For this mechanism to be in place, binding of latent TGF-β1 to LTBP-1 is mandatory. Interfering with mechanical activation of latent TGF-β1 by reducing integrin affinity, cell contractility, and binding of latent TGF-β1 to the ECM provides new possibilities to therapeutically modulate TGF-β1 actions.
authors.affiliation: Laboratory of Cell Biophysics, Ecole Polytechnique Fédérale de Lausanne, 1015 Lausanne, Switzerland.
authors.forename: Lara
authors.initials: L
authors.lastname: Buscemi
authors.forename: David
authors.initials: D
authors.lastname: Ramonet
authors.forename: Franco
authors.initials: F
authors.lastname: Klingberg
authors.forename: Aurélie
authors.initials: A
authors.lastname: Formey
authors.forename: Josiane
authors.initials: J
authors.lastname: Smith-Clerc
authors.forename: Jean-Jacques
authors.initials: JJ
authors.lastname: Meister
authors.forename: Boris
authors.initials: B
authors.lastname: Hinz
mesh_terms: D005109:Extracellular Matrix / Q000378:metabolism; D006801:Humans; D016023:Integrins / Q000378:metabolism*; D053779:Latent TGF-beta Binding Proteins / Q000378:metabolism*; D059346:Magnets; D008863:Microspheres; D013057:Spectrum Analysis; D053773:Transforming Growth Factor beta1 / Q000378:metabolism*
chemical_list: D016023:Integrins; C509032:LTBP1 protein, human; D053779:Latent TGF-beta Binding Proteins; D053773:Transforming Growth Factor beta1