Perturbation of transforming growth factor (TGF)-β1 association with latent TGF-β binding protein yields inflammation and tumors

Transforming growth factor-β (TGF-β) activity is controlled at many levels including the conversion of the latent secreted form to its active state. TGF-β is often released as part of an inactive tripartite complex consisting of TGF-β, the TGF-β propeptide, and a molecule of latent TGF-β binding protein (LTBP). The interaction of TGF-β and its cleaved propeptide renders the growth factor latent, and the liberation of TGF-β from this state is crucial for signaling. To examine the contribution of LTBP to TGF-β function, we generated mice in which the cysteines that link the propeptide to LTBP were mutated to serines, thereby blocking covalent association. Tgfb1^C33S/C33S mice had multiorgan inflammation, lack of skin Langerhans cells (LC), and a shortened lifespan, consistent with decreased TGF-β1 levels. However, the inflammatory response and decreased lifespan were not as severe as observed with Tgfb1^-/- animals. Tgfb1 ^C33S/C33S mice exhibited decreased levels of active TGF-β1, decreased TGF-β signaling, and tumors of the stomach, rectum, and anus. These data suggest that the association of LTBP with the latent TGF-β complex is important for proper TGF-β1 function and that Tgfb1 ^C33S/C33S mice are hypomorphs for active TGF-β1. Moreover, although mechanisms exist to activate latent TGF-β1 in the absence of LTBP, these mechanisms are not as efficient as those that use the latent complex containing LTBP.