The large latent complex (LLC) of TGF-beta-1 (TGFB1) is secreted by exocytosis to the extracellular region. TGF-beta-1 in the LLC (called small latent TGF-beta complex (SCL)) cannot interact with the receptors and for this reason we say that it requires "activation". This means release from the LLC. This release is achieved by many mechanisms: proteolytic cleavage of the LTBPs, thrombospondin-1 binding to the LLC, integrin alphaV-beta6 binding to the LLC, reactive oxygen species, plasmin or other proteases and low pH. The release of mature dimeric TGF-beta-1 is essentially a mechanical process that demands cleavage and opening of the LLC structure so that the caged mature C-terminal TGF-beta-1 polypeptide is released to reach the receptor (Annes et al. 2003, Keski-Oja et al. 2004).
Annes, JP, Rifkin, DB, Munger, JS
von Melchner, H, Keski-Oja, J, Koli, K
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