Fig. 3
From: Immunoregulatory functions and the therapeutic implications of GARP-TGF-β in inflammation and cancer
GARP functions in TGF-β maturation and activation. TGF-β is synthetized as an inactive homodimeric pro-protein that is cleaved by a furin-like protease to yield the formation of latent TGF-β. GARP enhances furin-dependent cleavage and associates with latent TGF-β. The master chaperone gp96 in the lumen of the endoplasmic reticulum (ER, not depicted) ensures the proper folding of GARP and its surface expression. On the cell surface, GARP/latent TGF-β complex associates with alpha-beta integrins (αVβ6 and αVβ8) to release the mature TGF-β peptide. Mature TGF-β interacts with TGF-β receptors on the cell surface in both an autocrine and paracrine fashion. In some cases, GARP/latent TGF-β complex can also be released from the cell surface, but how TGF-β is activated from the soluble complex is not clear