Description: Many different cells produce TGF beta and it mediates effects on the proliferation, differentiation and function of many cell types. TGF beta is synthesized as a precursor that contains Latency Associated Peptide(LAP) at the N-terminus and mature TGF beta at the C-terminus forming a complex called Small Latent Complex (SLC). This complex remains in the cell until it is bound to LTBP (latent TGF-b binding protein) to form a large latent complex (LLC). LTBP does not confer latency but is for efficient secretion of the complex to extracellular sites. It is LLC that get secreted to the Extra Cellular Matrix (ECM).
The initially sequestered, inactive LTGF-beta (latent TGF-beta) requires activation (cleavage and dissociation of ist LAP) before it can exert biological activity.
The non-covalent interactions between these molecules can be disrupted by heat, extremes of pH (e.g acid treatment denatures LAP) and other chaotropic factors in vitro.
Human LAP is a homodimer of 65-75 kDa that is important in regulating the activity of TGF beta. Processing and cleavage of the precursor protein between amino acids 278 and 279 results in the formation of LAP dimers and TGF beta dimers that then non-covalently associate with each other to form the small latent TGF beta complex. LAP is secreted and can be found in the extracellular matrix. LAP can induce epithelial cell migration and promote chemotaxis of monocytes and block inflammation. LAP also can enhance hepatocyte regeneration and reduce fibrosis. LAP is also a surface marker of activated regulatory T cells. In addition, LAP can also be expressed on platelets and activated regulatory T cells. It is believed that this surface-expressed LAP is due to the binding of LAP to GARP (LRRC32), which is a transmembrane protein that is also found at high levels on platelets and activated regulatory T cells.
Mutations within the LAP are associated with CamuratiEngelmann disease, a rare sclerosing bone dysplasia characterized by inappropriate presence of active TGF-beta1.
Measuring LAP has the advantage that samples do not need tob e pretreated with acid. The antibodies in this ELISA recognize the LAP/TGF-beta complex hence allow to draw conclusion upon TGF-beta levels.