Additional possibilities for functional consequences of DPP4 truncation of regulatory proteins. (A) Truncated molecules do not bind to their receptor and may signal through other receptors. An example of this is full-length GLP-1, which binds to its cognate receptor but is truncated quickly and subsequently is unable to efficiently bind to the GLP-1 receptor and therefore does not inhibit, or alter the function, of the full-length molecule. Exenatide (Byetta) is a synthetic GLP-1 agonist made to mimic the GLP-1 homolog extendin-4, found in the saliva of the Gila monster. Exenatide is used in the treatment of type 2 diabetes because it is stable, binds to the GLP-1 receptor to induce insulin secretion, and is resistant to DPP4 truncation. (B) Factors without truncation sites may regulate factors with truncation sites by altering their expression, or function, and proteins with DPP4 truncation sites may regulate expression of proteins with or without DPP4 truncation sites.