Fig. 1.

Gene structure, expression, processing, degradation, and elimination of proglucagon. The proglucagon gene is located in human chromosome 2 and transcribed as one single mRNA in three major tissues, namely, the pancreas, the intestine, and the CNS. The mRNA is first translated into one single protein and then processed by prohormone convertase (PC) in different tissues. In the pancreatic α cells, proglucagon protein is processed by PC2 into glicentin-related polypeptide (GRPP), glucagon (Gluc), intervening peptide-1 (IP-1), and major proglucagon fragment, whereas in L cells of the small intestine and the brain, proglucagon is processed by PC1/3 into oxyntomodulin, intervening peptide-2 (IP-2), GLP-1, and GLP-2. GLP-1 is degraded by DPP-4 via cleavage of two amino acids from the N terminus, or by NEP-24.11 through cleavage of the C terminus in vivo. The cleaved products are eventually eliminated in the kidney. UTR, untranslated region.