ROLE OF PROHORMONE CONVERTASES IN THE TISSUE-SPECIFIC PROCESSING OF PROGLUCAGON

Proglucagon (proG) is processed in a tissue-specific manner to glucago n in the pancreas and to glicentin, oxyntomodulin, glucagon-like pepti de (GLP)-1, and GLP-2 in the intestine. Recombinant vaccinia virus (vv ) vectors were used to infect prohormone convertase 1 (PC1) or PC2 int o nonendocrine (BHK-proG) cells, which stably express proG. Similarly, endocrine (GH(3), AtT-20) cells were coinfected with proG along with PC1 or PC2 alone, or in combination with furin, PACE4, PC5a, or PC5b. Cell extracts were analyzed for various proG-derived peptides by RIA o f fractions obtained from HPLC. Upon infection of BHK-proG cells with either vv: furin or vv:PC1, glicentin was produced, while vv: PC2 did not process proG. In GH(3) and AtT-20 cells, vv:PC1 produced glicentin , oxyntomodulin, GLP-1(1-37), GLP-1(7-37), and GLP-2. All other enzyme s tested produced only glicentin. Interestingly, no enzyme or combinat ion produced glucagon. Coinfection of GH(3) cells with vv:PC2 and memb ers of the chromogranin family of peptides, including chromogranin A a nd B and secretogranin II, as well as the PC2-binding protein 7B2, did not result in processing to glucagon. It is concluded that: 1) PC1 is responsible for the processing of proG to produce the intestinal pept ides glicentin, oxyntomodulin, GLP-1(1-37), GLP-1(7-37), and GLP-2, an d 2) PC2 processes proG to glicentin but does not produce glucagon, al one or in combination with other enzymes or with known molecular chape rones.