Altered proglucagon processing in an α-cell line derived from prohormone convertase 2 null mouse islets

The endoproteolytic processing of proproteins in the secretory pathway depends on the expression of selected members of a family of subtilisin-like endoproteases known as the prohormone convertases (PCs). The main PC family members expressed in mammalian neuroendocrine cells are PC2 and PC1/3. The differential processing of proglucagon in pancreatic α-cells and intestinal L cells leads to production of distinct hormonal products with opposing physiological effects from the same precursor. Here we describe the establishment and characterization of a novel α-cell line (αTC-ΔPC2) derived from PC2 homozygous null animals. The αTC-ΔPC2 cells are shown to be similar to the well characterized αTC1-6 cell line in both morphology and overall gene expression. However, the absence of PC2 activity in αTC-ΔPC2 leads to a complete block in the production of mature glucagon. Surprisingly, αTC-ΔPC2 cells are able to efficiently cleave the interdomain site in proglucagon (IM 70-71). Further analysis reveals that αTC-ΔPC2 cells, unlike αTC1-6 cells, express low levels of PC1/3 that lead to the generation of glicentin as well as low amounts of oxyntomodulin, GLP-1, truncated GLP-1, and N-terminally extended GLP-2. We conclude that αTC-ΔPC2 cells provide additional evidence for PC2 as the major convertase in α-cells leading to mature glucagon production and provide a robust model for further analysis of the mechanisms of proprotein processing by the prohormone convertases.