Dipeptidyl peptidase-4 and GLP-1 interplay in STC-1 and GLUTag cell lines.

Glucagon like peptide-1 (GLP-1) is an incretin hormone, secreted from L-cells of distal ileum and colon in response to nutrient ingestion in human. GLP-1 plays a major role in gut motility, appetite regulation, and insulin secretion. Dipeptidyl peptidase-4 (DPP4), a serine peptidase, cleaves N-terminal dipeptides of GLP-1, rendering it inactive and responsible for its short half-life. DPP4 is widely expressed in numerous tissues in a membrane bound or soluble form. The enteroendocrine cell lines STC-1 and GLUTag are extensively used as models for in vitro studies, however, the basic parallel characterization between these cell lines is still missing. Previously, we demonstrated that these cell lines exhibit different responses to α-linolenic acid (αLA)-induced GLP-1 secretion. Therefore, we examined the basal and stimulated GLP-1 and DPP4 secretion between the two cell lines. GPR120 and GPR40 are known to bind long chain fatty acids. We found that STC-1 cells secreted significantly more basal and αLA-induced GLP-1 than GLUTag cells. In addition, STC-1 secreted DPP4 and expressed higher amounts of DPP4 and GPR120 than GLUTag cells, while GLUTag cells expressed higher GPR40 protein levels than STC-1 cells. Interestingly, the secreted soluble DPP4 did not change the active GLP-1 concentrations in the buffer group, and only 5.5 % of GLP-1 was degraded in the αLA stimulated group. These results suggested that STC-1 cells have a higher potential to secrete GLP-1 and DPP4 than GLUTag cells, and the membrane bound DPP4 may play a more significant role in the inactivation of GLP-1 secretion.