In the pancreatic β-cells, cAMP is rapidly degraded by the cyclic 3′, 5′-nucleotide phosphodiesterase 3B (PDE3B), and overexpression of PDE3B in rodent islets or rat insulinoma INS-1 cells decreases insulin secretion in response to glucose and GLP-1 [644,645]. Here, GCG is linked to pancreatic insulinoma.