Preptin derived from proinsulin-like growth factor II (proIGF-II) is secreted from pancreatic islet β-cells and enhances insulin secretion

Pancreatic islet beta -cells secrete the hormones insulin, amylin and pancreastatin. To search for further beta -cell hormones, we purified peptides from secretory granules isolated from cultured murine beta TC6-F7 beta -cells. We identified a 34-amino-acid peptide (3948 Da), corresponding to Asp(69)-Leul(102) of the proinsulin-like growth factor II E-peptide, which we have termed 'preptin'. Preptin, is present in islet beta -cells and undergoes glucose-mediated co-secretion with insulin. Synthetic preptin increases insulin secretion from glucose-stimulated beta TC6-F7 cells in a concentration-dependent and saturable manner. Preptin infusion into the isolated, perfused rat pancreas increases the second phase of glucose-mediated insulin secretion by 30%, while antipreptin immunoglobulin infusion decreases the first and second phases of insulin secretion by 29 and 26% respectively. These findings suggest that preptin is a physiological amplifier of glucose-mediated insulin secretion.