Sigrun R Hugl, Michael Merger
Context Prolactin is one of the most potent growth stimulating growth hormones of pancreatic beta cells. Objective We investigated the role of prolactin on the proliferation of the beta-cell line INS-1. Design In particular, we investigated the involvement of intracellular signal transduction molecules in prolactin-dependent upregulation of INS-1 growth. Setting The effect of prolactin on the growth of INS-1 cells was assessed in vitro under various feeding conditions. Main outcome measures Cell proliferation was measured in the pancreatic beta-cell line INS-1 using 3H-thymidine incorporation. The activation of mitogenic signaling proteins was assessed by co-immunoprecipitation, immunoblot analysis and in proliferation assays using specific protein inhibitors. Results Prolactin (0.5-2 nM) increased INS-1 cell proliferation in the presence of 3-24 mM glucose up to 48 fold, having a maximum in the presence of physiological glucose concentrations (6 mM). Prolactin activated the JAK2/STAT5 pathway and phosphatidylinositol- 3’-kinase (PI3’K) in the presence of all the glucose concentrations used (3-15 mM). At low glucose concentrations (3 mM), PI3’K activation occurred through IRS-2 phosphorylation whereas, in the presence of physiological glucose concentration IRS4 and at high glucose concentrations (15 mM), IRS- 1 triggered a proliferative effect. PI3’K activation was essential for prolactin and glucose stimulated INS-1 cell proliferation. Co-stimulation with different growth factors (IGF-I, growth hormone) in addition to prolactin and glucose had no additive effects. Conclusion These results define prolactin as an important hormone. mediating glucosedependent pancreatic beta-cell proliferation primarily by the activation of PI3’Kdependent signaling pathways.