Prolactin stimulates proliferation of the glucose-dependent beta-cell line INS-1 via different IRS-proteins.
BACKGROUND
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.


METHODS
In particular, we investigated the involvement of intracellular signal transduction molecules in prolactin-dependent upregulation of INS-1 growth.


METHODS
The effect of prolactin on the growth of INS-1 cells was assessed in vitro under various feeding conditions.


METHODS
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.


CONCLUSIONS
These results define prolactin as an important hormone. mediating glucose-dependent pancreatic beta-cell proliferation primarily by the activation of PI3'K-dependent signaling pathways.
Hügl
Sigrun R
SR
Department of Internal Medicine, University of Ulm, Ulm, Germany. sigrun.merger@uniklinik-ulm.de
Merger
Michael
M
D000818:Animals; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005947:Glucose / Q000502:physiology; D055504:Insulin Receptor Substrate Proteins; D050417:Insulin-Secreting Cells / Q000473:pathology* / Q000502:physiology; D007340:Insulinoma / Q000473:pathology / Q000503:physiopathology; D047908:Intracellular Signaling Peptides and Proteins / Q000502:physiology*; D053614:Janus Kinase 2 / Q000502:physiology; D019869:Phosphatidylinositol 3-Kinases / Q000502:physiology; D010750:Phosphoproteins / Q000502:physiology*; D011388:Prolactin / Q000502:physiology*; D051381:Rats; D050799:STAT5 Transcription Factor / Q000502:physiology; D015398:Signal Transduction / Q000502:physiology
D004791:Enzyme Inhibitors; C491532:IRS4 protein, rat; D055504:Insulin Receptor Substrate Proteins; D047908:Intracellular Signaling Peptides and Proteins; C526296:Irs1 protein, rat; C526299:Irs2 protein, rat; D010750:Phosphoproteins; D050799:STAT5 Transcription Factor; D011388:Prolactin; D019869:Phosphatidylinositol 3-Kinases; D053614:Janus Kinase 2; D005947:Glucose