PROLACTIN REGULATION OF ISLET-DERIVED INS-1 CELLS - CHARACTERISTICS AND IMMUNOCYTOCHEMICAL ANALYSIS OF STAT5 TRANSLOCATION

The major changes in pancreatic islet function during pregnancy and af ter exposure to lactogens are an increase in beta-cell proliferation a nd enhanced insulin secretion. In this study we examined INS-1 cells a s a potential model for further inquiry into PRL signaling in beta-cel ls. Proliferation of beta-cells, insulin secretion, and quantitative i mmunocytochemical analysis of STAT5 translocation were studied. PRL tr eatment of INS-1 cells resulted in a 2- to 4-fold increase in cell pro liferation compared to that in the control group. In contrast, there w as no effect of PRL treatment on HIT cell proliferation and only a ver y small effect on RIN cell proliferation. A significant effect on INS- 1 cell proliferation was observed at 10 ng/ml and reached a maximum at 200 ng/ml. PRL treatment resulted in enhanced insulin secretion from INS-I cells. There was a time-dependent increase in insulin secretion, which when corrected for cell number was 1.5-fold greater in the PRL- treated cells. The effects of PRL on cell division and insulin secreti on were glucose dependent. The presence of the JAK family of tyrosine kinases and the transcription factor STAT5 in INS-1 cells was examined by immunocytochemical techniques. Although all members of the JAK fam ily of kinases were detected, the staining intensity of JAK-2 was noti ceably more intense. Initial studies of STAT5 translocation were perfo rmed using PRL-dependent Nb2 lymphoma cells, in which PRL treatment re sulted in a nearly complete translocation of cytoplasmic STATE to the nucleus. Under control conditions there was a near-equal fluorescence intensity of STAT5 staining in the nucleus and cytoplasm of INS-1 cell s. PRL treatment resulted in a time-dependent increase in STAT5 staini ng in the nucleus, with a corresponding decrease in the cytoplasm. The STAT5 staining intensity in the nucleus remained elevated for the dur ation of PRL treatment. This effect was reversible upon removal of PRL from the medium. Besides PRL, both GH and FBS induced a similar trans location of STAT5 to the nucleus. Although present in RIN cells, no de tectable changes in STAT5 were observed in RIN cells after exposure to PRL, GH, or FBS. INS-1 cells should provide a good model for further inquiry into the intracellular signaling pathways used by PRL and how these events alter islet function.