Constitutive expression of placental lactogen in pancreatic beta cells: effects on cell morphology, growth, and gene expression.
To explore the roles of lactogens in islet function, we generated a stable line of rat insulinoma (INS-1) cells that express rat placental lactogen II (rPLII) constitutively in culture. We used this cell line (Ins-rPLII) to examine the effects of endogenous rPLII on beta-cell growth, islet formation, and the expression of glucose transporter 2 (glut-2) and insulin mRNA. Growth and maturation of Ins-rPLII cells were compared with that of cells transfected stably with an empty expression plasmid (control) and of INS-1 cells treated with exogenous prolactin. The Ins-rPLII cells proliferated more rapidly than control cells in serumfree medium and showed distinct morphologic characteristics in culture. Whereas the control cells flattened readily on plastic and formed a branching monolayer, the Ins-rPLII cells remained more rounded, sent out fewer projections, and formed more numerous (p<0.01) and larger (p<0.01) beta-cell clusters. Larger clusters assumed a spherical form with well-delineated smooth borders and detached more readily from the culture plates. Maturational progression of the Ins-rPLII cells was associated with a 40% increase in preproinsulin mRNA (p<0.05) and a 2-3-fold increase in glut-2 mRNA (p<0.01). Induction of glut-2 mRNA was accompanied by a 1.4-2.4-fold increase (p< 0.01) in the uptake of radiolabeled 2-deoxyglucose. Similar effects were observed in INS-1 cells exposed for 48 h to exogenous prolactin. These findings suggest novel roles for the lactogenic hormones in the maturation and growth of pancreatic islets. Lactogen induction of beta-cell aggregation coupled with localized beta-cell growth may contribute to the expansion of islet mass that occurs in pregnancy and during the perinatal period. The induction of insulin and glut-2 mRNA provides a mechanism by which the lactogens may increase fetal and maternal insulin production and enhance the sensitivity of the pancreas to glucose.
Fleenor
D
D
Department of Pediatrics, Duke University Medical Center, Durham, North Carolina 27710, USA.
Petryk
A
A
Driscoll
P
P
Freemark
M
M
D000818:Animals; D015152:Blotting, Northern; D015153:Blotting, Western; D002455:Cell Division; D002460:Cell Line; D005786:Gene Expression Regulation; D051273:Glucose Transporter Type 2; D007150:Immunohistochemistry; D007328:Insulin / Q000235:genetics; D007515:Islets of Langerhans / Q000166:cytology / Q000254:growth & development / Q000378:metabolism*; D008223:Lymphoma / Q000473:pathology; D009004:Monosaccharide Transport Proteins / Q000235:genetics; D010928:Placental Lactogen / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics; D051381:Rats; D014407:Tumor Cells, Cultured
D051273:Glucose Transporter Type 2; D007328:Insulin; D009004:Monosaccharide Transport Proteins; D012333:RNA, Messenger; D010928:Placental Lactogen