Overexpression of glucagon-like peptide-1 receptor in an insulin-secreting cell line enhances glucose responsiveness.
Glucagon-like peptide-1 (GLP-1), secreted from intestine in response to food intake, enhances insulin secretion from pancreatic beta-cells. In this study, we evaluated the effects of stably transfecting the GLP-1 receptor into an insulinoma cell line, RIN 1046-38, on basal and glucose-mediated insulin secretion and on second messenger pathways involved in insulin secretion. The GLP-1 receptor transfected cells had similar insulin mRNA levels but higher insulin content compared with parental cells. In GLP-1 receptor transfected cells, glucose (0.5 mM)-mediated insulin release was increased compared with parental cells (4.52 +/- 0.79 pmol insulin/l per mg protein x h vs. 2.21 +/- 0.36 pmol insulin/l per mg protein x h; mean +/- S.E., n = 6, P = 0.015, in transfected vs. parental cells, respectively). By hemolytic plaque assay measuring single cell insulin secretion, we observed that in the GLP-1 receptor transfected cells versus parental cells the increased insulin secretion was due to the presence of more glucose-responsive cells as well as more insulin released in response to glucose per cell. Resting intracellular cAMP was higher in the GLP-1 transfected cells (35.96 +/- 3.88 vs. 18.6 +/- 2.01 nmol/l per mg protein x h; mean +/- S.E., n = 4, P = 0.039, in transfected vs. parental cells, respectively). In response to GLP-1, both GLP-1 receptor transfected cells and parental cells showed increased cAMP levels independent of glucose. Resting intracellular calcium was the same in both parental and GLP-1 receptor transfected cells. However, more cells were responsive to glucose in the GLP-1 receptor transfected cells and the calcium transients attained in the presence of glucose developed at a faster rate and reached a higher amplitude than in parental cells. We conclude that having an excess of GLP-1 receptors renders beta-cells more sensitive to glucose.
Montrose-Rafizadeh
C
C
Laboratory of Clinical Physiology, National Institute on Aging, NIH, Baltimore, MD 21224, USA.
Wang
Y
Y
Janczewski
A M
AM
Henderson
T E
TE
Egan
J M
JM
D000818:Animals; D002118:Calcium / Q000378:metabolism; D000242:Cyclic AMP / Q000378:metabolism; D015870:Gene Expression; D052216:Glucagon-Like Peptide 1; D000067757:Glucagon-Like Peptide-1 Receptor; D005947:Glucose / Q000494:pharmacology*; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007340:Insulinoma / Q000235:genetics / Q000378:metabolism; D017136:Ion Transport / Q000187:drug effects; D010190:Pancreatic Neoplasms / Q000235:genetics / Q000378:metabolism; D010455:Peptides / Q000494:pharmacology; D051381:Rats; D018027:Receptors, Glucagon / Q000235:genetics*; D014162:Transfection; D014407:Tumor Cells, Cultured
C000593835:Glp1r protein, rat; D000067757:Glucagon-Like Peptide-1 Receptor; D007328:Insulin; D010455:Peptides; D018027:Receptors, Glucagon; D052216:Glucagon-Like Peptide 1; D000242:Cyclic AMP; D005947:Glucose; D002118:Calcium