title: Different regulated expression of the tyrosine phosphatase-like proteins IA-2 and phogrin by glucose and insulin in pancreatic islets: relationship to development of insulin secretory responses in early life.
abstract: IA-2 and phogrin are tyrosine phosphatase-like proteins that may mediate interactions between secretory granules and cytoskeleton in islets and neuroendocrine tissues. We investigated factors that regulate IA-2 and phogrin expression and their relationship to maturation of insulin secretory responses that occur after birth. Islet content of IA-2, but not phogrin, increased during the first 10 days of life in rats, when insulin secretion in response to glucose increased to adult levels. In cultured 5-day-old rat islets, IA-2 protein and mRNA was increased by glucose and agents that potentiate insulin secretion by the cAMP pathway. Addition of insulin increased IA-2 protein levels and insulin biosynthesis without affecting IA-2 mRNA. Blocking insulin secretion with diazoxide or insulin action with insulin receptor antibodies inhibited glucose-induced increases in IA-2 protein, but not those of mRNA. Phogrin expression was unchanged by all agents. Thus, IA-2 is regulated at the mRNA level by glucose and elevated cAMP, whereas locally secreted insulin modulates IA-2 protein levels by stimulating biosynthesis. In contrast, phogrin expression is insensitive to factors that modify beta-cell function. These results demonstrate differential regulation of two closely related secretory granule components and identify IA-2 as a granule membrane protein subject to autocrine regulation by insulin.
mesh_terms: D000367:Age Factors; D000818:Animals; D002478:Cells, Cultured; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects / Q000502:physiology*; D005947:Glucose / Q000494:pharmacology*; D007004:Hypoglycemic Agents / Q000494:pharmacology*; D066298:In Vitro Techniques; D007328:Insulin / Q000378:metabolism / Q000494:pharmacology*; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000166:cytology / Q000196:embryology / Q000201:enzymology; D008565:Membrane Proteins / Q000235:genetics*; D017027:Protein Tyrosine Phosphatases / Q000235:genetics*; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017208:Rats, Wistar; D054635:Receptor-Like Protein Tyrosine Phosphatases, Class 8; D014158:Transcription, Genetic / Q000502:physiology
chemical_list: D007004:Hypoglycemic Agents; D007328:Insulin; D008565:Membrane Proteins; D012333:RNA, Messenger; C516862:PTPRN protein, human; C102889:PTPRN2 protein, human; D017027:Protein Tyrosine Phosphatases; C516864:Ptprn protein, rat; D054635:Receptor-Like Protein Tyrosine Phosphatases, Class 8; D005947:Glucose