Parathyroid hormone-related protein induces insulin expression through activation of MAP kinase-specific phosphatase-1 that dephosphorylates c-Jun NH2-terminal kinase in pancreatic beta-cells.
Parathyroid hormone-related protein (PTHrP) increases the content and mRNA level of insulin in a mouse beta-cell line, MIN6, and primary-cultured mouse islets. We examined the mechanism of PTHrP-induced insulin expression. The PTHrP effect was markedly augmented by SB203580, a mitogen-activated protein (MAP) kinase inhibitor, and SB203580 itself increased insulin expression extensively, even without PTHrP. Because SB203580 inhibits both p38 and c-jun NH(2)-terminal kinases (JNKs), we investigated the JNK-specific inhibitor SP600125. SP600125 also increased insulin content and its mRNA level. PTHrP induced dephosphorylation of JNK1/2, and PTHrP-induced insulin expression was blocked by a dominant-negative type JNK-APF. We suspected that dual specificity MAP kinase phosphatases (MKPs) may be involved in the PTHrP-induced insulin expression by inactivating JNK1/2. MIN6 cells contained at least five MKPs, among which only MKP-1 was inducible by PTHrP. PTHrP-induced insulin expression was blocked by the MKP-1 expression inhibitor Ro-31-8220, indicating that the PTHrP effect is mediated by MKP-1. Indeed, adenoviral MKP-1 expression increased insulin expression by decreasing a phosphorylation form of JNKs and a resulting phosphorylated form of c-jun in MIN6 cells. The phosphorylated form of c-jun is known to repress cAMP-dependent insulin gene promoter activity. Thus, MKP-1 controls the insulin expression by downregulating a JNK/c-jun pathway.
Zhang
Bin
B
Department of Molecular Medicine, Institute for Molecular and Cellular Regulation, Gunma University, Maebashi, Japan.
Hosaka
Masahiro
M
Sawada
Yoshie
Y
Torii
Seiji
S
Mizutani
Shin
S
Ogata
Masato
M
Izumi
Tetsuro
T
Takeuchi
Toshiyuki
T
D000818:Animals; D018797:Cell Cycle Proteins; D002460:Cell Line; D054638:Dual Specificity Phosphatase 1; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005786:Gene Expression Regulation; D007093:Imidazoles / Q000494:pharmacology; D017874:Immediate-Early Proteins / Q000378:metabolism*; D007328:Insulin / Q000235:genetics*; D007515:Islets of Langerhans / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D048031:JNK Mitogen-Activated Protein Kinases; D020935:MAP Kinase Signaling System / Q000187:drug effects / Q000502:physiology*; D051379:Mice; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D044162:Parathyroid Hormone-Related Protein / Q000494:pharmacology*; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1; D017027:Protein Tyrosine Phosphatases / Q000378:metabolism*; D011725:Pyridines / Q000494:pharmacology; D012333:RNA, Messenger / Q000235:genetics
D018797:Cell Cycle Proteins; D004791:Enzyme Inhibitors; D007093:Imidazoles; D017874:Immediate-Early Proteins; D007328:Insulin; D044162:Parathyroid Hormone-Related Protein; D011725:Pyridines; D012333:RNA, Messenger; D048031:JNK Mitogen-Activated Protein Kinases; D020928:Mitogen-Activated Protein Kinases; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1; D054638:Dual Specificity Phosphatase 1; C517020:Dusp1 protein, mouse; D017027:Protein Tyrosine Phosphatases; C093642:SB 203580