Regulation of glucose- and mitochondrial fuel-induced insulin secretion by a cytosolic protein histidine phosphatase in pancreatic beta-cells.
We report localization of a cytosolic protein histidine phosphatase (PHP; approximately 16 kDa) in INS 832/13 cells, normal rat islets, and human islets. siRNA-mediated knockdown of PHP markedly reduced glucose- or mitochondrial fuel-induced but not KCl-induced insulin secretion. siRNA-mediated knockdown of PHP also attenuated mastoparan-induced insulin secretion, suggesting its participation in G protein-sensitive signaling steps, leading to insulin secretion. Functional assays revealed that the beta-cell PHP catalyzes the dephosphorylation of ATP-citrate lyase (ACL). Silencing of PHP expression markedly reduced ACL activity, suggesting functional regulation of ACL by PHP in beta-cells. Coimmunoprecipitation studies revealed modest effects of glucose on the interaction between PHP and ACL. Confocal microscopic evidence indicated that glucose promotes association between ACL and nm23-H1, a known kinase histidine kinase, but not between PHP and ACL. Furthermore, metabolic viability of INS 832/13 cells was resistant to siRNA-PHP, suggesting no regulatory roles of PHP in cell viability. Finally, long-term exposure (24 h) of INS 832/13 cells or rat islets to high glucose (30 mM) increased the expression of PHP. Such increases in PHP expression were also seen in islets derived from the Zucker diabetic fatty rat compared with islets from the lean control animals. Together, these data implicate regulatory roles for PHP in a G protein-sensitive step involved in nutrient-induced insulin secretion. In light of the current debate on putative regulatory roles of ACL in insulin secretion, additional studies are needed to precisely identify the phosphoprotein substrate(s) for PHP in the cascade of events leading to nutrient-induced insulin secretion.
Kamath
Vasudeva
V
Department of Pharmaceutical Sciences, Wayne State University and Veterans Affairs Medical Center, Detroit, MI 48202, USA.
Kyathanahalli
Chandrashekara N
CN
Jayaram
Bhavaani
B
Syed
Ismail
I
Olson
Lawrence Karl
LK
Ludwig
Katrin
K
Klumpp
Susanne
S
Krieglstein
Josef
J
Kowluru
Anjaneyulu
A
D001275:ATP Citrate (pro-S)-Lyase / Q000378:metabolism; D000328:Adult; D000818:Animals; D002460:Cell Line; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism*; D003920:Diabetes Mellitus / Q000235:genetics / Q000378:metabolism; D004734:Energy Metabolism / Q000502:physiology*; D005260:Female; D005455:Fluorescent Antibody Technique; D005947:Glucose / Q000494:pharmacology / Q000502:physiology*; D006801:Humans; D007202:Indicators and Reagents; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D050417:Insulin-Secreting Cells / Q000187:drug effects / Q000201:enzymology* / Q000378:metabolism*; D008297:Male; D018613:Microscopy, Confocal; D008928:Mitochondria / Q000378:metabolism*; D010744:Phosphoric Monoester Hydrolases / Q000235:genetics* / Q000378:metabolism*; D011189:Potassium Chloride / Q000494:pharmacology; D034741:RNA, Small Interfering / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D011924:Rats, Zucker
D007202:Indicators and Reagents; D007328:Insulin; D034741:RNA, Small Interfering; D011189:Potassium Chloride; D001275:ATP Citrate (pro-S)-Lyase; C504019:PHPT1 protein, human; C504020:Phpt1 protein, rat; D010744:Phosphoric Monoester Hydrolases; D005947:Glucose