scholarly journals Mutation of the PDK1 PH Domain Inhibits Protein Kinase B/Akt, Leading to Small Size and Insulin Resistance

2008 ◽  
Vol 28 (10) ◽  
pp. 3258-3272 ◽  
Author(s):  
Jose R. Bayascas ◽  
Stephan Wullschleger ◽  
Kei Sakamoto ◽  
Juan M. García-Martínez ◽  
Carol Clacher ◽  
...  
Keyword(s):  
Insulin Resistance ◽  
Protein Kinase ◽  
Signaling Pathways ◽  
Protein Kinase B ◽  
Ph Domain ◽  
S6 Kinase ◽  
Downstream Signaling ◽  
Insulin Resistant ◽  
Ribosomal S6 Kinase ◽  
Mtor Complex 1

ABSTRACT PDK1 activates a group of kinases, including protein kinase B (PKB)/Akt, p70 ribosomal S6 kinase (S6K), and serum and glucocorticoid-induced protein kinase (SGK), that mediate many of the effects of insulin as well as other agonists. PDK1 interacts with phosphoinositides through a pleckstrin homology (PH) domain. To study the role of this interaction, we generated knock-in mice expressing a mutant of PDK1 incapable of binding phosphoinositides. The knock-in mice are significantly small, insulin resistant, and hyperinsulinemic. Activation of PKB is markedly reduced in knock-in mice as a result of lower phosphorylation of PKB at Thr308, the residue phosphorylated by PDK1. This results in the inhibition of the downstream mTOR complex 1 and S6K1 signaling pathways. In contrast, activation of SGK1 or p90 ribosomal S6 kinase or stimulation of S6K1 induced by feeding is unaffected by the PDK1 PH domain mutation. These observations establish the importance of the PDK1-phosphoinositide interaction in enabling PKB to be efficiently activated with an animal model. Our findings reveal how reduced activation of PKB isoforms impinges on downstream signaling pathways, causing diminution of size as well as insulin resistance.

scholarly journals Phosphorylation of the c-Fos transrepression domain by mitogen-activated protein kinase and 90-kDa ribosomal S6 kinase

1993 ◽  
Vol 90 (23) ◽  
pp. 10952-10956 ◽  
Author(s):  
R H Chen ◽  
C Abate ◽  
J Blenis
Keyword(s):  
Protein Kinase ◽  
Map Kinase ◽  
Mitogen Activated Protein Kinase ◽  
S6 Kinase ◽  
Downstream Signaling ◽  
C Terminus ◽  
Mitogen Activated Protein ◽  
Ribosomal S6 Kinase

Phosphorylation of the C terminus of c-Fos has been implicated in serum response element-mediated repression of c-fos transcription after its induction by serum growth factors. The growth-regulated enzymes responsible for this phosphorylation in early G1 phase of the cell cycle and the sites of phosphorylation have not been identified. We now provide evidence that two growth-regulated, nucleus- and cytoplasm-localized protein kinases, 90-kDa ribosomal S6 kinase (RSK) and mitogen-activated protein kinase (MAP kinase), contribute to the serum-induced phosphorylation of c-Fos. The major phosphopeptides derived from biosynthetically labeled c-Fos correspond to phosphopeptides generated after phosphorylation of c-Fos in vitro with both RSK and MAP kinase. The phosphorylation sites identified for RSK (Ser-362) and MAP kinase (Ser-374) are in the transrepression domain. Cooperative phosphorylation at these sites by both enzymes was observed in vitro and reflected in vivo by the predominance of the peptide phosphorylated on both sites, as opposed to singly phosphorylated peptides. This study suggests a role for nuclear RSK and MAP kinase in modulating newly synthesized c-Fos phosphorylation and downstream signaling.

scholarly journals Identification of p122RhoGAP (Deleted in Liver Cancer-1) Serine 322 as a Substrate for Protein Kinase B and Ribosomal S6 Kinase in Insulin-stimulated Cells

2005 ◽  
Vol 281 (8) ◽  
pp. 4762-4770 ◽  
Author(s):  
Ingeborg Hers ◽  
Matthew Wherlock ◽  
Yoshimi Homma ◽  
Hitoshi Yagisawa ◽  
Jeremy M. Tavaré
Keyword(s):  
Protein Kinase ◽  
Liver Cancer ◽  
Protein Kinase B ◽  
S6 Kinase ◽  
Ribosomal S6 Kinase

scholarly journals Betaine improves nonalcoholic fatty liver and associated hepatic insulin resistance: a potential mechanism for hepatoprotection by betaine

2010 ◽  
Vol 299 (5) ◽  
pp. G1068-G1077 ◽  
Author(s):  
Elango Kathirvel ◽  
Kengathevy Morgan ◽  
Ganesh Nandgiri ◽  
Brian C. Sandoval ◽  
Marie A. Caudill ◽  
...  
Keyword(s):  
Insulin Resistance ◽  
Fatty Liver ◽  
Signaling Pathways ◽  
Hepg2 Cells ◽  
Fasting Glucose ◽  
Hepatic Insulin Resistance ◽  
Nonalcoholic Fatty Liver ◽  
Downstream Signaling ◽  
Insulin Resistant ◽  
Hepatic Fat

Nonalcoholic fatty liver (NAFL) is a common liver disease, associated with insulin resistance. Betaine has been tested as a treatment for NAFL in animal models and in small clinical trials, with mixed results. The present study aims to determine whether betaine treatment would prevent or treat NAFL in mice and to understand how betaine reverses hepatic insulin resistance. Male mice were fed a moderate high-fat diet (mHF) containing 20% of calories from fat for 7 (mHF) or 8 (mHF8) mo without betaine, with betaine (mHFB), or with betaine for the last 6 wk (mHF8B). Control mice were fed standard chow containing 9% of calories from fat for 7 mo (SF) or 8 mo (SF8). HepG2 cells were made insulin resistant and then studied with or without betaine. mHF mice had higher body weight, fasting glucose, insulin, and triglycerides and greater hepatic fat than SF mice. Betaine reduced fasting glucose, insulin, triglycerides, and hepatic fat. In the mHF8B group, betaine treatment significantly improved insulin resistance and hepatic steatosis. Hepatic betaine content significantly decreased in mHF and increased significantly in mHFB. Betaine treatment reversed the inhibition of hepatic insulin signaling in mHF and in insulin-resistant HepG2 cells, including normalization of insulin receptor substrate 1 (IRS1) phosphorylation and of downstream signaling pathways for gluconeogenesis and glycogen synthesis. Betaine treatment prevents and treats fatty liver in a moderate high-dietary-fat model of NAFL in mice. Betaine also reverses hepatic insulin resistance in part by increasing the activation of IRS1, with resultant improvement in downstream signaling pathways.

scholarly journals Differential Effects of Protein Kinase B/Akt Isoforms on Glucose Homeostasis and Islet Mass

2009 ◽  
Vol 30 (3) ◽  
pp. 601-612 ◽  
Author(s):  
Francesca Buzzi ◽  
Linhua Xu ◽  
Richard A. Zuellig ◽  
Simone B. Boller ◽  
Giatgen A. Spinas ◽  
...  
Keyword(s):  
Insulin Resistance ◽  
Protein Kinase ◽  
Glucose Homeostasis ◽  
Metabolic Regulation ◽  
Protein Kinase B ◽  
Cell Mass ◽  
Metabolic Phenotype ◽  
Β Cell ◽  
Islet Mass ◽  
Insulin Resistant

ABSTRACT Protein kinase B (PKB)/Akt is considered to be a key target downstream of insulin receptor substrate 2 (IRS2) in the regulation of β-cell mass. However, while deficiency of IRS2 in mice results in diabetes with insulin resistance and severe failure of β-cell mass and function, only loss of the PKBβ isoform leads to a mild metabolic phenotype with insulin resistance. Other isoforms were reported not to be required for metabolic regulation. To clarify the roles of the three PKB isoforms in the regulation of islet mass and glucose homeostasis, we assessed the metabolic and pancreatic phenotypes of Pkbα, Pkbβ, and Pkbγ-deficient mice. Our study uncovered a novel role for PKBα in the regulation of glucose homeostasis, whereas it confirmed that Pkbβ−/ − mice are insulin resistant with compensatory increase of islet mass. Pkbα−/ − mice displayed an opposite phenotype with improved insulin sensitivity, lower blood glucose, and higher serum glucagon concentrations. Pkbγ−/ − mice did not show metabolic abnormalities. Additionally, our signaling analyses revealed that PKBα, but not PKBβ or PKBγ, is specifically activated by overexpression of IRS2 in β-cells and is required for IRS2 action in the islets.

Characterization of PF-4708671, a novel and highly specific inhibitor of p70 ribosomal S6 kinase (S6K1)

2010 ◽  
Vol 431 (2) ◽  
pp. 245-255 ◽  
Author(s):  
Laura R. Pearce ◽  
Gordon R. Alton ◽  
Daniel T. Richter ◽  
John C. Kath ◽  
Laura Lingardo ◽  
...  
Keyword(s):  
Insulin Resistance ◽  
Mammalian Target Of Rapamycin ◽  
Specific Inhibitor ◽  
Signalling Pathways ◽  
S6 Kinase ◽  
Ribosomal S6 Kinase ◽  
Phosphoinositide 3 Kinase ◽  
20 Nm ◽  
Mtor Complex 1

S6K1 (p70 ribosomal S6 kinase 1) is activated by insulin and growth factors via the PI3K (phosphoinositide 3-kinase) and mTOR (mammalian target of rapamycin) signalling pathways. S6K1 regulates numerous processes, such as protein synthesis, growth, proliferation and longevity, and its inhibition has been proposed as a strategy for the treatment of cancer and insulin resistance. In the present paper we describe a novel cell-permeable inhibitor of S6K1, PF-4708671, which specifically inhibits the S6K1 isoform with a Ki of 20 nM and IC50 of 160 nM. PF-4708671 prevents the S6K1-mediated phosphorylation of S6 protein in response to IGF-1 (insulin-like growth factor 1), while having no effect upon the PMA-induced phosphorylation of substrates of the highly related RSK (p90 ribosomal S6 kinase) and MSK (mitogen- and stress-activated kinase) kinases. PF-4708671 was also found to induce phosphorylation of the T-loop and hydrophobic motif of S6K1, an effect that is dependent upon mTORC1 (mTOR complex 1). PF-4708671 is the first S6K1-specific inhibitor to be reported and will be a useful tool for delineating S6K1-specific roles downstream of mTOR.

Sign in / Sign up

Export Citation Format

Share Document