scholarly journals Specific activity of phosphatidylinositol 3-kinase is increased by insulin stimulation

1993 ◽  
Vol 290 (2) ◽  
pp. 327-333 ◽  
Author(s):  
M Okamoto ◽  
T Hayashi ◽  
S Kono ◽  
G Inoue ◽  
M Kubota ◽  
...  
Keyword(s):  
Insulin Receptor ◽  
Protein Concentration ◽  
Specific Activity ◽  
Phosphatidylinositol 3 Kinase ◽  
Insulin Stimulation ◽  
Pi3k Activity ◽  
Before And After ◽  
Receptor Beta ◽  
Phosphatidylinositol 3

We investigated whether phosphatidylinositol 3-kinase (PI3K) is phosphorylated and whether its specific activity is increased by insulin stimulation in vivo using Fao cells and antibodies raised against the 85 kDa subunit of PI3K, insulin-receptor substrate-1 (IRS-1), and phosphotyrosine (pTyr). PI3K activity was detected in the immunoprecipitate produced with anti-PI3K at a basal state. The activity was increased 2-3-fold by insulin stimulation, although the protein concentration of kinase in the anti-PI3K immunoprecipitates was the same before and after insulin stimulation. Both anti-pTyr and anti-IRS-1 antibodies immunoprecipitated the kinase activity only after insulin stimulation. After the first immunoprecipitation with anti-pTyr, the supernatant was immunoprecipitated once more with anti-PI3K. PI3K activity in the second immunoprecipitate revealed little difference between the basal and insulin-stimulated states, suggesting that most of the insulin-activated portion of PI3K was precipitated by anti-pTyr. Both IRS-1 and the insulin-receptor beta-subunit (95 kDa) were phosphorylated on tyrosine residues by insulin stimulation and immunoprecipitated with anti-pTyr. However, phosphorylation of neither subunit of PI3K (85 kDa or 110 kDa) was detectable in the immunoprecipitate produced with anti-pTyr. The 185 kDa pTyr-containing protein was immunoprecipitated with anti-PI3K after insulin stimulation, although there was little phosphorylation of the 85 kDa protein. pTyr in the 110 kDa protein immunoprecipitated with anti-PI3K was below detectable levels. These results indicate that the specific activity of PI3K is increased by insulin stimulation without detectable tyrosine phosphorylation of PI3K itself in Fao cells. The majority of the insulin-activated portion of PI3K is associated with pTyr-containing proteins including IRS-1, which suggests that this is important for activation of PI3K by insulin.

Increased insulin receptor signaling and glycogen synthase activity contribute to the synergistic effect of exercise on insulin action

2003 ◽  
Vol 95 (6) ◽  
pp. 2519-2529 ◽  
Author(s):  
Christine Y. Christ-Roberts ◽  
Thongchai Pratipanawatr ◽  
Wilailak Pratipanawatr ◽  
Rachele Berria ◽  
Renata Belfort ◽  
...  
Keyword(s):  
Insulin Receptor ◽  
Insulin Infusion ◽  
Glycogen Synthase ◽  
Whole Body ◽  
Glucose Disposal ◽  
Phosphatidylinositol 3 Kinase ◽  
Insulin Stimulation ◽  
Glucose Storage ◽  
Exercise Induced ◽  
Phosphatidylinositol 3

The purpose of this study was to determine the factors contributing to the ability of exercise to enhance insulin-stimulated glucose disposal. Sixteen insulin-resistant nondiabetic and seven Type 2 diabetic subjects underwent two hyperinsulinemic (40 mU · m-2 · min-1) clamps, once without and once with concomitant exercise at 70% peak O2 consumption. Exercise was begun at the start of insulin infusion and was performed for 30 min. Biopsies of the vastus lateralis were performed before and after 30 min of insulin infusion (immediately after cessation of exercise). Exercise synergistically increased insulin-stimulated glucose disposal in nondiabetic [from 4.6 ± 0.4 to 9.5 ± 0.8 mg · kg fat-free mass (FFM)-1 · min-1] and diabetic subjects (from 4.3 ± 1.0 to 7.9 ± 0.7 mg · kg FFM-1 · min-1) subjects. The rate of glucose disposal also was significantly greater in each group after cessation of exercise. Exercise enhanced insulin-stimulated increases in glycogen synthase fractional velocity in control (from 0.07 ± 0.02 to 0.22 ± 0.05, P < 0.05) and diabetic (from 0.08 ± 0.03 to 0.15 ± 0.03, P < 0.01) subjects. Exercise also enhanced insulin-stimulated glucose storage (glycogen synthesis) in nondiabetic (2.9 ± 0.9 vs. 4.9 ± 1.1 mg · kg FFM-1 · min-1) and diabetic (1.7 ± 0.5 vs. 4.2 ± 0.8 mg · kg FFM-1 · min-1) subjects. Increased glucose storage accounted for the increase in whole body glucose disposal when exercise was performed during insulin stimulation in both groups; effects of exercise were correlated with enhancement of glucose disposal and glucose storage ( r = 0.93, P < 0.001). Exercise synergistically enhanced insulin-stimulated insulin receptor substrate 1-associated phosphatidylinositol 3-kinase activity ( P < 0.05) and Akt Ser473 phosphorylation ( P < 0.05) in nondiabetic subjects but had little effect in diabetic subjects. The data indicate that exercise, performed in conjunction with insulin infusion, synergistically increases insulin-stimulated glucose disposal compared with insulin alone. In nondiabetic and diabetic subjects, increased glycogen synthase activation is likely to be involved, in part, in this effect. In nondiabetic, but not diabetic, subjects, exercise-induced enhancement of insulin stimulation of the phosphatidylinositol 3-kinase pathway is also likely to be involved in the exercise-induced synergistic enhancement of glucose disposal.

scholarly journals Phosphatidylinositol 3-kinase-dependent stabilization of α1(I) collagen mRNA in human lung fibroblasts

2001 ◽  
Vol 281 (1) ◽  
pp. C99-C105 ◽  
Author(s):  
Dennis A. Ricupero ◽  
Christine F. Poliks ◽  
David C. Rishikof ◽  
Kelly A. Cuttle ◽  
Ping-Ping Kuang ◽  
...  
Keyword(s):  
Transforming Growth Factor ◽  
Transforming Growth Factor Β ◽  
Northern Blotting ◽  
Lung Fibroblasts ◽  
Mrna Levels ◽  
Phosphatidylinositol 3 Kinase ◽  
Collagen Mrna ◽  
Pi3k Activity ◽  
Phosphatidylinositol 3

We investigated the role of phosphatidylinositol 3-kinase (PI3K) in the expression of α1(I) collagen mRNA. We report that the basal level of α1(I) collagen mRNA was reduced when PI3K activity was inhibited by either LY-294002 or wortmannin. These PI3K inhibitors also blocked increases of α1(I) collagen mRNA levels after the addition of transforming growth factor-β. The effect of PI3K inhibition was abolished by the removal of the inhibitor or by the addition of cycloheximide. Inhibition of PI3K activity decreased the stability of the α1(I) collagen mRNA with no change in the rate of transcription of the α1(I) collagen gene as assessed by Northern blotting with actinomycin D-treated fibroblasts and nuclear run-on assays. Expression of a truncated α1(I) collagen minigene driven by a cytomegalovirus promoter in murine fibroblasts was decreased by LY-294002 treatment. These data indicate that PI3K activation results in increased stabilization of α1(I) collagen mRNA. In vivo, the PI3K activity in fibroblasts may regulate basal levels of α1(I) collagen mRNA expression.

Phosphatidylinositol 3-kinase and dynamics of insulin resistance in denervated slow and fast muscles in vivo

1997 ◽  
Vol 272 (4) ◽  
pp. E661-E670 ◽  
Author(s):  
J. S. Elmendorf ◽  
A. Damrau-Abney ◽  
T. R. Smith ◽  
T. S. David ◽  
J. Turinsky
Keyword(s):  
Insulin Receptor ◽  
Glucose Uptake ◽  
Soleus Muscle ◽  
Phosphatidylinositol 3 Kinase ◽  
Plantaris Muscle ◽  
Glut 1 ◽  
Glut 4 ◽  
Denervated Muscles ◽  
Phosphatidylinositol 3

Regulation of glucose uptake by 1- and 3-day denervated soleus (slow-twitch) and plantaris (fast-twitch) muscles in vivo was investigated. One day after denervation, soleus and plantaris muscles exhibited 62 and 65% decreases in insulin-stimulated 2-deoxyglucose uptake, respectively, compared with corresponding control muscles. At this interval, denervated muscles showed no alterations in insulin receptor binding and activity, amount and activity of phosphatidylinositol 3-kinase, and amounts of GLUT-1 and GLUT-4. Three days after denervation, there was no increase in 2-deoxyglucose uptake in response to insulin in soleus muscle, whereas plantaris muscle exhibited a 158% increase in basal and an almost normal absolute increment in insulin-stimulated uptake. Despite these differences, denervated soleus and plantaris muscles exhibited comparable decreases in insulin-stimulated activities of the insulin receptor (approximately 40%) and phosphatidylinositol 3-kinase (approximately 50%) and a pronounced decrease in GLUT-4. An increase in GLUT-1 in plantaris, but not soleus, muscle 3 days after denervation is consistent with augmented basal 2-deoxyglucose uptake in plantaris muscle at this interval. These results demonstrate that, in denervated muscles, there is a clear dissociation between insulin-stimulated 2-deoxyglucose uptake and upstream events involved in insulin-stimulated glucose uptake.

Changes in tyrosine phosphorylation of insulin receptor and insulin receptor substrate-1 (IRS-1) and association of p85 subunit of phosphatidylinositol 3-kinase with IRS-1 after feeding in rat liver in vivo

1997 ◽  
Vol 154 (2) ◽  
pp. 267-273 ◽  
Author(s):  
Y Ito ◽  
M Ariga ◽  
S-I Takahashi ◽  
A Takenaka ◽  
T Hidaka ◽  
...  
Keyword(s):  
Insulin Receptor ◽  
Tyrosine Phosphorylation ◽  
Rat Liver ◽  
Insulin Receptor Substrate ◽  
Β Subunit ◽  
Phosphatidylinositol 3 Kinase ◽  
Insulin Receptor Substrate 1 ◽  
Insulin Receptor Tyrosine Kinase ◽  
Phosphatidylinositol 3

Abstract The binding of insulin to its receptor rapidly induces intrinsic insulin receptor tyrosine kinase activity, resulting in tyrosine phosphorylation of various cytosolic substrates, such as insulin receptor substrate-1 (IRS-1) which, in turn, associates with a p85 subunit of phosphatidylinositol 3-kinase (PI 3-kinase) followed by activation of this enzyme. In the present study, we have examined these early steps of insulin signalling in rat liver in vivo after food ingestion. After fasting for 22 h, a 12% casein diet was available ad libitum throughout the 8-h experimental period. Plasma insulin concentrations increased within 45 min after feeding, reached a maximum at 1·5 h and gradually decreased until 8 h. Autophosphorylation of the insulin receptor β-subunit in liver was detected even during fasting and increased about 1·5-fold at 1·5 h after feeding. Basal tyrosine phosphorylation of IRS-1 was detectable during starvation, increased about twofold at 3 h after feeding and levels were maintained until 8 h. The content of the p85 subunit of PI 3-kinase associated with IRS-1 also increased after feeding in parallel with the changes in tyrosine phosphorylation of IRS-1. Because tyrosine phosphorylation of the insulin receptor β-subunit and IRS-1 and the association of the p85 subunit of PI 3-kinase with IRS-1 in liver were closely correlated with the changes in the plasma concentration of insulin, we concluded that endogenous insulin secreted in response to eating caused these insulin-dependent intracellular changes in the liver. Journal of Endocrinology (1997) 154, 267–273

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