Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.7.10.2 (focal adhesion kinase)
44,029 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Insulin can regulate the abundance and organization of filamentous actin within cells in culture. Early studies using cell lines that overexpress the insulin receptor demonstrated that insulin caused a rapid reversible disassembly of actin filaments that coincided with the rapid tyrosine dephosphorylation of focal adhesion kinase. We have extended these studies by demonstrating that paxillin, another focal adhesion protein, and Src undergo tyrosine dephosphorylation in response to insulin in Chinese hamster ovary (CHO) and rat hepatoma (HTC) cells that overexpress the insulin receptor. This contrasted with the effect of insulin in parental CHO and HTC cells in which focal adhesion proteins were not dephosphorylated in response to the hormone. In addition, insulin caused a dispersion of focal adhesion proteins and disruption of actin filament bundles only in cells that overexpressed the insulin receptor. Moreover, in 3T3-L1 adipocytes, which are considered prototypic insulin-responsive cells, actin filament assembly was stimulated, and focal adhesion protein tyrosine phosphorylation was not altered. 3T3-L1 cells have more insulin receptors than either parental CHO or HTC cells but have fivefold less insulin receptors than the overexpressing cell lines. We hypothesize that a threshold may exist in which the overexpression of insulin receptors determines how insulin signaling pathways regulate the actin cytoskeleton.
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PMID:Opposite effects of insulin on focal adhesion proteins in 3T3-L1 adipocytes and in cells overexpressing the insulin receptor. 980 96

Insulin is important for maintaining the responsiveness of the liver to growth hormone (GH). Insulin deficiency results in a decrease in liver GH receptor (GHR) expression, which can be reversed by insulin administration. In osteoblasts, continuous insulin treatment decreases the fraction of cellular GHR localized to the plasma membrane. Thus, it is not clear whether hyperinsulinemia results in an enhancement or inhibition of GH action. We asked whether continuous insulin stimulation, similar to what occurs in hyperinsulinemic states, results in GH resistance. Our present studies suggest that insulin treatment of hepatoma cells results in a time-dependent inhibition of acute GH-induced phosphorylation of STAT5B. Whereas total protein levels of JAK2 were not reduced after insulin pretreatment for 16 h, GH-induced JAK2 phosphorylation was inhibited. There was a concomitant decrease in GH binding and a reduction in immunoreactive GHR levels following pretreatment with insulin for 8-24 h. In summary, continuous insulin treatment in rat H4 hepatoma cells reduces GH binding, immunoreactive GHR, GH-induced phosphorylation of JAK2, and GH-induced tyrosine phosphorylation of STAT5B. These findings suggest that hepatic GH resistance may develop when a patient exhibits chronic hyperinsulinemia, a condition often observed in patients with obesity and in the early stage of Type 2 diabetes.
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PMID:Insulin inhibits growth hormone signaling via the growth hormone receptor/JAK2/STAT5B pathway. 1022 8

Insulin-like growth factors (IGFs) and their receptors in the fetus are essential for growth and postnatal survival but the role of maternal IGFs is less well understood. Animal and in vitro evidence suggests that maternal IGF-I may have important effects on placental function. Recent work in humans suggests that although there is no relationship between maternal serum IGF-I and normal fetal growth, levels are low in pregnancies complicated by fetal growth restriction due to placental dysfunction. A prospective and observational study was undertaken of the distribution and concentration of placental type I IGF receptors (IGF-IR) in women with small for gestational age (n=26) or appropriately grown (n=14) fetuses. Women were scanned biweekly from 24 weeks to delivery and cases (birthweight <5th centile) were assigned to two groups: 'fetal growth restriction' (FGR; umbilical artery pulsatility index [UAPI] > +2 s.d.; n=16) and 'normal small for gestational age' (SGA; normal UAPI, growth velocity and amniotic fluid; n=10). Immunohistochemistry of the IGF-IR was performed on formol saline-fixed placental biopsies obtained at delivery. In control pregnancies IGF-IR were present in villous endothelium and stroma, trophoblast and decidua and their distribution and density were unchanged in both SGA and FGR pregnancies. We hypothesize that a therapeutic elevation of maternal IGF-I in FGR pregnancy might lead to enhanced placental function and so fetal growth. Our findings of normal localization and density of placental IGF-IR in FGR encourage us to extend our work to look at the effects of maternal IGF-I on the transport of glucose and amino acids.
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PMID:An immunohistochemical study of type I insulin-like growth factor receptors in the placentae of pregnancies with appropriately grown or growth restricted fetuses. 1032 54

L6 myoblasts stably transfected with a GLUT4 cDNA harboring an exofacial myc epitope tag (L6-GLUT4myc myoblasts) were used to study the role of protein kinase B alpha (PKBalpha)/Akt1 in the insulin-induced translocation of GLUT4 to the cell surface. Surface GLUT4myc was detected by immunofluorescent labeling of the myc epitope in nonpermeabilized cells. Insulin induced a marked translocation of GLUT4myc to the plasma membrane within 20 min. This was prevented by transient transfection of a dominant inhibitory construct of phosphatidylinositol (PI) 3-kinase (Deltap85alpha). Transiently transfected cells were identified by cotransfection of green fluorescent protein. A constitutively active PKBalpha, created by fusion of a viral Gag protein at its N terminus (GagPKB), increased the cell surface density of GLUT4myc compared to that of neighboring nontransfected cells. A kinase-inactive, phosphorylation-deficient PKBalpha/Akt1 construct with the mutations K179A (substitution of alanine for the lysine at position 179), T308A, and S473A (AAA-PKB) behaved as a dominant-negative inhibitor of insulin-dependent activation of cotransfected wild-type hemagglutinin (HA)-tagged PKB. Furthermore, AAA-PKB markedly inhibited the insulin-induced phosphorylation of cotransfected BAD, demonstrating inhibition of the endogenous PKB/Akt. Under the same conditions, AAA-PKB almost entirely blocked the insulin-dependent increase in surface GLUT4myc. PKBalpha with alanine substitutions T308A and S473A (AA-PKB) or K179A (A-PKB) alone was a less potent inhibitor of insulin-dependent activation of wild-type HA-PKB or GLUT4myc translocation than was AAA-PKB. Cotransfection of AAA-PKB with a fourfold DNA excess of HA-PKB rescued insulin-stimulated GLUT4myc translocation. AAA-PKB did not prevent actin bundling (membrane ruffling), though this response was PI 3-kinase dependent. Therefore, it is unlikely that AAA-PKB acted by inhibiting PI 3-kinase signaling. These results outline an important role for PKBalpha/Akt1 in the stimulation of glucose transport by insulin in muscle cells in culture.
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PMID:Protein kinase B/Akt participates in GLUT4 translocation by insulin in L6 myoblasts. 1033 Jan 41

Insulin resistance in skeletal muscle is one of the earliest symptoms associated with non-insulin-dependent diabetes mellitus (NIDDM). Tumour necrosis factor (TNF) and nonesterified fatty acids have been proposed to be crucial factors in the development of the insulin-resistant state. We here show that, although TNF downregulated insulin-induced insulin receptor (IR) and IR substrate (IRS)-1 phosphorylation as well as phosphoinositide 3-kinase (PI3-kinase) activity in pmi28 myotubes, this was, unlike in adipocytes, not sufficient to affect insulin-induced glucose transport. Rather, TNF increased membrane expression of GLUT1 and glucose transport in these muscle cells. In contrast, the nonesterified fatty acid palmitate inhibited insulin-induced signalling cascades not only at the level of IR and IRS-1 phosphorylation, but also at the level protein kinase B (PKB/Akt), which is thought to be directly involved in the insulin-induced translocation of GLUT4, and inhibited insulin-induced glucose uptake. Palmitate also abrogated TNF-dependent enhancement of basal glucose uptake, suggesting that palmitate has the capacity to render muscle cells resistant not only to insulin but also to TNF with respect to glucose transport by GLUT4 and GLUT1, respectively. Our data illustrate the complexity of the mechanisms governing insulin resistance of skeletal muscle, questioning the role of TNF as a direct inhibitor of glucose homoeostasis in this tissue and shedding new light on an as yet unrecognized multifunctional role for the predominant nonesterified fatty acid palmitate in this process.
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PMID:Cross-talk mechanisms in the development of insulin resistance of skeletal muscle cells palmitate rather than tumour necrosis factor inhibits insulin-dependent protein kinase B (PKB)/Akt stimulation and glucose uptake. 1054 46

Insulin acutely up-regulates p85alpha phosphatidylinositol 3-kinase (p85alphaPI 3-K) mRNA levels in human skeletal muscle (Laville, M., Auboeuf, D., Khalfallah, Y., Vega, N., Riou, J. P., and Vidal, H. (1996) J. Clin. Invest. 98, 43-49). In the present work, we attempted to elucidate the mechanism of action of insulin in primary cultures of human muscle cells. Insulin (10(-7) M, 6 h of incubation) induced a 2-fold increase in p85alphaPI 3-K mRNA abundances (118 +/- 12 versus 233 +/- 35 amol/microgram total RNA, n = 5, p < 0.01) without changing the expression levels of insulin receptor, IRS-1, glycogen synthase, and Glut 4 mRNAs in differentiated myotubes from healthy subjects. The effect is most probably due to a transcriptional activation of the p85alphaPI 3-K gene because the half-life of the mRNA was not affected by insulin treatment (4.0 +/- 0.8 versus 3.1 +/- 0.4 h). PD98059 (50 microM) did not modify the insulin response but increased p85alphaPI 3-K mRNA levels in the absence of insulin, suggesting that the mitogen-activated protein kinase pathway exerts a negative effect on p85alphaPI 3-K mRNA expression in the absence of the hormone. On the other hand, the insulin effect was totally abolished by LY294002 (10 microM) and rapamycin (50 nM). In addition, overexpression of a constitutively active protein kinase B increased p85alphaPI 3-K mRNA levels. These results indicate that the phosphatidylinositol 3-kinase/PKB/p70S6 kinase pathway is required for the stimulation by insulin of p85alphaPI 3-K gene expression in human muscle cells.
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PMID:A phosphatidylinositol 3-Kinase/p70 ribosomal S6 protein kinase pathway is required for the regulation by insulin of the p85alpha regulatory subunit of phosphatidylinositol 3-kinase gene expression in human muscle cells. 1056 66

In order to study the role of phosphatidylinositol-3-kinase (PI3K), PKB, FRAP, S6 kinase, and MAP kinase in insulin-stimulated glycogen synthesis, we used a specific inhibitor of PI3K, LY294002, the immunosuppressant inhibitor of FRAP, rapamycin, and the inhibitor of MAPK kinase (MEK)/MAPK, PD98059, in rat HTC hepatoma cells overexpressing human insulin receptors. The PI3K inhibitor LY294002 completely blocks insulin-stimulated glycogen synthesis by inhibiting glycogen synthase, PKB (Akt-1), and FRAP (RAFT) autophosphorylation, as well as p70 S6 kinase activation, whereas insulin receptor substrates tyrosine phosphorylation and MEK activity were not affected. However, rapamycin only partially blocks insulin-stimulated glycogen synthesis by partial inhibition of glycogen synthase, whereas it completely blocks S6 kinase activation and FRAP autophosphorylation, but does not affect either PKB autophosphorylation, MEK activity, or insulin receptor tyrosine phosphorylation. Insulin-stimulated glycogen synthesis and glycogen synthase were not affected by the MEK/MAPK inhibitor PD98059. These data suggest that the PI3K, and not the MAPK pathway plays an important role in the insulin-stimulated glycogen synthesis in the hepatocyte, partly mediated by FRAP and S6 kinase activation. However, the inhibition of FRAP and S6 kinase activation is not sufficient to block insulin-stimulated glycogen synthesis, suggesting an important role of a branching pathway upstream of S6 kinase and downstream of PI3K, which is probably mediated by PKB in the signaling of the insulin receptor in hepatoma HTC cells.
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PMID:Stimulation of glycogen synthesis by insulin requires S6 kinase and phosphatidylinositol-3-kinase in HTC-IR cells. 1062 81

Insulin exerts wide variety of biological effects through interaction with its specific receptor, which belongs to a large family of receptor tyrosine kinases. The activated insulin receptor phosphorylates the intracellular substrate IRS protains, which then bind various signalling molecules that contain Src homology 2 domains. The first downstram molecule that was shown to associate with IRS protains is PI3-kinase. PI3-kinase contributes to a wide variety of biological actions. Both Akt(PKB), a serine-threonine kinase with a PH domain, and atypical PKC(PKC zeta, PKC lambda) have been implicated as downstream effectors of PI3-kinase. Insulin resistance contributes to the pathogenesis of NIDDM. Both primary, genetically, and secondary, environmentally factors are important for insulin resistance. The secondary factors include hyperglycemia, hyperlipidemia, obesity, TNF alpha, FFA(free fatty acid).
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PMID:[Insulin signalling system and mechanism of insulin resistance]. 1070 48

Insulin-stimulated signaling pathways are activated upon interactions between the intracellular domains of the receptor and its downstream effectors. Insulin receptor substrate proteins (IRS-1, -2, -3 and -4) are the best-studied substrates for the insulin receptor kinase (IRK). We have previously shown that IRS-1 and IRS-2 interact with the juxtamembrane (JM) but not with the carboxyl-terminal (CT) region of the insulin receptor (IR) in vitro. However, the precise role of these IR regions in mediating insulin's bioeffects is still unresolved. In the present work we made use of vaccinia virus as a vector for quantitative expression of the JM and CT domains within the cytoplasm of physiologically insulin-responsive primary rat adipocytes and rat hepatoma Fao cells. We could demonstrate that overexpression of either the JM or the CT domains did not inhibit either insulin binding or insulin-stimulated receptor autophosphorylation. In contrast, metabolic effects such as insulin-induced glucose utilization in adipocytes, and insulin-induced amino acid utilization in Fao hepatoma cells were inhibited (70-80%) in cells overexpressing the JM but not the CT domains of IR. The inhibitory effects of the overexpressed JM domain were accompanied by inhibition of insulin-stimulated IRS-1 phosphorylation, decreased IRS-1-associated PI3K activity, and decreased phosphorylation of the downstream effectors of PI3K, PKB and p70 S6K. Insulin-stimulated thymidine incorporation in Fao cells was also inhibited (40%) upon overexpression of the JM but not the CT region of IR. Our findings suggest that interactions between the JM region of IR and its downstream effectors are obligatory for insulin-stimulated metabolic functions in physiologically relevant insulin responsive cells. They also rule out the possibility that interaction of proteins, including PI3K, with the CT domain can provide an alternative pathway.
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PMID:The juxtamembrane but not the carboxyl-terminal domain of the insulin receptor mediates insulin's metabolic functions in primary adipocytes and cultured hepatoma cells. 1082 35

The effect of insulin on glucose transport, glucose transporter 4 (Glut4) translocation, and intracellular signaling were measured in fat cells from lean and obese Zucker rats of different ages. Insulin-stimulated glucose transport was markedly reduced in adipocytes from old and obese animals. The protein content of Glut4 and insulin receptor substrates (IRS) 1 and 2 were also reduced while other proteins, including the p85 subunit of PI3-kinase, Shc and the MAP kinases (ERK1 and 2) were essentially unchanged. There was a marked impairment in the insulin stimulated tyrosine phosphorylation of IRS-1 and 2 as well as activation of PI3-kinase and PKB in cells from old and obese animals. Furthermore, insulin-stimulated translocation of both Glut4 and PKB to the plasma membrane was virtually abolished. The phosphotyrosine phosphatase inhibitor, vanadate, increased the insulin-stimulated upstream signaling including PI3-kinase and PKB activities as well as rate of glucose transport. Thus, the insulin resistance in cells from old and obese Zucker rats can be accounted for by an impaired translocation process, due to signaling defects leading to a reduced activation of PI3-kinase and PKB, as well as an attenuated Glut4 protein content.
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PMID:Insulin resistance in fat cells from obese Zucker rats--evidence for an impaired activation and translocation of protein kinase B and glucose transporter 4. 1083 89


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