Effects of EGF on the mass of inositol 1,4,5-trisphosphate and sn(1,2)-diacylglycerol in freshly isolated rat hepatocytes: Comparison with vasopressin

Cerpovicz, Paul F.; Ochs, Raymond S.

doi:10.1016/0006-291x(92)91304-9

Cited by 13 publications

(8 citation statements)

References 28 publications

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“…17 In liver cells, EGF and other growth factors induce an elevation of [Ca 2ϩ ] i , but this response is associated with only a modest degree of tyrosine phosphorylation of PLC␥1, 6,21 and some authors have questioned the role of IP 3 formation in the EGF-induced Ca 2ϩ response. 25 Although we and others have reported EGF-induced PLC␥1 tyrosine phosphorylation, IP 3 formation and [Ca 2ϩ ] i elevation in isolated hepatocytes, 6,21,27 including cells in culture, 26,28 the factors controlling the strength of this response are not clear. It is not clear why the hepatocytes used in our studies were more strongly suppressed during overnight culture than the Ca 2ϩ response to EGF in hepatocytes used by some other groups 24,26,28 or, for that matter, the EGF-induced PLC␥1 activation in A431 cells or other cell lines.…”

Section: Discussionmentioning

confidence: 88%

“…Nevertheless, several groups reported a significant EGF-induced formation of IP 3 with an associated increase in [Ca 2ϩ ] i both in freshly isolated hepatocytes and in hepatocytes in primary culture, although the reported magnitude of the response and the EGF dose-dependency varied considerably between different groups. 6,[21][22][23][24][25][26][27][28] Thus, it appears that even a modest degree of tyrosine phosphorylation of PLC␥1 is sufficient to activate the enzymatic activity and bring about formation of IP 3 and increase of [Ca 2ϩ ] i , but the factors that determine the magnitude of the response may be subject to other regulatory factors that are poorly characterized. Interaction of the EGFR/PLC␥1 signaling system with the actin cytoskeleton may contribute to this regulation.…”

mentioning

confidence: 99%

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Suppression of Epidermal Growth Factor-Induced Phospholipase C Activation Associated With Actin Rearrangement in Rat Hepatocytes in Primary Culture

Nojiri

2000

Hepatology

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Hepatocytes maintained in primary culture for periods of 1 to 24 hours exhibited a rapid decline in epidermal growth factor (EGF)-induced activation of phospholipase C (PLC), as was evident in a loss of EGF-induced inositol 1,4,5-trisphosphate (IP 3 ) formation and mobilization of Ca 2؉ from intracellular Ca 2؉ stores. The loss of PLC activation was not the result of a decrease in EGF receptor or phospholipase C-␥1 (PLC␥1) protein levels, nor the result of a loss of tyrosine phosphorylation of these proteins, but was associated with a decrease in EGF-induced translocation of PLC␥1 to the Triton-insoluble fraction, presumably reflecting binding to the actin cytoskeleton. Disruption of F-actin by treatment of cultured hepatocytes with cytochalasin D recovered the EGF-induced IP 3 formation and Ca 2؉ mobilization to the same level and with the same dose-response relationship as was obtained in freshly isolated cells. Analysis of PLC␥1 colocalization with F-actin by confocal microscopy showed that PLC␥1 was mostly distributed diffusely in the cytosol, both in freshly plated cells and in cells in culture for 24 hours, despite marked differences in actin structures. EGF stimulation caused a modest redistribution of PLC␥1 and a detectable increase in colocalization with cortical actin structures in freshly plated cells or in cytochalasin D-treated cells, but in cells that had been maintained and spread in culture only a limited PLC␥1 relocation was detected to specific actin-structure associated with lamellipodia and membrane ruffles. We conclude that actin cytoskeletal structures can exert negative control over PLC␥1 activity in hepatocytes and the interaction of the enzyme with specific actin structures dissociates PLC␥1 tyrosine phosphorylation from activation of its enzymatic activity. (HEPATOLOGY 2000;32:947-957.)Binding of the epidermal growth factor (EGF) to its receptor (EGFR) initiates dimerization of the receptor protein and activation of its intrinsic tyrosine kinase, resulting in autophosphorylation of multiple tyrosine residues on the cytoplasmic domain of the receptor. 1-3 These phosphotyrosine residues act as specific docking sites for target proteins that contain characteristic protein domains, such as the src homology-2 (SH2) domain. 4,5 Activation of different target proteins initiates a branching network of signaling reactions in the cell, resulting in the appropriate biological response patterns. 6 One of the intracellular signaling pathways activated by EGF involves phospholipase C-␥1 (PLC␥1), a member of the phosphoinositide-specific phospholipase C family of proteins, which, in addition to the catalytic domain and Ca 2ϩ -binding domains shared with other PLC isoforms, contains several tyrosine phosphorylation sites (Tyr771, Tyr783, and Tyr 1254) that are targets for the tyrosine kinase activity of growth-factor receptors, two SH2 domains that bind to autophosphorylation sites on the receptor, an SH3 domain that interacts with proline-rich regions in proteins, and a pleckstrin homology (PH) domain...

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Section: Discussionmentioning

confidence: 88%

mentioning

confidence: 99%

Suppression of Epidermal Growth Factor-Induced Phospholipase C Activation Associated With Actin Rearrangement in Rat Hepatocytes in Primary Culture

Nojiri

2000

Hepatology

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“…In these cells, IGF-1 or IGF-2 increased Ca 21 uptake via a calcium-permeable cation channel only when these fibroblasts were primed with epidermal growth factor (EGF), but not in quiescent or proliferating BALB/c 3T3 fibroblasts. Since EGF acts on several intracellular signal tranduction pathways [Loza et al, 1995;Peppelenbosch et al, 1991Peppelenbosch et al, , 1992Casabiell et al, 1993;Cerpovicz and Ochs, 1992;Dean and Boyton, 1995;Dunlop and Clark, 1993;Yeo and Exton, 1995] and there are crosstalks between these signaling pathways, two mechanisms may be responsible for the apparent effect of IGF-1 or IGF-2 on intracellular calcium in EGF-primed BALB/c 3T3 fibroblasts and may explain the apparent lack in cells not primed with EGF. One is that protein kinase C (PKC) activation by EGF may exert a negative feedback control on phosphatidylinositol 4,5 bisphosphate hydrolysis [Loza et al, 1995;Peppelenbosch et al, 1991], masking a possible effect of IGF-1 or IGF-2 on PLC and on the mobilization of Ca 21 from intracellular Ca 21 stores.…”

Section: Discussionmentioning

confidence: 96%

Different mechanisms are involved in intracellular calcium increase by insulin-like growth factors 1 and 2 in articular chondrocytes: Voltage-gated calcium channels, and/or phospholipase C coupled to a pertussis-sensitive G-protein

et al. 1997

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This study describes the mechanisms involved in the IGF-1 and IGF-2-induced increases in intracellular calcium concentration [Ca2+]i in cultured chondrocytes and the involvement of type 1 IGF receptors. It shows that IGF-1, IGF-2, and insulin increased the cytosolic free calcium concentration [Ca2+]i in a dose-dependent manner, with a plateau from 25 to 100 ng/ml for both IGF-1 and IGF-2 and from 1 to 2 micrograms/ml for insulin. The effect of IGF-1 was twice as great as the one of IGF-2, and the effect of insulin was 40% lower than IGF-1 effect. Two different mechanisms are involved in the intracellular [Ca2+]i increase. 1) IGF-1 and insulin but not IGF-2 involved a Ca2+ influx through voltage-gated calcium channels: pretreatment of the cells by EGTA and verapamil diminished the IGF-1 or insulin-induced [Ca2+]i but did not block the effect of IGF-2. 2) IGF-1, IGF-2, and insulin also induced a Ca2+ mobilization from the endoplasmic reticulum: phospholipase C (PLC) inhibitors, neomycin, or U-73122 partially blocked the intracellular [Ca2+]i increase induced by IGF-1 and insulin and totally inhibited the effect of IGF-2. This Ca2+ mobilization was pertussis toxin (PTX) dependent, suggesting an activation of a PLC coupled to a PTX-sensitive G-protein. Lastly, preincubation of the cells with IGF1 receptor antibodies diminished the IGF-1-induced Ca2+ spike and totally abolished the Ca2+ influx, but did not modify the effect of IGF-2. These results suggest that IGF-1 action on Ca2+ influx involves the IGF1 receptor, while part of IGF-1 and all of IGF-2 Ca2+ mobilization do not implicate this receptor.

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“…Other studies have demonstrated EGF-induced activation of PLC␥1 and/or PLD and an increase in DAG (Wright et al, 1988(Wright et al, , 1990Nishibe et al, 1990;Cook and Wakelam, 1992;Reynolds et al, 1993;Yang et al, 1993;Pettitt et al, 1994;Yeo and Exton, 1995). However, in some cells these responses to EGF have not been detected (Cerpovicz and Ochs, 1992;Reynolds et al, 1993).…”

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confidence: 90%

Role of diacylglycerol (DAG) in hormonal induction of S phase in hepatocytes: The DAG-dependent protein kinase C pathway is not activated by epidermal growth factor (EGF), but is involved in mediating the enhancement of responsiveness to EGF by vasopressin, angiotensin II, and norepinephrine

et al. 1999

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The role of diacylglycerol (DAG) in hormonal induction of S phase was investigated in primary cultures of rat hepatocytes. In this model, several agonists that bind to G protein-coupled receptors act as comitogens when added to the cells soon after plating (i.e., in Go/early Gl phase), while the cells are most responsive to the mitogenic effect of epidermal growth factor (EGF) at 24-48 h of culturing (i.e., mid/late Gl). It was found that the cellular concentration of DAG rose markedly and progressively during the first 24 h of culturing. Exposure of the hepatocytes at 3 h to alpha1-adrenergic stimulation (norepinephrine with timolol), vasopressin, or angiotensin II further increased this rise, producing a sustained increase in the DAG level. Norepinephrine, which was the most efficient comitogen, produced the most prolonged DAG elevation. In contrast, no significant increase of DAG was found in response to EGF, neither at 3 nor at 24 h, using concentrations that markedly stimulated the ERK subgroup of the mitogen-activated protein kinases (MAPK) and DNA synthesis. Addition of Bacillus cereus phosphatidylcholine-specific phospholipase C (PC-PLC) strongly elevated DAG, while Streptomyces phospholipase D (PLD) increased phosphatidic acid (PA) but not DAG. B. cereus PC-PLC and the protein kinase C (PKC) activator tetradecanoyl phorbol-acetate (TPA), like norepinephrine, vasopressin, and angiotensin II, stimulated MAPK and enhanced the stimulatory effect of EGF on DNA synthesis. The PKC inhibitor GF109203X did not diminish the effect of EGF on MAPK or DNA synthesis, but strongly inhibited the effects of norepinephrine, vasopressin, angiotensin II, TPA and B. cereus PC-PLC on MAPK and almost abolished the enhancement by these agents of EGF-stimulated DNA synthesis. These results suggest that although generation of DAG is not a direct downstream response mediating the effects of the EGF receptor in hepatocytes, a sustained elevation of DAG with activation of PKC markedly increases the responsiveness to EGF. Mechanisms involving DAG and PKC seem to play a role in the comitogenic effects of various agents that bind to G protein-coupled receptors and activate the cells early in Gl, such as norepinephrine, angiotensin II, and vasopressin.

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Effects of EGF on the mass of inositol 1,4,5-trisphosphate and sn(1,2)-diacylglycerol in freshly isolated rat hepatocytes: Comparison with vasopressin

Cited by 13 publications

References 28 publications

Suppression of Epidermal Growth Factor-Induced Phospholipase C Activation Associated With Actin Rearrangement in Rat Hepatocytes in Primary Culture

Suppression of Epidermal Growth Factor-Induced Phospholipase C Activation Associated With Actin Rearrangement in Rat Hepatocytes in Primary Culture

Different mechanisms are involved in intracellular calcium increase by insulin-like growth factors 1 and 2 in articular chondrocytes: Voltage-gated calcium channels, and/or phospholipase C coupled to a pertussis-sensitive G-protein

Role of diacylglycerol (DAG) in hormonal induction of S phase in hepatocytes: The DAG-dependent protein kinase C pathway is not activated by epidermal growth factor (EGF), but is involved in mediating the enhancement of responsiveness to EGF by vasopressin, angiotensin II, and norepinephrine

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