Both activators and inhibitors of protein kinase C promote the inhibition of phenylephrine-induced [Ca2+]i oscillations in single intact rat hepatocytes

Berrie, Christopher P.; Cobbold, P H

doi:10.1016/0143-4160(95)90068-3

Cited by 21 publications

(15 citation statements)

References 43 publications

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“…Rapid desensitization of phosphoinositide hydrolysis is often only partial and accumulation of inositol 1,4,5-trisphosphate is biphasic (35)(36)(37). Moreover, levels of intracellular calcium have been shown to oscillate in the presence of hormone (38 -41), and PKC has been strongly implicated in these calcium oscillations (42)(43)(44)(45). Thus, studies of both receptor-promoted inositol 1,4,5-trisphosphate production and intracellular calcium levels are consistent with the concept that the role of PKC in regulating phosphoinositide hydrolysis may be more complex than mere signal inactivation.…”

Section: Resultsmentioning

confidence: 99%

Protein Kinase C Phosphorylates RGS2 and Modulates Its Capacity for Negative Regulation of Gα11 Signaling

Cunningham

Waldo

Hollinger

et al. 2001

Journal of Biological Chemistry

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RGS proteins (regulators of G protein signaling) attenuate heterotrimeric G protein signaling by functioning as both GTPase-activating proteins (GAPs) and inhibitors of G protein/effector interaction. RGS2 has been shown to regulate G␣ q -mediated inositol lipid signaling. Although purified RGS2 blocks PLC-␤ activation by the nonhydrolyzable GTP analog guanosine 5-O-thiophosphate (GTP␥S), its capacity to regulate inositol lipid signaling under conditions where GTPase-promoted hydrolysis of GTP is operative has not been fully explored. Utilizing the turkey erythrocyte membrane model of inositol lipid signaling, we investigated regulation by RGS2 of both GTP and GTP␥S-stimulated G␣ 11 signaling. Different inhibitory potencies of RGS2 were observed under conditions assessing its activity as a GAP versus as an effector antagonist; i.e. RGS2 was a 10 -20-fold more potent inhibitor of aluminum fluoride and GTP-stimulated PLC-␤t activity than of GTP␥S-promoted PLC-␤t activity. We also examined whether RGS2 was regulated by downstream components of the inositol lipid signaling pathway. RGS2 was phosphorylated by PKC in vitro to a stoichiometry of approximately unity by both a mixture of PKC isozymes and individual calcium and phospholipid-dependent PKC isoforms. Moreover, RGS2 was phosphorylated in intact COS7 cells in response to PKC activation by 4␤-phorbol 12␤-myristate 13␣-acetate and, to a lesser extent, by the P2Y 2 receptor agonist UTP. In vitro phosphorylation of RGS2 by PKC decreased its capacity to attenuate both GTP and GTP␥S-stimulated PLC-␤t activation, with the extent of attenuation correlating with the level of RGS2 phosphorylation. A phosphorylation-dependent inhibition of RGS2 GAP activity was also observed in proteoliposomes reconstituted with purified P2Y 1 receptor and G␣ q ␤␥. These results identify for the first time a phosphorylation-induced change in the activity of an RGS protein and suggest a mechanism for potentiation of inositol lipid signaling by PKC.A variety of hormone and neurotransmitter receptors transduce signals through heterotrimeric G proteins. In their inactive state, G proteins exist as heterotrimers consisting of ␣, ␤, and ␥ subunits with GDP bound to G␣. Upon agonist occupation, the receptor promotes GDP/GTP exchange, and the active GTP-bound G␣ subunit and G␤␥ dissociate to interact with target effector proteins. Signaling is terminated by the hydrolysis of GTP to GDP and the subsequent formation of the heterotrimer. Therefore, the magnitude and duration of signaling is determined by the length of time G␣ remains in the active GTP-bound conformation.A recently identified family of proteins termed RGS (regulators of G protein signaling) proteins interact directly with G␣ subunits to decrease the lifetime of the active GTP-bound complex (1-4). RGS proteins attenuate heterotrimeric G protein 1 signaling by functioning as both GTPase-activating proteins (GAPs) (5, 6) and inhibitors of G protein/effector interaction (6, 7). In vitro studies illustrate that RGS2 interacts with and fu...

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Section: Resultsmentioning

confidence: 99%

Protein Kinase C Phosphorylates RGS2 and Modulates Its Capacity for Negative Regulation of Gα11 Signaling

Cunningham

Waldo

Hollinger

et al. 2001

Journal of Biological Chemistry

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“…We are concerned with the intracellular pathway of these membrane events. Among the many effects of gangliosides on the cell metabolism, two deserve attention: (1) elevation by gangliosides of free cytoplasmic Ca 2+ concentration [Ca 2+ ] cyt ( see Discussion): and (2) influence of gangliosides on the protein kinase activity and accordingly on protein phosphorylation that can be mediated by Ca 2+ (Arakane et al, 1995;Berrie and Cobbold, 1995;Chan, 1989;Ferrari et al, 1995;Goldering et al, 1985;Kreuter et al, 1987;Nagai, 1995;Yates et al, 1989;Yu et al, 1994). Can [Ca 2+ ] cyt enhancement produce synchronization of protein synthesis oscillations?…”

Section: Introductionmentioning

confidence: 99%

Calcium ions as a factor of cell—cell cooperation in hepatocyte cultures

Brodsky

Zvezdina

Nechaeva

et al. 2003

Cell Biology International

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Ultradian protein synthesis rhythm was used as a marker of cell cooperation in synchronous dense and non-synchronous sparse hepatocyte cultures. Phenylephrine (2 microM, 2 min), an alpha (1)-adrenoreceptor agonist, which exerts [Ca(2+)](cyt)elevation from intracellular stores, affected protein synthesis rhythm in sparse cultures, i.e. initiated cooperative activity of the cells. The same effect was produced by 2,5-di(tertiary-butyl)-1,4-benzohydroquinone (10 microM, 2 min), which increases [Ca(2+)](cyt)by a non-receptor pathway. Pretreatment of dense cultures with the intracellular calcium chelator, 1,2-bis (2-aminophenoxy) ethane-N,N,N',N'- tetraacetic acid (acetoxymethyl) ester (BAPTA-AM) at 10-20 microM for, 30-60 min resulted in loss of the rhythm of protein synthesis, i.e. loss of cooperative activity between the cells. The medium conditioned by control dense cultures initiated rhythm in sparse cultures, whereas the conditioned medium of cultures pretreated with BAPTA-AM did not. [Ca(2+)](cyt)increase is known to occur with monosialoganglioside GM1 treatment. By ELISA estimation, the GM1 content in 3 h conditioned medium was similar in control dense cultures to that in cultures pretreated with BAPTA-AM. Bearing in mind data on the Ca(2+)-dependence of vesicle formation and shedding, the conditioned medium was separated by 150000 g centrifugation to supernatant containing monomers and micelles, and a pellet containing vesicular form of gangliosides. Only the latter initiated cooperative activity of the cells of sparse cultures. These cultures were also synchronized by GM1-containing liposomes at lower concentrations than added free GM1, 0.0003 and 0.06 microM respectively. Thus, GM1 and calcium are both involved in cell-cell synchronization. Activation of gangliosides, including GM1 and elevation of [Ca(2+)](cyt,)is known to lead to changes of protein kinase activity and protein phosphorylation resulting in modulation of oscillations in protein metabolism.

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“…Importantly, concurrent with Ca 2ϩ oscillations, repetitive translocation of PKC isoforms, both conventional and novel, to the plasma membrane have been reported (31,32), indicating cyclic activation of these enzymes. Furthermore, previous studies in hepatocytes have shown that both activation and inhibition of PKC can affect hormone-induced Ca 2ϩ oscillation kinetics (33,34).…”

Section: How Camentioning

confidence: 99%

“…2ϩ Mobilization-Previous studies have highlighted the complexity of PKC regulation of hormone-induced Ca 2ϩ oscillations in hepatocytes, reporting that both activators and inhibitors of PKC suppressed the responses to phenylephrine (33,34). We examined the effect of chronic down-regulation of conventional and novel PKCs (PKC-DR) by overnight treatment spike widths measured at half-peak height in phenylephrinestimulated control cells were very consistent, with a mean value of 24 Ϯ 0.6 s, whereas the spike durations in PKC-DR cells were almost 3-fold longer, with a width at half-peak height of 68 Ϯ 3.3 s (Fig.…”

Section: Pkc Down-regulation Perturbs Negative Feedback Inhibition Of Camentioning

confidence: 99%

Differential Regulation of Multiple Steps in Inositol 1,4,5-Trisphosphate Signaling by Protein Kinase C Shapes Hormone-stimulated Ca2+ Oscillations

Bartlett

Metzger

Gaspers

et al. 2015

Journal of Biological Chemistry

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Both activators and inhibitors of protein kinase C promote the inhibition of phenylephrine-induced [Ca2+]i oscillations in single intact rat hepatocytes

Cited by 21 publications

References 43 publications

Protein Kinase C Phosphorylates RGS2 and Modulates Its Capacity for Negative Regulation of Gα11 Signaling

Protein Kinase C Phosphorylates RGS2 and Modulates Its Capacity for Negative Regulation of Gα11 Signaling

Calcium ions as a factor of cell—cell cooperation in hepatocyte cultures

Differential Regulation of Multiple Steps in Inositol 1,4,5-Trisphosphate Signaling by Protein Kinase C Shapes Hormone-stimulated Ca2+ Oscillations

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