scholarly journals Effects of protein kinase C activation on the regulation of the stimulus-secretion coupling in pancreatic β-cells

1989 ◽  
Vol 264 (1) ◽  
pp. 207-215 ◽  
Author(s):  
P Arkhammar ◽  
T Nilsson ◽  
M Welsh ◽  
N Welsh ◽  
P O Berggren
Keyword(s):  
Protein Kinase C ◽  
Membrane Potential ◽  
Protein Kinase ◽  
Beta Cells ◽  
Insulin Release ◽  
Phorbol Ester ◽  
Glucose Concentration ◽  
Secretory Response ◽  
Kinase C ◽  
Pkc Activation

Effects of protein kinase C (PKC) activation on the insulin-secretory process were investigated, by using beta-cell-rich suspensions obtained from pancreatic islets of obese-hyperglycaemic mice. The phorbol ester 12-O-tetradecanoylphorbol 13-acetate (TPA), which is known to activate PKC directly, the muscarinic-receptor agonist carbamoylcholine and high glucose concentration enhanced the phosphorylation of a specific 80 kDa PKC substrate in the beta-cells. At a non-stimulatory glucose concentration, 10 nM-TPA increased insulin release, although there were no changes in either the cytoplasmic free Ca2+ concentration ([Ca2+]i) or membrane potential, as measured with the fluorescent indicators quin-2 and bisoxonol respectively. At a stimulatory glucose concentration TPA caused a lowering in [Ca2+]i, whereas membrane potential was unaffected. Despite the decrease in [Ca2+]i, there was a large stimulation of insulin release. Addition of TPA lowered [Ca2+]i also in beta-cells stimulated by tolbutamide or high K+, although to a lesser extent than in those stimulated by glucose. There was no effect of TPA on either Ca2+ buffering or the ability of Ins(1,4,5)P3 to release Ca2+ in permeabilized beta-cells. However, the phorbol ester inhibited the rise in [Ca2+]i in response to carbamoylcholine, which stimulates the formation of InsP3, in intact beta-cells. Down-regulation of PKC influenced neither glucose-induced insulin release nor the increase in [Ca2+]i. Hence, although PKC activation is of no major importance in glucose-stimulated insulin release, this enzyme can serve as a modulator of the glucose-induced insulin-secretory response. Such a modulation involves mechanisms promoting both amplification of the secretory response and lowering of [Ca2+]i.

scholarly journals Regulation of Ras Signaling Specificity by Protein Kinase C

2001 ◽  
Vol 21 (8) ◽  
pp. 2650-2658 ◽  
Author(s):  
Gabriel Rusanescu ◽  
Takaya Gotoh ◽  
Xuejun Tian ◽  
Larry A. Feig
Keyword(s):  
Protein Kinase C ◽  
Growth Factor ◽  
Protein Kinase ◽  
Signaling Pathway ◽  
Phorbol Ester ◽  
Catalytic Domain ◽  
Ras Signaling ◽  
Nucleotide Exchange ◽  
Kinase C ◽  
Pkc Activation

ABSTRACT Ras proteins have the capacity to bind to and activate at least three families of downstream target proteins: Raf kinases, phosphatidylinositol 3 (PI 3)-kinase, and Ral-specific guanine nucleotide exchange factors (Ral-GEFs). We have previously shown that the Ras/Ral-GEF and Ras/Raf pathways oppose each other upon nerve growth factor stimulation, with the former promoting proliferation and the latter promoting cell cycle arrest. Moreover, the pathways are not activated equally. While the Ras/Raf/Erk signaling pathway is induced for hours, the Ras/Ral-GEF/Ral signaling pathway is induced for only minutes. Here we show that this preferential down-regulation of Ral signaling is mediated, at least in part, by protein kinase C (PKC). In particular, we show that PKC activation by phorbol ester treatment of cells blocks growth factor-induced Ral activation while it enhances Erk activation. Moreover, suppression of growth factor-induced PKC activation enhances and prolongs Ral activation. PKC does not influence the basal activity of the Ral-GEF designated Ral-GDS but suppresses its activation by Ras. Interestingly, Ras binding to the C-terminal Ras binding domain of Ral-GDS is not affected by PKC activity. Instead, suppression of Ral-GDS activation occurs through the region N terminal to the catalytic domain, which becomes phosphorylated in response to phorbol ester treatment of cells. These findings identify a role for PKC in determining the specificity of Ras signaling by its ability to differentially modulate Ras effector protein activation.

scholarly journals The biphasic stimulation of insulin secretion by bombesin involves both cytosolic free calcium and protein kinase C

1988 ◽  
Vol 253 (1) ◽  
pp. 193-202 ◽  
Author(s):  
S L Swope ◽  
A Schonbrunn
Keyword(s):  
Protein Kinase C ◽  
Insulin Secretion ◽  
Protein Kinase ◽  
Insulin Release ◽  
Secretory Response ◽  
Pancreatic Cell ◽  
Secretory Rate ◽  
Kinase C ◽  
Stimulate Insulin Release ◽  
Stimulation Of

Members of the bombesin family of peptides potently stimulate insulin release by HIT-T15 cells, a clonal pancreatic cell line. The response to bombesin consists of a large burst in secretion during the first 30 s, followed by a smaller elevation of the secretory rate, which persists for 90 min. The aim of this study was to identify the intracellular messengers involved in this biphasic secretory response. Addition of 100 nM-bombesin to cells for 20 s increased the cellular accumulation of [3H]diacylglycerol (DAG) by 40% and that of [3H]inositol monophosphate (InsP), bisphosphate (InsP2) and trisphosphate (InsP3) by 40%, 300%, and 800%, respectively. In contrast, cyclic AMP concentrations were unaffected. Bombesin stimulation of [3H]InsP3 formation was detected at 2 s, before the secretory response, which was not measurable until 5 s. Furthermore, the potency of bombesin to stimulate [3H]InsP3 generation (ED50 = 14 +/- 9 nM) agreed with its potency to stimulate insulin release (ED50 = 6 +/- 2 nM). Consistent with its effects on [3H]InsP3 formation, bombesin raised the intracellular free Ca2+ concentration [(Ca2+]i) from a basal value of 0.28 +/- 0.01 microM to a peak of 1.3 +/- 0.1 microM by 20 s. Chelation of extracellular Ca2+ did not abolish either the secretory response to bombesin or the rise in [Ca2+]i, showing that Ca2+ influx was not required. Although the Ca2+ ionophore ionomycin (100 nM) mimicked the [Ca2+]i response to bombesin, it did not stimulate secretion. However, pretreating cells with ionomycin decreased the effects of bombesin on both [Ca2+]i and insulin release, suggesting that elevation of [Ca2+]i was instrumental in the secretory response to this peptide. To determine the role of the DAG produced upon bombesin stimulation, we examined the effects of another activator of protein kinase C, the phorbol ester 12-O-tetradecanoylphorbol 13-acetate (TPA). TPA did not affect [Ca2+]i, but it increased insulin secretion after a 2 min lag. However, an immediate increase in secretion was observed when ionomycin was added simultaneously with TPA. These data indicate that the initial secretory burst induced by bombesin results from the synergistic action of the high [Ca2+]i produced by InsP3 and DAG-activated protein kinase C. However, activation of protein kinase C alone appears to be sufficient for a sustained secretory response.

Phorbol ester-induced prostaglandin production in piglet cortical astroglia

1994 ◽  
Vol 267 (1) ◽  
pp. R34-R37
Author(s):  
C. R. Thore ◽  
M. Nam ◽  
D. Busija
Keyword(s):  
Protein Kinase C ◽  
Protein Kinase ◽  
Phorbol Ester ◽  
Prostaglandin Production ◽  
Prostaglandin F2 Alpha ◽  
Kinase C ◽  
Baseline Levels ◽  
Pkc Activation ◽  
Cultured Glia ◽  
Activate Protein Kinase

We examined effects of phorbol 12,13-dibutyrate (PDB), which activates protein kinase C (PKC), on prostaglandin and leukotriene production in piglet cultured glia derived from cerebral cortex and white matter. Levels of prostaglandins were determined using enzyme immunoassay. Baseline levels in media for prostaglandin F2 alpha (PGF2 alpha) were 730 +/- 116 pg/ml and increased to 1,551 +/- 196 pg/ml at 10(-8) M PDB (P < 0.05) and to 2,182 +/- 190 pg/ml at 10(-6) M PDB (P < 0.05) (n = 16). Little or no 6-keto-prostaglandin F1 alpha, prostaglandin E2, or leukotrienes C4/D4 were produced. PGF2 alpha levels in media did not increase in the presence of the vehicle for PDB (dimethyl sulfoxide) or 4 alpha-phorbol 12,13-didecanoate (PDD; a phorbol ester that does not activate protein kinase C) or when indomethacin (10 micrograms/ml), quinacrine (10(-6) M), or isoquinolinylsulfonylmethyl piperazine (10(-4) M) (an inhibitor of PKC activation) was coadministered with PDB. We conclude that glia can be important contributors of prostaglandins to extracellular-cerebrospinal fluids where they could influence cerebrovascular tone, and that PDB probably increases prostaglandin production via liberation of arachidonic acid by PKC-induced activation of phospholipase A2.

Endotoxin-Induced Tissue Factor in Human Monocytes is Dependent upon Protein Kinase C Activation

1993 ◽  
Vol 70 (05) ◽  
pp. 800-806 ◽  
Author(s):  
C Ternisien ◽  
M Ramani ◽  
V Ollivier ◽  
F Khechai ◽  
T Vu ◽  
...  
Keyword(s):  
Protein Kinase C ◽  
Protein Kinase ◽  
Tissue Factor ◽  
Factor Ix ◽  
Transcriptional Level ◽  
Mrna Levels ◽  
Dependent Manner ◽  
Human Monocytes ◽  
Kinase C ◽  
Pkc Activation

SummaryTissue factor (TF) is a transmembrane receptor which, in association with factors VII and Vila, activates factor IX and X, thereby activating the coagulation protease cascades. In response to bacterial lipopolysaccharide (LPS) monocytes transcribe, synthesize and express TF on their surface. We investigated whether LPS-induced TF in human monocytes is mediated by protein kinase C (PKC) activation. The PKC agonists phorbol 12- myristate 13-acetate (PMA) and phorbol 12, 13 dibutyrate (PdBu) were both potent inducers of TF in human monocytes, whereas 4 alpha-12, 13 didecanoate (4 a-Pdd) had no such effect. Both LPS- and PMA-induced TF activity were inhibited, in a concentration dependent manner, by three different PKC inhibitors: H7, staurosporine and calphostin C. TF antigen determination confirmed that LPS-induced cell-surface TF protein levels decreased in parallel to TF functional activity under staurosporine treatment. Moreover, Northern blot analysis of total RNA from LPS- or PMA-stimulated monocytes showed a concentration-dependent decrease in TF mRNA levels in response to H7 and staurosporine. The decay rate of LPS-induced TF mRNA evaluated after the arrest of transcription by actinomycin D was not affected by the addition of staurosporine, suggesting that its inhibitory effect occurred at a transcriptional level. We conclude that LPS-induced production of TF and its mRNA by human monocytes are dependent on PKC activation.

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