Identification of PKC-isoform-specific biological actions using pharmacological approaches

Interleukin-1 beta-induced expression of the prostaglandin E-receptor subtype EP3 in U373 astrocytoma cells depends on protein kinase C and nuclear factor-kappaB

Both interleukin-1beta (IL-1beta) and prostaglandins (PGs) are important mediators of physiological and pathophysiological processes in the brain. PGE2 exerts its effects by binding to four different types of PGE2 receptors named EP1-EP4. EP3 has found to be expressed in neurons, whereas expression of EP3 in glial cells has not been reported in the brain yet. Here we describe IL-1beta-induced EP3 receptor expression in human astrocytoma cells, primary astrocytes of rat and human origin and in rat brain. Using western blot, we found a marked up-regulation of EP3 receptor synthesis in human and rat primary glial cells. Intracerebroventricular administration of IL-1beta stimulated EP3 receptor synthesis in rat hippocampus. The analysis of involved signal transduction pathways by pathway-specific inhibitors revealed an essential role of protein kinase C and nuclear factor-kappaB in astrocytic IL-1beta-induced EP3 synthesis. Our data suggest that PGE2 signaling in the brain may be altered after IL-1beta release due to up-regulation of EP3 receptors. This might play an important role in acute and chronic conditions such as cerebral ischemia, traumatic brain injury, HIV-encephalitis, Alzheimer's disease and prion diseases in which a marked up-regulation of IL-1beta is followed by a prolonged increase of PGE2 levels in the brain.

Treatment for psychological dependence on morphine: usefulness of inhibiting NMDA receptor and its associated protein kinase in the nucleus accumbens

A growing body of evidence indicates that the mesolimbic dopaminergic (DAergic) pathway projecting from the ventral tegmental area (VTA) to the nucleus accumbens (N.Acc.) play a critical role in the initiation of psychological dependence on morphine. As well as DAergic system, the involvement of non-DAergic neurotransmitter and neuromodulator systems in rewarding effects induced by morphine has been recently documented. We previously demonstrated that the morphine-induced rewarding effect was dramatically suppressed by co-treatment with NMDA receptor antagonists, such as dizocilpine (MK-801), ketamine and ifenprodil. Therefore, we propose here that inhibiting the N-methyl-D-aspartate (NMDA) receptor and its associated protein kinase in the N.Acc. is useful for the treatment for psychological dependence on morphine. The following review provides a summary of recent our findings regarding the role of NMDA receptor and its associated protein kinase in the development of psychological dependence on morphine.

Signaling networks from Gβ1 subunit to transcription factors and actin remodeling via a membrane-located ERβ-related protein in the rapid action of daidzein in osteoblasts

Although estrogen replacement has been the main therapy to prevent and treat osteoporosis, there are concerns about its safety. Phytoestrogens have attracted attention to their potential impacts in osteoporosis prevention and treatment. Among phytoestrogens, the isoflavone daidzein (Dz) acts on transcription via the intracellular estrogen receptors (ER), mainly ERbeta, in osteoblasts, but mimics only part of the estrogen effects. Since estradiol also exerts rapid effects in osteoblasts, we investigated the multistep processes involved in the rapid actions of low (1-100 pM) doses of daidzein. Dz bound to a membrane moiety, related to ERbeta since the calcium response to Dz was blocked by an anti-ERbeta antibody directed against the C-terminus, but not by a double-stranded siRNA specific for ERbeta. This protein was coupled to a pertussis toxin (PTX)-sensitive Gbeta1 subunit whose transducer was PLC-beta2, which triggered a rapid (5 sec) mobilization of calcium from the endoplasmic reticulum. Dz phosphorylated within 15 sec ERK1/2 whose phosphorylation involved two routes: Gbeta1/PLC-beta2/PKC/c-Raf-1/MEK1/2 and Gbeta1/PI3K/cSrc/c-Raf-1/MEK1/2 as shown using several inhibitors. Dz induced rapid (1 min) changes in the actin cytoskeleton via the two routes. The rapid (20 sec) phosphorylation of Elk-1 and CREB by Dz involved Gbeta1 and ERK1/2. All the processes were insensitive to the estradiol antagonist ICI 182,780. In conclusion, the rapid effects of Dz seem to be biologically relevant for the function of osteoblast in bone since the isoflavone activates transcription factors linked to early genes controlling cellular proliferation and differentiation, and modulates actin cytoskeleton which controls cell adhesion, division, or secretion.

Angiotensin type 1 receptor is linked to inhibition of nitric oxide production in pulmonary endothelial cells

We previously demonstrated that angiotensin II (Ang II) stimulates an increase in nitric oxide synthase (NOS) mRNA levels, eNOS protein expression and NO production via the type 2 (AT2) receptor, whereas signaling via the type 1 (AT1) receptor negatively regulates NO production in bovine pulmonary artery endothelial cells (BPAECs). In the present study, we investigated the components of the AT1 receptor-linked signaling pathway(s) that are involved in the downregulation of eNOS protein expression in BPAECs. Treatment of BPAECs with either AT1 receptor antagonists or an anti-AT1 receptor antibody induced eNOS protein expression. Furthermore, intracellular delivery of GP-Antagonist-2A, an inhibitor of Galphaq proteins, and treatment of BPAECs with U73122, a phosphatidylinositol-phospholipase C (PLC)-specific inhibitor, enhanced eNOS protein expression. Treatment of BPAECs with the cell-permeable calcium chelator, BAPTA/AM, increased eNOS protein expression at 8 h, while increasing intracellular calcium with either thapsigargin or A23187 prevented Ang II-induced eNOS protein expression. Phorbol myristate acetate (PMA), a protein kinase C (PKC) activator, completely prevented Ang II-stimulated eNOS protein expression at 8 h, whereas depletion of PKC by long-term treatment with PMA, induced eNOS protein expression. Treatment of BPAECs with a PKCalpha-specific inhibitor or transfection of BPAECs with an anti-PKCalpha neutralizing antibody stimulated eNOS protein expression. Conversely, rottlerin, a PKCdelta specific isoform inhibitor had no effect on basal or Ang II-stimulated eNOS protein expression. Moreover, treatment of BPAECs with U73122, BAPTA/AM and PKCalpha-specific inhibitors increased NO production at 8 h. In conclusion, Ang II downregulates eNOS protein expression via an AT1 receptor-linked pathway involving Galphaq/PLC/calcium/PKCalpha signaling pathway in BPAECs.

Co-expression/co-location of S100 proteins (S100B, S100A1 and S100A2) and protein kinase C (PKC-beta, -eta and -zeta) in a rat model of cerebral basilar artery vasospasm

OBJECT

The cellular events leading to cerebral vasospasm after subarachnoid haemorrhages (SAH) involve a number of members of the protein kinase C (PKC) family. However, whereas calcium is thought to play a number of major roles in the pathophysiology of SAH, a number of PKCs function independently of calcium. We recently emphasized the potential role of the calcium-binding S100 proteins in a 'double haemorrhage' rat model of SAH-induced vasospasm. A number of S100 proteins are known to interfere directly with PKC, or indirectly with PKC substrates. We therefore investigated whether specific S100 proteins and PKCs are co-expressed/co-located in a rat model of SAH-induced vasospasm.

METHODS AND RESULTS

SAH-induced vasospasm in rats (by means of a double cisternal injection of autologous blood from a rat femoral artery) distinctly modified the expression levels of calcium-dependent PKC-alpha and PKC-beta and calcium-independent PKC-eta and PKC-zeta in endothelial and smooth-muscle cells. The RNA levels of these four PKC isotypes were determined by quantitative RT-PCR. The present study reveals that, in endothelial cells, the S100B expression/location correlate well with those of PKC-eta, and those of S100A1 with PKC-beta. In smooth-muscle cells S100A2 expression/location correlate with those of PKC-eta, and those of S100B with PKC-zeta.

CONCLUSION

The present data argue in favour of a joint action of the S100 protein network and the PKC signalling pathway during cerebral vasospasm.

The Role of Protein Kinase C in Cerebral Ischemic and Reperfusion Injury

Background and Purpose— Stroke is a leading cause of disability and death in the United States, yet limited therapeutic options exist. The need for novel neuroprotective agents has spurred efforts to understand the intracellular signaling pathways that mediate cellular response to stroke. Protein kinase C (PKC) plays a central role in mediating ischemic and reperfusion damage in multiple tissues, including the brain. However, because of conflicting reports, it remains unclear whether PKC is involved in cell survival signaling, or mediates detrimental processes.

Summary of Review— This review will examine the role of PKC activity in stroke. In particular, we will focus on more recent insights into the PKC isozyme-specific responses in neuronal preconditioning and in ischemia and reperfusion-induced stress.

Conclusion— Examination of PKC isozyme activities during stroke demonstrates the clinical promise of PKC isozyme-specific modulators for the treatment of cerebral ischemia.

Conventional protein kinase C isoforms mediate neuroprotection induced by phorbol ester and estrogen

Rapid signal transduction pathways play a prominent role in mediating neuroprotective actions of estrogen in the CNS. We have previously shown that estrogen-induced neuroprotection of primary cerebrocortical neurons from beta-amyloid peptide (Abeta) toxicity depends on activation of protein kinase C (PKC). PKC activation with phorbol-12-myristate-13-acetate (PMA) also provides neuroprotection in this paradigm. Because the PKC family includes several isoforms that have opposing roles in regulating cell survival, we sought to identify which PKC isoforms contribute to neuroprotection induced by PMA and estrogen. We detected protein expression of multiple PKC isoforms in primary neuron cultures, including conventional (alpha, betaI, betaII), novel (delta, epsilon, theta) and atypical (zeta, iota/lambda) PKC. Using a panel of isoform-specific peptide inhibitors and activators, we find that novel and atypical PKC isoforms do not participate in the mechanism of either PMA or estrogen neuroprotection. In contrast, a selective peptide activator of conventional PKC isoforms provides dose-dependent neuroprotection against Abeta toxicity. In addition, peptide inhibitors of conventional, betaI, or betaII PKC isoforms significantly reduce protection afforded by PMA or 17beta-estradiol. Taken together, these data provide evidence that conventional PKC isoforms mediate phorbol ester and estrogen neuroprotection of cultured neurons challenged by Abeta toxicity.

Role of PKC-α,γ isoforms in regulation of c-Fos and TH expression after naloxone-induced morphine withdrawal in the hypothalamic PVN and medulla oblongata catecholaminergic cell groups

We previously demonstrated that morphine withdrawal induced hyperactivity of the hypothalamus-pituitary-adrenocortical axis by activation of noradrenergic pathways innervating the hypothalamic paraventricular nucleus (PVN), as evaluated by Fos expression and corticosterone release. The present study was designed to investigate the role of protein kinase C (PKC) in this process by estimating changes in PKCalpha and PKCgamma immunoreactivity, and whether pharmacological inhibition of PKC would attenuate morphine withdrawal-induced c-Fos expression and changes in tyrosine hydroxylase (TH) immunoreactivity levels in the PVN and nucleus tractus solitarius/ ventrolateral medulla (NTS/VLM). Dependence on morphine was induced in rats by 7 day s.c. implantation of morphine pellets. Morphine withdrawal was induced on day 8 by an injection of naloxone. The protein levels of PKCalpha and gamma were significantly down-regulated in the PVN and NTS/VLM from the morphine-withdrawn rats. Morphine withdrawal induced c-Fos expression in the PVN and NTS/VLM, indicating an activation of neurons in those nuclei. TH immunoreactivity was increased in the NTS/VLM after induction of morphine withdrawal, whereas there was a decrease in TH levels in the PVN. Infusion of calphostin C, a selective protein kinase C inhibitor, produced a reduction in the morphine withdrawal-induced c-Fos expression. Additionally, the changes in TH levels in the PVN and NTS/VLM were significantly modified by calphostin C. The present results suggest that activated PKC in the PVN and catecholaminergic brainstem cell groups may be critical for the activation of the hypothalamic-pituitary adrenocortical axis in response to morphine withdrawal.

Modulation of the (Na(+)+K+)ATPase activity by Angiotensin-(1-7) in MDCK cells

In the present paper the effect of Ang-(1-7) on the distal tubule (Na(+)+K+)ATPase activity was evaluated by using MDCK cells as a model. Confluent cell monolayers were incubated with increasing concentrations of Ang-(1-7) for 30 min. Thereafter, the (Na(+)+K+)ATPase activity was evaluated and a dose-dependent (from 10(-12) to 10(-7) M) inhibition was observed. The maximal inhibitory effect (54%) was reached at the concentration of 10(-8) M. The inhibitory effect of Ang-(1-7) was not affected by the AT2 receptor selective antagonist PD123319 (from 10(-10) to 10(-7) M) but was blocked in a dose-dependent manner by the AT1 receptor selective antagonists losartan (10(-10) M), candesartan (10(-17) M), irbesartan (2 x 10(-12) M) and telmisartan (2 x 10(-16) M). The signaling pathway triggered by stimulation of the AT(1) receptor was also investigated. The PI-phospholipase C (PI-PLC) inhibitor U73122 (5 x 10(-8) M) blocked the inhibitory effect elicited by Ang-(1-7). Involvement of the protein kinase C (PKC) was evidenced by the sensitivity of the inhibitory effect of Ang-(1-7) to calphostin C (6.32 x 10(-7) M) and the lack of additive effects when the cells were co-incubated with Ang-(1-7) and 3.2 x 10(-8) M PMA. Altogether, these results demonstrate that Ang-(1-7) inhibits the (Na(+)+K+)ATPase activity of the prototypic distal tubule cell MDCK through the AT1 receptor-mediated stimulation of PI-PLC/PKC signaling pathway.

Ruboxistaurin, a protein kinase C beta inhibitor, as an emerging treatment for diabetes microvascular complications

OBJECTIVE

To review current clinical data regarding the pharmacologic actions of ruboxistaurin (LY333531) mesylate, an inhibitor of protein kinase C (PKC) beta, and its role to potentially reduce the development and/or the progression of diabetic microvascular complications.

DATA SOURCES

Primary literature was obtained via a MEDLINE search (1966-August 2004) and through review of pertinent abstracts and presentations at major medical meetings.

STUDY SELECTION AND DATA EXTRACTION

Literature relevant to PKC physiology, the pharmacokinetics of ruboxistaurin, and data evaluating the use of ruboxistaurin in treating diabetic microvascular complications in human and relevant animal models was reviewed.

DATA SYNTHESIS

PKC is part of a group of intracellular signaling molecules activated in response to various specific hormonal, neuronal, and growth factor stimuli. Hyperglycemia leads to PKC beta 1 and 2 isoform activation, which experimentally has been shown to contribute to the development and progression of diabetic microvascular complications (retinopathy, nephropathy, neuropathy) through various biochemical mechanisms. Animal and/or human studies using ruboxistaurin mesylate, a novel, highly selective inhibitor of PKC beta, have shown delay in the progression and, in some cases, reversal of diabetic retinopathy, nephropathy, and neuropathy.

CONCLUSIONS

Ruboxistaurin mesylate, by inhibiting excessive activation of certain PKC isoforms, has the potential to reduce the burden of microvascular complications for patients with diabetes.

Inhibition of protein kinases C prevents murine cytomegalovirus replication

For successful establishment of infection and initiation of the replication cycle, murine cytomegalovirus (MCMV) utilizes cellular structures and functions, including cell-membrane penetration, capsid dismantling and cytosolic transport of viral DNA into the nucleus. These early events of MCMV infections are dependent on cellular regulatory mechanisms, primarily protein phosphorylation. In the present study, protein kinase inhibitors were used to explore the role of protein phosphorylation mediated by protein kinases C (PKCs) in the very early events of MCMV infection. Inhibitory effects were determined by immunofluorescence and Western blot analysis of MCMV IE1 and E1 protein expression and by production of infectious virions in cell culture. It was found that H-7, a broadly specific inhibitor of cellular protein kinases, prevented virus replication in a dose-dependent and reversible manner, and that the block in replication occurred very early in infection. More specific PKC inhibitors (sangivamycin, calphostin C and bisindolylmaleimide II), Ca(2+)/calmodulin inhibitors (EDTA and W7) and phorbol esters (PMA) were used to dissect PKC-subclass contribution in the very early events of MCMV replication. The results indicate that the role of diacylglycerol/phorbol ester-dependent but calcium-independent PKCs is essential for establishment of MCMV infection in the host cell, starting at a very early stage of infection.

Specific modulation of Na+ channels in hippocampal neurons by protein kinase C epsilon

Acetylcholine binding to muscarinic acetylcholine receptors activates G-proteins, phospholipase C, and protein kinase C (PKC), which phosphorylates brain Na+ channels and reduces peak Na+ current in hippocampal neurons. Because multiple PKC isozymes with different regulatory properties are expressed in hippocampal neurons, we investigated which ones are responsible for mediating this effect. The diacylglycerol analog oleoylacetylglycerol (OAG) reduced the amplitude of Na+ current in dissociated mouse hippocampal neurons by 28.5 +/- 5.3% (p < 0.01). The reduction of peak Na+ current was similar with Ca2+-free internal solution and in 92 nm internal Ca2+, suggesting that calcium-dependent, conventional PKC isozymes were unlikely to mediate this response. Gö6976, which inhibits conventional PKC isozymes, reduced the effect of PKC activators only slightly, whereas rottlerin, which inhibits PKCdelta preferentially at 5 microm, had no effect. Ro-31-8425 (20 nm), which inhibits conventional PKC isozymes, did not reduce the response to OAG. However, higher concentrations of Ro-31-8425 (100 nm or 1 microm) that inhibit novel PKC isozymes effectively blocked OAG inhibition of Na+ current. Inclusion of a selective PKCepsilon-anchoring inhibitor peptide (PKCepsilon-I) in the recording pipette prevented the reduction of peak Na+ current by OAG, whereas an anchoring inhibitor peptide specific for PKCbeta and an inactive scrambled PKCepsilon-I peptide had no effect. In addition, OAG had no effect on Na+ current in hippocampal neurons from PKCepsilon null mice. Overall, our data from four experimental approaches indicate that anchored PKCepsilon is the isozyme responsible for PKC-mediated reduction of peak Na+ currents in mouse hippocampal neurons.

Synergistic effect of prostaglandin F2alpha and cyclic AMP on glucose transport in 3T3-L1 adipocytes

The combined effect of prostaglandin F2alpha (PGF2alpha) and cAMP on glucose transport in 3T3-L1 adipocytes was examined. In cells pretreated with PGF2alpha and 8-bromo cAMP for 8 h, a synergy between these two agents on glucose uptake was found. Insulin-stimulated glucose transport, on the other hand, was only slightly affected. The synergistic effect of these two agents was suppressed in the presence of cycloheximide and actinomycin D. In concord, immunoblot and Northern blot analyses revealed that GLUT1 protein and mRNA levels were both increased in cells pretreated with both PGF2alpha and 8-bromo cAMP, greater than the additive effect of each agent alone. The synergistic action of PGF2alpha with 8-bromo cAMP to enhance glucose transport was inhibited by GF109203X, a selective protein kinase C (PKC) inhibitor. In addition, in cells depleted of diacylglycerol-sensitive PKC by prolonged treatment with 4beta-phorbol 12beta-myristate 13alpha-acetate, a PKC activator, the synergistic effects of PGF2alpha and 8-bromo cAMP on glucose transport and GLUT1 mRNA accumulation were both abolished. Taken together, these results indicate that PGF2alpha may act with cAMP in a synergistic way to increase glucose transport, probably through enhanced GLUT1 expression by a PKC-dependent mechanism.

Evidence that protein kinase Calpha interacts with and regulates the glial glutamate transporter GLT-1

Many of the sodium-dependent neurotransmitter transporters are rapidly (within minutes) regulated by protein kinase C (PKC), with changes in activity being correlated with changes in transporter trafficking to or from the plasma membrane. Our recent studies suggest that one of the classical subtypes of PKC, PKCalpha, may selectively mediate redistribution of the neuronal glutamate transporter, excitatory amino acid carrier (EAAC)1, and show that PKCalpha can be co-immunoprecipitated with EAAC1. When the glial glutamate transporter GLT-1a is transfected into C6 glioma cells, this transporter is internalized in response to activation of PKC, but the PKC subtype involved in this regulation is unknown. In the present study, expression of the phorbol ester-activated subtypes of PKC was examined in C6 glioma transfected with GLT-1. Of the classical subtypes, only PKCalpha was detected, and of the non-classical subtypes, PKCdelta and PKCepsilon were detected. In this system, phorbol ester-dependent internalization of GLT-1 was blocked by a general inhibitor of PKCs (bisindolylmaleimide II) and by concentrations of Gö6976 that selectively block classical PKCs, but not by an inhibitor of PKCdelta (rottlerin). PKCalpha immunoreactivity was found in GLT-1 immunoprecipitates obtained from transfected C6 cells and from crude rat brain synaptosomes, a milieu that better mimics in vivo conditions. The amount of PKCalpha in both types of immunoprecipitate was modestly increased by phorbol ester, and this increase was blocked by a PKC antagonist. These studies suggest that PKCalpha may be required for the regulated redistribution of GLT-1.

PI3K and PKC contribute to membrane depolarization mediated by alpha2-adrenoceptors in the canine isolated mesenteric vein

BACKGROUND

Norepinephrine (NE), a classic neurotransmitter in the sympathetic nervous system, induces vasoconstriction of canine isolated mesenteric vein that is accompanied by a sustained membrane depolarization. The mechanisms underlying the NE-elicited membrane depolarization remain undefined. In the present study we hypothesized that phosphatidylinositol 3-kinase (PI3K) and protein kinase C (PKC) are involved in the electrical field stimulation (EFS)-induced slow membrane depolarization (SMD) in canine isolated mesenteric vein. EFS (0.1-2 Hz, 0.1 ms, 15V, 10 s)-induced changes in the membrane potential were recorded with a conventional intracellular microelectrode technique and evaluated in the absence and presence of inhibitors of neuronal activity, alpha-adrenoceptors, membrane ion channels, PI3K, inositol 1,4,5-triphosphate (InsP3) receptors, and PKC. Activation of PI3Kgamma and PKCzeta in response to exogenous NE and clonidine in the absence and presence of receptor and kinase inhibitors were also determined.

RESULTS

Contractile responses to NE and clonidine (0.05 - 10 microM) were significantly diminished in the presence of yohimbine (0.1 microM). Exogenous NE (0.1 microM) and clonidine (1 microM) elicited SMD. The resting membrane potential of canine mesenteric vein smooth muscle cells was -68.8 +/- 0.8 mV. EFS elicited a biphasic depolarization comprised of excitatory junction potentials and SMD that are purinergic and adrenergic in nature, respectively. The magnitude of the SMD in response to EFS at 0.5 Hz was 9.4 +/- 0.7 mV. This response was reduced by 65-98% by the fast Na+ channel inhibitor tetrodotoxin (1 microM), by the inhibitor of N-type Ca2+ channels omega-conotoxin GVIA (5 nM), the non-selective alpha-adrenoceptor blocker phentolamine (1 microM), the selective alpha2-adrenoceptor blocker yohimbine (0.1 microM), the ion channel inhibitors niflumic acid (NFA, 100 microM), 5-nitro-2-(3-phenylpropylamino) benzoic acid (NPPB, 30 microM), 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS, 200 microM), and Gd3+ (30 microM), and the PI3K inhibitors wortmannin (100 nM) and LY-294002 (10 microM). The SMD remained unchanged in the presence of the L-type Ca2+ channel blocker nicardipine (1 microM) and the InsP3 receptor blockers 2-aminoethoxydiphenylborate (2APB, 50 microM) and xestospongin C (3 microM). The inhibitor of PKC chelerythrine (1 microM), but not calphostin C (10 microM), diminished the SMD. Exogenous NE and clonidine (1 microM each) activated both PI3Kgamma and PKCzeta, and the activation of these kinases was abolished by preincubation of tissue with the alpha2-adrenoceptor blocker yohimbine.

CONCLUSION

Neuronally-released NE stimulates smooth muscle alpha2-adrenoceptors and activates PI3K and atypical PKC in the canine mesenteric vein. Events downstream of PKC lead to SMD and vasoconstriction. This represents a novel pathway for NE-induced membrane depolarization in a vascular smooth muscle preparation.

Serotonin via 5-HT7 receptors activates p38 mitogen-activated protein kinase and protein kinase C epsilon resulting in interleukin-6 synthesis in human U373 MG astrocytoma cells

Serotonin [5-hydroxytryptamine (5-HT)] is a widely distributed neurotransmitter which is involved in neuroimmunomodulatory processes. Previously, it has been demonstrated that 5-HT may induce interleukin (IL)-6 expression in primary rat hippocampal astrocytes. The present study was undertaken to investigate the molecular pathways underlying this induction of IL-6 synthesis. As a model system, we used the human astrocytoma cell line U373 MG, which synthesizes IL-6 upon stimulation with various inducers. 5-HT dose- and time-dependently induced IL-6 protein synthesis. We identified several 5-HT receptors to be expressed on U373 MG cells, including the 5-HT1D, 5-HT2A, 5-HT3 and 5-HT7 receptors. In this report, we show that the 5-HT-induced IL-6 release is mediated by the 5-HT7 receptor based on several agonist/antagonists that were used. 5-HT-induced IL-6 synthesis is inhibited by the partially selective 5-HT7 receptor antagonist, pimozide, and the selective antagonist SB269970. Furthermore, IL-6 synthesis was induced by the 5-HT7 receptor agonist carboxamidotryptamin. In addition, we found p38 MAPKs and protein kinase C (PKC) epsilon to be involved in 5-HT-induced IL-6 synthesis as specific inhibitors of these enzymes (SB202190 and RO-31-8425, respectively) blocked 5-HT-induced IL-6 synthesis. Furthermore, 5-HT mediated the phosphorylation of both p38 MAPK as well as the PKC epsilon isoform. The p42/44 MAPKs, however, were not involved in 5-HT-induced IL-6 synthesis. This study shows, for the first time, a central role of 5-HT7 receptor linked to p38 MAPK and PKC epsilon for the induction of cytokine synthesis in astrocytic cells.

Upregulation of PKC-delta contributes to antiestrogen resistance in mammary tumor cells

Acquired resistance to tamoxifen (Tam) in breast cancer patients is a serious therapeutic problem. We have previously reported that protein kinase C-delta (PKC-delta) plays a major role in estrogen (E2)-mediated cell proliferation. To determine if PKC-delta is one of the major alternate signaling pathways that supports cell growth in the presence of Tam, we determined the levels of PKC isoforms in four different models of antiestrogen-resistant cells. Three out of four antiestrogen resistance cell lines (Tam/MCF-7, ICI/MCF-7 and HER-2/MCF-7) expressed significantly high levels of both total and activated PKC-delta levels compared to sensitive cells. Estrogen receptor (ER) alpha content and function are maintained in all the antiestrogen-resistant cell lines. Overexpressing active PKC-delta in Tam-sensitive MCF-7 cells (PKC-delta/MCF-7) led to Tam resistance both in vitro and in vivo. Inhibition of PKC-delta by rottlerin (a relatively specific inhibitor of PKC-delta) or siRNA significantly inhibited estrogen- and Tam-induced growth in antiestrogen-resistant cells. PKC-delta levels are significantly higher in Tam-resistant tumors compared to Tam-sensitive tumors in xenograft model (P<0.05). Taken together, these data suggest that PKC-delta plays a major role in antiestrogen resistance in breast tumor cells and thus provides a new target for treatment.

Hypotonic shock mediation by p38 MAPK, JNK, PKC, FAK, OSR1 and SPAK in osmosensing chloride secreting cells of killifish opercular epithelium

Hypotonic shock rapidly inhibits Cl(-) secretion by chloride cells, an effect that is osmotic and not produced by NaCl-depleted isosmotic solutions, yet the mechanism for the inhibition and its recovery are not known. We exposed isolated opercular epithelia, mounted in Ussing chambers, to hypotonic shock in the presence of a variety of chemicals: a general protein kinase C (PKC) inhibitor chelerythrine, Gö6976 that selectively blocks PKC alpha and beta subtypes, H-89 that blocks PKA, SB203580 that blocks p38 mitogen-activated protein kinase (MAPK), as well as serine/threonine protein phosphatase (PP1 and 2A) inhibitor okadaic acid, and finally tamoxifen, a blocker of volume-activated anion channels (VSOAC). Chelerythrine has no effect on hypotonic inhibition but blocked the recovery, indicating PKC involvement in stimulation. Gö6976 had little effect, suggesting that PKC alpha and PKC beta subtypes are not involved. H-89 did not block hypotonic inhibition but decreased the recovery, indicating PKA may be involved in the recovery and overshoot (after restoration of isotonic conditions). SB203580 significantly enhanced the decrease in current by hypotonic shock, suggesting an inhibitory role of p38 MAPK in the hypotonic inhibition. Okadaic acid increased the steady state current, slowed the hypotonic inhibition but made the decrease in current larger; also the recovery and overshoot were completely blocked. Hypotonic stress rapidly and transiently increased phosphorylated p38 MAPK (pp38) MAPK (measured by western analysis) by eightfold at 5 min, then more slowly again to sevenfold at 60 min. Hypertonic shock slowly increased p38 by sevenfold at 60 min. Phosphorylated JNK kinase was increased by 40-50% by both hypotonic and hypertonic shock and was still elevated at 30 min in hypertonic medium. By immunoblot analysis it was found that the stress protein kinase (SPAK) and oxidation stress response kinase 1 (OSR1) were present in salt and freshwater acclimated fish with higher expression in freshwater. By immunocytochemistry, SPAK, OSR1 and phosphorylated focal adhesion kinase (pFAK) were colocalized with NKCC at the basolateral membrane. The protein tyrosine kinase inhibitor genistein (100 micromol l(-1)) inhibited Cl(-) secretion that was high, increased Cl(-) secretion that was low and reduced immunocytochemical staining for phosphorylated FAK. We present a model for rapid control of CFTR and NKCC in chloride cells that includes: (1) activation of NKCC and CFTR via cAMP/PKA, (2) activation of NKCC by PKC, myosin light chain kinase (MLCK), p38, OSR1 and SPAK, (3) deactivation of NKCC by hypotonic cell swelling, Ca(2+) and an as yet unidentified protein phosphatase and (4) involvement of protein tyrosine kinase (PTK) acting on FAK to set levels of NKCC activity.

Malondialdehyde-acetaldehyde adducts decrease bronchial epithelial wound repair

Most people who abuse alcohol are cigarette smokers. Previously, we have shown that malondialdehyde, an inflammation product of lipid peroxidation, and acetaldehyde, a component of both ethanol metabolism and cigarette smoke, form protein adducts that stimulate protein kinase C (PKC) activation in bronchial epithelial cells. We have also shown that PKC can regulate bronchial epithelial cell wound repair. We hypothesize that bovine serum albumin adducted with malondialdehyde and acetaldehyde (BSA-MAA) decreases bronchial epithelial cell wound repair via binding to scavenger receptors on bronchial epithelial cells. To test this, confluent monolayers of bovine bronchial epithelial cells were grown in serum-free media prior to wounding the cells. Bronchial epithelial cell wound closure was inhibited in a dose-dependent manner (up to 60%) in the presence of BSA-MAA than in media treated cells (Laboratory of Human Carcinogenesis [LHC]-9-Roswell Park Memorial Institute [RPMI]). The specific scavenger receptor ligand, fucoidan, also stimulated PKC activation and decreased wound repair. Pretreatment with fucoidan blocked malondialdehyde-acetaldehyde binding to bronchial epithelial cells. When bronchial epithelial cells were preincubated with a PKC alpha inhibitor, Gö 6976, the inhibition of wound closure by fucoidan and BSA-MAA was blocked. Western blot demonstrated the presence of several scavenger receptors on bronchial epithelial cell membranes, including SRA, SRBI, SRBII, and CD36. Scavenger receptor-mediated activation of PKC alpha may function to reduce wound healing under conditions of alcohol and cigarette smoke exposure where malondialdehyde-acetaldehyde adducts may be present.

IL-6 expression induced by adenosine A2b receptor stimulation in U373 MG cells depends on p38 mitogen activated kinase and protein kinase C

Adenosine binds to a class of G-protein coupled receptors, which are further distinguished as A(1), A(2a), A(2b) and A(3) adenosine receptors. As we have shown earlier, the stable adenosine analogue NECA (N6-(R)-phenylisopropyladenosine) stimulates IL-6 expression in the human astrocytoma cell line U373 MG via the A(2b) receptor. The mechanism by which NECA promotes astrocytic IL-6 expression has not been identified. By using various inhibitors of signal transduction, we found that p38 mitogen-activated protein kinases (MAPK) activation (inhibitor SB202190), but not extracellular signal-regulated kinase (ERK) (PD98059) and c-jun N-terminal kinase (JNK)(SP600125), is essential in the NECA-induced signalling cascade that leads to the increase in IL-6 synthesis in U373 MG cells. Results obtained with protein kinase C (PKC) inhibitors that have different substrate specificities, indicated that the PKC delta and epsilon isoforms are also involved in adenosine receptor A(2b) dependent upregulation of IL-6 expression. This is supported by the fact that NECA induced the activation of PKC delta and epsilon in U373 MG cells.

Introduction of hyperglycemia and dyslipidemia in the pathogenesis of diabetic vascular complications

Hyperglycemia and dyslipidemia are significant and independent risk factors for the vascular complications in patients with diabetes. They have been suggested to cause cardiovascular pathologic changes in diabetic states through the following molecular mechanisms: formation and accumulation of advanced glycation end products; increased oxidative stress; activation of protein kinase C pathway; increased activity of hexosamine pathway; and vascular inflammation and the impairment of insulin action in the vascular tissues.

Classical protein kinase C(s) regulates targeting of synaptotagmin IX to the endocytic recycling compartment

Neuronal and non-neuronal tissues show distinctly different intracellular localization of synaptotagmin (Syt) homologues. Therefore, cell type-specific mechanisms are likely to direct Syt homologues to their final cellular destinations. Syt IX localizes to dense core vesicles in PC12 cells. However, in the rat basophilic leukemia (RBL-2H3) mast cell line, as well as in CHO cells, Syt IX is localized at the endocytic recycling compartment (ERC). We show that targeting of Syt IX to the ERC involves constitutive trafficking to the plasma membrane followed by internalization and transport to the ERC. We further show that internalization from the plasma membrane and delivery to the ERC are dependent on phosphorylation by Ca(2+)-dependent protein kinase Calpha or beta. As such, correct targeting of Syt IX is facilitated by the phorbol ester TPA but prevented by the cPKC inhibitor Go 6976.

Rottlerin sensitizes glioma cells to TRAIL-induced apoptosis by inhibition of Cdc2 and the subsequent downregulation of survivin and XIAP

In the tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-resistant glioma cells, treatment with TRAIL in combination with subtoxic doses of rottlerin induced rapid apoptosis. While the proteolytic processing of procaspase-3 by TRAIL was partially blocked in these cells, treatment with rottlerin efficiently recovered TRAIL-induced activation of caspases. Treatment with rottlerin significantly decreased Cdc2 activity through the downregulation of cyclin A, cyclin B, and Cdc2 proteins, whereas the sensitizing effect of rottlerin on TRAIL-induced apoptosis was independent of PKCdelta activity. Furthermore, treatment with rottlerin downregulated the protein levels of survivin and X-chromosome-linked IAP (XIAP), two major caspase inhibitors. Forced expression of Cdc2 together with cyclin B attenuated rottlerin-potentiated TRAIL-induced apoptosis by over-riding the rottlerin-mediated downregulation of survivin and XIAP protein levels. Taken together, inhibition of Cdc2 activity and the subsequent downregulation of survivin and XIAP by subtoxic doses of rottlerin contribute to amplification of caspase cascades, thereby overcoming resistance of glioma cells to TRAIL-mediated apoptosis. Since rottlerin can sensitize Bcl-2- or Bcl-xL-overexpressing glioma cells but not human astrocytes to TRAIL-induced apoptosis, this combined treatment may offer an attractive strategy for safely treating resistant gliomas.

Candidate genes for antidepressant response to selective serotonin reuptake inhibitors

Selective serotonin reuptake inhibitors (SSRIs) can safely and successfully treat major depression, although a substantial number of patients benefit only partially or not at all from treatment. Genetic polymorphisms may play a major role in determining the response to SSRI treatment. Nonetheless, it is likely that efficacy is determined by multiple genes, with individual genetic polymorphisms having a limited effect size. Initial studies have identified the promoter polymorphism in the gene coding for the serotonin reuptake transporter as moderating efficacy for several SSRIs. The goal of this review is to suggest additional plausible polymorphisms that may be involved in antidepressant efficacy. These include genes affecting intracellular transductional cascades; neuronal growth factors; stress-related hormones, such as corticotropin-releasing hormone and glucocorticoid receptors; ion channels and synaptic efficacy; and adaptations of monoaminergic pathways. Association analyses to examine these candidate genes may facilitate identification of patients for targeted alternative therapies. Determining which genes are involved may also assist in identifying future, novel treatments.

Involvement of PKCα/β in TLR4 and TLR2 dependent activation of NF-κB

Protein kinase C (PKC)alpha/beta dependent signaling events downstream of TLR4 or TLR2 were investigated in neutrophils stimulated with LPS or PGN. Pretreatment of neutrophils with the structurally distinct PKCalpha/beta inhibitors Go6976 or GF109203X decreased nuclear translocation of NF-kappaB and production of the proinflammatory cytokine TNF-alpha. Inhibition of PKCalpha/beta also prevented LPS or PGN induced phosphorylation of IKKalpha/beta, phosphorylation and degradation of IkappaB-alpha, as well as phosphorylation of the p65 subunit of NF-kappaB. Activation of p38, JNK, and ERK 1/2 in response to TLR2 engagement was diminished in neutrophils in which PKCalpha/beta was inhibited. However, no alteration in the activation of these kinases was found in TLR4 stimulated neutrophils when PKCalpha/beta was blocked. Such results indicate that distinct intracellular signalling pathways leading to MAPK activation are induced by TLR4 and TLR2 stimulation. PKCalpha/beta can regulate NF-kappaB dependent transcription in neutrophils both by enhancing nuclear translocation of NF-kappaB and also by stimulating phosphorylation of the p65 subunit.

Myristoylated Alanine-rich C Kinase Substrate-mediated Neurotensin Release via Protein Kinase C-δ Downstream of the Rho/ROK Pathway

Myristoylated alanine-rich protein kinase C substrate (MARCKS) is a cellular substrate for protein kinase C (PKC). Recently, we have shown that PKC isoforms-alpha and -delta, as well as the Rho/Rho kinase (ROK) pathway, play a role in phorbol 12-myristate 13-acetate (PMA)-mediated secretion of the gut peptide neurotensin (NT) in the BON human endocrine cell line. Here, we demonstrate that activation of MARCKS protein is important for PMA- and bombesin (BBS)-mediated NT secretion in BON cells. Small interfering RNA (siRNA) to MARCKS significantly inhibited, whereas overexpression of wild-type MARCKS significantly increased PMA-mediated NT secretion. Endogenous MARCKS and green fluorescent protein-tagged wild-type MARCKS were translocated from membrane to cytosol upon PMA treatment, further confirming MARCKS activation. MARCKS phosphorylation was inhibited by PKC-delta siRNA, ROKalpha siRNA, and C3 toxin (a Rho protein inhibitor), suggesting that the PKC-delta and the Rho/ROK pathways are necessary for MARCKS activation. The phosphorylation of PKC-delta was inhibited by C3 toxin, demonstrating that the role of MARCKS in NT secretion was regulated by PKC-delta downstream of the Rho/ROK pathway. BON cell clones stably transfected with the receptor for gastrin releasing peptide, a physiologic stimulant of NT, and treated with BBS, the amphibian equivalent of gastrin releasing peptide, demonstrated a similar MARCKS phosphorylation as noted with PMA. BBS-mediated NT secretion was attenuated by MARCKS siRNA. Collectively, these findings provide evidence for novel signaling pathways, including the sequential regulation of MARCKS activity by Rho/ROK and PKC-delta proteins, in stimulated gut peptide secretion.

PKCδ plays opposite roles in growth mediated by wild-type Kit and an oncogenic Kit mutant

The Kit receptor tyrosine kinase is critical for normal hematopoiesis. Mutation of the aspartic acid residue encoded by codon 816 of human c-kit or codon 814 of the murine gene results in an oncogenic form of Kit. Here we investigate the role of protein kinase Cδ (PKCδ) in responses mediated by wild-type murine Kit and the D814Y mutant in a murine mast cell-like line. PKCδ is activated after wild-type (WT) Kit binds stem cell factor (SCF), is constitutively active in cells expressing the Kit catalytic domain mutant, and coprecipitates with both forms of Kit. Inhibition of PKCδ had opposite effects on growth mediated by wild-type and mutant Kit. Both rottlerin and a dominant-negative PKCδ construct inhibited the growth of cells expressing mutant Kit, while SCF-induced growth of cells expressing wild-type Kit was not inhibited. Further, overexpression of PKCδ inhibited growth of cells expressing wild-type Kit and enhanced growth of cells expressing the Kit mutant. These data demonstrate that PKCδ contributes to factor-independent growth of cells expressing the D814Y mutant, but negatively regulates SCF-induced growth of cells expressing wild-type Kit. This is the first demonstration that PKCδ has different functions in cells expressing normal versus oncogenic forms of a receptor.

Isoflurane induces a protein kinase C alpha-dependent increase in cell-surface protein level and activity of glutamate transporter type 3

Glutamate transporters regulate extracellular concentrations of glutamate, an excitatory neurotransmitter in the central nervous system. We have shown that the commonly used anesthetic isoflurane increased the activity of glutamate transporter type 3 (excitatory amino acid transporter 3, EAAT3) possibly via a protein kinase C (PKC)-dependent pathway. In this study, we showed that isoflurane induced a time- and concentration-dependent redistribution of EAAT3 to the cell membrane in C6 glioma cells. This redistribution was inhibited by staurosporine, a pan PKC inhibitor, or by 12-(2-cyanoethyl)-6,7,12,13-tetrahydro-13-methyl-5-oxo-5H-indolo(2,3-a)pyrrolo(3,4-c)-carbazole (Go6976) at a concentration that selectively inhibits conventional PKC isozymes (PKC alpha, -beta, and -gamma). This isoflurane-induced EAAT3 redistribution was also blocked when the expression of PKC alpha but not PKC beta proteins was down-regulated by the respective antisense oligonucleotides. The isoflurane-induced increase of glutamate uptake by EAAT3 was abolished by the down-regulation of PKC alpha expression. Immunoprecipitation with an anti-EAAT3 antibody pulled down more PKC alpha in cells exposed to isoflurane than in control cells. Isoflurane also increased the phosphorylated EAAT3 and the redistribution of PKC alpha to the particulate fraction of cells. Consistent with the results in C6 cells, isoflurane also increased EAAT3 cell-surface expression and enhanced the association of PKC alpha with EAAT3 in rat hippocampal synaptosomes. Our results suggest that the isoflurane-induced increase in EAAT3 activity requires an increased amount of EAAT3 protein in the plasma membrane. These effects are PKC alpha-dependent and may rely on the formation of an EAAT3-PKC alpha complex. Together, these results suggest an important mechanism for the regulation of glutamate transporter functions and expand our understanding of isoflurane pharmacology at cellular and molecular levels.

CaV2.3 channel and PKClambda: new players in insulin secretion

Insulin secretion is critically dependent on the proper function of a complex molecular network. Ca(V)2.3-knockout (Ca(V)2.3(-/-)) and PKClambda-knockout (PKClambda(-/-)) mouse models now suggest that these 2 players, the Ca(v)2.3 channel and PKClambda, are important constituents of this molecular network. Subsequent to glucose stimulation, insulin is released from the pancreatic beta cell in a biphasic pattern, i.e., a rapid initial phase followed by a slower, more sustained phase. Interestingly, Ca(2+) influx through the Ca(V)2.3 channel regulates only the second phase of insulin secretion. PKClambda seems to enter the beta cell nucleus and in turn modulates the expression of several genes critical for beta cell secretory function. Studies by Hashimoto et al. and Jing et al. in this issue of the JCI set out to answer the question of why numerous isoforms of proteins with similar functions are present in the beta cell. This is important, since it has been difficult to understand the modulatory and/or regulatory roles of different isoforms of proteins in defined subcellular compartments and at various times during the secretory process in both beta cell physiology and pathophysiology.

Proatherosclerotic mechanisms involving protein kinase C in diabetes and insulin resistance

In diabetes and insulin resistance, activation of protein kinase C (PKC) in vascular cells may be a key link between elevated plasma and tissue concentrations of glucose and nonesterified fatty acids and abnormal vascular cell signaling. Initial studies of PKC activation in diabetes focused on microvascular complications, but increasing evidence supports that PKC plays a role in several mechanisms promoting atherosclerosis. This review explains how PKC is thought to be activated in diabetes and insulin resistance through de novo synthesis of diacylglycerol. Furthermore, the review summarizes studies that implicate PKC in promoting proatherogenic mechanisms or inhibiting antiatherogenic mechanisms, including studies of endothelial dysfunction; gene induction and activation of vascular NAD(P)H oxidase; endothelial nitric oxide synthase expression and function; endothelin-1 expression; growth, migration, and apoptosis of vascular smooth muscle cells; induction of adhesion molecules; and oxidized low-density lipoprotein uptake by monocyte-derived macrophages.

Mouse brain localization of the protein kinase C-enhanced phosphatase 1 inhibitor KEPI (Kinase C-Enhanced PP1 Inhibitor)

We recently identified the protein kinase C-enhanced protein phosphatase 1 (PP1) inhibitor KEPI based on its morphine-induced upregulation in striatum. Regulation of protein serine/threonine dephosphorylation by PP1 can modulate important brain signaling pathways. To improve understanding of KEPI's role in the brain, we have developed anti-KEPI sera in rabbits immunized with a hemocyanin conjugate of KEPI residues 66-80, characterized the specificity that this serum provides, mapped the distribution of immunoreactive KEPI (iKEPI) in mouse brain, rat dorsal root ganglia and striatal cultures and documented KEPI binding to PP1 in vitro. Staining is found in apparently neuronal processes and, often less intensely, in neuronal perikarya in primary cultures and in neurons and neuronal elements from a number of brain regions. iKEPI fiber/terminal patterns are relatively densely distributed in striatum, nucleus accumbens, septum, bed nucleus of the stria terminalis, hippocampus, paraventricular thalamus, ventromedial hypothalamus, interpeduncular nucleus, raphe nuclei, nucleus caudalis of the spinal tract of the trigeminal and dorsal horn of the spinal cord. iKEPI-positive cell bodies lie in the nucleus accumbens, striatum, lateral septal nucleus, granular layer of dentate gyrus, interpeduncular nucleus, dorsal root ganglia and cerebellar vermis. These expression patterns point to possible roles for KEPI in regulating protein dephosphorylation by inhibiting PP1 activities in a number of brain pathways likely to use several different neurotransmitters and to participate in a number of brain functions. Dense KEPI immunoreactivity in nucleus accumbens perikarya, combined with evidence for its regulation by opiates, supports possible roles for KEPI in molecular signal transduction pathways important for drug reward and addiction.

Early and delayed glutamate effects in rat primary cortical neurons

Glutamate-induced changes in the subcellular distribution of protein kinase C isoforms and in the intracellular calcium concentration were investigated in rat primary cortical neurons. Western blot analysis of protein kinase C isoforms (alpha, beta1, beta2, gamma, delta, epsilon, zeta and theta), performed 30 min after a 10 min treatment with 30 microM glutamate, revealed a decrease in the total beta1 (-24%) and beta2 (-40%) isoform levels, without any significant change in any of the other isozymes. All conventional isoforms translocated to the membrane compartment, while delta, epsilon, zeta and theta; maintained their initial subcellular distribution. Twenty-four hours after glutamate treatment, the total protein kinase C labelling had increased, particularly the epsilon isoform, which accounted for 34% of the total densitometric signal. At this time, protein kinase C beta1, delta, epsilon and zeta isoforms were mainly detected in the membrane compartment, while gamma and theta; signals were displayed almost solely in the cytosol. Basal intracellular calcium concentration (FURA 2 assay) was concentration-dependently increased (maximum effect +77%) 30 min, but not 24h after a 10 min glutamate (10-100 microM) treatment, while the net increase induced by electrical stimulation (10 Hz, 10s) was consistently reduced (maximum effect -64%). The N-methyl-d-aspartate receptor antagonist, MK-801, 1 microM, prevented glutamate action both 30 min and 24 h after treatment, while non-selective protein kinase C inhibitors, ineffective at 30 min, potentiated it at 24 h. These findings show that protein kinase C isoforms are differently activated and involved in the early and delayed glutamate actions, and that the prevailing effect of their activation is neuroprotective.

T cell receptor-induced lipid raft recruitment of the I kappa B kinase complex is necessary and sufficient for NF-kappa B activation occurring in the cytosol

TCR-induced NF-kappa B activation is necessary for the innate immune response and involves induced lipid raft recruitment of the I kappa B kinase (IKK) complex. In this study, we systematically investigated lipid raft recruitment of members of the NF-kappa B activation pathway in human T cells. All upstream components leading to IKK activation were found constitutively or inducibly in lipid rafts, while the NF-kappa B/I kappa B complex and phosphorylated forms of IKK alpha/beta, I kappa B alpha and p65 are exclusively found in the cytosolic fraction. Disruption of raft organization precluded NF-kappaB activation induced by T cell costimulation, but IL-1-triggered NF-kappa B activation remained unaffected. Targeting of the IKK complex to lipid rafts caused constitutive IKK activation and NF-kappa B DNA binding, which was further triggered upon T cell costimulation. Various experimental approaches revealed that costimulation-induced IKK alpha/beta activation loop phosphorylation is independent from IKK beta-mediated transautophosphorylation, but rather involves phosphorylation by the IKK-interacting protein NIK and its upstream activator COT.

Synergistic effect of endothelin-1 and cyclic AMP on glucose transport in 3T3-L1 adipocytes

We have demonstrated previously that chronic exposure to endothlin-1 enhances glucose transport in 3T3-L1 adipocytes via augmented GLUT1 mRNA and protein accumulation. In the present study, we further examined the combined effect of endothelin-1 (ET-1) and cAMP on glucose transport. In cells pretreated with ET-1 and 8-bromo cAMP for 8 h, a synergy between these two agents on glucose uptake was found. Insulin-stimulated glucose transport, on the other hand, was only slightly affected. The synergistic effect of these two agents was suppressed in the presence of cycloheximide and actinomycin D. Immunoblot and Northern blot analyses revealed that GLUT1 protein and mRNA levels were both increased in cells pretreated with both ET-1 and 8-bromo cAMP, greater than the additive effect of each agent alone. Further examination demonstrated that the stability of GLUT1 mRNA was markedly enhanced in the presence of both ET-1 and cAMP. To investigate the transcriptional activation of Glut1 gene, transient transfection of cells with luciferase reporter construct driven by Glut1 promoter was performed. We found that Glut1 transcription was also increased by ET-1 and cAMP in a synergistic fashion. In addition, similar synergy between ET-1 and beta-adrenergic agonists on glucose transport was found. The synergistic action of ET-1 with 8-bromo cAMP to enhance glucose transport was inhibited by GF109203X, a selective protein kinase C (PKC) inhibitor, and was mimicked by 4beta-phorbol 12beta-myristate 13alpha-acetate (PMA), a PKC activator. Furthermore, PMA was found to act synergistically with 8-bromo cAMP to induce Glut1 transcription and ET-1 was shown to activate novel PKCdelta and PKC. Taken together, these results indicate that ET-1 may act with cAMP in a synergistic way to increase glucose transport, probably through enhanced GLUT1 expression via a PKC-dependent mechanism.

From hyperglycemia to diabetic kidney disease: the role of metabolic, hemodynamic, intracellular factors and growth factors/cytokines

At present, diabetic kidney disease affects about 15-25% of type 1 and 30-40% of type 2 diabetic patients. Several decades of extensive research has elucidated various pathways to be implicated in the development of diabetic kidney disease. This review focuses on the metabolic factors beyond blood glucose that are involved in the pathogenesis of diabetic kidney disease, i.e., advanced glycation end-products and the aldose reductase system. Furthermore, the contribution of hemodynamic factors, the renin-angiotensin system, the endothelin system, and the nitric oxide system, as well as the prominent role of the intracellular signaling molecule protein kinase C are discussed. Finally, the respective roles of TGF-beta, GH and IGFs, vascular endothelial growth factor, and platelet-derived growth factor are covered. The complex interplay between these different pathways will be highlighted. A brief introduction to each system and description of its expression in the normal kidney is followed by in vitro, experimental, and clinical evidence addressing the role of the system in diabetic kidney disease. Finally, well-known and potential therapeutic strategies targeting each system are discussed, ending with an overall conclusion.

Tumor necrosis factor alpha and epidermal growth factor act additively to inhibit matrix gene expression by chondrocyte

The failure of chondrocytes to replace the lost extracellular matrix contributes to the progression of degenerative disorders of cartilage. Inflammatory mediators present in the joint regulate the breakdown of the established matrix and the synthesis of new extracellular matrix molecules. In the present study, we investigated the effects of tumor necrosis factor alpha (TNF-alpha) and epidermal growth factor (EGF) on chondrocyte morphology and matrix gene expression. Chondrocytes were isolated from distal femoral condyles of neonatal rats. Cells in primary culture displayed a cobblestone appearance. EGF, but not TNF-alpha, increased the number of cells exhibiting an elongated morphology. TNF-alpha potentiated the effect of EGF on chondrocyte morphology. Individually, TNF-alpha and EGF diminished levels of aggrecan and type II collagen mRNA. In combination, the effects of TNF-alpha and EGF were additive, indicating the involvement of discrete signaling pathways. Cell viability was not compromised by TNF-alpha or by EGF, alone or in combination. EGF alone did not activate NF-kappaB or alter NF-kappaB activation by TNF-alpha. Pharmacologic studies indicated that the effects of TNF-alpha and EGF alone or in combination were independent of protein kinase C signaling, but were dependent on MEK1/2 activity. Finally, we analyzed the involvement of Sox-9 using a reporter construct of the 48 base pair minimal enhancer of type II collagen. TNF-alpha attenuated enhancer activity as expected; in contrast, EGF did not alter either the effect of TNF-alpha or basal activity. TNF-alpha and EGF, acting through distinct signaling pathways, thus have additive adverse effects on chondrocyte function. These findings provide critical insights into the control of chondrocytes through the integration of multiple extracellular signals.

Differential participation of protein kinase C and Rho kinase in α1-adrenoceptor mediated contraction in rat arteries

The major functional α1-adrenoceptor in the rat aorta is of the α1Dsubtype and that in the caudal artery is of the α1Asubtype. In the present study, the participation of protein kinase C (PKC) and Rho kinase (RhoK) in contractile responses to stimulation of the α1-adrenoceptors in these two arteries was investigated. Both the PKC inhibitor Ro-318220 and the RhoK inhibitor Y-27632 significantly blocked contractile responses of the aorta to phenylephrine (PE) and the selective α1A-adrenoceptor agonist A61603. When used in combination, the inhibitors had an additive blocking effect. In the caudal artery, Y-27632 but not Ro-318220 inhibited contractile responses to PE and A61603, and, in combination, the antagonism produced was no greater than that by Y-27632 alone. Contractile responses to direct activation of PKC with phorbol 12,13-dibutyrate were much smaller and levels of CPI-17 (PKC-activated protein phosphatase inhibitor of 17 kDa) were much lower in the caudal artery than the aorta. The results suggest that both PKC and RhoK contribute independently to contractile responses to stimulation of α1D-adrenoceptors in the aorta. However, RhoK, but not PKC, participates in contractile responses to stimulation of α1A-adrenoceptors in the caudal artery. This difference may largely be due to differences between the two arteries in the extent to which PKC participates in contraction.Key words: vascular smooth muscle, α1-adrenoceptors, protein kinase C, rho kinase, phenylephrine.

Role of protein kinase C delta in reactivation of Kaposi's sarcoma-associated herpesvirus

TPA (12-O-tetradecanoylphorbol-13-acetate), a well-known activator of protein kinase C (PKC), can experimentally induce reactivation of Kaposi's sarcoma-associated herpesvirus (KSHV) in certain latently infected cells. We selectively blocked the activity of PKC isoforms by using GF 109203X or rottlerin and demonstrated that this inhibition largely decreased lytic KSHV reactivation by TPA. Translocation of the PKCdelta isoform was evident shortly after TPA stimulation. Overexpression of the dominant-negative PKCdelta mutant supported an essential role for the PKCdelta isoform in virus reactivation, yet overexpression of PKCdelta alone was not sufficient to induce lytic reactivation of KSHV, suggesting that additional signaling molecules participate in this pathway.

Protein kinase C mediates cisplatin-induced loss of adherens junctions followed by apoptosis of renal proximal tubular epithelial cells

Cisplatin is a commonly used antitumor agent in the treatment of various human cancers, with nephrotoxicity as a major side effect. Cisplatin causes the loss of cell-cell contacts of renal proximal tubular epithelial cells prior to the onset of apoptosis. We studied the involvement of protein kinase C in these events in the renal epithelial cell line LLC-PK1. Cisplatin caused apoptosis in LLC-PK1 cells, which was directly related to the activation of caspase-3 and DNA fragmentation. Apoptosis was almost completely inhibited by the protein kinase C inhibitors bisindolylmaleimide (Bis) I and Go6983 [2-[1-(3-dimethylaminopropyl)-5-methoxyindol-3-yl]-3-(1H-indol-3-yl) maleimide], but not by Go6976 [12-(2-cyanoethyl)-6,7,12,13-tetrahydro-13-methyl-5-oxo-5H-indolo(2,3-a)pyrrolo(3,4-c)-carbazole]. Also, in primary cultured rat renal proximal tubular cells, inhibition of protein kinase C (PKC) inhibited apoptosis. Cisplatin also caused the early loss of cell-cell adhesions, which was associated with the altered localization of the adherens junction-associated protein beta-catenin in association with PKC-mediated phosphorylation of the actincapping protein adducin. These events preceded and were independent of caspase activation. beta-Catenin did not dissociate from E-cadherin. Cisplatin-induced loss of cell-cell contacts was associated with the increased formation of F-actin stress fibers, which was inhibited by Bis I and Go6983 as well as dominant-negative PKC-epsilon. Also, the loss of cell-cell adhesions by cisplatin was prevented by Bis I and Go6983. Activation of protein kinase C with phorbol esters promoted cisplatin-induced loss of cell-cell adhesions as well as apoptosis. In conclusion, the combined data fit a model whereby protein kinase C mediates the cisplatin-induced loss of cellular interactions. Such a loss of these interactions has a role in the onset of apoptosis.

Role of protein kinase Cζ in thrombin-induced endothelial permeability changes: inhibition by angiopoietin-1

Endothelial cell leakiness is regulated by mediators such as thrombin, which promotes endothelial permeability, and anti-inflammatory agents, such as angiopoietin-1. Here we define a new pathway involved in thrombin-induced permeability that involves the atypical protein kinase C isoform, PKCζ. Chemical inhibitor studies implicated the involvement of an atypical PKC isoform in thrombin-induced permeability changes in human umbilical vein endothelial cells. Thrombin stimulation resulted in PKCζ, but not the other atypical PKC isoform, PKCλ, translocating to the membrane, an event known to be critical to enzyme activation. The involvement of PKCζ was confirmed by overexpression of constitutively active PKCζ, resulting in enhanced basal permeability. Dominant-negative PKCζ prevented the thrombin-mediated effects on endothelial cell permeability and inhibited thrombin-induced activation of PKCζ. Rho activation does not appear to play a role, either upstream or downstream of PKCζ, as C3 transferase does not block thrombin-induced PKCζ activation and dominant-negative PKCζ does not block thrombin-induced Rho activation. Finally, we show that angiopoietin-1 inhibits thrombin-induced PKCζ activation, Rho activation, and Ca++ flux, thus demonstrating that the powerful antipermeability action of angiopoietin-1 is mediated by its action on a number of signaling pathways induced by thrombin and implicated in permeability changes. (Blood. 2004; 104:1716-1724)

Protein kinase C mediates phosphorylation, desensitization, and trafficking of the D2 dopamine receptor

Previously, D2 dopamine receptors (D2 DARs) have been shown to undergo G-protein-coupled receptor kinase phosphorylation in an agonist-specific fashion. We have now investigated the ability of the second messenger-activated protein kinases, protein kinase A (PKA) and protein kinase C (PKC), to mediate phosphorylation and desensitization of the D2 DAR. HEK293T cells were transiently transfected with the D2 DAR and then treated with intracellular activators and inhibitors of PKA or PKC. Treatment with agents that increase cAMP, and activate PKA, had no effect on the phosphorylation state of the D2 DAR, suggesting that PKA does not phosphorylate the D2 DAR in HEK293T cells. In contrast, cellular treatment with phorbol 12-myristate 13-acetate (PMA), a PKC activator, resulted in an approximately 3-fold increase in D2 DAR phosphorylation. The phosphorylation was specific for PKC as the PMA effect was mimicked by phorbol 12,13-dibutyrate, but not by 4alpha-phorbol 12,13-didecanoate, active and inactive, phorbol diesters, respectively. The PMA-mediated D2 DAR phosphorylation was completely blocked by co-treatment with the PKC inhibitor, bisindolylmaleimide II, and augmented by co-transfection with PKCbetaI. In contrast, PKC inhibition had no effect on agonist-promoted phosphorylation, suggesting that PKC is not involved in this response. PKC phosphorylation of the D2 DAR was found to promote receptor desensitization as reflected by a decrease in agonist potency for inhibiting cAMP accumulation. Most interestingly, PKC phosphorylation also promoted internalization of the D2 DAR through a beta-arrestin- and dynamin-dependent pathway, a response not usually associated with PKC phosphorylation of G-protein-coupled receptors. Site-directed mutagenesis experiments resulted in the identification of two domains of PKC phosphorylation sites within the third intracellular loop of the receptor. Both of these domains are involved in regulating sequestration of the D2 DAR, whereas only one domain is involved in receptor desensitization. These results indicate that PKC can mediate phosphorylation of the D2 DAR, resulting in both functional desensitization and receptor internalization.

Mechanism of oleic acid-induced gap junctional disassembly in rat cardiomyocytes

This study investigated the mechanism of oleic acid (OA) on gap junctions and identified the protein kinase C (PKC) isoforms involved in OA-mediated gap junction disassembly in cardiomyocytes. Control cardiomyocytes showed continuous staining of the plasma membrane at cell-cell contact areas using antibodies reacting with connexin 43 (Cx43). The spontaneous contraction rate of cultured cardiomyocytes was reduced in a time-dependent manner by OA. In addition, Cx43 expression at cell-cell junction decreased, suggesting the disassembly of gap junction. Staining for PKC and PKCalpha, which were shown to colocalize with Cx43, also decreased with increased duration of OA treatment. The effects of OA on these distributional changes at cell junctions were reversed by 24 h incubation in fresh culture medium devoid of OA. Immunoprecipitation assays confirmed the biochemical binding between Cx43 and PKC/PKCalpha, and this protein interaction was not affected by OA. This may provide the basis for simultaneous detachment of Cx and PKC/PKCalpha from the cell-cell junction to the cytosol upon OA stimulation. Western blot analysis showed that OA-induced Cx43 Ser368 phosphorylation, and that this effect could be blocked by cotreatment with the general PKC inhibitor, calphostin C, the PKC inhibitor, eV1-2, or the Src kinase inhibitor, PP1, but not by the PKCalpha inhibitor, Gö6976. eV1-2 also prevented the OA-induced disassembly of gap junctions. Taken together, these data suggest that OA-induced Cx43 Ser368 phosphorylation is mediated by activation of PKC and Src kinase and might be responsible for OA-induced gap junctional disassembly.

Short-term delay of Fas-stimulated apoptosis by GM-CSF as a result of temporary suppression of FADD recruitment in neutrophils: evidence implicating phosphatidylinositol 3-kinase and MEK1-ERK1/2 pathways downstream of classical protein kinase C

Granulocyte/macrophage colony-stimulating factor (GM-CSF) inhibits Fas-induced apoptosis of neutrophils. However, the exact step in the apoptotic pathway blocked by GM-CSF remained unclear. Here, we found that pretreatment of neutrophils with GM-CSF inhibits the recruitment of Fas-associated protein with death domain (FADD) to Fas, abolishing the formation of the death-inducing signaling complex required for Fas-induced apoptosis. Two-dimensional electrophoresis revealed that GM-CSF modifies the ratio of FADD subspecies. These GM-CSF-triggered changes were abrogated, and Fas-induced apoptosis was restored by an inhibitor of classical protein kinase C (PKC), Go6976, and by the combination of a phosphatidylinositol 3-kinase (PI-3K) inhibitor, LY294002, and an inhibitor of mitogen-activated protein kinase kinase (MEK)1, PD98059. Go6976 blocked GM-CSF-elicited phosphorylation of Akt/PKB and extracellular signal-regulated kinase (ERK)1/2. These results indicated that GM-CSF suppresses Fas-induced neutrophil apoptosis by inhibiting FADD binding to Fas, through redundant actions of PI-3K and MEK1-ERK1/2 pathways downstream of classical PKC.

The Role of Protein Kinase D in Neurotensin Secretion Mediated by Protein Kinase C-α/-δ and Rho/Rho Kinase

Neurotensin (NT) is a gut peptide that plays an important role in gastrointestinal (GI) secretion, motility, and growth as well as the proliferation of NT receptor positive cancers. Secretion of NT is regulated by phorbol ester-sensitive protein kinase C (PKC) isoforms-alpha and -delta and may involve protein kinase D (PKD). The purpose of our present study was: (i) to define the role of PKD in NT release from BON endocrine cells and (ii) to delineate the upstream signaling mechanisms mediating this effect. Here, we demonstrate that small interfering RNA (siRNA) targeted against PKD dramatically inhibited both basal and PMA-stimulated NT secretion; NT release is significantly increased by overexpression of PKD. PKC-alpha and -delta siRNA attenuated PKD activity, whereas overexpression of PKC-alpha and -delta enhanced PKD activity. Rho kinase (ROK) siRNA significantly inhibited NT secretion, whereas overexpression of ROKalpha effectively increased NT release. Rho protein inhibitor C3 dramatically inhibited both NT secretion and PKD activity. In conclusion, our results demonstrate that PKD activation plays a central role in NT peptide secretion; upstream regulators of PKD include PKC-alpha and -delta and Rho/ROK. Importantly, our results identify novel signaling pathways, which culminate in gut peptide release.

Cytokine-induced upregulation of NF-κB, IL-8, and ICAM-1 is dependent on colonic cell polarity: implication for PKCδ

As described for a long time, carcinoma-derived Caco-2 cells form a polarized epithelium in culture, whereas HT29-D4 cells are nonpolarized and undifferentiated but can form a polarized monolayer when cultured in a galactose-supplemented medium. Using NF-kappaB translocation and IL-8 and ICAM-1 gene activation as an index, we have studied the relationship between the differentiation state and the cell response to cytokines. We found that differentiated Caco-2 and HT29-D4 cells were responsive to both cytokines TNFalpha- and IL-1beta-mediated activation of NF-kappaB but that undifferentiated HT29-D4 cells were unresponsive to IL-1beta. However, the expression of endogenous ICAM-1 and IL-8 genes was upregulated by these cytokines in either cell lines differentiated or not. Upregulation of ICAM-1 gene occurred when IL-1beta or TNFalpha was added to the basal, but not apical surface of the differentiated epithelia. Finally, it appeared that in polarized HT29-D4 cells, the IL-1beta-induced translocation of NF-kappaB was connected to PKCdelta translocation.

Intracellular calcium changes induced by the endozepine triakontatetraneuropeptide in human polymorphonuclear leukocytes: role of protein kinase C and effect of calcium channel blockers

Background

The endozepine triakontatetraneuropeptide (TTN) induces intracellular calcium ([Ca⁺⁺]_i) changes followed by activation in human polymorphonuclear leukocytes (PMNs). The present study was undertaken to investigate the role of protein kinase (PK) C in the modulation of the response to TTN by human PMNs, and to examine the pharmacology of TTN-induced Ca⁺⁺ entry through the plasma membrane of these cells.

Results

The PKC activator 12-O-tetradecanoylphorbol-13-acetate (PMA) concentration-dependently inhibited TTN-induced [Ca⁺⁺]_i rise, and this effect was reverted by the PKC inhibitors rottlerin (partially) and Ro 32-0432 (completely). PMA also inhibited TTN-induced IL-8 mRNA expression. In the absence of PMA, however, rottlerin (but not Ro 32-0432) per se partially inhibited TTN-induced [Ca⁺⁺]_i rise. The response of [Ca⁺⁺]_i to TTN was also sensitive to mibefradil and flunarizine (T-type Ca⁺⁺-channel blockers), but not to nifedipine, verapamil (L-type) or ω-conotoxin GVIA (N-type). In agreement with this observation, PCR analysis showed the expression in human PMNs of the mRNA for all the α1 subunits of T-type Ca⁺⁺ channels (namely, α1G, α1H, and α1I).

Conclusions

In human PMNs TTN activates PKC-modulated pathways leading to Ca⁺⁺ entry possibly through T-type Ca⁺⁺ channels.

Arthropod 5-HT2 receptors: a neurohormonal receptor in decapod crustaceans that displays agonist independent activity resulting from an evolutionary alteration to the DRY motif

The stomatogastric nervous system (STNS) is a premiere model for studying modulation of motor pattern generation. Whereas the cellular and network responses to monoamines have been particularly well characterized electrophysiologically, the transduction mechanisms that link the different monoaminergic signals to specific intracellular responses are presently unknown in this system. To begin to elucidate monoaminergic signal transduction in pyloric neurons, we used a bioinformatics approach to predict the existence of 18 monoamine receptors in arthropods, 9 of which have been previously cloned in Drosophila and other insects. We then went on to use the two existing insect databases to clone and characterize the 10th putative arthropod receptor from the spiny lobster, Panulirus interruptus. This receptor is most homologous to the 5-HT2 subtype and shows a dose-dependent response to 5-HT but not to any of the other monoamines present in the STNS. Through a series of pharmacological experiments, we demonstrate that this newly described receptor, 5-HT2betaPan, couples with the traditional G(q) pathway when expressed in HEK293 cells, but not to G(s) or G(i/o). Moreover, it is constitutively active, because the highly conserved DRY motif in transmembrane region 3 has evolved into DRF. Site-directed mutagenesis that reverts the motif back to DRY abolishes this agonist-independent activity. We further demonstrate that this receptor most likely participates in the modulation of stomatogastric motor output, because it is found in neurites in the synaptic neuropil of the stomatogastric ganglion as well as in the axon terminals at identified pyloric neuromuscular junctions.