Antisense oligodeoxynucleotide inhibition of delta protein kinase C expression accelerates induced differentiation of murine erythroleukaemia cells

Protein kinase C as a target for new anti-cancer agents

Cancer joins the category of diseases involving abnormalities in the rate of proliferation of cells and is associated with uncontrolled cell division, where cells either generate their own growth-promoting stimuli or neighboring cells or do not respond to growth inhibitory signals. Protein kinase C (PKC) is one of the key elements in the tumor growth signal transduction pathways and is found to be overexpressed in several malignant cell types. A way to control cell proliferation and cell differentiation is by influencing signal transduction pathways by modulation of PKC. PKC encloses 12 different isoenzymes, and each isoenzyme is found to have a different functional property. Because specific PKC isoenzyme types are present in different (malignant) cell species, they may be an attractive target in the development of anti-cancer agents. Classification and identification of the available PKC isoenzymes in different tumor cells could be useful in targeting specific tumors. PKC also tends to be overexpressed in association with the multidrug resistance pheno-type. This concise review deals with the role of PKC isoenzymes in (tumor) cell biology and evaluates the antineoplastic agents interacting on PKC isoenzymes.

Genome-Wide Analysis Uncovers Novel Recurrent Alterations in Primary Central Nervous System Lymphomas

PURPOSE

Primary central nervous system lymphoma (PCNSL) is an aggressive non-Hodgkin lymphoma confined to the central nervous system. Whether there is a PCNSL-specific genomic signature and, if so, how it differs from systemic diffuse large B-cell lymphoma (DLBCL) is uncertain.

EXPERIMENTAL DESIGN

We performed a comprehensive genomic study of tumor samples from 19 immunocompetent PCNSL patients. Testing comprised array-comparative genomic hybridization and whole exome sequencing.

RESULTS

Biallelic inactivation of TOX and PRKCD was recurrently found in PCNSL but not in systemic DLBCL, suggesting a specific role in PCNSL pathogenesis. In addition, we found a high prevalence of MYD88 mutations (79%) and CDKN2A biallelic loss (60%). Several genes recurrently affected in PCNSL were common with systemic DLBCL, including loss of TNFAIP3, PRDM1, GNA13, TMEM30A, TBL1XR1, B2M, CD58, activating mutations of CD79B, CARD11, and translocations IgH-BCL6. Overall, B-cell receptor/Toll-like receptor/NF-κB pathways were altered in >90% of PNCSL, highlighting its value for targeted therapeutic approaches. Furthermore, integrated analysis showed enrichment of pathways associated with immune response, proliferation, apoptosis, and lymphocyte differentiation.

CONCLUSIONS

In summary, genome-wide analysis uncovered novel recurrent alterations, including TOX and PRKCD, helping to differentiate PCNSL from systemic DLBCL and related lymphomas.

PKCδ sensitizes neuroblastoma cells to L-buthionine-sulfoximine and etoposide inducing reactive oxygen species overproduction and DNA damage

Neuroblastoma is a type of pediatric cancer. The sensitivity of neuroblastoma (NB) cancer cells to chemotherapy and radiation is inhibited by the presence of antioxidants, such as glutathione (GSH), which is crucial in counteracting the endogenous production of reactive oxygen species (ROS). We have previously demonstrated that cells depleted of GSH undergo apoptosis via oxidative stress and Protein kinase C (PKC) δ activation. In the present study, we transfected PKCδ in NB cells resistant to oxidative death induced by L-buthionine-S,R-sulfoximine (BSO), a GSH-depleting agent. Cell responses, in terms of ROS production, apoptosis and DNA damage were evaluated. Moreover, PKCδ activation was monitored by analyzing the phosphorylation status of threonine 505 residue, carrying out PKC activity assay and investigating the subcellular localization of the kinase. The cell responses obtained in BSO-resistant cells were also compared with those obtained in BSO-sensitive cells subjected to the same experimental protocol. Our results demonstrate, for the first time, that PKCδ induces DNA oxidation and ROS overproduction leading to apoptosis of BSO-resistant NB cells and potentiates the cytotoxic effects induced by BSO in sensitive cells. Moreover, PKCδ overexpression enhances the sensitivity of NB cells to etoposide, a well-characterised drug, commonly used in neuroblastoma therapy. Altogether our data provide evidence of a pro-oxidant role of PKCδ that might be exploited to design new therapeutic strategies aimed at selective killing of cancer cells and overcoming drug resistance. However, it becomes evident that a more detailed understanding of ROS-mediated signaling in cancer cells is necessary for the development of redox-modulated therapeutic approaches.

Defective translocation of PKCepsilon in EtOH-induced inhibition of Mg2+ accumulation in rat hepatocytes

BACKGROUND

Rats chronically fed ethanol for 3 weeks presented a marked decreased in total hepatic Mg(2+) content and required approximately 12 days to restore Mg(2+) homeostasis upon ethanol withdrawal. This study was aimed at investigating the mechanisms responsible for the EtOH-induced delay.

METHODS

Hepatocytes from rats fed ethanol for 3 weeks (Lieber-De Carli diet-chronic model), rats re-fed a control diet for varying periods of time following ethanol withdrawal, and age-matched control rats fed a liquid or a pellet diet were used. As acute models, hepatocytes from control animals or HepG2 cells were exposed to varying doses of ethanol in vitro for 8 minutes.

RESULTS

Hepatocytes from ethanol-fed rats presented a marked inhibition of Mg(2+) accumulation and a defective translocation of PKCepsilon to the cell membrane. Upon ethanol withdrawal, 12 days were necessary for PKCepsilon translocation and Mg(2+) accumulation to return to normal levels. Exposure of control hepatocytes or HepG2 cells to a dose of ethanol as low as 0.01% for 8 minutes was already sufficient to inhibit Mg(2+) accumulation and PKCepsilon translocation for more than 60 minutes. Also in this model, recovery of Mg(2+) accumulation was associated with restoration of PKCepsilon translocation. The use of specific antisense in HepG2 cells confirmed the involvement of PKCepsilon in modulating Mg(2+) accumulation.

CONCLUSIONS

Translocation of PKCepsilon isoform to the hepatocyte membrane is essential for Mg(2+) accumulation to occur. Both acute and chronic ethanol administrations inhibit Mg(2+) accumulation by specifically altering PKCepsilon translocation to the cell membrane.

Elevated expression of protein kinase C delta induces cell scattering upon serum deprivation

Tumor metastasis might be evoked in response to microenvironmental stress, such as a shortage of oxygen. Although the cellular response to hypoxia has been well established, we know little about how tumors adapt themselves to deprivation of growth factor. Protein kinase Cdelta (PKCdelta), a stress-sensitive protein kinase, has been implicated in tumor progression. In this study, we demonstrate that elevated expression of PKCdelta in Madin-Darby canine kidney cells induces a scatter response upon serum starvation, a condition that mimics growth-factor deprivation. Serum starvation stimulates the catalytic activity and Y311 phosphorylation of PKCdelta through reactive oxygen species (ROS) and the Src family kinases. Mutation of PKCdelta at Y311 and Y322, both of which are phosphorylation sites for Src, impairs its activation and ability to promote cell scattering upon serum deprivation. Once activated by ROS, PKCdelta itself activates ROS production at least partially through NADPH oxidase. In addition, the c-Jun N-terminal kinase is identified as a crucial downstream mediator of ROS and PKCdelta for induction of cell scattering upon serum deprivation. We demonstrate that the C1B domain of PKCdelta is essential not only for its localization at the Golgi complex, but also for its activation and ability to induce cell scattering upon serum deprivation. Finally, depletion of PKCdelta in human bladder carcinoma T24 cells restores their cell-cell contacts, which thereby reverses a scattered growth pattern to an epithelial-like growth pattern. Collectively, our results suggest that elevated expression of PKCdelta might facilitate the scattering of cells in order to escape stress induced by growth-factor deprivation.

Functional suppression of E-cadherin by protein kinase Cdelta

Protein kinase C (PKC) delta, a member of the novel PKC subfamily, has been shown to have an important role in cell proliferation, differentiation, apoptosis and cell motility. In this study, we investigated the effect of green fluorescent protein (GFP)-PKCdelta and GFP-PKCalpha on cell-cell junctions of Madin-Darby canine kidney (MDCK) cells and found that only GFP-PKCdelta suppressed the homophilic interactions between the ectodomains of E-cadherins, accompanied by a weaker cell-cell adhesion. The kinase-deficient mutant of GFP-PKCdelta retained its localization at cell-cell junctions but failed to suppress the function of E-cadherin. In addition, we demonstrated that the hinge region (residues 280-347) that links the regulatory domain and the catalytic domain of PKCdelta is essential for both its kinase activity and the targeting of cell-cell junctions. A PKCdelta mutant with the deletion of amino acids 280-323 within the hinge region, which is catalytically active but defective in the targeting of cell-cell junctions, failed to suppress the function of E-cadherin. Moreover, expression of GFP-PKCdelta in MDCK cells expedited the detachment of cells from their neighbors and facilitated cell scatter induced by hepatocyte growth factor. By contrast, the GFP-PKCdelta mutants including the kinase-deficient mutant and the truncated mutant lacking residues 280-323 suppressed hepatocyte-growth-factor-induced cell scattering. Finally, siRNA-mediated knockdown of endogenous PKCdelta in MDCK cells was found to delay the onset of cell-cell detachment and cell scattering induced by hepatocyte growth factor. Taken together, our results demonstrate that the catalytic activity of PKCdelta and its localization to cell-cell junctions are necessary for PKCdelta to suppress the function of E-cadherin, which thereby facilitates scattering of epithelial cells in response to extracellular cues.

Mechanisms of BSO (L-buthionine-S,R-sulfoximine)-induced cytotoxic effects in neuroblastoma

Glutathione (GSH) depletion is widely used to sensitize cells to anticancer treatment inducing the progression of programmed cell death and overcoming chemoresistance. It has been reported that neuroblastoma cells with MYCN amplification are unable to start TRAIL-dependent death and MYCN, in concert with cytotoxic drugs, efficiently induces the mitochondrial pathway of apoptosis through oxidative mechanisms. In this study, we show that GSH loss induced by L-buthionine-S,R-sulfoximine (BSO), an inhibitor of GSH biosynthesis, leads to overproduction of reactive oxygen species (ROS) and triggers apoptosis of MYCN-amplified neuroblastoma cells. BSO susceptibility of SK-N-BE-2C, a representative example of MYCN-amplified cells, has been attributed to stimulation of total SOD activity in the absence of changes in the level and the activity of catalase. Therefore, the unbalanced intracellular redox milieu has been demonstrated to be critical for the progression of neuroblastoma cell death that was efficiently prevented by antioxidants and rottlerin. These results describe a novel pathway of apoptosis dependent on ROS formation and PKC-delta activation and independent of p53, bcl-2, and bax levels; the selective redox modulation of PKC-delta might be suggested as a potential strategy for sensitizing MYCN-amplified cells to therapeutic approaches.

PKC delta and NADPH oxidase in AGE-induced neuronal death

Advanced glycation end product (AGE) accumulation in brain is believed to contribute to neuronal death in several neurodegenerative diseases. Neurons exposed to AGEs undergo oxidative stress, but the molecular mechanisms able to induce ROS generation and cell death are not yet clear. In this work, we exposed SH-SY5Y neuroblastoma cells to glycated albumin, as a model of AGE-modified protein, and we observed that cells differentiated by retinoic acid died after AGE exposure, through anion superoxide and peroxide generation, while undifferentiated cells resulted resistant. Retinoic acid induced marked increase in p47phox expression and in catalytic activity of PKC delta: the upregulation of a pathway involving NADPH oxidase and PKC delta is likely to be responsible for neuronal susceptibility to AGE. This hypothesis is confirmed by the fact that pre-treatments of differentiated cells with DPI, an inhibitor of NADPH oxidase, or with rottlerin, an inhibitor of PKC delta, were able to prevent AGE-induced neuronal death.

Phosphorylation of adducin by protein kinase Cdelta promotes cell motility

Protein kinase Cdelta (PKCdelta) has been implicated to play a crucial role in cell proliferation, differentiation and apoptosis. In this study, we have investigated the role of PKCdelta in cell motility using Madin-Darby canine kidney cells. Overexpression of PKCdelta promoted membrane protrusions, concomitant with increased cell motility. By contrast, suppression of PKCdelta expression by RNA interference inhibited cell motility. Moreover, a fraction of PKCdelta was detected at the edge of membrane protrusions in which it colocalized with adducin, a membrane skeletal protein whose phosphorylation state is important for remodeling of the cortical actin cytoskeleton. Elevated expression of PKCdelta correlated with increased phosphorylation of adducin at Ser726 in intact cells. In vitro, PKCdelta, but not PKCalpha, directly phosphorylated the Ser726 of adducin. Finally, we demonstrated that overexpression of both adducin and PKCdelta could generate a synergistic effect on promoting cell spreading and cell migration. Our results support a positive role for PKCdelta in cell motility and strongly suggest a link between PKCdelta activity, adducin phosphorylation and cell motility.

Parathyroid hormone activates PKC-delta and regulates osteoblastic differentiation via a PLC-independent pathway

PTH exerts major effects upon bone by activating PTH/PTHrP receptors (PTH1Rs) expressed on osteoblasts. The PTH1R is capable of engaging multiple signaling pathways in parallel, including Gs/adenylyl cyclase (AC), Gq/phospholipase C/protein kinase C (PLC/PKC) and a distinct mechanism, involving activation of PKC via a PLC-independent pathway, that depends upon ligand determinants within the PTH(29-34) sequence. The involvement of PLC-dependent vs. PLC-independent PKC activation in PTH action was studied in clonal PTH1R-expressing murine calvarial osteoblasts ("Wt9") using two signal-selective analogs, [G1,R19]hPTH(1-28) and [G1,R19]hPTH(1-34). Both analogs lack PLC signaling but differ in their capacity to activate the PLC-independent PKC pathway. Both hPTH(1-34) and [G1,R19]hPTH(1-34), but not [G1,R19]hPTH(1-28), increased differentiation of Wt9 cells during a 16-day alternate-daily treatment protocol. Wt9 cells expressed PKC-betaI, -delta, -epsilon and -zeta, none of which exhibited net translocation to membranes in response to hPTH(1-34) or either analog. hPTH(1-34) induced activation of membrane-associated PKC-delta, however, and a time- and concentration-dependent increase in cytosolic [phospho-Thr505]PKC-delta which was maximal within 40 s at 100 nM in both Wt9 cells and primary osteoblasts. This response was mimicked by [G1,R19]hPTH(1-34) but not by [G1,R19]hPTH(1-28). Increased expression of bone sialoprotein (BSP) and osteocalcin (OC) mRNAs induced by PTH(1-34) and [G1,R19]hPTH(1-34) in Wt9 cells was blocked by rottlerin, a PKC-delta inhibitor. We conclude that PTH1Rs activate PKC-delta by a PLC-independent, PTH(29-34)-dependent mechanism that promotes osteoblastic differentiation.

Insulin rapidly upregulates protein kinase Cdelta gene expression in skeletal muscle

Recent studies in our laboratories have shown that Protein Kinase C delta (PKCdelta) is essential for insulin-induced glucose transport in skeletal muscle, and that insulin rapidly stimulates PKCdelta activity skeletal muscle. The purpose of this study was to examine mechanisms of regulation of PKCdelta protein availability. Studies were done on several models of mammalian skeletal muscle and utilized whole cell lysates of differentiated myotubes. PKCdelta protein levels were determined by Western blotting techniques, and PKCdelta RNA levels were determined by Northern blotting, RT-PCR and Real-Time RT-PCR. Insulin stimulation increased PKCdelta protein levels in whole cell lysates. This effect was not due to an inhibition by insulin of the rate of PKCdelta protein degradation. Insulin also increased 35S-methionine incorporation into PKCdelta within 5-15 min. Pretreatment of cells with transcription or translation inhibitors abrogated the insulin-induced increase in PKCdelta protein levels. We also found that insulin rapidly increased the level of PKCdelta RNA, an effect abolished by inhibitors of transcription. The insulin-induced increase in PKCdelta expression was not reduced by inhibition of either PI3 Kinase or MAP kinase, indicating that these signaling mechanisms are not involved, consistent with insulin activation of PKCdelta. Studies on cells transfected with the PKCdelta promoter demonstrate that insulin activated the promoter within 5 min. This study indicates that the expression of PKCdelta may be regulated in a rapid manner during the course of insulin action in skeletal muscle and raise the possibility that PKCdelta may be an immediate early response gene activated by insulin.

Central role of PKCdelta in glycoxidation-dependent apoptosis of human neurons

Accumulation of advanced glycation end products (AGEs) induces alterations in the intracellular redox balance, leading cells to functional injury. Current literature reports that intracellular signaling triggered by the interaction of AGEs with their specific receptors RAGEs depends on the cell type and the state of activation/stress. In this work, NT2 human neurons were exposed for 48 h to glycated fetal serum containing 750-3000 pmol/ml pentosidine; the treatment induced an increase in apoptosis rate linear with AGE concentration up to 1500 pmol/ml, but necrotic death was elicited with the highest AGE amount employed (3000 pmol/ml pentosidine). Pentosidine at 1500 pmol/ml, which was the concentration responsible for the highest apoptotic effect (40% of apoptotic neurons), was able to determine early generation of intracellular reactive oxygen species and increase in RAGE levels. Under these conditions, protein kinase C (PKC) delta activity was increased approximately 2-fold, and DNA binding activity of redox-sensitive transcription factor activator protein-1 (AP-1) was enhanced 2.5-fold. A relationship among oxidative stress, PKCdelta activity, AP-1 activation, and apoptosis was demonstrated by pretreating neurons with 500 muM vitamin E, with 20 mug/ml Ginkgo biloba extract, or with 3 muM Rottlerin, inhibitor of PKCdelta; these pretreatments were able to protect neurons from the glycoxidation-dependent effects.

Altered PDGF-BB-induced p38 MAP kinase activation in diabetic vascular smooth muscle cells: roles of protein kinase C-delta

OBJECTIVE

We investigated the regulation of p38 mitogen-activated protein kinase (MAPK) by platelet-derived growth factor (PDGF)-BB and its biological effects in cultured normal and diabetic rat vascular smooth muscle cells (VSMCs).

METHODS AND RESULTS

VSMC growth from diabetic rats was faster than that from normal rats. The expression of the PDGF beta-receptor in diabetic VSMCs was significantly elevated compared with that in normal cells, and PDGF-BB-induced p38 phosphorylation in diabetic cells was more enhanced via MAPK kinase (MKK) 3/6. The level of PKC activity in diabetic cells increased more than that in normal cells with or without PDGF-BB. Although protein kinase C (PKC)-betaII and PKC-delta were activated by diabetes, PDGF-BB could further enhance the level of PKC-delta alone. PDGF-BB-induced cell migration was more elevated in diabetic VSMCs, and the increase was significantly inhibited by SB-203580, rottlerin, and antisense oligodeoxynucleotides for PKC-delta. PDGF-BB-induced p38 phosphorylation also regulated cell growth, cyclooxygenase-2 levels, and arachidonic acid release, but not apoptosis. These levels were more elevated in diabetic cells, which were inhibited by SB-203580.

CONCLUSIONS

Our study established that PDGF-BB phosphorylated p38 via PKC-delta and the subsequent MKK 3/6, leading to cell growth regulation and the progression of a chronic inflammatory process in diabetic VSMCs.

Protein kinase C zeta transactivates hypoxia-inducible factor alpha by promoting its association with p300 in renal cancer

Hydroxylation at an asparagine residue at the COOH-terminal activation domain of hypoxia-inducible factor (HIF)-1/2 alphas is essential for its inactivation under normoxic condition. To date, the mechanism by which HIF-alpha avoids the inhibitory effect of asparagine hydroxylase in renal cell carcinoma (RCC) in normoxia is undefined. We have shown herein that protein kinase C (PKC) zeta has an important role in HIF-alpha activation in RCC. By using dominant negative mutant and small interference RNA approaches, we have demonstrated that the association between HIF-alpha and p300 is modulated by PKCzeta. Moreover, a novel signaling pathway involving phosphatidylinositol 3'-kinase and PKCzeta has been shown to be responsible for the activation of HIF-alpha by inhibiting the mRNA expression of FIH-1 (factor inhibiting HIF-1) in RCC and thereby promoting the transcription of hypoxia-inducible genes such as vascular permeability factor/vascular endothelial growth factor.

Role of PKC-delta activity in glutathione-depleted neuroblastoma cells

Protein kinases C (PKCs) are a family of isoenzymes sensitive to oxidative modifications and involved in the transduction signal pathways that regulate cell growth. As such, they can act as cellular sensors able to intercept intracellular redox changes and promote the primary adaptive cell response. In this study, we have demonstrated that PKC isoforms are specifically influenced by the amount of intracellular glutathione (GSH). The greatest GSH depletion is associated with a maximal reactive oxygen species (ROS) production and accompanied by an increase in the activity of the delta isoform and a concomitant inactivation of alpha. ROS generation induced early morphological changes in GSH-depleted neuroblastoma cells characterized, at the intracellular level, by the modulation of PKC-delta activity that was involved in the pathway leading to apoptosis. When cells were pretreated with rottlerin, their survival was improved by the ability of this compound to inhibit the activity of PKC-delta and to counteract ROS production. These results define a novel role of PKC-delta in the cell signaling pathway triggered by GSH loss normally associated with many neurodegenerative diseases and clinically employed in the treatment of neuroblastoma.

Calcium and protein kinase C (PKC)-related kinase mediate alpha 1A-adrenergic receptor-stimulated activation of phospholipase D in rat-1 cells, independent of PKC

A previous study conducted in rat-1 cells expressing alpha(1A)-adrenergic receptors showed that phenylephrine (PHE) stimulates phospholipase D (PLD) activity. This study was conducted to determine the contribution of protein kinase C (PKC) to PHE-induced PLD activation in these cells. PKC inhibitors bisindolylmaleimide (BIM) I and Ro 31-8220, but not Gö 6976 or a pseudosubstrate peptide inhibitor of PKCalpha, decreased PLD activity and arachidonic acid release elicited by PHE. However, antisense oligonucleotides directed against PKC alpha, delta, epsilon, and eta reduced PKC isoform levels by about 80% but failed to alter PHE-induced PLD activation, indicating that these PKC isoforms are not involved in PLD activation elicited by alpha1A-adrenergic receptor stimulation. Ectopic expression of a kinase-deficient mutant of the PKC-related kinase PKN significantly attenuated PHE-induced PLD activation. On the other hand, BIM I and Ro 31-8220 blocked PHE-mediated increase in intracellular Ca2+ but Gö 6976 and the peptide inhibitor did not. In the absence of extracellular Ca2+, PHE failed to increase PLD activity. These results indicate that alpha1A-adrenergic receptor-stimulated PLD activation is mediated by a mechanism independent of PKCalpha, delta, epsilon, and eta, but dependent on a PKC-related kinase, PKN. Moreover, PKC inhibitors BIM I and Ro 31-8220 block PHE-induced PLD activity by inhibiting calcium signal. Caution should be used in interpreting the data obtained with PKC inhibitors in vivo.

Phospholipase D1 is threonine-phosphorylated in human-airway epithelial cells stimulated by sphingosine-1-phosphate by a mechanism involving Src tyrosine kinase and protein kinase Cdelta

The regulatory role of protein kinase C (PKC) delta isoform in the stimulation of phospholipase D (PLD) by sphingosine-1-phosphate (SPP) in a human-airway epithelial cell line (CFNPE9o(-)) was revealed by using antisense oligodeoxynucleotide to PKCdelta, in combination with the specific inhibitor rottlerin. Cell treatment with antisense oligodeoxynucleotide, but not with sense oligodeoxynucleotide, completely eliminated PKCdelta expression and resulted in the strong inhibition of SPP-stimulated phosphatidic acid formation. Indeed, among the PKCalpha, beta, delta, epsilon and zeta isoforms expressed in these cells, only PKCdelta was activated on cell stimulation with SPP, as indicated by translocation into the membrane fraction. Furthermore, pertussis toxin and genistein eliminated both PKCdelta translocation and PLD activation. In particular, a significant reduction in phosphatidylbutanol formation by SPP was observed in the presence of 4-amino-5-(4-methylphenyl)-7-(t-butyl) pyrazolo [3,4-d] pyrimidine (PP1), an inhibitor of Src tyrosine kinase. Furthermore, the activity of Src kinase was slightly increased by SPP and inhibited by PP1. However, the level of PKCdelta tyrosine phosphorylation was not increased in SPP-stimulated cells, suggesting that Src did not directly phosphorylate PKCdelta. Finally, the level of serine phosphorylation of PLD1 and PLD2 isoforms was not changed, whereas the PLD1 isoform alone was threonine-phosphorylated in SPP-treated cells. PLD1 threonine phosphorylation was strongly inhibited by rottlerin, by anti-PKCdelta oligodeoxynucleotide and by PP1. In conclusion, in CFNPE9o(-) cells, SPP interacts with a membrane receptor linked to a G(i) type of G-protein, leading to activation of PLD, probably the PLD1 isoform, by a signalling pathway involving Src and PKCdelta.

Activation of PKC-beta isoforms mediates HNE-induced MCP-1 release by macrophages

4-Hydroxynonenal (HNE) in the concentration range detectable in many pathophysiologic conditions is able to modulate signal transduction cascades and gene expression. Here, we report the stimulating effect of 1 microM HNE on the release of the monocyte chemotactic protein-1 (MCP-1) by murine macrophages. MCP-1-increased export following 1-h cell treatment with HNE proved to be comparable to that exerted by standard amounts of bacterial lipopolysaccharide (LPS). However, the key molecular event in HNE-induced secretion of MCP-1 appeared to be the increased activity of beta-PKC isoforms, which are recognized as playing a role in the regulation of cell protein transport and secretion. On the other hand, in LPS-stimulated cells, the delta isoform was seen to be involved and was probably related to LPS-mediated effects on MCP-1 expression and synthesis. In conclusion, HNE might interact with other pro-inflammatory stimuli, like LPS, in a concerted amplification of MCP-1 production and secretion.

Increased proliferation of B cells and auto-immunity in mice lacking protein kinase Cdelta

Protein kinase C (PKC), which comprises 11 closely related isoforms, has been implicated in a wide variety of cellular processes, such as growth, differentiation, secretion, apoptosis and tumour development. Among the PKC isotypes, PKC-delta is unique in that its overexpression results in inhibition of cell growth. Here we show that mice that lack PKC-delta exhibit expansion of the B-lymphocyte population with the formation of numerous germinal centres in the absence of stimulation. The rate of proliferation in response to stimulation was greater for B cells from PKC-delta-deficient mice than for those from wild-type mice. Adoptive transfer experiments suggested that the hyperproliferation phenotype is B-cell autonomous. Production of interleukin-6 was markedly increased in B cells of PKC-delta-null mice as a result of an increase in the DNA-binding activity of NF-IL6. Furthermore, the PKC-delta-deficient mice contain circulating autoreactive antibodies and display immune-complex-type glomerulonephritis, as well as lymphocyte infiltration in many organs. These results suggest that PKC-delta has an indispensable function in negative regulation of B-cell proliferation, and is particularly important for the establishment of B-cell tolerance.

An important role for protein kinase C-delta in human keratinocyte migration on dermal collagen

Migration of human keratinocytes plays a critical role in the re-epithelialization of human skin wounds, the process by which the wound bed is resurfaced and closed by keratinocytes as it forms a new epidermis. While the importance of ECM components and serum factors in the regulation of keratinocytes motility is well established, the intracellular signaling mechanisms remain fragmentary. In this study, we investigated the role of protein kinase Cdelta (PKCdelta) signaling in the promotion of human keratinocyte migration by a collagen matrix and bovine pituitary extract. We found that pharmacological inhibition of the PKCdelta pathway completely blocks migration. Using a lentivirus-based vector system, which offers more than 90% gene transduction efficiency to human keratinocytes, we show that the kinase-defective mutant of PKCdelta (K376R) dramatically inhibits human keratinocyte migration. Furthermore, PKCdelta is activated in migrating human keratinocytes. These observations indicate for the first time that the PKCdelta pathway plays an important role in the control of human keratinocyte migration.

PKC-delta inhibits anchorage-dependent and -independent growth, enhances differentiation, and increases apoptosis in CaCo-2 cells

BACKGROUND & AIMS

Previous studies showed decreased protein kinase C (PKC)-delta expression in azoxymethane-induced rat and sporadic human colonic tumors. To elucidate the role of PKC-delta on the neoplastic phenotype of human colon cancer cells, we established stable transfectants of this isoenzyme in CaCo-2 cells.

METHODS

Human PKC-delta complementary DNA was subcloned into 2 distinct metallothionein-regulated expression vectors. Polyclonal populations of PKC-delta transfectants were characterized by Western blotting. PKC-delta activity was measured in situ using a PKC-delta-specific substrate. Proliferation was determined by Coulter counter, and cell cycle distribution was analyzed by flow cytometry. In vitro transformation was assessed by growth in soft agar and differentiation by changes in alkaline phosphatase and sucrase isomaltase. Apoptosis was evaluated by 4',6-diamidino-2-phenylindole dihydrochloride and terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling staining.

RESULTS

In the presence of Zn(2+), PKC-delta transfectants expressed a 4-fold increase in the protein and a 2-fold increase in activity of PKC-delta. PKC-delta transfectants exhibited a 30% decrease (P < 0.05) in cell growth and an enhanced differentiation phenotype. Increased PKC-delta expression induced a significant G0/G1 arrest, inhibited anchorage-independent growth (50%, P < 0.05), and caused a 2-fold increase in apoptosis (P < 0.05).

CONCLUSIONS

Our studies show that increased expression of PKC-delta inhibits anchorage-dependent and -independent growth, while inducing cellular differentiation and limiting survival of this human colon cancer cell line.

Protein kinase C delta regulates neural cell adhesion molecule polysialylation state in the rat brain

Polysialylation of neural cell adhesion molecule (NCAM PSA) modulates cell-cell homophilic binding and signalling during brain development and the remodelling of discrete brain regions in the adult. Following learning, a transient increase in the frequency of polysialylated neurones occurs in the dentate gyrus of the hippocampal formation, and this has been correlated with the selective retention and/or elimination of synapses that are transiently overproduced during memory consolidation. We now demonstrate that protein kinase C delta (PKCdelta) negatively regulates polysialyltransferase activity in the rat brain during development and also in the hippocampus during memory consolidation, where its down-regulation in the Golgi membrane fraction coincides with the transient increase in NCAM PSA expression. Decreased expression of PKCdelta was also observed in the hippocampus of rats reared in a complex environment and this directly contrasted the significant increase in frequency of hippocampal polysialylated neurones observed in these animals. These effects were isoform-specific as no change in total PKC enzyme activity was detected during memory consolidation and complex environment rearing had no effect on the hippocampal expression of PKCalpha, beta, gamma or epsilon. By sequential immunoprecipitation and immunoblot analysis, phosphorylation of polysialyltransferase protein(s) was (were) demonstrated to occur on both serine and tyrosine residues and this was associated with decreased enzyme activity. Moreover, a similar experimental approach revealed the degree of PKCdelta co-precipitation with polysialyltransferase protein(s) to be inversely correlated with polysialyltransferase activity. These findings support in vitro evidence indicating PKCdelta to regulate polysialyltransferase activity and NCAM polysialylation state.

Differential regulation of Cl- transport proteins by PKC in Calu-3 cells

Cl- transport proteins expressed in a Calu-3 airway epithelial cell line were differentiated by function and regulation by protein kinase C (PKC) isotypes. mRNA expression of Cl- transporters was semiquantitated by RT-PCR after transfection with a sense or antisense oligonucleotide to the PKC isotypes that modulate the activity of the cystic fibrosis transmembrane conductance regulator [CFTR (PKC-epsilon)] or of the Na/K/2Cl (NKCC1) cotransporter (PKC-delta). Expression of NKCC1 and CFTR mRNAs and proteins was independent of antisense oligonucleotide treatment. Transport function was measured in cell monolayers grown on a plastic surface or on filter inserts. With both culture methods, the antisense oligonucleotide to PKC-epsilon decreased the amount of PKC-epsilon and reduced cAMP-dependent activation of CFTR but not alpha(1)-adrenergic activation of NKCC1. The antisense oligonucleotide to PKC-delta did not affect CFTR function but did block alpha(1)-adrenergic activation of NKCC1 and reduce PKC-delta mass. These results provide the first evidence for mRNA and protein expression of NKCC1 in Calu-3 cells and establish the differential regulation of CFTR and NKCC1 function by specific PKC isotypes at a site distal to mRNA expression and translation in airway epithelial cells.

Glutathione depletion induces apoptosis of rat hepatocytes through activation of protein kinase C novel isoforms and dependent increase in AP-1 nuclear binding

Treatment of isolated rat hepatocytes with the glutathione depleting agents L-buthionine-S,R-sulfoximine or diethylmaleate reproduced various cellular conditions of glutathione depletion, from moderate to severe, similar to those occurring in a wide spectrum of human liver diseases. To evaluate molecular changes and possible cellular dysfunction and damage consequent to a pathophysiologic level of GSH depletion, the effects of this condition on protein kinase C (PKC) isoforms were investigated, since these are involved in the intracellular specific regulatory processes and are potentially sensitive to redox changes. Moreover, a moderate perturbation of cellular redox state was found to activate novel PKC isoforms, and a clear relationship was shown between novel kinase activation and nuclear binding of the redox-sensitive transcription factor, activator protein-1 (AP-1). Apoptotic death of a significant number of cells, confirmed in terms of internucleosomal DNA fragmentation was a possible effect of these molecular reactions, and was triggered by a condition of glutathione depletion usually detected in human liver diseases. Finally, the inhibition of novel PKC enzymatic activity in cells co-treated with rottlerin, a selective novel kinase inhibitor, prevented glutathione-dependent novel PKC up-regulation, markedly moderated AP-1 activation, and protected cells against apoptotic death. Taken together, these findings indicate the existence of an apoptotic pathway dependent on glutathione depletion, which occurs through the up-regulation of novel PKCs and AP-1.

Regulation of neural cell adhesion molecule polysialylation state by cell-cell contact and protein kinase C delta

Post-translational modification of neural cell adhesion molecule (NCAM) with alpha2,8-linked polysialic acid, which regulates homophilic adhesion and/or signal transduction events, is crucial to synaptic plasticity in the developing and adult brain. Evidence from in vitro models has implicated polysialylation in the regulation of cell growth, migration, and differentiation. Here, using two in vitro models, we demonstrate that polysialylation is downregulated by cell-cell contact and correlated with a state of neuronal differentiation. Furthermore, we report a role for protein kinase C delta (PKCdelta) in the regulation of NCAM polysialylation. Pharmacological studies using the PKC activator, phorbol myristate acetate, and inhibitors, calphostin-C, and staurosporine, demonstrated PKC activity to be inversely related to NCAM polysialylation in the mouse neuro-2A cell line. Isoform-specific immunoblot studies indicated this effect to be mediated by the calcium-independent PKCdelta isozyme, as its expression was inversely related to NCAM polysialylation state in both neuro-2A and rat PC-12 cell lines. Isoform specificity was further confirmed using the PKCdelta-selective inhibitor rottlerin, which produced a marked increase in PSA expression (36.9+/-5.25 a.u. vs. 24.7+/-0.80 arbitrary units control) coupled with a neuritogenic response. Likewise, decreased expression of PKCdelta was seen in nerve growth factor (NGF)-differentiated PC-12 cells. These findings suggest that the neuronal differentiation process may involve inhibition of PKCdelta, resulting in enhanced morphological plasticity, as evidenced by activation of NCAM polysialylation.

Oxidative stress induces increase in intracellular amyloid beta-protein production and selective activation of betaI and betaII PKCs in NT2 cells

Amyloid beta-protein (Abeta) aggregation produces an oxidative stress in neuronal cells that, in turn, may induce an amyloidogenic shift of neuronal metabolism. To investigate this hypothesis, we analyzed intra- and extracellular Abeta content in NT2 differentiated cells incubated with 4-hydroxy-2,3-nonenal (HNE), a major product of lipid peroxidation. In parallel, we evaluated protein kinase C (PKC) isoenzymes activity, a signaling system suspected to modulate amyloid precursor protein (APP) processing. Low HNE concentrations (0.1-1 microM) induced a 2-6 fold increase of intracellular Abeta production that was concomitant with selective activation of betaI and betaII PKC isoforms, without affecting either cell viability or APP full-length expression. Selective activation of the same PKC isoforms was observed following NT2 differentiation. Our findings suggest that PKC beta isoenzymes are part of cellular mechanisms that regulate production of the intracellular Abeta pool. Moreover, they indicate that lipid peroxidation fosters intracellular Abeta accumulation, creating a vicious neurodegenerative loop.

Protein kinase C-α isoform is involved in erythropoietin-induced erythroid differentiation of CD34+ progenitor cells from human bone marrow

Protein kinase C (PKC) is a family of serine/threonine protein kinases involved in many cellular responses. Although the analysis of PKC activity in many systems has provided crucial insights to its biologic function, the precise role of different isoforms on the differentiation of normal hematopoietic progenitor cells into the various lineages remains to be investigated. The authors have assessed the state of activation and protein expression of PKC isoforms after cytokine stimulation of CD34+ progenitor cells from human bone marrow. Freshly isolated CD34+ cells were found to express PKC-, PKC-β2, and PKC-ɛ, whereas PKC-δ, PKC-γ, and PKC-ζ were not detected. Treatment with erythropoietin (EPO) or with EPO and stem cell factor (SCF) induced a predominantly erythroid differentiation of CD34+ cells that was accompanied by the up-regulation of PKC- and PKC-β2 protein levels (11.8- and 2.5-fold, respectively) compared with cells cultured in medium. Stimulation with EPO also resulted in the nuclear translocation of PKC- and PKC-β2 isoforms. Notably, none of the PKC isoforms tested were detectable in CD34+ cells induced to myeloid differentiation by G-CSF and SCF stimulation. The PKC inhibitors staurosporine and calphostin C prevented EPO-induced erythroid differentiation. Down-regulation of the PKC-, PKC-β2, and PKC-ɛ expression by TPA pretreatment, or the down-regulation of PKC- with a specific ribozyme, also inhibited the EPO-induced erythroid differentiation of CD34+ cells. No effect was seen with PKC-β2–specific ribozymes. Taken together, these findings point to a novel role for the PKC- isoform in mediating EPO-induced erythroid differentiation of the CD34+ progenitor cells from human bone marrow.

PKC signaling in CF/T43 cell line: regulation of NKCC1 by PKC-delta isotype

Cystic fibrosis (CF) airway epithelial cells have a reduced mass of ether-linked diacylglycerols which might alter protein kinase C (PKC)-regulated Cl secretion. PKC regulation of basolateral Na-K-2Cl cotransport (NKCC1) was investigated in CF nasal polyp epithelial cells and a CF/T43 cell line to ascertain whether PKC signaling was altered in CF. NKCC1 was detected as bumetanide-sensitive (86)Rb influx. Methoxamine, a alpha(1)-adrenergic agonist, increased PKC activity in cytosol and a particulate fraction for a prolonged time period, as predicted from previous studies on the generation of diglycerides induced with methoxamine. Short-term stimulation of CF/T43 cells for 40 s promoted a shift in PKC-delta and -zeta to a particulate fraction, increased activity of immune complexes of cytosolic PKC-delta and of particulate PKC-zeta and increased activity of NKCC1. Pretreatment with antisense oligonucleotide to PKC-delta blocked methoxamine-stimulated PKC-delta activity, reduced PKC-delta mass by 61.4%, and prevented methoxamine-stimulated activity of NKCC1. Sense and missense oligonucleotide to PKC-delta and antisense oligonucleotide to PKC-zeta did not alter expression of PKC-delta or the effects of methoxamine. These results demonstrate that PKC-delta-dependent activation of NKCC1 is preserved in CF cells and suggest that regulation of NKCC1 is independent of low ether-linked diglyceride mass.

Protein kinase C delta

The protein kinase C (PKC) family consists of 11 isoenzymes that, due to structural and enzymatic differences, can be subdivided into three groups: The Ca(2+)-dependent, diacylglycerol (DAG)-activated cPKCs (conventional PKCs: alpha, beta 1, beta 2, gamma); the Ca(2+)-independent, DAG-activated nPKCs (novel PKCs: delta, epsilon, eta, theta, mu), and the Ca(2+)-dependent, DAG non-responsive aPKCs (atypical PKCs: zeta, lambda/iota). PKC mu is a novel PKC, but with some special structural and enzymatic properties.

Protein kinase C-theta is specifically localized on centrosomes and kinetochores in mitotic cells

In this study we provide evidence that the protein kinase C (PKC)-straight theta isoenzyme is recruited on to the mitotic spindle in dividing murine erythroleukaemia (MEL) cells and associates specifically with centrosome and kinetochore structures. None of the other PKC isoenzymes (-alpha, -delta, -epsilon, -mu and -zeta) expressed by MEL cells shows this localization on the mitotic spindle. An identical subcellular distribution of PKC-straight theta is also observed in dividing murine P3 myeloma cells and human LAN-5 neuroblastoma cells, indicating that this PKC isoenzyme interacts with the mitotic apparatus in mammalian cells. In phorbol-ester-treated non-growing MEL cells, a rapid change in the intracellular distribution of PKC-straight theta occurs. Under these conditions, PKC-straight theta is translocated from the nuclear to the cytosolic cell compartment, an event that is accompanied by phosphorylation of the PKC-straight theta molecule and is followed by its down-regulation. The recovery of cell growth capacity results in the concomitant reappearance of PKC-straight theta. Furthermore, when MEL cells acquire the differentiated non-growing phenotype, the level of PKC-straight theta is reduced to less than 5%, suggesting that this PKC isoenzyme is no longer required. We propose that, unlike other members of the PKC family, PKC-straight theta may play a role in cell proliferation.

Induction of differentiation in normal human keratinocytes by adenovirus-mediated introduction of the eta and delta isoforms of protein kinase C

Protein kinase C (PKC) plays a crucial role(s) in regulation of growth and differentiation of cells. In the present study, we examined possible roles of the alpha, delta, eta, and zeta isoforms of PKC in squamous differentiation by overexpressing these genes in normal human keratinocytes. Because of the difficulty of introducing foreign genes into keratinocytes, we used an adenovirus vector system, Ax, which allows expression of these genes at a high level in almost all the cells infected for at least 72 h. Increased kinase activity was demonstrated in the cells overexpressing the alpha, delta, and eta isoforms. Overexpression of the eta isoform inhibited the growth of keratinocytes of humans and mice in a dose (multiplicity of infection [MOI])-dependent manner, leading to G1 arrest. The eta-overexpressing cells became enlarged and flattened, showing squamous cell phenotypes. Expression and activity of transglutaminase 1, a key enzyme of squamous cell differentiation, were induced in the eta-overexpressing cells in dose (MOI)- and time-dependent manners. The inhibition of growth and the induction of transglutaminase 1 activity were found only in the cells that express the eta isoform endogenously, i.e., in human and mouse keratinocytes but not in human and mouse fibroblasts or COS1 cells. A dominant-negative eta isoform counteracted the induction of transglutaminase 1 by differentiation inducers such as a phorbol ester, 1alpha,25-dihydroxyvitamin D3, and a high concentration of Ca2+. Among the isoforms examined, the delta isoform also inhibited the growth of keratinocytes and induced transglutaminase 1, but the alpha and zeta isoforms did not. These findings indicate that the eta and delta isoforms of PKC are involved crucially in squamous cell differentiation.

Granulocyte-Macrophage Colony-Stimulating Factor Rescues TF-1 Leukemia Cells From Ionizing Radiation-Induced Apoptosis Through a Pathway Mediated by Protein Kinase Cα

Protein kinase C (PKC) activity has a recognized role in mediating apoptosis. However, the role of individual PKC isoforms in apoptosis is poorly defined. Therefore, we investigated the translocation of individual PKC isoforms during radiation-induced apoptosis with and without rescue from apoptosis by granulocyte-macrophage colony-stimulating factor (GM-CSF) in the human erythroleukemia cell line TF-1. PKCα was translocated from the particulate to cytosolic fraction of TF-1 cells within 5 minutes of treatment with apoptosis-inducing levels of ionizing radiation. However, this postirradiation translocation did not occur when cells were rescued from apoptosis by GM-CSF. Furthermore, treatment of cells with Gö6976, an inhibitor of classical PKC isoforms, abrogated the rescue effect of GM-CSF. The calcium-independent novel PKC isoform, PKCδ appeared to be degraded in both the particulate and cytosolic fractions of TF-1 cells after treatment with apoptosis-inducing levels of ionizing radiation in either the presence or absence of GM-CSF rescue. Levels of ceramide, a lipid mediator of apoptosis, were measured at 2, 4, 8, 10, and 60 minutes after treatment with ionizing radiation and were substantially reduced in TF-1 cells rescued from apoptosis by GM-CSF compared with apoptotic TF-1 cells. The largest decrease in ceramide production seen was at 4 minutes postirradiation, with a 46% reduction in ceramide levels in TF-1 cells rescued from apoptosis by GM-CSF compared with those in apoptotic TF-1 cells. Because ceramide has been shown to affect PKCα subcellular distribution, these data implicate a role for ceramide in mediating the rapid postirradiation translocation and inhibition of PKCα in TF-1 cells not rescued from apoptosis by GM-CSF. Expression of the antiapoptotic protein Bcl-2 doubled in TF-1 cells rescued from apoptosis by GM-CSF, but did not increase in unrescued cells. Our findings suggest that activated PKCα and increased expression of Bcl-2 after γ irradiation determine survival in TF-1 cells rescued from apoptosis with GM-CSF and that PKCδ plays a role in mediating signals involved in sensing cellular damage and/or regulation of cell damage repair.

Granulocyte-Macrophage Colony-Stimulating Factor Rescues TF-1 Leukemia Cells From Ionizing Radiation-Induced Apoptosis Through a Pathway Mediated by Protein Kinase Cα

Protein kinase C (PKC) activity has a recognized role in mediating apoptosis. However, the role of individual PKC isoforms in apoptosis is poorly defined. Therefore, we investigated the translocation of individual PKC isoforms during radiation-induced apoptosis with and without rescue from apoptosis by granulocyte-macrophage colony-stimulating factor (GM-CSF) in the human erythroleukemia cell line TF-1. PKCα was translocated from the particulate to cytosolic fraction of TF-1 cells within 5 minutes of treatment with apoptosis-inducing levels of ionizing radiation. However, this postirradiation translocation did not occur when cells were rescued from apoptosis by GM-CSF. Furthermore, treatment of cells with Gö6976, an inhibitor of classical PKC isoforms, abrogated the rescue effect of GM-CSF. The calcium-independent novel PKC isoform, PKCδ appeared to be degraded in both the particulate and cytosolic fractions of TF-1 cells after treatment with apoptosis-inducing levels of ionizing radiation in either the presence or absence of GM-CSF rescue. Levels of ceramide, a lipid mediator of apoptosis, were measured at 2, 4, 8, 10, and 60 minutes after treatment with ionizing radiation and were substantially reduced in TF-1 cells rescued from apoptosis by GM-CSF compared with apoptotic TF-1 cells. The largest decrease in ceramide production seen was at 4 minutes postirradiation, with a 46% reduction in ceramide levels in TF-1 cells rescued from apoptosis by GM-CSF compared with those in apoptotic TF-1 cells. Because ceramide has been shown to affect PKCα subcellular distribution, these data implicate a role for ceramide in mediating the rapid postirradiation translocation and inhibition of PKCα in TF-1 cells not rescued from apoptosis by GM-CSF. Expression of the antiapoptotic protein Bcl-2 doubled in TF-1 cells rescued from apoptosis by GM-CSF, but did not increase in unrescued cells. Our findings suggest that activated PKCα and increased expression of Bcl-2 after γ irradiation determine survival in TF-1 cells rescued from apoptosis with GM-CSF and that PKCδ plays a role in mediating signals involved in sensing cellular damage and/or regulation of cell damage repair.

Ethanol-induced effects on expression level, activity, and distribution of protein kinase C isoforms in rat liver Golgi apparatus

Acute ethanol administration induces significant modifications both in secretive and formative membranes of rat liver Golgi apparatus. The decrease in glycolipoprotein secretion and their retention into the hepatocyte contribute to the pathogenesis of alcohol-induced fatty liver. Molecular and cellular mechanisms behind the ethanol-induced injury of the liver secretory pathway are not yet completely defined. In this study on intact livers from ethanol-treated rats, the involvement of the Golgi compartment in the impairment of hepatic glycolipoprotein secretion has been correlated with changes in the expression level, subcellular distribution and enzymatic activity of protein kinase C (PKC) isoforms. Acute ethanol exposure determined a translocation of classic PKCs and delta isoform from the cytosol to cis and trans Golgi membranes, the site of glycolipoprotein retention in the hepatic cell. A marked stimulation of cytosolic epsilon PKC activity was observed throughout the period of treatment. The presence of activated PKC isozymes at the Golgi compartment of alcohol-treated rat livers may play a role in hepatic secretion and protein accumulation. Direct and indirect effects of ethanol consumption on PKC isozymes and Golgi function are discussed.

Delta-protein kinase C phosphorylation parallels inhibition of nerve growth factor-induced differentiation independent of changes in Trk A and MAP kinase signalling in PC12 cells

We investigated the ability of bryostatin 1 to block nerve growth factor (NGF)-induced differentiation of pheochromocytoma PC12 cells and to effect expression of protein kinase C (PKC) isoforms. Compared with phorbol myristate acetate (PMA), a likewise potent activator of PKC, high doses of bryostatin (> 200 nM) failed to down-regulate delta-PKC, as with zeta-PKC, whereas, alpha-PKC was completely down-regulated. Two forms of delta-PKC were expressed in PC12 cells, a phosphorylated 78.000 M(r) species and a de-phosphorylated 76.000 M(r) form. High-dose bryostatin treatment resulted in a 4.5-fold increase in phosphorylated delta-PKC and a 2.5-fold increase in phosphotyrosine. Inhibition of tyrosine kinase activity, with either herbimycin or genistein, prior to addition of bryostatin abrogated protection from down-regulation and led to simultaneous increases in ubiquitinated 110.000 M(r)-delta-PKC. Similarly, pre-treatment of cells with N-acetyl-L-leucinyl-L-leucinyl-L-norleucinal, an inhibitor of the proteasome pathway, prior to low-dose treatment with bryostatin resulted in a dose-dependent accumulation of delta-PKC and inhibition of down-regulation. Protection of delta-PKC from down-regulation by high-dose bryostatin requires a counter-balance between protein tyrosine kinase and phosphatase systems. High doses of bryostatin blocked NGF-induced neurite outgrowth without altering Y-490 TrK A phosphorylation or an alteration in pp44/42 mitogen-activated protein kinase. Our findings suggest that the phosphorylation state of delta-PKC may regulate its ability to participate in signal coupling and modulation of cell growth and differentiation pathways. Moreover, these data reveal the existence of a signalling pathway independent of MAP kinase that affects NGF differentiation in a negative fashion.

Antisense oligodeoxynucleotide to PKC-delta blocks alpha 1-adrenergic activation of Na-K-2Cl cotransport

A role for protein kinase C (PKC)-delta and -zeta isotypes in alpha 1-adrenergic regulation of human tracheal epithelial Na-K-2Cl cotransport was studied with the use of isotype-specific PKC inhibitors and antisense oligodeoxy-nucleotides to PKC-delta or -zeta mRNA. Rottlerin, a PKC-delta inhibitor, blocked 72% of basolateral-to-apical, bumetanide-sensitive 36Cl flux in nystatin-permeabilized cell monolayers stimulated with methoxamine, an alpha 1-adrenergic agonist, with a 50% inhibitory concentration of 2.3 microM. Methoxamine increased PKC activity in cytosol and a particulate fraction; the response was insensitive to PKC-alpha and -beta II isotype-specific inhibitors, but was blocked by general PKC inhibitors and rottlerin. Rottlerin also inhibited methoxamine-induced PKC activity in immune complexes of PKC-delta, but not PKC-zeta. At the subcellular level, methoxamine selectively elevated cytosolic PKC-delta activity and particulate PKC-zeta activity. Pretreatment of cell monolayers with antisense oligodeoxynucleotide to PKC-delta for 48 h reduced the amount of whole cell and cytosolic PKC-delta, diminished whole cell and cytosolic PKC-delta activity, and blocked methoxamine-stimulated Na-K-2Cl cotransport. Sense oligodeoxynucleotide to PKC-delta and antisense oligodeoxynucleotide to PKC-zeta did not alter methoxamine-induced cotransport activity. These results demonstrate the selective activation of Na-K-2Cl cotransport by cytosolic PKC-delta.

Interleukin-1-induced ether-linked diglycerides inhibit calcium-insensitive protein kinase C isotypes. Implications for growth senescence

It is hypothesized that inflammatory cytokines and vasoactive peptides stimulate distinct species of diglycerides that differentially regulate protein kinase C isotypes. In published data, we demonstrated that interleukin-1, in contrast to endothelin, selectively generates ether-linked diglyceride species (alkyl, acyl- and alkenyl, acylglycerols) in rat mesangial cells, a smooth muscle-like pericyte in the glomerulus. We now demonstrate both in intact cell and in cell-free preparations that these interleukin-1 receptor-generated ether-linked diglycerides inhibit immunoprecipitated protein kinase C delta and epsilon but not zeta activity. Neither interleukin-1 nor endothelin affect de novo protein expression of these protein kinase C isotypes. As down-regulation of calcium-insensitive protein kinase C isotypes has been linked to antimitogenic activity, we investigated growth arrest as a functional correlate for IL-1-generated ether-linked diglycerides. Cell-permeable ether-linked diglycerides mimic the effects of interleukin-1 to induce a growth-arrested state in both G-protein-linked receptor- and tyrosine kinase receptor-stimulated mesangial cells. This signaling mechanism implicates cytokine receptor-induced ether-linked diglycerides as second messengers that inhibit the bioactivity of calcium-insensitive protein kinase C isotypes resulting in growth arrest.