Interferon-alpha selectively activates the beta isoform of protein kinase C through phosphatidylcholine hydrolysis

Metabolomic changes in Mycobacterium avium subsp. paratuberculosis (MAP) challenged Holstein-Friesian cattle highlight the role of serum amino acids as indicators of immune system activation

INTRODUCTION

Paratuberculosis, commonly known as Johne's disease, is a chronic granulomatous infection of ruminants caused by Mycobacterium avium subspecies paratuberculosis (MAP). Clinical signs, including reduced milk yields, weight loss and diarrhoea, are typically absent until 2 to 6 years post exposure.

OBJECTIVES

To identify metabolomic changes profiles of MAP challenged Holstein-Friesian (HF) cattle and correlate identified metabolites to haematological and immunological parameters.

METHODS

At approximately 6 weeks of age, calves (n = 9) were challenged with 3.8 × 10⁹ cells of MAP (clinical isolate CIT003) on 2 consecutive days. Additional unchallenged calves (n = 9) formed the control group. The study used biobanked serum from cattle sampled periodically from 3- to 33-months post challenge. The assessment of sera using flow infusion electrospray high resolution mass spectrometry (FIE-HRMS) for high throughput, sensitive, non-targeted metabolite fingerprinting highlighted differences in metabolite levels between the two groups.

RESULTS

In total, 25 metabolites which were differentially accumulated in MAP challenged cattle were identified, including 20 which displayed correlation to haematology parameters, particularly monocyte levels.

CONCLUSION

The targeted metabolites suggest shifts in amino acid metabolism that could reflect immune system activation linked to MAP and as well as differences in phosphocholine levels which could reflect activation of the Th1 (tending towards pro-inflammatory) immune response. If verified by future work, selected metabolites could be used as biomarkers to diagnose and manage MAP infected cattle.

Interferon-α suppresses hepatitis B virus enhancer II activity via the protein kinase C pathway

HBV has two enhancer (En) regions each of which promotes its own transcription. En II regulates production of pregenomic RNA, a key product of HBV replication, more strongly than En I. Although IFN-α has been found to suppress En I activity, its effect on En II activity has not been examined. Here we used luciferase assay to demonstrate that IFN-α suppresses En II activity. Analysis with several deletion/mutation constructs identified two major segments, nt 1703-1727 and nt 1746-1770, within the En II sequence as being responsible for the suppressive effects of IFN-α. Pre-treatment with protein kinase C (PKC) inhibitors blocked this effect regardless of the expression levels of phospho-STAT1 and Mx upon IFN-α stimulation. These results indicate that IFN-α suppresses En II activity via the PKC pathway, which may be an alternative suppressive pathway for HBV replication. (136 words).

CD38 signaling regulates B lymphocyte activation via a phospholipase C (PLC)-gamma 2-independent, protein kinase C, phosphatidylcholine-PLC, and phospholipase D-dependent signaling cascade

The CD38 cell surface receptor is a potent activator for splenic, B lymphocytes. The molecular mechanisms regulating this response, however, remain incompletely characterized. Activation of the nonreceptor tyrosine kinase, Btk, is essential for CD38 downstream signaling function. The major Btk-dependent substrate in B cells, phospholipase C-gamma2 (PLC-gamma2), functions to generate the key secondary messengers, inositol-1,4,5 trisphosphate and diacylglycerol. Surprisingly, CD38 ligation results in no detectable increase in phosphoinositide metabolism and only a minimal increase in cytosolic calcium. We hypothesized that Btk functioned independently of PLC-gamma2 in the CD38 signaling pathway. Accordingly, we demonstrate that CD38 cross-linking does not result in the functional phosphorylation of PLC-gamma2 nor an increase in inositol-1,4,5 trisphosphate production. Furthermore, splenic B cells exhibit a normal CD38-mediated, proliferative response in the presence of the phosphoinositide-PLC inhibitor, U73122. Conversely, protein kinase C (PKC) beta-deficient mice, or PKC inhibitors, indicated the requirement for diacylglycerol-dependent PKC isoforms in this pathway. Loss of PKC activity blocked CD38-dependent, B cell proliferation, NF-kappaB activation, and subsequent expression of cyclin-D2. These results suggested that an alternate diacylglycerol-producing phospholipase must participate in CD38 signaling. Consistent with this idea, CD38 increased the enzymatic activity of the phosphatidylcholine (PC)-metabolizing enzymes, PC-PLC and phospholipase D. The PC-PLC inhibitor, D609, completely blocked CD38-dependent B cell proliferation, IkappaB-alpha degradation, and cyclin-D2 expression. Analysis of Btk mutant B cells demonstrated a partial requirement for Btk in the activation of both enzymes. Taken together, these data demonstrate that CD38 initiates a novel signaling cascade leading to Btk-, PC-PLC-, and phospholipase D-dependent, PLC-gamma2-independent, B lymphocyte activation.

Regulation of beta-amyloid precursor protein and inositol 1,4,5-trisphosphate receptor gene expression during differentiation of a human neuronal cell line

Retinoic acid-induced differentiation of SH-SY5Y human neuroblastoma cells results in the development of extensive neurite processes as well as changes in cell body morphology toward a neuronal phenotype. The authors have examined concurrent regulation of beta-amyloid precursor protein (APP) and inositol 1,4,5-trisphosphate receptor (insP(3)R) gene expression in SY5Y cells during neuronal differentiation. Of the multiple APP mRNA transcripts expressed in this cell line, retinoic acid treatment significantly increased the expression of APP(695) transcript while the level of total APP remained unchanged. In the same time course, neuronal differentiation decreased the expression of insP(3)R at both the mRNA and protein levels. These findings demonstrate an inverse relationship between APP and insP(3)R gene expression during neuronal differentiation of SH-SY5Y cells and suggest a possible change in intracellular calcium homeostasis.

Activation of phospholipase D is not mediated by direct phosphorylation on tyrosine residues

The activation of phospholipase D (PLD) in PC12/PC2 pheochromocytoma cells involves a tyrosine kinase. However, it is not clear whether this is due to direct phosphorylation of the enzyme or some other intermediary protein. In this manuscript, we examined this issue by two methods: (1) immunoprecipitation of phosphotyrosine containing proteins and assay of phospholipase D; (2) overexpression of HA-phospholipase D2 and susbsequent immunoprecipitation. The only agent that caused phosphorylation of phospholipase D on tyrosine residues was the phosphatase inhibitor, peroxyvanadate. Other agents that activate phospholipase D, including bradykinin, ionomycin, and phorbol dibutyrate did not cause phosphorylation of the enzyme. In addition, there was a lack of correlation between the peroxyvanadate-mediated phosphorylation and activation of phospholipase D, both in terms of time course and concentration dependence. These data demonstrate that phospholipase D is directly phosphorylated on tyrosine residues. However, phosphorylation of tyrosine residues does not correlate with activation of the enzyme.

A PI-3 kinase-dependent, Stat1-independent signaling pathway regulates interferon-stimulated monocyte adhesion

Type I interferon (IFN)-alpha/beta and type II IFN-gamma induce the expression of early response genes through activation of the Janus tyrosine kinase/signal transducer and activator of transcription (Stat) pathway. Although IFNs regulate a variety of other signaling cascades, little is known about how they contribute to the biological activities of these cytokines. In this study, we demonstrate that IFN-beta or IFN-gamma induces the phosphorylation of the serine/threonine kinase Akt in primary human peripheral blood monocytes. Abrogation of the IFN-stimulated Akt activation by phosphatidylinositol-3 kinase (PI-3K) inhibitors prevents IFN-induced adhesion in these cells, and IFN activation of the Stat1-dependent guanylate-binding protein (GBP) gene is not affected. Importantly, Stat1-deficient bone marrow macrophages displayed a similar level of IFN-gamma-stimulated adhesion compared with macrophages derived from wild-type littermates. These findings demonstrate for the first time that IFN stimulation of a PI-3K signaling cascade modulates the ability of these cytokines to regulate monocyte adhesion, and this process does not require the expression of Stat1, a primary mediator of IFN-gamma signaling.

Translocation of PKC isoforms in bovine aortic smooth muscle cells exposed to strain

Our laboratory has previously reported that the exposure of smooth muscle cells (SMC) to the cyclic strain results in significant stimulation of protein kinase C (PKC) activity by translocating the enzyme from the cytosol to the particulate fraction. We now sought to examine the strain-induced translocation of individual PKC isoforms in SMC. Confluent bovine aortic SMC grown on collagen type I-coated plates were exposed to cyclic strain for up to 100 s at average 10% strain with 60 cycles/min. Immunoblotting analysis demonstrates that SMC express PKC-alpha, -beta and -zeta in both cytosolic and particulate fractions. Especially, PKC-alpha and -zeta were predominantly expressed in the cytosolic fraction. However, cyclic strain significantly (P < 0.05) increased PKC-alpha and -zeta in the particulate fraction and decreased in the cytosolic fraction. Thus, the cyclic strain-mediated stimulation of PKC activity in SMC may be due to the translocation of PKC-alpha and -zeta from the cytosolic to the particulate fraction. These results demonstrate that mechanical deformation causes rapid translocation of PKC isoforms, which may initiate a cascade of proliferation responses of SMC since NF-kappaB, which is involved in the cellular proliferation has been known to be activated by these PKC isoforms.

Receptor for activated C-kinase (RACK-1), a WD motif-containing protein, specifically associates with the human type I IFN receptor

The cytoplasmic domain of the human type I IFN receptor chain 2 (IFNAR2c or IFN-alphaRbetaL) was used as bait in a yeast two-hybrid system to identify novel proteins interacting with this region of the receptor. We report here a specific interaction between the cytoplasmic domain of IFN-alphaRbetaL and a previously identified protein, RACK-1 (receptor for activated C kinase). Using GST fusion proteins encoding different regions of the cytoplasmic domain of IFN-alphaRbetaL, the minimum site for RACK-1 binding was mapped to aa 300-346. RACK-1 binding to IFN-alphaRbetaL did not require the first 91 aa of RACK-1, which includes two WD domains, WD1 and WD2. The interaction between RACK-1 and IFN-alphaRbetaL, but not the human IFN receptor chain 1 (IFNAR1 or IFN-alphaRalpha), was also detected in human Daudi cells by coimmunoprecipitation. RACK-1 was shown to be constitutively associated with IFN-alphaRbetaL, and this association was not effected by stimulation of Daudi cells with type I IFNs (IFN-beta1b). RACK-1 itself did not become tyrosine phosphorylated upon stimulation of Daudi cells with IFN-beta1b. However, stimulation of cells with either IFN-beta1b or PMA did result in an increase in detectable immunofluorescence and intracellular redistribution of RACK-1.

Acute effects of interferon on estrogen receptor function do not involve the extracellular signal-regulated kinases p42mapk and p44mapk

Exposure to type I interferons (IFN) increased estrogen receptor (ER) ligand binding and induced protein kinase C (PKC) translocation within 30 min but had no effect on net incorporation of [32P] into ER in Madin Darby bovine kidney (MDBK) cells. Ligand binding was also increased within 30 min by phorbol ester and the protein phosphatase inhibitor okadaic acid. Mitogen-activated protein (MAP) kinase phosphorylation was initially inhibited between 2 and 30 min and subsequently activated between 30 and 60 min after treatment with IFN. The activatory response was blocked by the PKC inhibitor Ro 31-8220. Following transient transfection with an ERE-CAT reporter construct, IFN increased CAT expression after 6 h but decreased ER ligand binding, transcriptional activity and phosphorylation after 48 h, probably as a result of decreased ER concentrations. The results rule out rapid activation of ER ligand binding through phosphorylation at Ser118 by MAP kinase because (1) the increase in ligand binding preceded activation of MAP kinase, and (2) IFN had no short-term effect on [32P]incorporation or ER transcriptional activity. The rapid effect of IFN on ER ligand binding is postulated to reflect phosphorylation of the receptor at Tyr537 by p56lck, a member of the Src family of PKC-activated tyrosine kinases.

Effects of interferons on cortisol production in bovine adrenal fasciculata cells stimulated by adrenocorticotropin

The effects of interferons (IFNs) IFN-alpha, IFN-beta and IFN-gamma on the production of cortisol in bovine adrenal fasciculata cells have been investigated. Pretreatment of the fasciculata cells with recombinant interferon-alpha-2b from man (over 300 units mL(-1)), but not with fibroblast IFN-beta or recombinant IFN-gamma from man, reduced the production of cortisol in cells stimulated with adrenocorticotropin (ACTH) (1 nM). IFN-alpha-2b inhibited ACTH-induced cortisol production in a concentration- (300-15000 units mL(-1)) and time- (2-24h) dependent manner. The inhibitory effect of IFN-alpha-2b on the production was abolished when the cells were simultaneously treated with anti-IFN-alpha antibody, and it was reversible. IFN-alpha-2b also inhibited dibutyryl cyclic AMP-induced production of cortisol but not pregnenolone-induced production. The effect of IFN-alpha-2b was not influenced by increases in external ACTH and Ca2+ concentrations and IFN-alpha-2b did not affect the ACTH-induced increase in cyclic AMP level in the cells. These results strongly suggest that IFN-alpha-2b reduces ACTH-induced production of cortisol in bovine adrenal fasciculata cells by affecting the early process of cortisol synthesis. The results also indicate that IFNs might not directly affect steroidogenesis in the adrenal cortex in-vivo, because of the requirement of high concentrations of IFN-alpha-2b for inhibition, and because of the ineffectiveness of IFN-beta and IFN-gamma.

STAT3 complements defects in an interferon-resistant cell line: evidence for an essential role for STAT3 in interferon signaling and biological activities

STAT proteins play critical roles in the signal transduction pathways for various cytokines. The type I interferons (IFNalpha/beta) promote the DNA-binding activity of the transcription factors STAT1, STAT2, and STAT3. Although the requirement for STAT1 and STAT2 in IFNalpha/beta signaling and action is well documented, the biological importance of STAT3 to IFN action has not yet been addressed. We found that STAT3 plays a critical role in signal transduction by IFNalpha/beta. A human cell line that is resistant to the antiviral and antiproliferative activities of IFN but is still IFN-responsive by virtue of STAT1 and STAT2 activation was found to be defective in STAT3 activation and in induction of NF-kappaB DNA-binding activity. Expression of STAT3 in these resistant cells complemented these signaling defects and also markedly increased cellular sensitivity to the antiviral and antiproliferative effects of IFN. Because STAT3 is involved in the induction of NF-kappaB DNA-binding activity and in the induction of antiviral and antiproliferative activity, our results place STAT3 as an important upstream element in type I IFN signal transduction and in the induction of biological activities. Therefore, our results indicate that STAT1 and STAT2 are not the only STATs required for the expression of the key biological activities of IFNalpha/beta.

The antiviral action of interferon is potentiated by removal of the conserved IRTAM domain of the IFNAR1 chain of the interferon alpha/beta receptor: effects on JAK-STAT activation and receptor down-regulation

The first cloned chain (IFNAR1) of the human interferon-alpha (IFN alpha) receptor acts as a species-specific transducer for type 1 IFN action when transfected into heterologous mouse cells. Stably transfected mouse L929 cell lines expressing truncation mutants of the intracellular domain of the human IFNAR1 chain were tested for biological responses to human IFN alpha. Deletion of the intracellular domain resulted in a complete loss of sensitivity to the biological activity of human IFN but markedly increased IFNAR1 cell surface expression, demonstrating that the intracellular domain is required for biological function and contains a domain that negatively regulates its cell surface expression. Removal of the conserved membrane distal 16-amino-acid IRTAM (Interferon Receptor Tyrosine Activation Motif) sequence: (1) increased sensitivity to IFN alpha's antiviral activity, (2) increased the rapid IFN alpha-dependent formation of STAT-containing DNA-binding complexes, (3) prolonged tyrosine phosphorylation kinetics of the JAK-STAT pathway, and (4) blocked the IFN-dependent down-regulation of the IFNAR1 chain. These results indicate that the IRTAM negatively regulates signalling events required for the induction of IFN's biological actions via regulating receptor down-regulation.

cAMP/phorbol ester response element is involved in transcriptional regulation of the human replacement histone gene H3.3B

The human histone H3.3B gene belongs to the group of replacement histone genes, which are up-regulated during differentiation of cells. Here we provide evidence that a cAMP response element/PMA response element (CRE/TRE) located in the proximal promoter contributes to the expression of the H3.3B gene. (1) Band shift and supershift analysis demonstrated the binding of AP-1 and transcription factors of the CRE-binding protein/activating-transcription-factor family to the H3.3B CRE/TRE. (2) Treatment of HeLa cells with PMA led to a 4-fold increase in H3. 3B mRNA levels within 2 h, whereas transcription of the cell cycle-dependent H3 histone genes remained constant. In contrast with PMA, cAMP did not affect H3.3B transcription. (3) PMA treatment of cells transiently transfected with H3.3B promoter constructs linked to a luciferase gene caused a 4-5-fold increase in reporter gene activity, whereas mutation of the CRE/TRE element abolished the PMA response. These results demonstrate that activation of the protein kinase C pathway by PMA results in an early up-regulation of H3.3B gene expression via the CRE/TRE element. Furthermore treatment with PMA apparently leads to differential induction of H3 histone subtype genes and this in turn can result in a remodelling of chromatin structure of cells before or during differentiation processes.

Regulation of magnesium efflux from rat spleen lymphocytes

Rat spleen lymphocytes (RSL) incubated at 37 degrees C in Mg-free medium (O-trans conditions) exibited Mg2+ efflux with apparent velocity of 0.2 nmol/mg protein/min. After 30 min, this process accounted for the mobilization of about 15% of cell total Mg2+. Half of the Mg2+ efflux depended on extracellular Na+ and was stimulated by cAMP. IFN-alpha significantly enhanced Mg2+ efflux under O-trans conditions as well as in the presence of physiological extracellular Mg2+. Pretreatment of RSL with indomethacin completely abolished IFN-alpha-induced Mg2+ efflux, suggesting a crucial role for cyclooxygenase-dependent arachidonate metabolism. On the other hand, pretreatment of RSL with the PKA inhibitor (Rp)8-Br-cAMPS prevented IFN-alpha stimulation of Mg2+ efflux, indicating the involvement of cAMP. Consistently, both IFN-alpha and exogenous PGE1 increased cAMP from 50 to 125 pmol/mg protein. Altogether these results show that IFN-alpha stimulates Mg2+ efflux by activating arachidonate metabolism and synthesis of prostaglandins. By influencing adenylcyclase activity, PGEs can eventually promote cAMP-dependent Mg2+ efflux, possibly through the activity of a Na-Mg antiport. In RSL, therefore, magnesium movements can be under the control of IFN-alpha and, perhaps, of other cytokines, suggesting the involvement of Mg2+ in cell response to receptor-mediated stimuli.

Protein kinase C is required for induction of 2',5'-oligoadenylate synthetases

Induction of the p40/46 and p69/71 isoforms of the 2',5'-oligoadenylate (2-5A) synthetase by interferon-alpha (IFN-alpha) is variable among six different Burkitt lymphoma cell lines with Ramos cells expressing among the highest levels of these enzymes. Inhibitors of protein kinase C (PKC) block induction of mRNAs encoding both isoforms; however, induction of the p69/71 isoform is more sensitive to these inhibitors. Down-regulation of PKC by prolonged treatment with 12-O-tetradecanoylphorbol-13-acetate (TPA) also blocks induction of 2-5A synthetase mRNAs and decreases both constitutive and IFN-alpha-induced enzymatic activity. Cotreatment of cells with TPA and IFN-alpha increases induction of 2-5A synthetase mRNAs above that seen in cells treated with IFN-alpha alone. IFN-alpha does not directly activate PKC-alpha or PKC-delta, the two most abundant PKC isoforms present in Ramos cells, suggesting that PKC activation by another signaling pathway is necessary for maximal induction of 2-5A synthetases by IFN-alpha.

Formation of the early-region-2 transcription-factor-1-retinoblastoma-protein (E2F-1-RB) transrepressor and release of the retinoblastoma protein from nuclear complexes containing cyclin A is induced by interferon alpha in U937V cells but not in interferon-alpha-resistant U937VR cells

We have analysed the different regulation of cell-cycle-relevant proteins by interferon alpha (IFN alpha) in IFN alpha-sensitive and resistant U937 leukemic cell lines. In contrast to the INF alpha-sensitive U937 variant cell line U937V, the IFN alpha-resistant derivative (U937VR) is insensitive to the antiproliferative activity of IFN alpha. As we found no differences between these cell lines concerning the induction by IFN alpha of the pathway involving tyrosine-protein kinases and the signal transducer and activator of transcription (Jak-Stat), we examined whether cell-cycle-regulating proteins are differently affected by IFN alpha in U937VR and U937VR cells. In U937V cells IFN alpha induced the formation of the complex between early-region-2 transcription factor 1 (E2F-1) and retinoblastoma protein (RB) which is known to repress transcription of E2F-1-inducible genes, necessary for cell cycle progression. Formation of this complex was not inducible by IFN alpha in U937VR cells, although the suitable binding partners (E2F-1 and under-phosphorylated RB) were present. Interestingly, treatment of nuclear extracts from logarithmically growing U937V and U937VR cells with an antiserum against cyclin A that disrupts cyclin-A-containing complexes, led to the formation of the E2F-1-RB complex, suggesting the presence of under-phosphorylated (active) RB, trapped in nuclear complexes that contain cyclin A. This suggestion was supported by combined immunoprecipitation/western blot experiments that revealed a physical interaction between phosphorylated as well as under-phosphorylated forms of RB and cyclin A complex(es) in U937V and U937VR cells. RB, especially the under-phosphorylated form, was released by treatment with IFN alpha from this complex(es) in the case of U937V cells but not U937VR cells. We conclude that the missing induction of the E2F-1-RB transrepressor by IFN alpha and the failure to release RB from cyclin-A-containing complexes might contribute to the resistance of U937VR cells to the antiproliferative effects of IFN alpha.

STAT3 as an adapter to couple phosphatidylinositol 3-kinase to the IFNAR1 chain of the type I interferon receptor

STAT (signal transducers and activators of transcription) proteins undergo cytokine-dependent phosphorylation on serine and tyrosine. STAT3, a transcription factor for acute phase response genes, was found to act as an adapter molecule in signal transduction from the type I interferon receptor. STAT3 bound to a conserved sequence in the cytoplasmic tail of the IFNAR1 chain of the receptor and underwent interferon-dependent tyrosine phosphorylation. The p85 regulatory subunit of phosphatidylinositol 3-kinase, which activates a series of serine kinases, bound to phosphorylated STAT3 and subsequently underwent tyrosine phosphorylation. Thus, STAT3 acts as an adapter to couple another signaling pathway to the interferon receptor.

Protein kinase C in IL-2 signal transduction

Interleukin-2 (IL-2), secreted principally by activated helper T-cells, plays a pivotal role in the generation and regulation of the immune response. The various biologic functions of IL-2 have been the focus of intensive study over the years and have been well worked out. By contrast, an understanding of the intracellular signals coupled to the IL-2 receptor and responsible for mediating IL-2 effects in T-cells is far less developed, and the role that protein kinase C (PKC) may play in the various cellular responses to IL-2 receptor activation is unclear. In this article we will discuss IL-2, its receptors, and IL-2 signal transduction in relation to the physiological roles PKC activation may play in IL-2-mediated activation of T-cells and other hematopoietic cells.

Role of protein kinase activity in apoptosis

The transmission of signals from the plasma membrane to the nucleus involves a number of different pathways all of which have in common protein modification. The modification is primarily in the form of phosphorylation which leads to the activation of a series of protein kinases. It is now evident that these pathways are common to stimuli that lead to mitogenic and apoptotic responses. Even the same stimuli under different physiological conditions can cause either cell proliferation or apoptosis. Activation of specific protein kinases can in some circumstances protect against cell death, while in others it protects the cell against apoptosis. Some of the pathways involved lead to activation of transcription factors and the subsequent induction of genes involved in the process of cell death or proliferation. In other cases, such as for the tumour suppressor gene product p53, activation may be initiated both at the level of gene expression or through pre-existing proteins. Yet in others, while the initial steps in the pathway are ill-defined, it is clear that downstream activation of a series of cystein proteases is instrumental in pushing the cell towards apoptosis. In this report we review the involvement of protein kinases at several different levels in the control of cell behaviour.

Antiproliferative effects of interferon alpha on human pancreatic carcinoma cell lines are associated with differential regulation of protein kinase C isoenzymes

BACKGROUND

The molecular mechanisms mediating the antiproliferative effects of interferon alpha on human pancreatic carcinoma cells are poorly understood.

AIM

To characterise the effects of interferon alpha on protein kinase C isoenzyme expression in interferon alpha sensitive and resistant human pancreatic tumour cell lines.

METHODS

The ductal human pancreatic carcinoma cell lines Capan 1 and Capan 2 were investigated. Anchorage dependent and independent growth was determined by cell number and a human tumour clonogenic assay. Interferon alpha receptor expression was examined by reverse-transcriptase polymerase chain reaction and electrophoretic mobility shift assay. Protein kinase C isoenzyme expression was evaluated by western blotting using monospecific polyclonal antibodies.

RESULTS

Interferon alpha treatment results in a time and dose dependent inhibition of anchorage dependent and independent growth in Capan 1 cells while Capan 2 cells were not affected by interferon alpha. Both cell lines express interferon alpha receptor mRNA transcripts. Growth inhibition by interferon alpha in Capan 1 cells was paralleled by a profound decrease of protein kinase C alpha and zeta expression while these isoenzymes were unaffected in the interferon resistant cell line Capan 2.

CONCLUSION

Inhibition of protein kinase C isoenzyme expression might determine the sensitivity of a given pancreatic carcinoma to respond to the antiproliferative action of interferon alpha.

Regulation of phospholipase D by protein kinase C

In nearly all mammalian cells and tissues examined, protein kinase C (PKC) has been shown to serve as a major regulator of a phosphatidylcholine-specific phospholipase D (PLD) activity. At least 12 distinct isoforms of PKC have been described so far; of these enzymes only the alpha- and beta-isoforms were found to regulate PLD activity. While the mechanism of this regulation has remained unknown, available evidence suggests that both phosphorylating and non-phosphorylating mechanisms may be involved. A phosphatidylcholine-specific PLD activity was recently purified from pig lung, but its possible regulation by PKC has not been reported yet. Several cell types and tissues appear to express additional forms of PLD which can hydrolyze either phosphatidylethanolamine or phosphatidylinositol. It has also been reported that at least one form of PLD can be activated by oncogenes, but not by PKC activators. Similar to activated PKC, some of the primary and secondary products of PLD-mediated phospholipid hydrolysis, including phosphatidic acid, 1,2-diacylglycerol, choline phosphate and ethanolamine, also exhibit mitogenic/co-mitogenic effects in cultured cells. Furthermore, both the PLD and PKC systems have been implicated in the regulation of vesicle transport and exocytosis. Recently the PLD enzyme has been cloned and the tools of molecular biology to study its biological roles will soon be available. Using specific inhibitors of growth regulating signals and vesicle transport, so far no convincing evidence has been reported to support the role of PLD in the mediation of any of the above cellular effects of activated PKC.

Regulation and functional significance of phospholipase D in myocardium

There is now clear evidence that receptor-dependent phospholipase D is present in myocardium. This novel signal transduction pathway provides an alternative source of 1,2-diacylglycerol, which activates isoforms of protein kinase C. The members of the protein kinase C family respond differently to various combinations of Ca2+, phosphatidylserine, molecular species of 1,2-diacylglycerol and other membrane phospholipid metabolites including free fatty acids. Protein kinase C isozymes are responsible for phosphorylation of specific cardiac substrate proteins that may be involved in regulation of cardiac contractility, hypertrophic growth, gene expression, ischemic preconditioning and electrophysiological changes. The initial product of phospholipase D, phosphatidic acid, may also have a second messenger role. As in other tissues, the question how the activity of phospholipase D is controlled by agonists in myocardium is controversial. Agonists, such as endothelin-1, atrial natriuretic factor and angiotensin II that are shown to activate phospholipase D, also potently stimulate phospholipase C-beta in myocardium. PMA stimulation of protein kinase C inactivates phospholipase C and strongly activates phospholipase D and this is probably a major mechanism by which agonists that promote phosphatidyl-4,5-bisphosphate hydrolysis secondary activate phosphatidylcholine-hydrolysis. On the other hand, one group has postulated that formation of phosphatidic acid secondary activates phosphatidyl-4,5-bisphosphate hydrolysis in cardiomyocytes. Whether GTP-binding proteins directly control phospholipase D is not clearly established in myocardium. Phospholipase D activation may also be mediated by an increase in cytosolic free Ca2+ or by tyrosine-phosphorylation.

Interleukin-1 and endothelin stimulate distinct species of diglycerides that differentially regulate protein kinase C in mesangial cells

Diglycerides are phospholipid-derived second messengers that serve as cofactors for protein kinase C activation. We have previously shown that, in rat glomerular mesangial cells, the cytokine, interleukin-1 alpha, and the vasoactive peptide, endothelin, generate diglycerides from unique phospholipid precursors. However, neither the molecular species of these diglycerides nor their biological actions were determined. It is now hypothesized that interleukin-1- and endothelin-treated mesangial cells form distinct molecular species of diglycerides which may serve different roles as intracellular signaling molecules. Diglyceride molecular species were resolved and quantified by TLC and high performance liquid chromatography as diglyceride-[14C]acetate derivatives. Endothelin stimulates predominantly ester-linked species (diacylglycerols) in contrast to interleukin-1 which stimulates only ether-linked species (alkyl, acyl- and alkenyl,acylglycerols). In support of these data, interleukin-1-treated mesangial cells hydrolyze ethanolamine plasmalogens, vinyl ether-linked phospholipids. It has been reported that ether-linked, in contrast to ester-linked, diglyceride species do not activate protein kinase C activity. Thus, we next assessed membrane protein kinase C activity in endothelin- or interleukin-1-treated mesangial cells. Even though interleukin-1 has no effect upon basal protein kinase C activity, this cytokine, through the formation of ether-linked diglyceride second messengers, inhibits endothelin, platelet-activating factor, or arginine vasopressin-stimulated protein kinase C activity. We further demonstrate that ester-linked diacylglycerols but not alkyl,acyl- or alkenyl,acylglycerols substitute for phorbol esters in a cell-free protein kinase C assay. In addition, alkenyl,acylglycerols inhibit diacylglycerol-stimulated immunoprecipitated protein kinase C alpha activity in vitro and total protein kinase C activity in permeabilized mesangial cells ex vivo. Taken together, these data suggest that interleukin-1-induced formation of ether-linked diglycerides may physiologically serve to down-regulate receptor-mediated protein kinase C activity and that individual molecular species of diglycerides may serve different roles as intracellular signaling molecules.

Inhibition of protein phosphorylation modulates expression of the Jak family protein tyrosine kinases

Treatment of murine Friend cells with a dose of the protein kinase inhibitor staurosporine, which is able to block the response of the cells to interferons, appears to inhibit phosphorylation of Jak proteins and, interestingly, to specifically reduce tyk2 and Jak1 expression and to increase Jak2 both in the presence and in the absence of interferons. Therefore, a potential role for phosphorylation events in the regulation of expression of the Jak family members is suggested.

T-cell antigen receptor-induced signal-transduction pathways--activation and function of protein kinases C in T lymphocytes

CONTENTS. T-cell activation--Structure of the T-cell antigen receptor--Modular organisation of the T-cell antigen receptor--T-cell antigen receptor-coupled signaling pathways: Activation of protein-tyrosine kinase by the T-cell antigen receptor; Signal transduction in lymphoid cells involves several protein-tyrosine kinases in parallel; Regulation of T-cell antigen receptor signaling by the phosphoprotein phosphatase CD45--Consequences of T-cell antigen receptor-induced tyrosine phosphorylation: Activation of phosphoinositol-lipid-turnover pathways--Activation of phospholipase C-gamma-1: p59fyn or p56lck?--G-protein motif of CD3-gamma: relevance for signal transduction--Association of lipid kinase with the T-cell antigen receptor--Intracellular signaling by phospholipid metabolites and calcium: activation of protein kinase C--Protein kinase C isoenzymes--Heterogenity of protein kinase C and mode of activation--Phospholipid-derived mediators in activation of protein kinase C in T-cells--Role of phospholipase D metabolites in activation of protein kinase C--Polyunsaturated fatty acids and lysophosphatidylcholine as activators of protein kinase C--Potein kinase C and p21ras function in interdependent and distinct signaling pathways during T-cell activation--Raf-1 kinase: regulator or target of protein kinase C?--Summary and perspectives.

Changes in protein kinases in brain aging and Alzheimer's disease. Implications for drug therapy

There is ample evidence for the involvement of aberrant protein phosphorylation reactions in aging and age-associated neurological disorders. Alzheimer's disease (AD) in particular. The exact nature of this involvement, however, is not yet elucidated. In the brain tissue of AD patients, there are numerous examples of altered protein phosphorylation pathways. Individual protein kinases and phosphorylation by these kinases in AD brain tissues have been found to be altered. Protein kinases studied include protein kinase C (PKC), protein tyrosine kinase (PTK), casein kinase II (CKII), Ca++/calmodulin-dependent kinase II and mitogen-activated protein (MAP) kinases, all of which are thought to be necessary for cell survival. Interestingly, different protein kinases are involved in different aspects of AD pathology. It is postulated that the perturbation of amyloid beta/A4-protein precursor (APP) metabolism triggers abnormal protein phosphorylation reactions responsible for dysfunction and eventual death of neurons in the brain. The association of APP mutation with certain familial types of AD strongly suggests that there might be a link between aberrant APP metabolism, protein phosphorylation cascades and the eventual expression of AD pathology (plaques and tangles) and neurodegeneration. In summary, recent studies emphasise the prime importance of protein phosphorylation in aging and AD. This raises the possibility that future pharmacological interventions might be devised to interfere with this kinase cascade for the prevention or treatment of age-associated neurological disorders.

Role of protein kinase C activation in synthesis of complement components C2 and factor B in interferon-gamma-stimulated human fibroblasts, glioblastoma cell line A172 and monocytes

The synthesis of C2 and factor B, the key components of complement system, is performed by various kinds of cells and is also up-regulated by interferon-gamma (IFN-gamma). By using human fibroblasts, human glioblastoma cell line A172 and monocytes, we investigated the signal-transduction mechanism for IFN-gamma-induced synthesis of C2 and factor B. The C2 and factor B synthesis induced by IFN-gamma in all three cell types was inhibited by a protein kinase C (PKC) inhibitor, 1-(5-isoquinolinyl-sulphonyl)-2-methylpiperazine (H-7). The depletion of PKC in these cell types after treatment with phorbol 12-myristate 13-acetate (PMA) resulted in inhibition of IFN-gamma-induced C2 production. In addition, IFN-gamma treatment elicited a decrease in cytoplasmic PKC in A172 cells, indicating that PKC is activated by IFN-gamma. These results suggest that PKC is crucial for IFN-gamma-induced C2 and factor B synthesis. Northern-blot analysis showed that the effects at H-7 were at least partly mediated by modulation of C2 and factor B mRNA abundance in A172 cells. Since treatment of fibroblasts and A172 cells with IFN-gamma had no effect on intracellular Ca2+ concentration, and since neither EGTA nor nifedipine inhibited C2 or factor B synthesis induced by IFN-gamma, we concluded that intracellular Ca2+ mobilization was not involved in the effect of IFN-gamma. In addition, genistein, herbimycin A and N-(6-aminohexyl)-5-chloro-1-naphthalene-sulphonamide (W-7) had no inhibitory effect on IFN-gamma-mediated action in any of the three cell types, which suggests that IFN-gamma acts independently of tyrosine kinases and calmodulin-dependent protein kinases.

Interleukin 4 receptor signaling in human monocytes and U937 cells involves the activation of a phosphatidylcholine-specific phospholipase C: a comparison with chemotactic peptide, FMLP, phospholipase D, and sphingomyelinase

Interleukin 4 (IL-4) diminishes cytokine activation of human macrophage. IL-4 binding to monocyte IL-4R is associated with protein kinase C (PKC) translocation to a nuclear fraction. The cleavage of diacyglycerol (DAG), an activator of PKC, from membrane phospholipids was investigated to define the proximal events of IL-4R signaling. IL-4 induced a statistically significant time-and dose-dependent generation of DAG. The IL-4-triggered production of DAG was not derived from phosphatidylinositol 4,5-bisphosphate (PIP2) hydrolysis, since neither cytosolic calcium flux nor liberation of inositol phosphates was detected in response to IL-4. Experiments were performed using [14C-methyl]choline-labeled U937 cells and monocytes to determine whether IL-4R activated phospholipase C (PLC), PLD, or PLA2 to use membrane phosphatidylcholine (PC) to form DAG. IL-4 induced a time- and dose-dependent increase of phosphocholine (pchol) with concomitant degradation of membrane PC (p < 0.05 compared with control). The finding that the peak reduction of PC was equivalent to peak production of pchol suggested that IL-4R signaling involved the activation of a PC-specific PLC. Changes in choline (chol) or lyso-PC and glycerolphosphocholine, the respective products of PC cleavage by PLD or PLA2, were not detected in IL-4-treated cells. In contrast, exogenous PLD induced an increase in chol and concomitant loss of membrane PC. Additional investigation suggested that IL-4R signaling does not involve PLD. In cells labeled with L-lyso-3-PC 1-[1-14C]palmitoyl, PLD but not IL-4, increased the production of phosphatidic acid (PA) and phosphatidyl-ethanol when pretreated with ethanol. Propranolol, an inhibitor of phosphatidate phosphohydrolase, and calyculin A, a phosphatase 1 and 2A inhibitor, blocked DAG production in response to FMLP but not to IL-4. In propranolol pretreated cells, PMA but not IL-4 triggered the production of PA and lowered the amount of DAG. Evidence that PLA2 is not coupled to IL-4R is the detection of arachidonate production in response to FMLP but not to IL-4. Furthermore, IL-4R is not coupled to sphingomyelinase (SMase) since IL-4, unlike exogenous SMase, did not generate ceramide but induced the hydrolysis of PC to pchol that was comparable to exogenous PLC. In summary, IL-4R signaling in monocytes and U937 cells involves PLC and not PLD, PLA2, or SMase, and it uses PC and not PIP2 to form DAG.

Selective interferon-alpha/beta effects on platelet-derived growth factor-stimulated processes in quiescent BALB/c-3T3 fibroblasts

Interferon-alpha/beta (IFN-alpha/beta) suppresses cell cycle activation by platelet-derived growth factor (PDGF) as well as the induction of the 31-kD (pI) and the 35-kD (pII) proteins in density-arrested BALB/c-3T3 cells. We report that elevation of [Ca2+]i by ionomycin induces the synthesis of the 31-kD protein, but not that of the 35-kD protein. Since IFN blocks the PDGF-induced elevation of [Ca2+]i, these results suggest that IFN treatment may suppress pI induction by impairing this PDGF-activated signal transduction pathway. In contrast, because ionomycin did not induce the 35-kD protein, the suppression by IFN of PDGF-induced pII appears to be mediated via a pathway distinct from that operating in the suppression of pI. In BALB/c-3T3 cells, IFN-alpha/beta did not itself affect the turnover or de novo synthesis of inositol phospholipids and the cellular content of diacylglycerol, nor did IFN block the enhancement of these parameters by PDGF.

Role of interferon alpha/beta receptor chain 1 in the structure and transmembrane signaling of the interferon alpha/beta receptor complex

A previously cloned cDNA encodes one subunit of the human interferon alpha/beta receptor (IFN alpha R), denoted IFN alpha R1. To study the expression and signaling of IFN alpha R1, we used monoclonal antibodies (mAbs) generated against the baculovirus-expressed ectodomain of IFN alpha R1. Immunoprecipitation and immunoblotting of lysates from a variety of human cell lines showed that IFN alpha R1 has an apparent molecular mass of 135 kDa. Binding analysis with 125I-labeled mAb demonstrated high levels of cell surface expression of IFN alpha R1 in human cells and in mouse cells transfected with IFN alpha R1 cDNA, whereas no cross-reactivity was observed in control mouse L929 cells expressing only the endogenous mouse receptor. The subunit was rapidly down-regulated by IFN alpha (80% decrease within 2 hr) and degraded upon internalization. The IFN alpha R1 chain appeared to be constitutively associated with the 115-kDa subunit of the IFN alpha/beta receptor, since the mAbs coprecipitated this protein. IFN alpha/beta treatment induced tyrosine phosphorylation of IFN alpha R1 within 1 min, with kinetics paralleling that of the IFN-activated protein-tyrosine kinases Jak1 and Tyk2. Ligand-induced tyrosine phosphorylation of IFN alpha R1 was blocked by the kinase inhibitors genistein or staurosporine. Although IFN alpha R1 cDNA-transfected mouse cells expressed high levels of this subunit when compared with empty vector-transfected cells the number of binding sites for human IFN alpha (50-75 sites per cell) was not increased. Human IFN alpha induced the expression of a mouse IFN alpha/beta-responsive gene (the 204 gene) in mouse L929 cells transfected with the IFN alpha R1 cDNA, but not in mock-transfected cells. These results suggest that the IFN alpha R1 subunit acts as a species-specific signal transduction component of the IFN alpha/beta receptor complex.

An immunohistochemical study of protein kinase C distribution in fetal mouse vertebral column

Using polyclonal antibodies we have studied the distribution of protein kinase C in fetal mouse low thoracic vertebrae. By means of a pan protein kinase C antiserum recognizing the catalytic domain of the enzyme, we show that protein kinase C is markedly expressed in chondrocytes before birth. The enzyme seems to be very abundant in the more mature cells that are close to ossification centres as well as the periphery of the intervertebral disc, although it can also be detected in chondrocytes. In order to establish which protein kinase C isoenzyme(s) the chondrocytes produce, we employed polyclonal isoenzyme-specific antisera developed against three calcium-dependent isoforms (alpha, beta, gamma) and three calcium-independent isoforms (delta, epsilon, zeta). Secondary antibody conjugated to alkaline phosphatase revealed that chondrocytes markedly express the beta-isoform. Cells were also weakly stained by the anti-epsilon serum. The immunostaining was completely abolished by pre-incubating primary antibodies with the peptide antigens to which they were raised. These results suggest that protein kinase C (and particularly the beta isoform) could play an important role in mouse fetal chondrogenesis of the vertebral column.

Involvement of protein kinase C in macrophage activation by poly(I.C)

The expression of cytocidal activity is initiated by the interaction of macrophages with priming [e.g., interferon (IFN)] and triggering stimuli (polyinosinic-polycytidylic acid). We have shown that the triggering step can be initiated in a Ca(2+)-dependent fashion and hypothesized that protein kinase C (PKC) may couple the Ca2+ signal to the expression of a gene product, Bf, that accompanies the expression of macrophage cytocidal activity. Exposure of IFN-primed macrophages to polyinosinic-polycytidylic acid in the presence of the PKC inhibitors H-7 or sphingosine or after downregulation of PKC with phorbol myristate acetate markedly inhibited Bf synthesis. Western blots of macrophage lysates revealed the presence of the alpha-, delta-, and zeta-isozymes of PKC, and all were found to be downregulated by phorbol myristate acetate. Inhibition of PKC also prevented the increase in IFN-beta mRNA levels and partially blocked the response to IFN-beta. These data suggest that the alpha-, delta-, and zeta-isozymes of PKC are involved in signaling leading to Bf expression and that the level of involvement is restricted to the induction and response to IFN-beta.

Nerve growth factor activates calcium-insensitive protein kinase C-epsilon in PC-12 rat pheochromocytoma cells

Protein kinase C (PKC) family members were examined in PC-12 rat pheochromocytoma cells to evaluate their role in the action of nerve growth factor (NGF). Immunoblot analysis of whole cell lysates using antibodies against various PKC isoforms revealed that PC-12 cells contained PKC-alpha, -delta, -epsilon and zeta. Assay of the protein kinase activity in these different anti-PKC immunoprecipitates demonstrated that NGF stimulated the kinase activity of PKC-epsilon, but not PKC-alpha, -delta and -zeta. Both histone phosphorylation and autophosphorylation of PKC-epsilon were increased by treatment of PC-12 cells with NGF. This increased phosphorylation observed in vitro is rapid, occurring maximally at 2.5 min and declining thereafter. Moreover, this effect of NGF is dose-dependent over physiological concentrations of the growth factor. Although the mechanistic basis for this specificity in PKC activation is not clear, NGF acutely stimulated the production of diacylglycerol without causing corresponding changes in intracellular Ca2+ concentrations. These results suggest that NGF may selectively stimulate the Ca(2+)-insensitive epsilon isoform of PKC by a phosphatidylinositol-independent mechanism.

A role for protein kinase C-epsilon in angiotensin II stimulation of phospholipase D in rat renal mesangial cells

The role of Ca2+ and protein kinase C (PKC) in the regulation of phosphatidylcholine-hydrolyzing phospholipase D (PLD) was investigated in angiotensin II-stimulated mesangial cells. Elevation of cytosolic free Ca2+ by the calcium ionophore, A23187, or the Ca(2+)-ATPase inhibitor, thapsigargin, slightly increased PLD-stimulated phosphatidylethanol formation. However, chelation of cytosolic Ca2+ with high concentrations of quin 2 did not attenuate angiotensin II-induced phosphatidylethanol production, thus suggesting that Ca2+ is not crucially involved in agonist-stimulated PLD activation. Stimulation of PKC by phorbol esters increased PLD activity in mesangial cells. Down-regulation of PKC-alpha and -delta isoenzymes by 8 h phorbol ester treatment still resulted in full PLD activation. In contrast, a 24 h treatment of mesangial cells with phorbol ester, a regimen that also causes depletion of PKC-epsilon, abolished angiotensin II-evoked phosphatidylethanol formation. In addition, the selective PKC inhibitor, calphostin C, attenuated hormone-induced PLD activity. In summary, these data suggest that angiotensin II stimulation of phospholipase D appears to involve the PKC-epsilon isoenzyme, activated by DAG derived from phosphoinositide hydrolysis.

Differential expression of protein kinase C isoenzymes in normal and psoriatic adult human skin: reduced expression of protein kinase C-beta II in psoriasis

Psoriatic lesions contain elevated levels of 1,2-diacylglycerol, the physiologic activator of protein kinase C (PKC), suggesting that PKC activation may be aberrant in psoriasis. We therefore have investigated the expression and properties of PKC isozymes in normal and psoriatic skin and in human skin cells. Chromatographic and immunoblot analyses revealed the presence of the calcium-dependent PKC isozymes PKC-alpha and -beta, but not -gamma, in normal human epidermis. PKC-beta was more prominent, constituting two thirds of the total calcium-dependent PKC activity. In psoriatic lesions, expression of both PKC-alpha and -beta was decreased, with preferential reduction (80%) of PKC-beta. Northern analysis and semi-quantitative polymerase chain reaction (PCR) indicated no change in the mRNA levels of PKC-alpha and -beta between normal and psoriatic epidermis. In normal epidermis, PKC-alpha was expressed mainly in the lower epidermis, whereas PKC-beta was localized to the upper cell layers, with very intense staining of CD1a+ Langerhans cells. In psoriasis, PKC-alpha staining was present in the lower epidermis, whereas PKC-beta staining was essentially absent, with the exception of some positive inflammatory cells. In addition to PKC-alpha and beta, immunoblot and Northern/PCR analysis revealed expression of four calcium-independent PKC isozymes, delta, epsilon, zeta, and eta, in both normal and psoriatic skin. There were no significant differences in mRNA levels among any of these PKC isozymes, between normal and psoriatic skin. Soluble PKC-zeta protein was modestly increased (twofold) in psoriatic, compared to normal, skin, whereas the levels of PKC-delta, epsilon, and eta were unchanged. Analysis of PKC isozyme expression in the three major cell types of human epidermis revealed that Langerhans cells and keratinocytes were the major sources of PKC-beta and PKC-zeta, respectively. These data demonstrate the diversity of PKC isozyme expression in human skin, and suggest that alterations of PKC-beta and -zeta may participate in the aberrant regulation of growth and differentiation observed in psoriasis.

Transcription termination/polyadenylation occurs at multiple sites in the human type I interferon receptor gene

Based on the previously reported sequence, we isolated an independent cDNA clone encoding a binding component of the human type I interferon receptor (IFN-R). This cDNA is identical to the published sequence except that it lacks 62 bases of 5' untranslated sequence and terminates at the first of two potential polyadenylation sites. In Northern blot analyses of poly(A)+RNAs from both IFN-sensitive and IFN-resistant Daudi cells, this cloned cDNA hybridized to a predominant mRNA of 2.4 kb, as well as to mRNAs of 1.8, 4.8, and 5.6 kb, and occasionally 6.9 kb. These various transcripts, which were also observed at similar levels in Raji B cells and two T-cell lines, Jurkat and MOLT-4, were detected after high-stringency washes, and by alternate probes corresponding to subfragments of the cDNA. In contrast, only the 4.8- and 5.6-kb transcripts hybridized to a polymerase chain reaction (PCR)-derived probe that corresponded to genomic sequences immediately down-stream from the second polyadenylation site. These results indicate that the latter transcripts arise from the same gene as the predominant 2.4-kb mRNA due to incomplete transcription termination at either of the known polyadenylation sites. Finally, Northern blot analysis of total RNAs revealed the presence of the predominant 2.4-kb type I IFN-R transcript in numerous tissues from second trimester human fetuses, suggesting that the type I IFN-R gene is constitutively expressed in multiple cell types.

Extracellular ATP and UTP activation of phospholipase D is mediated by protein kinase C-epsilon in rat renal mesangial cells

1. We have studied whether a nucleotide receptor mediates the effects of extracellular ATP and UTP on phosphatidylcholine metabolism in rat cultured glomerular mesangial cells. 2. ATP and UTP stimulated a biphasic 1,2-diacylglycerol (DAG) formation in [3H]-arachidonic acid-labelled mesangial cells. In contrast, in cells labelled with [3H]-myristic acid, a tracer that preferentially marks phosphatidylcholine, both nucleotides induced a delayed monophasic production of DAG with a concomitant increase in phosphatidic acid and choline formation. 3. A phospholipase D-mediated phosphatidylcholine hydrolysis was further suggested by the observation that ATP and UTP stimulate the accumulation of phosphatidylethanol, when ethanol was added to mesangial cells. 4. The rank order of potency of a series of nucleotide analogues for stimulation of phosphatidylethanol formation was UTP = ATP > ITP > ATP gamma S > beta gamma-imido-ATP = ADP > 2-methylthio-ATP = beta gamma-methylene-ATP = ADP beta S, while AMP, adenosine, CTP and GTP were inactive, indicating the presence of a nucleotide receptor. 5. Elevation of cytosolic free Ca2+ by the calcium ionophore A23187 (1 microM) or the Ca(2+)-ATPase inhibitor, thapsigargin (200 nM) slightly increased phosphatidylethanol formation. However, chelation of cytosolic Ca2+ with high concentrations of Quin 2 did not attenuate ATP- and UTP-induced phosphatidylethanol production, thus suggesting that Ca2+ is not crucially involved in agonist-stimulated phospholipase D activation. 6. The protein kinase C (PKC) activator, phorbol 12-myristate 13-acetate (PMA), but not the biologically inactive 4 alpha-phorbol 12,13-didecanoate, increased phospholipase D activity in mesangial cells, suggesting that PKC may mediate nucleotide-induced phosphatidylcholine hydrolysis. 7. Down-regulation of PKC-alpha and -delta isoenzymes by 8 h PMA treatment still resulted in full phospholipase D activation. In contrast, a 24 h treatment of mesangial cells with PMA, a regimen that also causes depletion of PKC-epsilon, markedly attenuated nucleotide-evoked phosphatidylethanol formation. In addition, the selective PKC inhibitor, calphostin C attenuated ATP- and UTP-induced phosphatidylethanol production.8. In summary, these data suggest that extracellular ATP and UTP use a common nucleotide receptor to activate phospholipase D-mediated phosphatidylcholine hydrolysis. Stimulation of phospholipase D appears to involve the PKC-epsilon isoenzyme, activated by DAG derived from phosphoinositide hydrolysis by phospholipase C.

Interferon alpha induces protein kinase C-epsilon (PKC-epsilon) gene expression and a 4.7-kb PKC-epsilon-related transcript

Protein kinases play key roles in the induction by human interferon alpha (IFN-alpha) of specific gene expression and biological activity in various human cell lines. We now report that IFN-alpha increased the 7-kb transcript for the epsilon isotype of protein kinase C (PKC-epsilon) and the cellular content of PKC-epsilon 24 and 48 hr after IFN-alpha addition (a 2-fold and 6-fold increase, respectively). Furthermore, IFN-alpha markedly induced a 4.7-kb transcript that hybridized to a PKC-epsilon-specific, but not to a PKC-eta-specific, cDNA probe. The induction of the 4.7-kb PKC-epsilon-related mRNA by IFN-alpha had the following properties reported for the classical IFN-alpha-stimulated genes: rapid kinetics of induction, high maintained levels in IFN-alpha-sensitive but not in IFN-alpha-resistant cell lines, protein synthesis-independent induction, and high sensitivity to inhibitors of protein tyrosine kinase activity. These results show that the regulation of gene expression by IFN-alpha include not only the classical IFN-alpha-stimulated genes but also the coordinated regulation of two PKC-epsilon-related transcripts that appeared to be highly relevant to the biological actions of IFN-alpha.

Role of protein kinase C during interferon-gamma- and phorbol ester-stimulated immunocytochemical expression of ICAM-1 in human renal carcinoma cells

Incubation of the human renal carcinoma cell line CaKi-1 with interferon-gamma (IFN-gamma) or the phorbol ester, phorbol-12-myristate 13-acetate (PMA) strongly stimulated the immunocytochemical expression of the intercellular adhesion molecule-1 (ICAM-1) in a dose-dependent manner. Since PMA is capable of activating the Ca2+/phospholipid-dependent protein kinase C (PKC), we investigated the role of this kinase during IFN-gamma signal transduction. Calcium ionophore A23187 significantly enhanced IFN-gamma- and PMA-induced ICAM-1 staining. While staurosporine, H7 and sphingosine, three known PKC inhibitors, blocked the PMA effect, only staurosporine abrogated the action of IFN-gamma. Finally, 24 h of PMA pretreatment with subsequent IFN-gamma stimulation enhanced ICAM-1 staining above values from cultures where IFN-gamma was omitted. This occurred despite the fact that 24 h of PMA pretreatment abolished the effect of IFN-gamma on PKC activation, as determined by acetylated myelin basic protein 4-14 phosphorylation. In conclusion, these results suggest that additional events other than PKC activation are required for complete regulation of ICAM-1 antigen by IFN-gamma in the whole cell population. Hence, other Ca(2+)-dependent signalling pathway(s) mediated by IFN-gamma receptors must act. Further studies are needed to elucidate these specific pathway(s) activated during IFN-gamma stimulation in our model.

Activation of purified human protein kinase C alpha and beta I isoenzymes in vitro by Ca2+, phosphatidylinositol and phosphatidylinositol 4,5-bisphosphate

The increasing number of eukaryotic protein kinase C (PKC) isoenzymes which have been described has raised great interest in potential differences in the cellular expression, the mode of activation and the substrate specificity of these isoenzymes. The last two aspects have mostly been studied with isoenzymes purified from rat or bovine brain or from recombinant-baculovirus-infected insect cells. In this study, we have expressed the human PKC isoenzymes alpha and beta I in recombinant-baculovirus-infected insect cells. The isoenzymes were purified to homogeneity by a four-step procedure which included a reversible Ca(2+)-dependent association/dissociation to and from the endogenous membranes of the lysed insect cells. Characterization of the purified enzymes with respect to ATP requirement and substrate specificity, using the epidermal-growth-factor receptor peptide and histone III-S respectively, revealed no isoenzyme-specific differences. Activation by trypsin or Ca2+ and a variety of different phospholipids and phosphoinositides (in a mixed-micellar assay) gave the following results. Proteolytic cleavage of the PKC isoenzymes by trypsin generated fully activated phospholipid-independent PKC beta I, whereas PKC alpha reached only 50% of the activity obtained in the presence of phospholipids. PKC alpha and beta I showed no difference in their dependence on Ca2+, diacylglycerol (DAG) and phosphatidylserine (PS). Replacement of either DAG or PS by phosphatidylglycerol, cardiolipin, phosphatidylcholine and several phosphoinositides revealed that PtdIns(4,5)P2 can act as a PKC activator similar to DAG, whereas PtdIns can substitute for PS as a cofactor of activation. Thus, at least for the PKC isoenzymes alpha and beta I, a combination of PtdIns and PtdIns(4,5)P2 can fully replace PS and DAG in vitro as the classical activators of PKC.