Protein Kinase C Located in Rat Liver Nuclei

Antioxidant effects of cranberry powder in lipopolysaccharide treated hypercholesterolemic rats

This study was conducted to investigate the effects of cranberry power on antioxidant defense system in rats fed an atherogenic diet and injected with lipopolysaccharide (LPS). Sprague-Dawley rats were divided into the following 5 groups: normal diet+saline (NS), atherogenic diet+saline (AS), atherogenic diet+LPS (AL), atherogenic diet with 5% cranberry powder+LPS (AL-C5), and atherogenic diet with 10% cranberry powder+LPS (AL-C10). Total antioxidant status measured by ferric reducing ability of plasma (FRAP) was significantly reduced by LPS injection (24%) and was restored by the cranberry powder treatment (P<0.05). In addition, the mean level of plasma total phenolics was significantly decreased by LPS injection (P<0.05) and tended to be increased when cranberry powder was incorporated in to the diet. Activity of serum superoxide dismutase (SOD) tended to be lowered by LPS injection and declined further in cranberry powder fortified groups. Overall results indicate that dietary cranberry powder may provide appropriate antioxidants to counter the diminished antioxidant status induced by exposing hypercholesterolemic rats to LPS.

Effects of cranberry powder on biomarkers of oxidative stress and glucose control in db/db mice

Increased oxidative stress in obese diabetes may have causal effects on diabetic complications, including dyslipidemia. Lipopolysccharides (LPS) along with an atherogenic diet have been found to increase oxidative stress and insulin resistance. Cranberry has been recognized as having beneficial effects on diseases related to oxidative stress. Therefore, we employed obese diabetic animals treated with an atherogenic diet and LPS, with the aim of examining the effects of cranberry powder (CP) on diabetic related metabolic conditions, including lipid profiles, serum insulin and glucose, and biomarkers of oxidative stress. Forty C57BL/KsJ-db/db mice were divided into the following five groups: normal diet + saline, atherogenic diet + saline, atherogenic diet + LPS, atherogenic diet + 5% CP + LPS, and atherogenic diet + 10% CP + LPS. Consumption of an atherogenic diet resulted in elevation of serum total cholesterol and atherogenic index (AI) and reduction of high density lipoprotein (HDL)-cholesterol. However, with 10% CP, the increase in mean HDL-cholesterol level was close to that of the group with a normal diet, whereas AI was maintained at a higher level than that of the group with a normal diet. LPS induced elevated serum insulin level was lowered by greater than 60% with CP (P < 0.05), and mean serum glucose level was reduced by approximately 19% with 5% CP (P > 0.05). Mean activity of liver cytosolic glutathione peroxidase was significantly increased by LPS injection, however it was reduced back to the value without LPS when the diet was fortified with 10% CP (P < 0.05). In groups with CP, a reduction in mean levels of serum protein carbonyl tended to occur in a dose dependent manner. Particularly with 10% CP, a reduction of approximately 89% was observed (P > 0.05). Overall results suggest that fortification of the atherogenic diet with CP may have potential health benefits for obese diabetes with high oxidative stress, by modulation of physical conditions, including some biomarkers of oxidative stress.

Induction of Sca-1 via activation of STAT3 system in the duct cells of the mouse submandibular gland by ligation of the main excretory duct

To examine the very initial step that takes place immediately after tissue injury and is linked to tissue regeneration, we employed the submandibular gland (SMG), which was injured by ligation of its main excretory duct (MED). Ligation of the MED of the SMG in mice induced the expression of Sca-1, a protein marker of hematopoietic stem cells. In the normal gland, a low level of Sca-1 was expressed, which was localized predominantly in the excretory duct cells. At 1 day after ligation, Sca-1 expression increased prominently in almost all of cells in the duct system, but not in the acinar cells. The level of Sca-1 mRNA had begun to increase at 6 h after ligation and continuously rose thereafter until it reached a plateau, which occurred ∼12 h after ligation. STAT3 phosphorylated at its tyrosine-705 (p-STAT3) in the ligated gland increased immediately after ligation, and it was localized in the nuclei of all duct cells. The results of an EMSA revealed the specific binding of a nuclear extract to the sequence of the γ-interferon activation site (GAS) present in the Sca-1 promoter and confirmed that such binding increased after ligation. Thus the present study suggests that STAT3, having been phosphorylated following MED ligation, was transferred to the nucleus, where it bound to the GAS element in the promoter of Sca-1 gene, resulting in promotion of Sca-1 gene expression. Actual prevention of STAT3 phosphorylation reduced the ligation-induced Sca-1 elevation.

Serotonin modifies cytoskeleton and brush-border membrane architecture in human intestinal epithelial cells

Serotonin or 5-hydroxytryptamine (5-HT) influences numerous functions in the gastrointestinal tract. We previously demonstrated that 5-HT treatment of Caco-2 cells inhibited Na(+)/H(+) exchangers (NHE) and Cl(-)/OH(-) exchange activities via distinct signaling mechanisms. Since regulation of several ion transporters such as NHE3 is influenced by intact cytoskeleton, we hypothesized that 5-HT modifies actin cytoskeleton and/or brush-border membrane architecture via involvement of signaling pathways. Ultrastructural analysis showed that 5-HT (0.1 muM, 1 h) treatment of Caco-2 cells caused the apical membrane to assume a convex dome shape that was associated with shortening of microvilli. To examine whether these cellular architecture changes are cytoskeleton driven, we analyzed actin cytoskeleton by fluorescence microscopy. 5-HT induced basal stress fibers with prominent cortical actin filaments via 5-HT3 and 5-HT4 receptor subtypes. This induction was partially attenuated by chelation of intracellular Ca(2+) and PKCalpha inhibition (Go6976). In vitro assays revealed that PKCalpha interacted with actin and this association was increased by 5-HT. Our data provide novel evidence that 5-HT-induced signaling via 5-HT3/4 receptor subtypes to cause Ca(2+) and PKCalpha-dependent regulation of actin cytoskeleton may play an important role in modulation of ion transporters that contribute to pathophysiology of diarrheal conditions associated with elevated levels of 5-HT.

PTEN down-regulates IL-17 expression in a murine model of toluene diisocyanate-induced airway disease

Toluene diisocyanate (TDI)-induced airway disease is a disorder characterized by chronic airway inflammation and airway remodeling. A recently discovered group of cytokines is the IL-17 family, which has been introduced as an important regulator of immune and inflammatory responses, including airway inflammation. Recently, we have reported that phosphatase and tensin homologue deleted on chromosome 10 (PTEN) plays a pivotal role in the pathogenesis of bronchial asthma. However, there are no available data for the effects of PTEN or IL-17 on TDI-induced airway disease and the relationship between PTEN and IL-17. We used a murine model to determine the role of PTEN in the pathogenesis of TDI-induced airway disease and the regulation of IL-17 production. These mice developed the typical pathophysiological features of TDI-induced airway disease and increased IL-17 expression in the lungs. Administration of phosphoinositide 3-kinase inhibitors or adenoviruses carrying PTEN cDNA (AdPTEN) reduced the pathophysiological features of TDI-induced airway disease and decreased the increased levels of IL-17 expression. Our results also showed that PI3K inhibitors or AdPTEN down-regulated a transcription factor, NF-kappaB activity, and BAY 11-7085 substantially reduced the increased levels of IL-17 after TDI inhalation. We also found that inhibition of IL-17 activity with an anti-IL-17 Ab reduced airway inflammation and airway hyperresponsiveness. These results suggest that PTEN plays a protective role in the pathogenesis of TDI-induced airway disease, at least in part through the regulation of IL-17 expression. Thus, PTEN may be a useful target for treating TDI-induced airway disease by modulating IL-17 expression.

Cysteinyl leukotriene upregulates IL-11 expression in allergic airway disease of mice

BACKGROUND

Chronic airway inflammation and airway remodeling are important features of bronchial asthma. IL-11 is one of the important mediators involved in the process of airway inflammation and remodeling. Cysteinyl leukotrienes (cysLTs) play roles in recruitment of inflammatory cells, airway smooth muscle contraction, vascular leakage, increased mucus secretion, decreased mucociliary clearance, and airway fibrosis.

OBJECTIVE

An aim of the present study was to determine the effect of the cysLTs on the regulation of IL-11 expression.

METHODS

We used a C57BL/6 mouse model of allergic airway disease and murine tracheal epithelial cells to examine the effects of cysLTs on the regulation of IL-11 expression.

RESULTS

Our present study with an ovalbumin-induced murine model of allergic airway disease revealed that levels of leukotriene C(4) (LTC(4)) in bronchoalveolar lavage fluids were increased and that administration of montelukast or pranlukast reduced the increased levels of LTC(4); the increased expression of IL-11 protein and mRNA in lung tissues; airway inflammation, bronchial hyperresponsiveness; the increased levels of TGF-beta(1), IL-4, and IL-13 in bronchoalveolar lavage fluids and lung tissues; and airway fibrosis. In addition, LTC(4) stimulates epithelial cells to produce IL-11. Our results also showed that cysLT type 1 receptor antagonists downregulated the activity of a transcription factor, nuclear factor kappaB, and BAY 11-7085 substantially reduced the increased levels of IL-11 after ovalbumin inhalation.

CONCLUSION

These results suggest that cysLTs regulate the IL-11 expression in allergic airway disease.

CLINICAL IMPLICATIONS

These findings provide one of the molecular mechanisms for the effects of cysLTs on airway inflammation and fibrosis in allergic airway diseases.

N-hexacosanol ameliorates streptozotocin-induced diabetic rat nephropathy

In this study we investigated the effects of N-hexacosanol on streptozotocin-induced rat diabetic nephropathy. Diabetes was induced in 8-week-old male Sprague-Dawley rats by administering an intraperitoneal injection of streptozotocin (50 mg/kg). The rats were divided into four groups and maintained for 8 weeks: control rats, diabetic rats without treatment with N-hexacosanol, and diabetic rats treated with N-hexacosanol (2 mg/kg and 8 mg/kg i.p. every day). Although N-hexacosanol failed to modify the diabetic status, increases in serum creatinine as well as in kidney weight were significantly reduced. The malonaldehyde and transforming growth factor beta-1 (TGF-beta1) concentrations as well as the protein kinase C (PKC) activities in the diabetic kidney were significantly higher than those of the control, which were decreased by treatment with N-hexacosanol. Histological examinations revealed that N-hexacosanol significantly ameliorated diabetic-induced tubulointerstitial pathological changes. Our data suggest that N-hexacosanol could prevent increases in the malonaldehyde and TGF-beta1 concentrations and PKC activities in the kidney, and ameliorate diabetic-induced nephropathy.

Mechanism regulating nuclear calcium signalingThis paper is one of a selection of papers published in this Special Issue, entitled The Nucleus: A Cell Within A Cell

Although the outer nuclear membrane is continuous with the endoplasmic reticulum, it is possible to isolate nuclei both intact and free from endoplasmic reticulum contaminants. The outer and the inner nuclear membranes can be purified free from cross-contamination. Evidence in support of autonomous regulation of nuclear calcium signaling relies upon the investigations with isolated nuclei. Mechanisms for generating calcium signaling in the nucleus have been identified. Two calcium transporting systems, an ATP-dependant nuclear Ca2+-ATPase and an IP4-mediated inositol 1,3,4,5-tetrakisphosphate receptor, are located on the outer nuclear membrane. Thus, ATP and IP4, depending on external free calcium concentrations, are responsible for filling the nuclear envelope calcium pool. The inositol 1,4,5-trisphosphate receptor is located on the inner nuclear membrane with its ligand binding domain facing toward the nucleoplasm. Likewise, the ryanodine receptor is located on the inner nuclear membrane and its ligand cADP-ribose is generated within the nucleus. A 120 kDa protein fragment of nuclear PLC-γ1 is stimulated in vivo by epidermal growth factor nuclear signaling coincident with the time course of nuclear membrane epidermal growth factor receptor activation. Stimulated 120 kDa protein fragment interacts with PIKE, a nuclear GTPase, and together they form a complex with PI[3]kinase serving as a module for nuclear PI[3]K stimulation. Thus, the nucleus has its own IP3generating system.

Molecular alterations of cells resistant to platinum drugs: role of PKCalpha

Development of resistance to platinum compounds may involve not only overexpression of defence mechanisms but also alterations in cellular response to the drug-induced genotoxic stress. To investigate the cellular bases of response to platinum compounds, we examined the profile of gene expression of ovarian carcinoma cells exhibiting sensitivity (A2780) or resistance (A2780/BBR3464) to platinum compounds. Using display PCR, we found that acquisition of resistance to the multinuclear platinum complex BBR3464 was associated with modulation of several transcripts, including up-regulation of the major substrate of protein kinase C (PKC), the myristoylated alanine-rich C kinase substrate (MARCKS). This feature was associated with PKCalpha down-regulation. To explore the role of PKCalpha in cellular sensitivity to platinum compounds, resistant cells were transfected with a PKCalpha-containing vector. PKCalpha-overexpressing resistant cells exhibited a decrease in sensitivity to cisplatin, whereas no significant change in sensitivity to BBR3464 was observed. A number of approaches designed to modulate the function or expression of PKCalpha support that the isoenzyme may play a role in determining resistance only to cisplatin but not to BBR3464, which is known to activate a different pathway of cell response. In conclusion, in spite of PKCalpha down-regulation in our model, its regulatory function was not apparently implicated in the development of resistance to platinum compounds and the present results do not support a general role of PKCalpha as a determinant of the resistance status.

Opposing effects of PKCalpha and PKCepsilon on basolateral membrane dynamics in intestinal epithelia

PKC is a critical effector of plasma membrane dynamics, yet the mechanism and isoform-specific role of PKC are poorly understood. We recently showed that the phorbol ester PMA (100 nM) induces prompt activation of the novel isoform PKCepsilon followed by late activation of the conventional isoform PKCalpha in T84 intestinal epithelia. PMA also elicited biphasic effects on endocytosis, characterized by an initial stimulatory phase followed by an inhibitory phase. Activation of PKCepsilon was shown to be responsible for stimulation of basolateral endocytosis, but the role of PKCalpha was not defined. Here, we used detailed time-course analysis as well as selective activators and inhibitors of PKC isoforms to infer the action of PKCalpha on basolateral endocytosis. Inhibition of PKC by the selective conventional PKC inhibitor Gö-6976 (5 microM) completely blocked the late inhibitory phase and markedly prolonged the stimulatory phase of endocytosis measured by FITC-dextran uptake. The PKCepsilon-selective agonist carbachol (100 microM) induced prolonged stimulation of endocytosis devoid of an inhibitory phase. Actin disassembly caused by PMA was completely blocked by Gö-6850 but not by Gö-6976, implicating PKCepsilon as the key isoform responsible for actin disruption. The Ca2+ agonist thapsigargin (5 microM) induced early activation of PKC when added simultaneously with PMA. This early activation of PKCalpha blocked the ability of PMA to remodel basolateral F-actin and abolished the stimulatory phase of basolateral endocytosis. Activation of PKCalpha stabilizes F-actin and thereby opposes the effect of PKCepsilon on membrane remodeling in T84 cells.

Nuclear UDP-glucuronosyltransferases: identification of UGT2B7 and UGT1A6 in human liver nuclear membranes

We have demonstrated the subcellular localization of the human UDP-glucuronosyltransferases (UGTs), UGT2B7 and UGT1A6, in endoplasmic reticulum (ER) and nuclear membrane from human hepatocytes and cell lines, by in situ immunostaining and Western blot. Double immunostaining for UGT2B7 and calnexin, an ER resident protein, showed that UGT2B7 was equally present in ER and nuclear membrane whereas calnexin was present almost exclusively in ER. Immunogold labeling of HK293 cells expressing UGT2B7 established the presence of UGT2B7 in both nuclear membranes. Enzymatic assays with UGT2B7 substrates confirmed the presence of functional UGT2B7 protein in ER, whole nuclei, and both outer and inner nuclear membranes. This study has identified, for the first time, the presence of UGT2B7 and UGT1A6 in the nucleus and of UGT2B7 in the inner and outer nuclear membranes. This localization may play an important functional role within nuclei: protection from toxic compounds and/or control of steady-state concentrations of nuclear receptor ligands.

Identification and characterization of nuclear CD38 in the rat spleen

CD38 is an ectoenzyme, which can produce metabolites with intracellular Ca(2+) mobilizing properties and has multiple immunological functions. However, we have recently shown that CD38 is also localized to the nucleus of rat hepatocyte whereby its metabolite cADPR, is able to mobilize nuclear Ca(2+) stores. In this study, we further characterize the localization of nuclear CD38 in the spleen, an important immune organ. We managed to detect the presence of ADP-ribosyl cyclase activity in the nuclear fraction. With Western blotting, we managed to characterize a 42-45 kDa protein band that is typical of CD38 under reducing and non-reducing conditions. However, as a comparison, other nuclear fractions from tissues like thymus, cardiac muscle and cerebellum yielded an additional 85 kDa protein band under non-reducing conditions. Both protein bands could be blocked with a CD38 blocking peptide. Immunohistochemical studies revealed the expression of CD38 in the marginal zone and in the red pulp. In contrast, the germinal center remained largely immunonegative for CD38. This is the first report of a functionally active ADP-ribosyl cyclase/CD38 in the spleen nuclear fraction. The results here suggest that the presence of CD38 in the nuclear environment might have a corollary to functional and regulatory roles in the nucleus.

Localization of the cyclic ADP-ribose-dependent calcium signaling pathway in hepatocyte nucleus

CD38 is a type II transmembrane glycoprotein found on both hematopoietic and non-hematopoietic cells. It is known for its involvement in the metabolism of cyclic ADP-ribose (cADPR) and nicotinic acid adenine dinucleotide phosphate, two nucleotides with calcium mobilizing activity independent of inositol trisphosphate. It is generally believed that CD38 is an integral protein with ectoenzymatic activities found mainly on the plasma membrane. Here we show that enzymatically active CD38 is present intracellularly on the nuclear envelope of rat hepatocytes. CD38 isolated from rat liver nuclei possessed both ADP-ribosyl cyclase and NADase activity. Immunofluorescence studies on rat liver cryosections and isolated nuclei localized CD38 to the nuclear envelope of hepatocytes. Subcellular localization via immunoelectron microscopy showed that CD38 is located on the inner nuclear envelope. The isolated nuclei sequestered calcium in an ATP-dependent manner. cADPR elicited a rapid calcium release from the loaded nuclei, which was independent of inositol trisphosphate and was inhibited by 8-amino-cADPR, a specific antagonist of cADPR, and ryanodine. However, nicotinic acid adenine dinucleotide phosphate failed to elicit any calcium release from the nuclear calcium stores. The nuclear localization of CD38 shown in this study suggests a novel role of CD38 in intracellular calcium signaling for non-hematopoietic cells.

Differential redistribution of protein kinase C isoforms by cyclic AMP in HL60 cells

In this study we have analyzed the distribution of protein kinase C isoforms in cytosol, membrane, and nucleus in HL60 cells. Furthermore, we have studied the redistribution of these isoforms after cyclic AMP treatment. Protein kinase C localization and cyclic AMP-induced translocation was demonstrated by Western blot analysis. Cytosol, membrane and nucleus in HL60 cells expressed the abundance of protein kinase C alpha, betaI, betaII, delta, lambda, and zeta isoforms. After cyclic AMP treatment, the amount of protein kinase C betaI and zeta increased only in the nucleus, while protein kinase C delta increased in the three fractions tested. These effects were dependent on the cyclic AMP concentration and duration of action. Our results suggest the existence of cross-talk between the cyclic AMP system and protein kinase C in HL60 cells. Taking into account the processes regulated by protein kinase C, these findings also suggest that cyclic AMP plays a regulatory role in various cellular responses in HL60 cells, such as differentiation and gene expression. The increase observed in PKC delta was due to cyclic AMP-dependent protein kinase C activation, and the synthesis of enzyme was probably activated by the nucleotide.

Age-dependent modulation of PKC isoforms and NOS activity and expression in rat cortex, striatum, and hippocampus

Recently, PKC has been shown to play a pivotal role in physiological brain functions, connected with the memorizing processes and their correspondent progressive decline with brain aging. We have studied the age-dependent changes of PKC isoforms activity in connection with NOS expression and activity in specific brain areas such as hippocampus, cortex and striatum. Starting from middle aged rats, a significant inactivation of c-PKC isoforms occurred, with respect to young animals, in all the brain areas analysed. However, in middle aged animals, no significant changes in the protein level of the main PKC isoforms expressed in brain were demonstrated. Moreover, in the hippocampus and in the cortex of middle aged rats, an increased level of NOS activity--a substrate of PKC whose phosphorylation by the kinase inhibits NOS activity--has been demonstrated, reaching the same level that occurs in striatum. However, only in the hippocampus, deeply implicated in learning and memory functions, an increase of nuclear c-PKC activity and of i- and n-NOS mRNA levels was shown. Taken together, these results indicate that down-regulation of c-PKC activity occurring in middle aged rats, leads to higher levels of NO that may contribute to cell damage and to alter the neuronal physiological functions as described in older animals. Moreover, in the hippocampus, our results suggest a relationship between the translocation of c-PKC to the nucleus and the enhancement of the expression of i- and n-NOS.

Phospholipid signalling in the nucleus. Een DAG uit het leven van de inositide signalering in de nucleus

Diverse methodologies, ranging from activity measurements in various nuclear subfractions to electron microscopy, have been used to demonstrate and establish that many of the key lipids and enzymes responsible for the metabolism of inositol lipids are resident in nuclei. PtdIns(4)P, PtdIns(4,5)P2 and PtdOH are all present in nuclei, as well as the corresponding enzyme activities required to synthesise and metabolise these compounds. In addition other non-inositol containing phospholipids such as phosphatidylcholine constitute a significant percentage of the total nuclear phospholipid content. We feel that it is pertinent to include this lipid in our discussion as it provides an alternative source of 1, 2-diacylglycerol (DAG) in addition to the hydrolysis of PtdIns(4, 5)P2. We discuss at length data related to the sources and possible consequences of nuclear DAG production as this lipid appears to be increasingly central to a number of general physiological functions. Data relating to the existence of alternative pathways of inositol phospholipid synthesis, the role of 3-phosphorylated inositol lipids and lipid compartmentalisation and transport are reviewed. The field has also expanded to a point where we can now also begin to address what role these lipids play in cellular proliferation and differentiation and hopefully provide avenues for further research.

cAMP-dependent protein kinase phosphorylates and activates nuclear Ca2+-ATPase

A Ca2+-pump ATPase, similar to that in the endoplasmic reticulum, has been located on the outer membrane of rat liver nuclei. The effect of cAMP-dependent protein kinase (PKA) on nuclear Ca2+-ATPase (NCA) was studied by using purified rat liver nuclei. Treatment of isolated nuclei with the catalytic unit of PKA resulted in the phosphorylation of a 105-kDa band that was recognized by antibodies specific for sarcoplasmic reticulum Ca2+-ATPase type 2b. Partial purification and immunoblotting confirmed that the 105-kDa protein band phosphorylated by PKA is NCA. The stoichiometry of phosphorylation was 0.76 mol of phosphate incorporated/mol of partially purified enzyme. Measurement of ATP-dependent 45Ca2+ uptake into purified nuclei showed that PKA phosphorylation enhanced the Ca2+-pumping activity of NCA. We show that PKA phosphorylation of Ca2+-ATPase enhances the transport of 10-kDa fluorescent-labeled dextrans across the nuclear envelope. The findings reported in this paper are consistent with the notion that the crosstalk between the cAMP/PKA- and Ca2+-dependent signaling pathways identified at the cytoplasmic level extends to the nucleus. Furthermore, these data support a function for crosstalk in the regulation of calcium-dependent transport across the nuclear envelope.

Phosphoinositide 3-kinase in rat liver nuclei

Biochemical and immunochemical data from the present investigation reveal the existence of a p85/p110 phosphoinositide 3-kinase (PI 3-kinase) in rat liver nuclei. 32P-Labeling of membrane phosphoinositides by incubating intact nuclei with [gamma-32P]ATP results in the formation of [32P]phosphatidyl-inositol 3,4, 5-trisphosphate [PtdIns(3,4,5)P3], accompanied by small quantities of [32P]phosphatidylinositol 3-phosphate [PtdIns(3)P]. Studies with subnuclear fractions indicate that the PI 3-kinase is not confined to nuclear membranes. The nuclear soluble fraction also contains PI 3-kinase and an array of inositide-metabolizing enzymes, including phospholipase C (PLC), phosphoinositide phosphatase, and diacylglycerol (DAG) kinase. As a result, exposure of phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2] to the nuclear extract in the presence of [gamma-32P]ATP generates a series of 32P-labeled D-3 phosphoinositides and phosphatidic acid (PA) in an interdependent manner. On the basis of the immunological reactivity and kinetic behavior, the nuclear PI 3-kinase is analogous, if not identical, to PI 3-kinase alpha, and constitutes about 5% of the total PI 3-kinase in the cell. Moreover, we test the premise that nuclear PI 3-kinase may, in part, be regulated through the control of substrate availability by PtdIns(4,5)P2-binding proteins. Effect of CapG, a nuclear actin-regulatory protein, on PI 3-kinase activity is examined in view of its unique Ca2+-dependent PtdIns(4, 5)P2-binding capability. In vitro data show that the CapG-mediated inhibition of nuclear PI 3-kinase is prompted by PKC phosphorylation of CapG and elevated [Ca2+]. This CapG-dependent regulation provides a plausible link between nuclear PLC and PI 3-kinase pathways for cross-communications. Taken together, these findings provide definite data concerning the presence of an autonomous PI 3-kinase cycle in rat liver nuclei. The nuclear location of PI 3-kinase may lead to a better understanding regarding its functional role in transducing signals from the plasma membrane to the nucleus in response to diverse physiological stimuli.

Regulation of nuclear calcium uptake by inositol phosphates and external calcium

Factors affecting Ins(1,3,4,5)P4-mediated nuclear Ca2+ uptake are investigated, which include Ins(1,3,4,5)P4 receptor ligand specificity and free external Ca2+ concentrations. Among various inositol phosphates examined, Ins(1,3,4,5)P4, Ins(3,4,5,6)P4, and Ins(1,3,4,5,6)P5 can also stimulate 45Ca2+ influx into isolated rat liver nuclei by activating the Ins(1,3,4,5)P4 receptor-mediated Ca2+ uptake into the nucleus. The EC50 values of these polyphosphates range between 200 and 300 nM, which are 3-4 folds higher than that of Ins(1,3,4,5)P4. It is plausible that these polyphosphates in conjunction with Ins(1,3,4,5)P4 take part in the regulation of nuclear Ca2+ uptake in view of their intracellular levels during cell activation. Moreover, the inositol phosphate-induced Ca2+ uptake is facilitated by increasing Ca2+ levels in the uptake milieu, suggesting a possible link between cytosolic and nuclear Ca2+ signals through the Ins(1,3,4,5)P4 receptor.

The presence of an unusual PKC isozyme profile in rat liver cells

We have previously shown that protein kinase C (PKC) is involved in the mitogenic response of T51B cells to epidermal growth factor. In fact, epidermal growth factor was an excellent mitogen, even after prolonged pretreatment of cells with TPA, suggesting that the PKC isoform implicated in proliferation is not down-regulated by 12-O-tetradecanoyl phorbol-13-acetate (TPA). We have now determined that the PKC isozymes -α, -βI, -δ, -ε, and -ζ are present in T51B cells. All five isoforms are associated with the plasma membrane and the cytoplasm and are either in or around the nucleus. PKC-βI has a slightly different subcellular profile from that of the other isoforms in that it is clearly and strongly associated with the nuclear membrane. Also, a unique and novel pattern is obtained from immunoblots with anti-PKC-βI. PKC-βI is detected as a single band of 70 kDa in the cytosolic fraction and as a doublet of 65 and 77 kDa in the membrane fraction. PKC-α, -δ, and -ε were down-regulated by pretreatment of cells with TPA, while PKC-ζ was unaffected. Of particular interest was the fact that TPA did not down-regulate PKC-βI. In fact, the amount of this isoform associated with the plasma membrane increased. These findings indicate that it is probably PKC-βI that is involved in the mitogenic response of T51B cells to epidermal growth factor. Since PKC-ζ is also not down-regulated by TPA, the possible involvement of this isoform needs to be resolved.Key words: protein kinase C, intracellular localization, cell proliferation, liver.

Localization of two forms of phospholipase C-beta1, a and b, in C6Bu-1 cells

Phospholipase C-beta1 (PLC-beta1), one of the PLC-beta isozymes, exists as two immunologically distinguishable polypeptides of 150 (PLC-beta1a) and 140 kDa (PLC-beta1b) which are encoded in two distinct transcripts and generated by alternative splicing of a single gene. In this study, the subcellular localization of the two phospholipases C-beta1 proteins was examined in rat C6Bu-1 glioma cells using immunological techniques. Immunoblot analysis revealed that the two forms of PLC-beta1 were detectable in both cytosolic and nuclear fractions. PLC-beta1a appeared to be located preferentially in the cytosol, whereas PLC-beta1b was found predominantly in the nuclei of C6Bu-1 cells. Immunocytochemical experiments confirmed the differential localization of the two PLC-beta1 species in C6Bu-1 cells. These results suggest that the two PLC-beta1 proteins may have different physiological roles in the cell.

Modulation of aflatoxin B1 activated protein kinase C by phenolic compounds

Several natural phenolic compounds were tested in vitro for their effect on the activity of protein kinase C isolated from liver cytosol, particulate and nuclear fractions of normal and aflatoxin B1 treated rats. Quercetin and kaempferol inhibited the enzyme activity of all these fractions at very low dose levels. These phenolics were particularly effective in inhibiting the elevated enzyme activity following aflatoxin B1 administration. Ellagic acid and curcumin were found to be inhibitory only towards particulate enzymes obtained after carcinogen treatment, while curcumin and rutin were moderately active against nuclear enzymes. Constitutive activation of protein kinase C can drive the cell to a proliferative state, thereby initiating the process of carcinogenesis, however, suppression of this activation by phenolic compounds may be an effective way to control carcinogenesis.

Erythropoietin stimulates nuclear localization of diacylglycerol and protein kinase C beta II in B6SUt.EP cells

Erythropoietin (EPO) is a hormone, as well as a hematopoietic growth factor, that specifically regulates the proliferation and differentiation of erythroid progenitor cells. Although the membrane-bound receptor for EPO has no intrinsic kinase activity, it triggers the activation of protein kinases via phospholipases A2, C, and D. A cascade of serine and threonine kinases, including Raf-1, MAP kinase and protein kinase C (PKC) is activated following tyrosine phosphorylation. In this study, we have examined whether changes in nuclear PKC and 1,2-diacylglycerol (DAG) are induced following EPO treatment of the murine target cell line, B6SUt.EP. Western blot analysis using isoform-specific antibodies demonstrated the presence of PKC beta II, but not PKC alpha, beta I, gamma, epsilon, delta, eta, or zeta in the nuclei of cells stimulated with EPO. The increase in nuclear beta II levels was accompanied by an immediate rise in DAG mass levels with both of the increases peaking by 1 min. These rapid increases in nuclear DAG and PKC beta II expression suggest a mechanism for EPO-induced changes in gene expression necessary for cell proliferation.

Does the nuclear envelope contain two types of ligand-gated Ca2+ release channels?

The nuclear envelope is composed of two membranes deliminating a perinuclear space which displays functional properties similar to those of a Ca2+-storing compartment. ATP-driven Ca2+ uptake and InsP3-induced Ca2+ release processes have been described in isolated nuclei. Recently, it was reported that cADP-ribose and InsP3 can trigger a nucleoplasmic Ca2+ increase. It was hypothesized that the inner nuclear membrane possesses Ca2+ channels that are regulated by ryanodine or InsP3. Radio-ligand binding assays and Western blot experiments were performed in order to investigate their presence in sheep cardiac and rat liver nuclear envelopes. Ryanodine receptors (RyR) were not detected in liver nuclear envelopes by either binding assay or Western blot analysis. However, cardiac nuclear envelopes were found to retain a very low level of specific ryanodine binding, which was not detected on immuno-blots obtained with three types of isoform-specific RyR antibodies. In contrast, nuclear InsP3-binding sites were consistently detected in both cardiac and liver nuclear envelopes. Altogether, these results provide evidence for the major contributor InsP3-gated Ca2+ channels in control of Ca2+ release from the perinuclear space in liver and cardiac cells.

Chromatin neutral sphingomyelinase and its role in hepatic regeneration

Ceramide acts as a second messenger and modulates many cellular functions. This molecule can be produced by enzymatic digestion of sphingomyelin, a phospholipid which has been shown to be in high concentration in a chromatin phospholipidic fraction. In order to clarify whether chromatin sphingomyelin has a role in this signal transduction pathway, it is necessary to define the sphingomyelin cycle. Neutral sphingomyelinase represents the first step of the cycle. In this paper we demonstrate that sphingomyelinase activity can be detected also in the chromatin of rat hepatocyte nuclei and it increases in relation to the entrance in S phase of hepatocyte after hepatectomy. The enzyme can be distinguished from that present in the nuclear envelope on the basis of optimum pH and Km. The role of the spingomyelin pathway in relation to liver regeneration is discussed.

Nuclear ADP-ribosylation factor (ARF)- and oleate-dependent phospholipase D (PLD) in rat liver cells. Increases of ARF-dependent PLD activity in regenerating liver cells

Two forms of phospholipase D (PLD) have been found to be present in nuclei isolated from rat hepatocytes by measuring phosphatidylbutanol produced from exogenous radiolabeled phosphatidylcholine in the presence of butanol. In nuclear lysates from either rat liver or ascites hepatoma AH 7974 cells, the PLD activity was markedly stimulated by a recombinant ADP-ribosylation factor (rARF) in the presence of the guanosine 5'-O-(3-thiotriphosphate) (GTPgammaS) and phosphatidylinositol 4, 5-bisphosphate. ATP and phorbol-12-myristate 13-acetate had no synergistic effect on this PLD activity. On the other hand, the nuclear PLD was stimulated by unsaturated fatty acids, especially by oleic acid. The ARF-dependent nuclear PLD activity was increased in the S-phase of the regenerating rat liver after partial hepatectomy and also was much higher in AH 7974 cells than in the resting rat liver. In contrast, the levels of the oleate-dependent PLD activity remained constant throughout the cell cycle in liver regeneration. The intranuclear levels of the stimulating proteins of the nuclear PLD activity, e.g. ARF, RhoA, and protein kinase Cdelta increased in the S-phase of the regenerating liver. These results suggested that the nuclear ARF-dependent PLD activity may be associated with cell proliferation.

A three-dimensional collagen lattice induces protein kinase C-zeta activity: role in alpha2 integrin and collagenase mRNA expression

A three-dimensional collagen lattice can provide skin fibroblasts with a cell culture environment that simulates normal dermis. Such a collagen matrix environment regulates interstitial collagenase (type I metalloproteinase [MMP-1], collagenase-1) and collagen receptor alpha2 subunit mRNA expression in both unstimulated or platelet-derived growth factor-stimulated dermal fibroblasts (Xu, J., and R.A.F. Clark. 1996. J. Cell Biol. 132:239-249). Here we report that the collagen gel can signal protein kinase C (PKC)-zeta activation in human dermal fibroblasts. An in vitro kinase assay demonstrated that autophosphorylation of PKC-zeta immunoprecipitates was markedly increased by a collagen matrix. In contrast, no alteration in PKC-zeta protein levels or intracellular location was observed. DNA binding activity of nuclear factor kappaB (NF-kappaB), a downstream regulatory target of PKC-zeta, was also increased by fibroblasts grown in collagen gel. The composition of the NF-kappaB/Rel complexes that contained p50, was not changed. The potential role of PKC-zeta in collagen gel-induced mRNA expression of collagen receptor alpha2 subunit and human fibroblast MMP-1 was assessed by the following evidence. Increased levels of alpha2 and MMP-1 mRNA in collagen gel-stimulated fibroblasts were abrogated by bisindolylmaleimide GF 109203X and calphostin C, chemical inhibitors for PKC, but retained when cells were depleted of 12-myristate 13-acetate (PMA)-inducible PKC isoforms by 24 h of pretreatment with phorbol PMA. Antisense oligonucleotides complementary to the 5' end of PKC-zeta mRNA sequences significantly reduced the collagen lattice-stimulated alpha2 and MMP-1 mRNA levels. Taken together, these data indicate that PKC-zeta, a PKC isoform not inducible by PMA or diacylglycerol, is a component of collagen matrix stimulatory pathway for alpha2 and MMP-1 mRNA expression. Thus, a three-dimensional collagen lattice maintains the dermal fibroblast phenotype, in part, through the activation of PKC-zeta.

Inhibition of protein kinase C and proto-oncogene expression by crocetin in NIH/3T3 cells

Crocetin, a carotenoid isolated from the seeds of Gardenia jasminoides, was found to be a potent inhibitor of tumor promotion induced by 12-O-tetradecanoylphorbol-13-acetate (TPA) in mouse skin. When mouse fibroblast NIH/3T3 cells were treated with TPA alone, protein kinase C (PKC) translocated from the cytosolic fraction to the particulate fraction. Pretreatment with 60 and 120 microM crocetin for 15 min inhibited the TPA-induced PKC activity in the particulate fraction by 50% and 66%, respectively, but did not affect the level of PKC protein. Crocetin also reduced the level of TPA-stimulated phosphorylation of cellular proteins. Cells pretreated with crocetin (120 microM) had 55% less PKC [3H]phorbol dibutyrate-binding capacity. Suppression of TPA (100 ng/mL)-induced c-jun and c-fos gene expression was also observed in the mouse fibroblast cells pretreated with crocetin (30, 60, and 120 microM). Our results provided a basis for understanding the inhibitory effect of crocetin on TPA-mediated tumor promotion.

Isoform-specific redistribution of protein kinase C in living cells

We have used confocal laser scanning microscopy to determine the dynamics of distribution of activated protein kinase C (PKC) in living Madin Darby canine kidney (MDCK) cells. Using fluorescently tagged phorbol myristate acetate (PMA) as a probe for PKC we have demonstrated its distribution in association with the cell periphery and with the nucleus. Dual labeling experiments using PKC alpha and PKC beta II specific antisera indicate that activated PKC alpha is found in association with the periphery whereas activated PKC beta II is translocated to the nucleus. We have demonstrated increased activity of PKC in nuclear fractions isolated from cells treated with PMA and other PKC activators. These data indicate that upon activation individual isoforms of PKC translocate to different subcellular locations where they are likely to mediate different actions.

Calcium transported to isolated rat liver nuclei by nicotinamide adenine dinucleotide is insensitive to thapsigargin

Calcium uptake by isolated nuclei was mediated by nicotinamide adenine dinucleotide. Oxidized nicotinamide nucleotide analogues were more effective mediators of nuclear calcium uptake. Thapsigargin inhibited ATP-mediated nuclear calcium transport without affecting NAD-mediated nuclear calcium uptake. Whilst DBHQ did not influence ATP-induced calcium transport, it did stimulate NAD-mediated nuclear calcium entry. Calcium channel blockers did not influence the action of NAD. This study provides a further mechanism for nuclear calcium transport regulated by changes in the cytosolic NAD(+)/NADH ratio.

High affinity inositol 1,3,4,5-tetrakisphosphate receptor from rat liver nuclei: purification, characterization, and amino-terminal sequence

Inositol 1,3,4,5-tetrakisphosphate (InsP4) mediates nuclear calcium signalling [Köppler P., Matter, N., Malviya A.N. (1993) J. Biol. Chem. 268, 26248-26252], and a distinct high affinity InsP4 binding site is identified with rat liver nuclei [Köppler, P., Mersel, M., & Malviya, A.N. (1994) Biochemistry 33, 14707-14713] as compared with other rat liver membrane fractions. A novel InsP4 receptor protein derived from rat liver nuclei has been purified to apparent homogeneity employing preparative isoelectric focusing, electrophoretic mobility, nondenaturating polyacrylamide gel electrophoresis, and electroelution. Isoelectric focusing indicated an isoelectric pH around 4.3 +/- 0.2 which was further confirmed by bidimensional electrophoresis. The high affinity nuclear InsP4 receptor was identified as a 74 kDa protein both on the SDS-PAGE and on the bidimensional electrophoresis. Partial microsequence analysis showed that the N-terminal end of nuclear InsP4 receptor consists of amino acids: PNHKNEIAGNFS. The 74 kDa nuclear InsP4 receptor protein is a distinct protein from the other InsP4 receptors purified from other sources and documented in the literature.

Signal transduction mechanism in response to aflatoxin B1 exposure: protein kinase C activity

A single dose of the carcinogen aflatoxin B1 (7 mg/kg body weight) to male Wistar rats significantly enhanced the hepatic activity of protein kinase C in the particulate and nuclear fractions. The particulate fraction showed stimulation at 4 and 7 h, while the nuclear activity was increased at 17 h following administration of aflatoxin B1. The enzyme activity in cytosol revealed a significant decline corresponding to stimulation in particulate fraction. The carcinogen-activated protein kinase C stimulated autophosphorylation, and was found to accelerate in vitro phosphorylation of two model DNA synthesizing enzymes--the Klenow fragment of replicative DNA polymerase of E. Coli and a DNA primase-polymerase complex of yeast mitochondrial origin. Prior phosphorylation of these enzymes led to significant enhancement of their activities. The results imply that activation of protein kinase C and consequently the activation of DNA synthesizing enzymes may play an important role in the initiation of carcinogenesis.

Inositol 1,4,5-trisphosphate receptor is located to the inner nuclear membrane vindicating regulation of nuclear calcium signaling by inositol 1,4,5-trisphosphate. Discrete distribution of inositol phosphate receptors to inner and outer nuclear membranes

Transient rise in nuclear calcium concentration is implicated in the regulation of events controlling gene expression. Mechanism by which calcium is transported to the nucleus is vehemently debated. Inositol 1,4,5-trisphosphate (InsP3) and inositol-1,3,4,5-tetrakisphosphate (InsP4) receptors have been located to the nucleus and their role in nuclear calcium signaling has been proposed. Outer nuclear membrane was separated from the inner membrane. The two membrane preparations were, as best as possible, devoid of cross contamination as attested by marker enzyme activity, Western blotting with antilamin antibody, and electron microscopy. InsP4 receptor and Ca(2+)-ATPase were located to the outer nuclear membrane. InsP3 receptor was located to the inner nuclear membrane. ATP or InsP4 induced nuclear calcium uptake. External free calcium concentration, in the medium bathing the nuclei, determined the choice for ATP or InsP4-mediated calcium transport. We present a mechanistic model for nuclear calcium transport. According to this model, calcium can reach the nucleus envelope either by the action of ATP or InsP4. However, the calcium release from the nucleus envelope to the nucleoplasm is mediated by InsP3 through the activation of InsP3 receptor, which is located to the inner nuclear membrane. The action of InsP3 in this process was instantaneous and transient and was sensitive to heparin.

Inhibitions of protein kinase C and proto-oncogene expressions in NIH 3T3 cells by apigenin

Apigenin, a low-toxic and non-mutagenic plant flavonoid, suppresses 12-O-tetradecanoyl-phorbol-13-acetate (TPA)-mediated tumour promotion of mouse skin. TPA has the ability to activate protein kinase C (PKC) and induce proto-oncogene expression. Our study shows that apigenin inhibits PKC by competing with ATP, and exhibits an IC50 value of 10 +/- 0.5 microM. Apigenin also reduces the level of TPA-stimulated phosphorylation of cellular proteins. Of the protein tyrosine kinases tested, the fibroblast growth factor (FGF) receptor was most strongly affected by apigenin (IC50 20 microM), and pp60v-src most weakly affected (IC50 > 200 microM). Treatment of NIH 3T3 cells with 100 ng/ml TPA and 10, 50 and 100 microM apigenin resulted in 50, 80 and 100% suppression of TPA-induced C-JUN expression, respectively. Treatment of TPA with 10 microM apigenin inhibited TPA-induced C-FOS expression. TPA-stimulated cell growth was suppressed by 25 microM apigenin. Our results provide some evidence for understanding apigenin's inhibitory effects of TPA-mediated tumour promotion.

A Mg(2+)-dependent, Ca(2+)-inhibitable serine/threonine protein phosphatase from bovine brain

The Mg(2+)-dependent serine/threonine protein phosphatases, also known as type 2C phosphatases (PP2C), belong to a gene family distinct from the other serine/threonine phosphatases and tyrosine phosphatases. Here we report the purification to apparent homogeneity of a novel Mg(2+)-dependent, Ca(2+)-inhibitable serine/threonine protein phosphatase from bovine brain. It is a type 2C enzyme in view of its Mg2+ requirement, resistance to okadaic acid and calyculin A, inability to use phosphorylase alpha as substrate, and a segment of amino acid sequence typical of all PP2C type phosphatases known to date. However, it differs from the other PP2C enzymes, particularly the mammalian PP2C alpha and -beta isoforms, in that its molecular weight, 76,000, is considerably larger and that it is inhibited by Ca2+, NaF, and polycations, but not by orthovanadate. The Ca2+ inhibition may not be related to its cellular regulation because of Ki values in the 20-90 microM range, but this property permits distinction of this enzyme from the other phosphatases. Although the precise physiological role of this phosphatase is not yet known, its ability to dephosphorylate a wide variety of phosphoproteins and its broad distribution, as shown by a survey of mouse tissues for its activity, suggest that it may serve an important cellular function.

C2 region-derived peptides inhibit translocation and function of beta protein kinase C in vivo

RACK1 is a protein kinase C (PKC)-binding protein that fulfills the criteria previously established for a receptor for activated C-kinase (RACK). If binding of PKC to RACK anchors the activated enzyme near its protein substrates, then inhibition of this binding should inhibit translocation and function of the enzyme in vivo. Here, we have identified such inhibitors that mimic the RACK1-binding site on beta PKC. We first found that a C2-containing fragment, but not a C1-containing fragment of beta PKC, bound to RACK1 and inhibited subsequent beta PKC binding. The RACK1-binding site was further mapped; peptides beta C2-1 (beta PKC(209-216), beta C2-2 (beta PKC(186-198)), and beta C2-4 (beta PKC(218-226), but not a number of control peptides, bound to RACK1 and inhibited the C2 fragment binding to RACK1. Peptides beta C2-1, beta C2-2, and beta C2-4 specifically inhibited phorbol ester-induced translocation of the C2-containing isozymes in cardiac myocytes and insulin-induced beta PKC translocation and function in Xenopus oocytes. Therefore, peptides corresponding to amino acids 186-198, and 209-226 within the C2 region of the beta PKC are specific inhibitors for functions mediated by beta PKC.

Pronounced activation of protein kinase C, ornithine decarboxylase and c-jun proto-oncogene by paraquat-generated active oxygen species in WI-38 human lung cells

Paraquat (methyl viologen, PQ) is a widely used herbicide that produces oxygen-derived free radicals and severely injures human lungs. In this study we examined the effects of PQ on the protein kinase C (PKC), ornithine decarboxylase (ODC) and c-jun oncogene expression in WI-38 human lung cells. Exposure of cells to 25-200 microM PQ resulted in an increase of [3H]phorbol dibutyrate (PDBu) binding and PKC redistribution in a dose-dependent manner. Interestingly, a superoxide dismutase mimic, 4-hydroxyl-2,2,6,6-tetramethyl-piperidine-1-oxyl (Tempol, 2.5 mM) and catalase (400 micrograms/ml) could significantly reduce the PQ-stimulated increase of phorbol ester binding and particular PKC phosphorylating activity, but dimethylsulfoxide (DMSO, 1.5%), an effective .OH trapping agent, failed to prevent this stimulation. In addition, an endogenous substrate of PKC, 80 kDa protein, was found to be highly phosphorylated in intact WI-38 cells treated with 50 microM PQ. The increase of phosphorylated proteins could be completely or partly abolished by Tempol or catalase, but only the phosphorylation of 80 kDa protein was diminished by protein kinase C inhibitor, 1-(5-isoquinolinyl-sulfonyl)-2-methylpiperazine (H-7). A maximal peak of ODC activity was observed at 6 h of treatment with 50 microM PQ. PQ induced activity was reduced at the following rates, Tempol 85%, DMSO 80% and catalase 45%, but H-7 failed to do so. Furthermore, we found that the level of c-jun mRNA was transiently increased by PQ and the peak appeared at 1 h of treatment. When correlated with the PKC result, Tempol, catalase and H-7 all effectively blocked PQ-elicited c-jun transcript expression, but DMSO only exhibited a weakly inhibitory effect. We therefore propose that superoxide anion (O2- and H2O2 generated by PQ could activate PKC and lead to induction of c-jun gene expression; on the other hand, O2- and .OH might trigger other kinase pathways to elevate ODC activity. Finally, the sequential expression of c-jun oncogene and ODC may cooperate to relieve the oxidative damages elicited by PQ.

Immunocytochemical evaluation of protein kinase C translocation to the inner nuclear matrix in 3T3 mouse fibroblasts after IGF-I treatment

The complex pathway which links the agonist-cell membrane receptor binding to the response at the genome level involves, among other elements, protein kinase C (PKC). Agonists acting at the cell membrane can affect an autonomous nuclear polyphosphoinositide signaling system inducing an activation of nuclear phosphoinositidase activity and a subsequent translocation of PKC to the nuclear region. The fine localization of PKC has been investigated by means of electron microscopy quantitative immunogold labeling in 3T3 mouse fibroblasts, mitogenically stimulated by IGF-I. The enzyme, which in untreated cells is present in the cytoplasm, except for the organelles, and in the nucleoplasm, after IGF-I treatment is reduced in the cytoplasm and almost doubled in the nucleus. The PKC isoform translocated to the nucleus is the alpha isozyme, which is found not only associated with the nuclear envelope but mainly with the interchromatin domains. By using in situ matrix preparations, PKC appears to be retained at the nuclear matrix level, both at the nuclear lamina and at the inner nuclear matrix, suggesting a direct involvement in the phosphorylation of nuclear proteins which are responsible for the regulation of DNA replication.

Retinoic acid induces translocation of protein kinase C (PKC) and activation of nuclear PKC (nPKC) in rat splenocytes

Retinoic acid (RA), a vitamin A metabolite, has marked effects on growth of normal and malignant cells; however, the exact mechanism of action remains unclear. The effect of two RA analogs, 13-cis-RA and all-trans-RA, on transmembrane signalling processes was investigated in rat splenocytes. Treatment of rat splenic cells with these retinoic acid analogs resulted in translocation of protein kinase C (PKC) from the cytosol to the membrane. Previous studies have described nuclear RA receptors (RARs and RXRs) for several species and the biologic activity of RA has been shown to be mediated by specific interaction with these nuclear receptors. Thus, activation of nuclear pool(s) of protein kinase C (nPKC) by RA analogs was also studied. Rat splenocyte nuclei pure by enzymatic and electron microscope criteria demonstrated a biphasic pattern of bell-shaped curves for both cis- and trans-RA with maximum statistically significant peak of phosphate incorporation into endogenous substrates at 10(-16) M cis-RA and 10(-16)-10(-17) M trans-RA. A monoclonal antibody to PKC and the PKC inhibitors, H-7, sphingosine, and staurosporine, blocked the RA-stimulated nuclear phosphorylation. The ability of RA to activate cell membrane PKC resulting in an increase in particulate PKC activity correlates well with the activation of nPKC since the particulate fraction would include nuclear enzyme systems. This ability of RA to activate nPKC and possibly affect the growth status of a cell may provide a missing link to our understanding of the cellular sites of action for this vitamin.

Subnanomolar concentration of VIP induces the nuclear translocation of protein kinase C in neonatal rat cortical astrocytes

At subnanomolar concentrations, vasoactive intestinal peptide (VIP) can act as an astroglial mitogen and as a secretagogue for neurotrophic substances released from glia (Brenneman et al.: J Neurosci Res 25:386-394, 1990). Here we report that treatment with subnanomolar (0.1 nM) VIP, that does not produce an increase in intracellular cAMP levels, induced the translocation of protein kinase C (PKC) from the cytoplasm to the nucleus in neonatal cortical astrocytes, as revealed by immunohistochemistry, Western blot analysis, and measurements of the enzyme activity. Western blot analysis of subcellular fractions, using PKC isotype-specific antisera, showed PKC alpha as well as the two novel PKC isotypes, delta and zeta immunoreactivities, whereas PKC beta or gamma immunoreactivities were not detected. PKC alpha was associated predominantly with the cytosolic compartment, while PKC delta was found in the plasma membrane and in nuclear fractions. In contrast, PKC zeta was distributed ubiquitously within the major subcellular fractions. Treatment of the cells with 0.1 nM VIP caused a marked increase in nuclear PKC alpha and, to a lesser extent, PKC delta and PKC zeta immunoreactivities. Western blot analysis showed that a low (1 nM) concentration of phorbol, 12-myristate, 13 acetate also caused the subcellular redistribution of PKC immunoreactivities from the cytoplasm to the nuclear fraction, similar to VIP treatment. Exposure of astrocytes to high concentrations (1 microM) of phorbol, 12-myristate, 13 acetate resulted in the down-regulation of PKC alpha and PKC delta, while distribution of PKC zeta immunoreactivities were only slightly altered.(ABSTRACT TRUNCATED AT 250 WORDS)

The nuclear inositol 1,4,5-trisphosphate and inositol 1,3,4,5-tetrakisphosphate receptors

IP3R is located to the inner nuclear membrane. Nuclear IP3R is recognized as a 220 kD immunoreactive protein by antisera raised against purified rat brain IP3R. Antisera against C-terminal 95-108 peptide fragment derived from rat brain IP3R does not reveal immunoreactivity in the nucleus. Nuclear IP3R is sensitive to heparin and is phosphorylated by nuclear PKC, enhancing the efficiency of IP3 in nuclear calcium release. There are two IP4 binding sites located to the nuclear envelope. The nuclear IP4R is sensitive to pH and pH 6.5 is found optimum for the ligand binding. The high affinity IP4R is associated with the outer nuclear membrane and mediates nuclear calcium uptake by IP4. Low affinity IP4R is identified with the inner nuclear membrane and is not involved in IP4 mediated calcium entry into the nucleus. The nature of IP4R associated with the outer nuclear membrane as compared with the one identified with the inner nuclear membrane remains to be elucidated.

Internalization and nuclear localization of peptide hormones

The presence of neuropeptide receptors on the plasma membrane is well accepted, as is its internalization and down-regulation. The analysis of the fate of these peptides within their target-cells is difficult. Endogenous peptides or administered native peptides are visualized in these cells using immunocytology after cryoultramicrotomy. Labelled peptides can be injected and their internalization kinetics studied using ultrastructural autoradiography. The pituitary gland is a suitable model for the study of the neuropeptide mechanism, with the lactotroph function being taken as an example in the present case. Prolactin (PRL) release depends on two main neuropeptides: thyrotropin-releasing hormone (TRH) and somatostatin (SS). The TRH immunoreactivity obtained from endogenous as well as injected material was restricted to the plasma membrane, secretory granules, cytoplasmic matrix and nucleus. The internalization kinetics of exogenous native TRH showed an increase of immunoreactive material in all compartments including the nucleus. The endogenous SSs (SS14 and SS28) were detected in the same subcellular lactotroph compartments. Injection of 125I-SS showed a rapid binding of SS at the plasma membrane level before internalization. For 60 min of in vivo uptake, 125I-SS28, the large SS molecule, was detected in the cytoplasm only, while 125I-SS14 was found in the nuclear matrix. In vitro 125I-SS28 was restricted to the nuclear membrane. Under physiological conditions the endogenous neuropeptides were visualized in the nucleus, but after injection of labelled peptides only small molecules were found in the nucleus. The significance of the presence of these neuropeptides is discussed.

Differential accumulation of a protein kinase homolog in Trypanosoma brucei

Using degenerate oligonucleotide primers derived from conserved regions in the catalytic domains of protein kinases, we have identified transcripts of the protein kinase families in Trypanosoma brucei by the polymerase chain reaction technique. From the cDNAs synthesized from poly(A)+ RNA purified from the bloodstream form of the pathogen, we have obtained seven distinct partial cDNA sequences. Deduced amino acid sequences of these seven clones contain conserved regions characteristic of catalytic domains of eukaryotic protein serine/threonine kinases. DNA gel blots showed that one of the clones, TbPK-A4 is most likely a member of a subfamily in the protein kinase gene family, whereas the other six are probably each encoded by a single gene in the genome of T. brucei. The full-length cDNA of TbPK-A1 was cloned, sequenced, and found to encode an open reading frame of 350 amino acid residues. Its gene (designated KFR1) demonstrated high sequence similarity to KSS1 and FUS3 from Saccharomyces cerevisiae and rat MAP kinase at the amino acid level. There are a 3- to 4-fold higher level of KFR1 transcript and a 2-fold increase of KFR1 protein in the bloodstream form when compared with the insect form of T. brucei. This preferential expression of KFR1 in the bloodstream form of T. brucei may play a role in controlling the cell cycle and thus the growth rate of the organism.

Secretagogue-induced calcium wave shows higher and prolonged transients of nuclear calcium concentration in mast cells

To clarify the mechanism of secretagogue (compound 48/80)-induced calcium signaling in rat peritoneal mast cells, we analyzed serial confocal calcium images with high spatial and temporal resolution using different Ca(2+)-probes. The Ca(2+)-wave began at the periphery of the cytoplasm, and then spread to the center of the nucleus. Nuclear [Ca2+]i was clearly higher than cytoplasmic [Ca2+]i. The heterogeneity of [Ca2+]i continued until about 2 min after degranulation. These results suggest the existence of an intranuclear Ca(2+)-store which possesses a Ca(2+)-releasing mechanism similar to that in the cytoplasm.

Protein kinase C substrates and ganglioside inhibitors in bovine mammary nuclei

In cow mammary gland, unlike in other tissues, gangliosides (putative physiologic regulators of protein kinase C) may be distributed in nuclei and on the cell surface. This study was designed to determine whether gangliosides and the protein kinase C system (the enzyme and its substrate proteins) are present in cow mammary gland nuclei and to examine the effect of gangliosides detected in nuclei on protein phosphorylation catalyzed by protein kinase C. Gangliosides GM3, GD3, and GT1b were detected in the highly purified nuclear fraction. The nuclear ganglioside pattern was different from those of whole tissue and cytosol, thereby suggesting the presence of the gangliosides in nuclei. Protein kinase C and its substrate proteins (120, 97, 56, 43, 38, and 36 kDa) were extracted by Triton X-100 treatment of nuclei. Both protein kinase C activity (histone phosphorylation) and the nuclear substrate phosphorylation were effectively inhibited by the three gangliosides. Of the gangliosides, GT1b was the most potent in inhibiting phosphorylation, followed by GD3 and GM3. These results suggest that signal transduction mediated by protein kinase C in cow mammary gland nuclei may be regulated by gangliosides.