Epidermal growth factor inhibits cytokine-dependent nitric oxide synthase expression in hepatocytes

Liver cells express a wide range of extracellular receptors involved in the control of cell growth and arrest that can be studied ex vivo. Incubation of primary cultures of hepatocytes with IL-1 beta, TNF-alpha or lipopolysaccharide promotes the expression of the inducible form of nitric oxide synthase and NO release, a process that is inhibited to a different extent by incubation of the cells with EGF. In addition to this growth factor, IL-6 and TGF-beta also inhibited NO synthesis. Therefore, EGF by itself or in combination with other cytokines may be involved in the down-regulation of the NO synthesis that occurs in the early steps of liver regeneration.

Nitric oxide synthesis in rat peritoneal macrophages is induced by IgE/DNP complexes and cyclic AMP analogues. Evidence in favor of a common signaling mechanism

The production of nitric oxide was studied in rat adherent peritoneal cells stimulated with preformed IgE/DNP-BSA complexes made of IgE obtained from a secreting hybridoma. Stimulation with complexes at equivalence induced both the production of NO and an increased expression of the mRNA of the inducible isoform of NO synthase (iNOS). Production of NO was also elicited by a rabbit polyclonal F(ab')2 anti-CD23 cross-reacting with rat CD23. Because IgE/DNP-BSA complexes did not elicit Ca2+ mobilization and genistein did not influence the production of NO, cyclic AMP was considered as an alternative signaling molecule. Combination of a suboptimal concentration of dibutyryl cyclic AMP and IgE/DNP-BSA complexes showed an additive effect on NO production, whereas this was not observed when the agonists were used at supraoptimal doses. The inhibitor of cyclic AMP-specific phosphodiesterase IV, rolipram, which acts on the enzyme isoform predominantly expressed in inflammatory cells, also induced the production of NO. Furthermore, IgE/DNP-BSA complexes increased intracellular levels of cyclic AMP. Taken together, these data indicate that stimulation of mononuclear phagocytes via the low-affinity receptor Fc epsilon RII or rising intracellular concentrations of cyclic AMP leads to an enhanced expression of iNOS. Evidence in favor of the involvement of cyclic AMP in the signaling pathway linked to Fc epsilon RII is provided by the effect of IgE/DNP-BSA complexes on intracellular cyclic AMP levels and by the additive effect produced by dibutyryl cyclic AMP on NO production elicited by IgE/DNP-BSA complexes.

Splenic B lymphocyte programmed cell death is prevented by nitric oxide release through mechanisms involving sustained Bcl-2 levels

Incubation of ex vivo cultured mature B cells in the presence of nitric oxide or nitric oxide-donor substances delays programmed cell death as determined by the appearance of DNA laddering in agarose gel electrophoresis or by flow-cytometry analysis of DNA. Nitric oxide also rescues B cells from antigen-induced apoptosis but fails to provide a co-stimulatory signal that converts the signal elicited by the antigen into a proliferative response. The protective effects of nitric oxide against programmed cell death can be reproduced by treatment of the cells with permeant analogues of cyclic GMP. Regarding the mechanisms by which nitric oxide prevents apoptosis in B cells, we have observed that nitric oxide release prevents the drop in the expression of the protooncogene bcl-2, both at the mRNA and protein levels, suggesting the existence of an unknown pathway that links nitric oxide signaling with Bcl-2 expression.

Bacterial lipopeptides induce nitric oxide synthase and promote apoptosis through nitric oxide-independent pathways in rat macrophages

Stimulation of resident peritoneal macrophages with S-[2,3-bis(pamitoyloxy)-(2R,2S)-propyl]-N-palmytoyl-(R)-C ysSerLys4 or S(-)[2,3-bis(pamitoyloxy)-(2R,2S)-propyl]-N-palmytoyl-(R)-++ +CysAlaLys4, two synthetic bacterial lipopeptides, promoted the expression of the inducible form of nitric oxide synthase, exhibiting a temporal pattern of nitric oxide release that was delayed with respect to the induction elicited by bacterial lipopolysaccharide. Treatment of macrophages with genistein blocked the nitric oxide synthesis triggered by the lipopeptides or lipopolysaccharide. Simultaneous incubation with lipopolysaccharide and lipopeptide resulted in an antagonistic effect on nitric oxide synthase mRNA levels and on nitrite plus nitrate release to the medium. Triggering with bacterial lipopeptides induced macrophage programmed cell death. In macrophages activated with lipopeptide, apoptosis was observed even in the absence of nitric oxide synthesis, therefore indicating the existence of alternative pathways in the control of programmed cell death in these cells.

Nitric oxide is released in regenerating liver after partial hepatectomy

The induction of hepatic nitric oxide synthase (NOS) and the biosynthesis of nitric oxide (NO) were studied in liver after partial hepatectomy (PH). NOS activity in the liver remnant was observed 4 to 6 hours after PH, and no differences were evidenced between the proximal and distal surgical areas. The form of NOS expressed in liver was independent of calcium and calmodulin, and the messenger RNA levels were first detected 2 hours after hepatectomy using a probe corresponding to the cytokine-induced macrophage NOS. The seric concentration of nitrites remained unchanged after hepatectomy, whereas the content in nitrates and in S-nitrosylated proteins progressively increased in parallel with the NOS activity. The spectra of hemoglobin in the 400-to 460-nm region failed to exhibit the characteristic shift caused by the formation of the nitrosyl-hemoglobin complex, suggesting that NO was rapidly metabolized in liver. Treatment of the animals with substrate analogue NOS inhibitors blocked the pattern of DNA ploidy elicited after hepatectomy, suggesting a role for NO in the regenerative process. Peritoneal resident macrophages were used as an alternative reporter cell system for the assessment of NOS expression. Incubation ex vivo of peritoneal macrophages from animals that underwent hepatectomy induced the expression of NOS in a cytokine-modulated fashion, suggesting that macrophages were primed as a result of the hepatectomy. When peritoneal macrophages from control rats were incubated with the sera of animals that underwent hepatectomy, a time-dependent induction of NOS was observed, with a maximal induction corresponding to sera collected 2 hours after PH. These results indicate that NO might be involved in the control of early responses after PH.

Platelet-activating factor: the effector of protein-rich plasma extravasation and nitric oxide synthase induction in rat immune complex peritonitis

1. The involvement of platelet-activating factor (PAF) in immune complex-induced/polymorphonuclear-mediated tissue injury was studied by use of a reverse passive Arthus (RPA) model in the peritoneal cavity of rats. 2. Extravasation of protein-rich plasma, accumulation of polymorphonuclear leukocytes (PMN), and the production of nitric oxide (NO) by resident peritoneal mononuclear phagocytes were assayed. 3. Treatment of rats with either UR-12460 or BB-823, two compounds which possess different chemical structures, but elicit the same antagonistic effect on the PAF receptor, abrogated protein-rich plasma extravasation. In contrast, they did not show any effect on the accumulation of PMN. 4. Inhibition of NO production with both NG-mono methyl-L-arginine and NG-nitro-L-arginine failed to prevent protein-rich plasma extravasation. 5. The production of NO by peritoneal adherent cells following RPA was measured in cells maintained for 2 to 28 h in culture, and it was significantly increased in cells removed as early as 15 min after RPA induction, as compared to controls. 6. Addition of 10 nM PAF to the culture medium reduced the generation of NO by peritoneal cells from RPA rats, whereas this mediator enhanced NO production in cells from naive control animals. 7. Treatment with either UR-12460 or BB-823 prior to the induction of RPA produced an almost complete inhibition of NO production. 8. Assay of nitric oxide synthase activity in cell homogenates from peritoneal cells showed that the activity was due to the inducible form of the enzyme. 9. Study by Northen blotting of mRNA coding for the inducible NO synthase (iNOS) showed transcription at 6 and 18 h after the induction of RPA, which was inhibited in UR-12460-treated rats.10. These data indicate that PAF is the main mediator of the early plasma leakage observed in RPA,and also that PAF is implicated in the triggering of long-term changes via induction of specific genes, as judged from its ability to promote the expression of iNOS.

Nitric oxide implication in the control of neurosecretion by chromaffin cells

In this work, we have studied the effects of pure nitric oxide (NO) on the regulation of catecholamine (CA) secretion by chromaffin cells, as well as the possible presence of its synthesizing enzyme L-arginine:NO synthase (NOS) in these cells. Our results show that NO produces a large stimulation of basal CA secretion. This effect was calcium- and concentration-dependent (EC50 = 64 +/- 8 microM) and was not due to nonspecific damage of the tissue by NO. NO also modulates the CA secretion evoked by nicotine in a dose-dependent manner. Although it has a stimulatory effect on the CA secretion evoked by low doses of nicotine (< 3 microM; EC50 = 16 +/- 3 microM), it produces a dose-dependent inhibition of the CA secretion induced by high doses of nicotine (> or = 30 microM; IC50 = 52 +/- 6 microM). The mechanism by which NO modulates CA secretion seems to be through the increase in the cyclic GMP levels, because there was a close correlation between the CA secretion and the cyclic GMP levels. The presence of a specific activity of NOS in chromaffin cells has been demonstrated by two independent methods: release of [14C]citrulline from [14C]arginine and formation of an NO-hemoglobin complex. NOS activity was about 0.5 pmol/min/mg of protein. It was calcium- and mainly calmodulin-dependent and could be specifically blocked by the NOS inhibitor N-methyl-L-arginine. These results suggest that NO could be an important intracellular messenger in the regulation of neurosecretion in chromaffin cells.

CD2-CD48 interaction prevents apoptosis in murine B lymphocytes by up-regulating bcl-2 expression

Antigen receptor engagement initiates clonal expansion and antibody secretion in B lymphocytes in response to foreign antigens. However, binding of self antigen to antigen receptors targets self-reactive B cell clones for elimination or inactivation. The antigen-triggered biochemical events and the eventual response of the cells are dependent on the simultaneous occupancy of co-stimulatory receptors. CD2 is an intercellular adhesion molecule implicated in cell activation and expressed in human T and natural killer cells as well as in mouse B lymphocytes. Mouse B cells specific for allogeneic major histocompatibility complex (MHC) class I initiate a suicide program that leads to DNA fragmentation and cell death when confronted with soluble MHC class I while undergoing clonal expansion when the antigen is present on mitomycin C-treated cells. Here we show that occupancy of CD2 in mouse B cells by the presence of either monoclonal antibody (mAb) specific for CD2, or soluble recombinant mouse CD48, its natural ligand in mouse, prevents the induction of apoptosis. Furthermore, the in vitro activation by mitomycin C-treated allogeneic cells, is abrogated in the presence of anti-CD48 mAb (OX78). These results indicate that a CD2-CD48 interaction is involved in the control of B cell activation.

Cocaine-induced liver injury in mice elicits specific changes in DNA ploidy and induces programmed death of hepatocytes

Liver injury was induced by a single dose (60 mg/kg) of cocaine in male albino Swiss mice untreated or pretreated with phenobarbital (in drinking water 1 gm/L), for 5 days before cocaine administration. One parameter of liver injury, serum isocitrate dehydrogenase activity, showed sharp increases at 24 hr of cocaine treatment; we also noted decrease hepatic levels of ATP, GSH, cytochrome P-450 and NADPH/NADP+ ratio and increases in malondialdehyde concentration. Histopathological study of liver slices showed perivenous and periportal necrosis induced by cocaine in untreated mice and mice pretreated with phenobarbital, respectively. A regenerative postnecrotic response, which peaked at 48 hr, was demonstrated by the appearance of mitotic cells. Mitotic index analysis showed that proliferative cells appear to be unevenly distributed in the hepatic acinus and were mainly located in the vicinity of the damaged acinar region. Genomic DNA ploidy and the distribution of DNA in the phases of the cell cycle were studied in nuclei of isolated hepatocytes. At 12 hr of cocaine administration, both in untreated and phenobarbital-pretreated mice, the following changes were observed: a sharp decrease in tetraploid (4N) cells (40% to 17% and 25% to 6%, respectively) and octoploid (8N) cells (5% to 2% and 2% to 1%, respectively), together with the appearance of a hypodiploid population (13% and 31%, respectively). Hypodiploid population was characterized as apoptotic cells by detection of DNA fragmentation in agarose gel. These results suggest that a significant percentage of cell death induced by cocaine occurs by means of the apoptosis death program. Comparison of the initial values of DNA ploidy with those obtained at 7 days of cocaine administration showed remarkable increases in polyploid populations (4N and 8N) and a decrease in diploid cells (2N), indicating that the process of differentiation occurs when liver restores its functionality.

Protein kinase C V3 domain mutants with differential sensitivities to m-calpain are not resistant to phorbol-ester-induced down-regulation

Distinct linker sequences were introduced into the protease-sensitive V3 domain of protein kinase C-alpha and the mutant proteins were expressed in COS-1 cells. Partially purified preparations of these mutants were functionally similar to wild-type protein kinase C-alpha, however their susceptibility to m-calpain was quite distinct, with one mutant being insensitive to cleavage. The three mutants, after expression in COS-1 cells, were found to behave in a manner indistinguishable from wild-type protein kinase C-alpha with respect to subcellular distribution, acute responses to 12-O-tetradecanoyl-phorbol 13-acetate and 12-O-tetradecanoyl-phorbol-13-acetate-induced down-regulation. The data imply that down-regulation of protein kinase C-alpha is likely to involve a general degradative process rather than cleavage by a site-specific protease.

Induction of nitric oxide release by MRC OX-44 (anti-CD53) through a protein kinase C-dependent pathway in rat macrophages

Many membrane proteins are implicated in the control of cell function by triggering specific signaling pathways. There is a new family of membrane proteins, defined by its structural motifs, which includes several lymphoid antigens, but lacks a function. To study its biological role, we determined which signaling pathways are affected by the CD53 antigen, a prototypic member of this family, in rat macrophages. Activation of CD53 by cross-linking results in an increase in inositol phosphates and diacylglycerol and in Ca2+ mobilization, which are insensitive to pertussis or cholera toxins. There is a translocation of protein kinase C to the membrane accompanied by nitric oxide (NO) release in macrophages. This effect is the result of the expression of the inducible nitric oxide synthase (iNOS), which is dependent on protein kinase C and protein synthesis. These results have linked a new receptor with a specific pathway of NO induction and thus have opened up a novel aspect of NO regulation in cell biology.

[Changes in distribution and isoenzymatic expression of protein kinase C in B lymphocytes induced by alloantigenic stimulation]

Protein kinase C comprises a family of distinct isoenzymes that are involved in signal transduction pathway triggered by activation of membrane receptor. These isoenzymes differ in their tissue distribution, activation requirements and substrate specificity. Recent reports have shown the regulation of PKC-isoenzymes expression in physiological and pathological models. Recently, we shown PKC participation in B cells allogeneic response to intact cells and solubilized alloantigen. Here, alloimmunization influence upon PKC isoforms expression on murine B cells was analyzed. Our data indicates that PKC beta is the main isoform expressed on B cells with a lesser amount of alpha, epsilon and zeta and a very small amount of delta isoform. When analyzing B cells from alloimmunized mice we observed an increment of isoforms a and e and a decrease of the beta isoforms while increasing the number of immunizations. An increase of membrane bound PKC enzyme was also observed. Furthermore with increasing number of immunizations a decrease in LPS induce proliferation was found. In contrary, while normal B cells showed non proliferation when stimulated with solubilized alloantigen, they displayed a strong proliferation when they were obtained from animals with 5-6 alloimmunizations. This results shown that alloimmunization induces changes in the distribution and expression of PKC isoenzymes that are correlated to changes in the biological response triggered by B cell stimulation.

Relationship between genomic DNA ploidy and parameters of liver damage during necrosis and regeneration induced by thioacetamide

Thioacetamide proved to be a potent necrogenic agent when a single dose of 6.6 mmol/kg was administered intraperitoneally to rats. Its necrogenic ability was assessed on the basis of morphological and biochemical changes. The injury of centrilobular hepatocytes showed a peak of cell death 24 hr after thioacetamide administration; it was followed immediately by the regenerative response. Parallel increases of serum aminotransferases, isocitrate dehydrogenase and gamma-glutamyl transferase activities were observed. Severe liver damage was also evident at 24 hr on the basis of glutathione depletion (29% of control), malondialdehyde production (169%), cytochrome P-450 level decrease (26%) and increased activity of glutathione S-transferase (160%). We checked the regenerative response by determining nuclear DNA content in isolated hepatocytes 0, 6, 12, 18, 24, 36, 48 and 72 hr after thioacetamide administration. Changes in DNA cell distribution between G0-G1, S and G2 + M phases of the cell cycle were observed. The sharp decrease in the percentage of the tetraploid cell population (G2 + M phases) and the abrupt increase of the S-phase cells at 36 and 48 hr suggest transition from adult to fetal in hepatocyte populations obtained 24 and 36 hr after thioacetamide treatment. At 72 hr of treatment, hepatocyte populations showed recovery to adult state. In the shift from the adult to fetal, registered at 24, 36 and 48 hr after thioacetamide administration, mitosis seemed to precede the synthesis of DNA.

Rat liver messenger ribonucleic acid and enzyme activity of 6-phosphofructo 2-kinase/fructose 2,6-bisphosphatase impairment during the late period of pregnancy

Fructose 2,6-bisphosphate concentration, 6-phosphofructo 2-kinase/fructose 2,6-bisphosphatase (PFK-2/FBPase2) activity, and messenger RNA decreased in maternal rat liver during the last days of gestation, and the recovery started after delivery. Phospho(enol)pyruvate carboxykinase activity and messenger RNA increased in contrast to PFK-2 changes. Measurement of the glycolytic capacity in isolated hepatocytes prepared from rats 1 h after parturition showed a low glucose consumption and an impaired capacity to metabolize glucose. These results stress the relevance of the PFK-2/fructose 2,6-bisphosphate system in the control of the glycolytic flux in liver, and these changes are intended to prevent glucose consumption by maternal liver and contribute to allow gluconeogenesis to proceed at the end of gestation. The physiological basis of this adaptation may lay on the diversion of glucose from maternal to fetal metabolism.

Early signals in alloantigen induced B-cell proliferation. Comparison between B-cell triggering by intact allogeneic cells and solubilized alloantigen

Stimulation of B cells from BALB/c with allogeneic lymphocytes from C57BL/6 mice resulted in a slight increase in cytosolic Ca2+ but in the absence of proliferative response. Immunization of BALB/c mice with C57BL/6 total lymphocytes resulted in an enhancement of cytosolic Ca2+ and of B cell proliferation. Phosphatidylinositol specific phospholipase C was activated immediately after allogeneic stimulation as deduced by the concomitant rise in inositol 1,4,5-trisphosphate and 1,2-diacylglycerol. Translocation of protein kinase C from the cytosol toward the membranes paralleled the elevation in cytosolic free Ca2+. Activation of BALB/c B cells with solubilized alloantigen from the plasma membrane of C57BL/6 lymphocytes produced qualitatively the same early responses as the treatment with allogeneic cells, although quantitatively more intense. Concerning protein kinase C, an important degradation was observed in these conditions. Soluble alloantigen failed to promote B cell proliferation, being observed when cells were costimulated with a low concentrations (2 ng/ml) of phorbol 12,13-dibutyrate before alloantigen addition. Analysis of the molecular weight of the active fraction of the solubilized alloantigen revealed the presence of a 51 kDa protein that mimicked all properties of the alloantigen preparation. This molecule was also recognized in Western blot by an anticlass I mAb and by the sera of immunized animals. A putative MHC class I antigen is proposed as the nature of the active molecule, and its interaction with specific membrane Ig on the B cell is analyzed. Although the results fit with a cellular response mediated through membrane Ig, the involvement of other B cell surface molecules interacting with the alloantigens cannot be disregarded.

Sulfonylureas activate glycogen phosphorylase and increase cytosolic free-Ca2+ levels in isolated rat hepatocytes

Without causing significant changes in cellular levels of cyclic adenosine monophosphate (cAMP), the addition of either glibenclamide or gliquidone to isolated rat hepatocytes caused a transient dose- and Ca(2+)-dependent activation of glycogen phosphorylase. The calculated concentrations corresponding to half-maximal activation were 5 and 2 mumol/L, respectively. In connection with this, it was observed that glibenclamide provoked a dose-dependent increase in cytosolic free-calcium concentration ([Ca2+]i) in Fura-2-loaded hepatocytes. Moreover, the presence of glibenclamide in the incubation medium accelerated the rate of Ca2+ uptake by Ca(2+)-depleted hepatocytes. These findings suggest that an increase in [Ca2+]i could mediate some of the effects of sulfonylureas in liver metabolism.

Phorbol esters induce nitric oxide synthase and increase arginine influx in cultured peritoneal macrophages

Incubation of peritoneal macrophages with beta-phorbol 12,13-dibutyrate promotes a time-dependent release of NO to the incubation medium. This effect was antagonized by LPS, a well known inducer of nitric oxide synthase (NOS) expression in macrophages, and was inhibited by NG-methyl-L-arginine and N omega-nitro-L-arginine. An increase in intracellular cGMP and NOS activity was observed in parallel with NO release. The induction of NOS was accompanied by a stimulation of arginine influx within the cell. These results suggest that activation of protein kinase C by phorbol esters is sufficient to promote NOS induction in macrophages.

Circular dichroism analysis of ligand-induced conformational changes in protein kinase C. Mechanism of translocation of the enzyme from the cytosol to the membranes and its implications

The structural changes following the binding to protein kinase C (PKC) of activators that promote its translocation to lipid environments were studied by far-u.v. c.d. and intrinsic fluorescence measurements of the protein. In the absence of activators, PKC contained 40% alpha-helix, with an average size of 13 amino acids per alpha-helix segment, and 12% beta-structure as deduced from c.d. spectral analysis while fitting a set of model proteins of known structure. Ligands that promote translocation and activation of the enzyme, such as Ca2+ ions and phorbol esters, produced drastic changes in the c.d. spectra which may be interpreted as a reduction in the average number of consecutive amino acids in the alpha-helix. Most of the total alpha-helix structure was conserved and an increase in beta-structure was produced by active phorbol esters. These activators differentially affected the fluorescence of PKC: phorbol esters shifted the emission maximum to the red, whereas Ca2+ produced a marked decrease in the intensity of the fluorescence emission, suggesting in both cases that tryptophan residues were exposed to increased polar environments after binding of the ligands.

Differential calcium mobilization by vasopressin, angiotensin II, gastrin-releasing peptide, and adenosine triphosphate in adult and fetal hepatocytes. Relevance for the activation of calcium-dependent enzymes

Early signals elicited after membrane receptor binding of agonists, the transmembrane signaling pathway of which involves activation of phosphoinositide-specific phospholipase C, were compared in fetal (22 days gestation) and adult rat hepatocytes. Free cytosolic calcium changes varied depending on the agonist and type of stimulated cells. Angiotensin II and ATP elicited the maximal responses in both types of cells, whereas the maximal Ca2+ increase produced by vasopressin was twice as much in adult than in fetal hepatocytes. The opposite response was observed for bombesin- or gastrin-releasing peptide-stimulated cells. Triggering of fetal and adult hepatocytes with substances that maximally promote endoplasmic reticulum calcium release or phosphoinositide-specific phospholipase C activation revealed that at least for the actions mediated through the angiotensin II and P2 purinergic receptor, the agonist stimulation was near the maximal response capacity of the signaling pathway. Agreement was observed between the relative number of membrane receptors and the biological responses.

Phorbol esters induce nitric oxide synthase activity in rat hepatocytes. Antagonism with the induction elicited by lipopolysaccharide

The incubation of primary cultures of rat hepatocytes with lipopolysaccharide (LPS) or biologically active phorbol esters promotes the release of nitric oxide to the incubation medium. This process is the result of the induction of the Ca(2+)-and calmodulin-independent form of nitric oxide synthase. Both the release of nitric oxide to the incubation medium and the expression of nitric oxide synthase activity exhibited a lag period of about 45-60 min after cell stimulation. Exposure of hepatocytes to both stimuli produced an antagonistic effect on nitric oxide release, with a half-maximal inhibition obtained with 14 nM phorbol 12,13-dibutyrate at saturating concentration of LPS. Incubation of cells with alpha-phorbol 12,13-didecanoate failed to counteract the effect of LPS or to induce nitric oxide synthase, suggesting that activation of protein kinase C was involved in this process.

Protein kinase C isoenzymes display differential affinity for phorbol esters. Analysis of phorbol ester receptors in B cell differentiation

Protein kinase C (PKC) comprises a family of distinct isoenzymes that are involved in signal transduction pathways linking the cell to triggers perceived via membrane receptors. These isoenzymes differ in their tissue distribution, activation requirements, and substrate specificity. One common denominator among different PKC subspecies is their activation by phorbol esters. We have developed a sensitive method permitting the measurement of phorbol ester binding sites, their quantitation, as well as their dissociation kinetics, by performing cytofluorometric analyses on intact cells or on isolated PKC associated to phosphatidylserine vesicles incubated in the presence of fluorochrome-labeled phorbol ester. Both PKC isozymes beta I/beta II and alpha from brain and spleen after incorporation into phosphatidylserine vesicles, display affinities with apparent Kd of 120 and 50 nM, respectively; although PKC gamma from brain exhibits a Kd of 210 nM. In addition to these receptors, on PKC isozymes from spleen, an intermediate affinity phorbol ester receptor (Kd of 3 nM) and an additional high affinity phorbol ester binding site with a Kd of 0.1 to 0.5 nM were also detected. This latter receptor comigrates with high m.w. PKC isoforms. In different cell lines, the phorbol ester binding patterns, as well as the expression of individual PKC isoenzymes, could be positively correlated.

Isoenzymes of carbohydrate metabolism in primary cultures of hepatocytes from thioacetamide-induced rat liver necrosis: responses to growth factors

Hepatocytes isolated from the liver of rats after a necrotizing dose of thioacetamide (6.6 mmol/kg) were used to study the postnecrotic process of liver regeneration. Flow cytometry analysis revealed populations of dedifferentiated hepatocytes exhibiting physical properties (size and fluorescence emission at 530 nm) similar to those found in fetal (22 days old) liver cells. The percentage of these cells increased progressively from 24 to 48 and 72 hr after thioacetamide administration. In primary cultures of hepatocytes the effects of phorbol 12-myristate 13-acetate, bombesin and insulin were investigated on the 6-phosphofructo 2-kinase/fructose 2,6 bisphosphate system. Bombesin and insulin stimulated 6-phosphofructo 2-kinase activity and fructose 2,6-bisphosphate content both in control and in thioacetamide-treated hepatocytes. However, phorbol 12-myristate 13-acetate stimulated 6-phosphofructo 2-kinase activity and increased fructose 2,6-bisphosphate concentration in thioacetamide-treated liver cells, whereas no similar response was found in hepatocytes from control rats. The response of postnecrotic thioacetamide-treated hepatocytes to phorbol 12-myristate 13-acetate was similar to that obtained from 22-day-old fetal liver cells, which reveals that different methods might control fructose 2,6-bisphosphate content and therefore the mechanisms of glycolysis and gluconeogenesis at this regulatory step. The lack of response to glucagon of glycogen phosphorylase a and 6-phosphofructo 2-kinase from thioacetamide-treated hepatocytes may indicate that the expression of specific enzymes of carbohydrate metabolism undergoes transitions to less-differentiated isoenzymatic forms. Moreover, the isoenzyme pattern of hexokinases elicits a complete disturbance in glucokinase and hexokinases activities.(ABSTRACT TRUNCATED AT 250 WORDS)