Modulation of VIPergic phenotype of enteric neurons by colonic biopsy supernatants from patients with inflammatory bowel diseases: Involvement of IL-6 in Crohn's disease

BACKGROUND

Neuroplastic changes in the enteric nervous system (ENS) observed during IBD might participate in physiopathological processes. Vasoactive intestinal polypeptide has been shown to be involved in intestinal inflammation and barrier functions. We aimed to investigate the modulation of VIP expression in colonic biopsies of IBD patient, the ability of soluble factors from biopsies to reproduce in vitro these modulations and identify soluble factors responsible.

METHODS

VIP and cytokines mRNA expressions were assessed in colonic biopsies of healthy subjects (HS) and IBD patients from inflamed (I) and non-inflamed areas (NI). Supernatants (SUP) of biopsies were applied to primary culture of ENS and VIP and cytokines mRNA expressions were assessed. The role of cytokines in SUP induced changes in VIP expression was evaluated.

KEY RESULTS

VIP mRNA expression was lower in biopsies of patients with Crohn's disease (CD) than Ulcerative Colitis (UC) but unchanged as compared to HS. VIP mRNA and protein expression were lower in primary culture of ENS incubated with SUP-CD than with SUP-UC. Furthermore, in CD but not UC, SUP-I reduced VIP expression in the ENS as compared to SUP-NI. Next, IL-6 but not IL-5, IL-10, IL-17, IFN-γ or TNF-α reduced VIP expression in the ENS. Finally, in CD, SUP-I incubated with anti-IL-6 antibody increased VIP expression as compared to SUP-I alone.

CONCLUSIONS & INFERENCES

Mucosal soluble factors from IBD induce VIP neuroplastic changes in the ENS. IL-6 was identified as a putative soluble factor responsible in part for changes in VIP expression in CD.

IL-22BP is produced by eosinophils in human gut and blocks IL-22 protective actions during colitis

Crohn's disease and ulcerative colitis, the two major forms of inflammatory bowel diseases (IBDs), are characterized by high levels of IL-22 production. Rodent studies revealed that this cytokine is protective during colitis but whether this is true in IBDs is unclear. We show here that levels of the soluble inhibitor of IL-22, interleukin 22-binding protein (IL-22BP), are significantly enhanced during IBDs owing to increased numbers of IL-22BP-producing eosinophils, that we unexpectedly identify as the most abundant source of IL-22BP protein in human gut. In addition, using IL-22BP-deficient rats, we confirm that endogenous IL-22BP is effective at blocking protective actions of IL-22 during acute colitis. In conclusion, our study provides new important insights regarding the biology of IL-22 and IL-22BP in the gut and indicates that protective actions of IL-22 are likely to be suboptimal in IBDs thus making IL-22BP a new relevant therapeutic target.

Enteric glia and neuroprotection: basic and clinical aspects

The enteric nervous system (ENS), a major regulatory system for gastrointestinal function, is composed of neurons and enteric glial cells (EGCs). Enteric glia have long been thought to provide only structural support to neurons. However, recent evidence indicates enteric glia-neuron cross talk significantly contributes to neuronal maintenance, survival, and function. Thus damage to EGCs may trigger neurodegenerative processes thought to play a role in gastrointestinal dysfunctions and symptoms. The purpose of this review is to provide an update on EGCs, particularly focusing on their possible neuroprotective features and the resultant enteric neuron abnormalities subsequent to EGC damage. These neuroprotective mechanisms may have pathogenetic relevance in a variety of functional and inflammatory gut diseases. Basic and clinical (translational) studies support a neuroprotective role mediated by EGCs. Different models have been developed to test whether selective EGC damage/ablation has an impact on gut functions and the ENS. Preclinical data indicated that selective EGC alterations were associated with changes in gut physiology related to enteric neuron abnormalities. In humans, a substantial loss of EGCs was described in patients with various functional and/or inflammatory gastrointestinal diseases. However, whether EGC changes precede or follow neuronal degeneration and loss and how this damage occurs is not defined. Additional studies on EGC neuroprotective capacity are expected to improve knowledge of gut diseases and pave the way for targeted therapeutic strategies of underlying neuropathies.

The omega-6 fatty acid derivative 15-deoxy-Δ¹²,¹⁴-prostaglandin J2 is involved in neuroprotection by enteric glial cells against oxidative stress

Increasing evidence suggests that enteric glial cells (EGCs) are critical for enteric neuron survival and functions. In particular, EGCs exert direct neuroprotective effects mediated in part by the release of glutathione. However, other glial factors such as those identified as regulating the intestinal epithelial barrier and in particular the omega-6 fatty acid derivative 15-deoxy-Δ¹²,¹⁴-prostaglandin J2 (15d-PGJ2) could also be involved in EGC-mediated neuroprotection. Therefore, our study aimed to assess the putative role of EGC-derived 15d-PGJ2 in their neuroprotective effects. We first showed that pretreatment of primary cultures of enteric nervous system(ENS)or humann euroblastoma cells (SH-SY5Y)with 15d-PGJ2 dose dependently prevented hydrogen peroxide neurotoxicity. Furthermore, neuroprotective effects of EGCs were significantly inhibited following genetic invalidation in EGCs of the key enzyme involved in 15d-PGJ2 synthesis, i.e. L-PGDS. We next showed that 15d-PGJ2 effects were mediated by an Nrf2 dependent pathway but were not blocked by PPARγ inhibitor (GW9662) in SH-SY5Y cells and enteric neurons. Finally, 15d-PGJ2 induced a significant increase in glutamate cysteine ligase expression and intracellular glutathione in SH cells and enteric neurons. In conclusion, we identified 15d-PGJ2 as a novel glial-derived molecule with neuroprotective effects in the ENS. This study further supports the concept that omega-6 derivatives such as 15d-PGJ2 might be used in preventive and/or therapeutic strategies for the treatment of enteric neuropathies.

Enteric glia modulate epithelial cell proliferation and differentiation through 15-deoxy-12,14-prostaglandin J2

The enteric nervous system (ENS) and its major component, enteric glial cells (EGCs), have recently been identified as a major regulator of intestinal epithelial barrier functions. Indeed, EGCs inhibit intestinal epithelial cell (IEC) proliferation and increase barrier resistance and IEC adhesion via the release of EGC-derived soluble factors. Interestingly, EGC regulation of intestinal epithelial barrier functions is reminiscent of previously reported peroxisome proliferator-activated receptor gamma (PPARgamma)-dependent functional effects. In this context, the present study aimed at identifying whether EGC could synthesize and release the main PPARgamma ligand, 15-deoxy-(12,14)-prostaglandin J2 (15dPGJ2), and regulate IEC functions such as proliferation and differentiation via a PPARgamma dependent pathway. First, we demonstrated that the lipocalin but not the haematopoetic form for prostaglandin D synthase (PGDS), the enzyme responsible of 15dPGJ2 synthesis, was expressed in EGCs of the human submucosal plexus and of the subepithelium, as well as in rat primary culture of ENS and EGC lines. Next, 15dPGJ2 was identified in EGC supernatants of various EGC lines. 15dPGJ2 reproduced EGC inhibitory effects upon IEC proliferation, and inhibition of lipocalin PGDS expression by shRNA abrogated these effects. Furthermore, EGCs induced nuclear translocation of PPARgamma in IEC, and both EGC and 15dPGJ2 effects upon IEC proliferation were prevented by the PPARgamma antagonist GW9662. Finally, EGC induced differentiation-related gene expression in IEC through a PPARgamma-dependent pathway. Our results identified 15dPGJ2 as a novel glial-derived mediator involved in the control of IEC proliferation/differentiation through activation of PPARgamma. They also suggest that alterations of glial PGDS expression may modify intestinal epithelial barrier functions and be involved in the development of pathologies such as cancer or inflammatory bowel diseases.

Enteric glial cells protect neurons from oxidative stress in part via reduced glutathione

Enteric glial cells (EGCs) are essential in the control of gastrointestinal functions. Although lesions of EGCs are associated with neuronal degeneration in animal models, their direct neuroprotective role remains unknown. Therefore, the aims of this study were to demonstrate the direct neuroprotective effects of EGCs and to identify putative glial mediators involved. First, viral targeted ablation of EGCs in primary cultures of enteric nervous system increased neuronal death both under basal conditions and in the presence of oxidative stress (dopamine, hydrogen peroxide). Second, direct or indirect coculture experiments of EGC lines with primary cultures of enteric nervous system or neuroblastoma cell lines (SH-SY5Y) prevented neurotoxic effects induced by oxidative stress (increased membrane permeability, release of neuronal specific enolase, caspase-3 immunoreactivity, changes in [Ca(2+)](i) response). Finally, combining pharmacological inhibition and mRNA silencing methods, we demonstrated that neuroprotective effects of EGCs were mediated in part by reduced glutathione but not by oxidized glutathione or by S-nitrosoglutathione. Our study identified the neuroprotective effects of EGCs via their release of reduced glutathione, extending their critical role in physiological contexts and in enteric neuropathies.-Abdo, H., Derkinderen, P., Gomes, P., Chevalier, J., Aubert, P., Masson, D., Galmiche, J.-P., Vanden Berghe, P., Neunlist, M., Lardeux, B. Enteric glial cells protect neurons from oxidative stress in part via reduced glutathione.

Neurochemical plasticity in the enteric nervous system of a primate animal model of experimental Parkinsonism

Emerging evidences suggest that the enteric nervous system (ENS) is affected by the degenerative process in Parkinson's disease (PD). In addition lesions in the ENS could be associated with gastrointestinal (GI) dysfunctions, in particular constipation, observed in PD. However, the precise alterations of the ENS and especially the changes in the neurochemical phenotype remain largely unknown both in PD and experimental Parkinsonism. The aim of our study was thus to characterize the neurochemical coding of the ENS in the colon of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated monkeys, a well-characterized model of PD. In the myenteric plexus, there was a significant increase in the number of neurons per ganglia (identified with Hu), especially nitric oxide synthase immunoreactives (IR) neurons in MPTP-treated monkeys compared to controls. A concomitant 72% decrease in the number of tyrosine hydroxylase-IR neurons was observed in MPTP-treated monkeys compared to controls. In contrast no change in the cholinergic or vasoactive intestinal peptide-IR population was observed. In addition, the density of enteric glial cells was not modified in MPTP-treated monkeys. Our results demonstrate that MPTP induces major changes in the myenteric plexus and to a lesser extent in the submucosal plexus of monkeys. They further reinforce the observation that lesions of the ENS occur in the course of PD that might be related to the GI dysfunction observed in this pathology.

The microtubule-associated protein tau is phosphorylated by Syk

Aberrant phosphorylation of tau protein on serine and threonine residues has been shown to be critical in neurodegenerative disorders called tauopathies. An increasing amount of data suggest that tyrosine phosphorylation of tau might play an equally important role in pathology, with at least three putative tyrosine kinases of tau identified to date. It was recently shown that the tyrosine kinase Syk could efficiently phosphorylate α-synuclein, the aggregated protein found in Parkinson's disease and other synucleinopathies. We report herein that Syk is also a tau kinase, phosphorylating tau in vitro and in CHO cells when both proteins are expressed exogenously. In CHO cells, we have also demonstrated by co-immunoprecipitation that Syk binds to tau. Finally, by site-directed mutagenesis substituting the tyrosine residues of tau with phenylalanine, we established that tyrosine 18 was the primary residue in tau phosphorylated by Syk. The identification of Syk as a common tyrosine kinase of both tau and α-synuclein may be of potential significance in neurodegenerative disorders and also in neuronal physiology. These results bring another clue to the intriguing overlaps between tauopathies and synucleinopathies and provide new insights into the role of Syk in neuronal physiology.

Beclin 1 mRNA strongly correlates with Bcl-XLmRNA expression in human hepatocellular carcinoma

Beclin 1 physically associates with Bcl-x(L) and is considered as a haploinsufficient tumor suppressor. As the role of Beclin 1 in hepatocellular carcinoma (HCC) is unknown, we determined Beclin 1 mRNA expression in 27 pairs of tumoral/nontumoral (T/NT) liver samples. The Beclin 1 mRNA T/NT ratio was less than 0.5 in 2 tumors and more than 2 in 1 tumor, and was positively correlated with the Bcl-X(L) mRNA T/NT ratio (P < 0.001), but not with the proliferating cell nuclear antigen mRNA T/NT ratio. Coregulation of Beclin 1 and Bcl-X(L) expression in HCC may suggest cooperation in the regulation of apoptosis.

Enteric glia inhibit intestinal epithelial cell proliferation partly through a TGF-beta1-dependent pathway

Although recent studies have shown that enteric neurons control intestinal barrier function, the role of enteric glial cells (EGCs) in this control remains unknown. Therefore, our goal was to characterize the role of EGCs in the control of intestinal epithelial cell proliferation using an in vivo transgenic and an in vitro coculture model. Assessment of intestinal epithelial cell proliferation after ablation of EGCs in transgenic mice demonstrated a significant increase in crypt cell hyperplasia. Furthermore, mucosal glial network (assessed by immunohistochemical detection of S-100beta) is altered in colon adenocarcinoma compared with control tissue. In an in vitro coculture model of subconfluent Caco-2 cells seeded onto Transwell filters with EGCs, Caco-2 cell density and [3H]thymidine incorporation were significantly lower than in control (Caco-2 cultured alone). Flow cytometry analysis showed that EGCs had no effect on Caco-2 cell viability. EGCs induced a significant increase in Caco-2 cell surface area without any sign of cellular hypertrophy. These effects by EGCs were also seen in various transformed or nontransformed intestinal epithelial cell lines. Furthermore, TGF-beta1 mRNA was expressed, and TGF-beta1 was secreted by EGCs. Exogenously added TGF-beta1 reproduced partly the EGC-mediated effects on cell density and surface area. In addition, EGC effects on Caco-2 cell density were significantly reduced by a neutralizing TGF-beta antibody. In conclusion, EGCs have profound antiproliferative effects on intestinal epithelial cells. Functional alterations in EGCs may therefore modify intestinal barrier functions and be involved in pathologies such as cancer or inflammatory bowel diseases.

Hepatic PCSK9 expression is regulated by nutritional status via insulin and sterol regulatory element-binding protein 1c

Familial autosomal dominant hypercholesterolemia is associated with high risk for cardiovascular accidents and is related to mutations in the low density lipoprotein receptor or its ligand apolipoprotein B (apoB). Mutations in a third gene, proprotein convertase subtilisin kexin 9 (PCSK9), were recently associated to this disease. PCSK9 acts as a natural inhibitor of the low density lipoprotein receptor pathway, and both genes are regulated by depletion of cholesterol cell content and statins, via sterol regulatory element-binding protein (SREBP). Here we investigated the regulation of PCSK9 gene expression during nutritional changes. We showed that PCSK9 mRNA quantity is decreased by 73% in mice after 24 h of fasting, leading to a 2-fold decrease in protein level. In contrast PCSK9 expression was restored upon high carbohydrate refeeding. PCSK9 mRNA increased by 4-5-fold in presence of insulin in rodent primary hepatocytes, whereas glucose had no effect. Moreover, insulin up-regulated hepatic PCSK9 expression in vivo during a hyperinsulinemic-euglycemic clamp in mice. Adenoviral mediated overexpression of a dominant or negative form of SREBP-1c confirmed the implication of this transcription factor in insulin-mediated stimulation of PCSK9 expression. Liver X receptor agonist T0901317 also regulated PCSK9 expression via this same pathway (a 2-fold increase in PCSK9 mRNA of primary hepatocytes cultured for 24 h in presence of 1 microm T0901317). As our last investigation, we isolated PCSK9 proximal promoter and verified the functionality of a SREBP-1c responsive element located from 335 bp to 355 bp upstream of the ATG. Together, these results show that PCSK9 expression is regulated by nutritional status and insulinemia.

Pretreatment of starved rats with ornithine alpha-ketoglutarate: effects on hepatic mRNA levels and plasma concentrations of three liver-secreted proteins

OBJECTIVE

Ornithine alpha-ketoglutarate (OKG) displays anabolic properties at the hepatic level, but the mechanisms involved remain unclear. This study investigated in vivo the ability of OKG to modulate hepatic gene expression of three liver-secreted proteins: albumin, transthyretin, and retinol binding protein.

METHODS

One hundred eighty rats were fed for 5 d with a balanced regimen enriched with OKG (5 g.kg(-1).d(-1)) or an isonitrogenous mixture (alanine, glycine, and serine). Hepatic mRNA levels and plasma concentrations of the three proteins studied were determined at the end of the nutrition period and after 1, 2, and 3 d of food deprivation. Results were compared by analysis of variance and Bonferroni-Dunn tests.

RESULTS

At the end of the nutrition period, hepatic mRNA levels and plasma concentrations of the three proteins were not modified by OKG supplementation. However, OKG largely increased mRNA levels of albumin, transthyretin, and retinol binding protein on the first day of starvation compared with control animals (+68%, +64% and +51%, respectively; P < 0.01 versus control). OKG precociously increased albuminemia (on day 2) but had no effect on plasma concentrations of transthyretin and retinol binding protein. Neither regulation of polyamine hepatic concentration nor alteration in hepatic amino acid content seemed to be implicated in these actions.

CONCLUSION

This study is the first to demonstrate that OKG regulates in vivo liver gene expression during acute malnutrition by modulating hepatic mRNA levels.

Progesterone induces BRCA1 mRNA decrease, cell cycle alterations and apoptosis in the MCF7 breast cancer cell line

BACKGROUND

Inherited mutations of the BRCA1 gene are responsible for hereditary breast and ovarian cancer syndrome. However, little is known of how disruption of BRCA1 functions preferentially increases cancer risk in hormone-dependent organs. We aimed to study whether BRCA1 was regulated by progesterone in the MCF7 breast cancer cell line.

MATERIALS AND METHODS

MCF7 breast cancer cells were incubated with 10(-4) or 10(-10) M progesterone for 24 or 48 hours. BRCA1 expression, proliferation and apoptosis were analysed.

RESULTS

10(-4) M progesterone decreased cell proliferation, cell cycle progression and induced apoptosis. In addition, BRCA1 and cyclin A mRNA decreased. In contrast, none of these effects were observed in MCF7 cells incubated with 10(-10) M progesterone.

CONCLUSION

The down-regulation of BRCA1 in MCF7 cells incubated with 10(-4) M progesterone seems to be a consequence of cell cycle alterations rather than a direct effect of the hormone on BRCA1.

Expression of tissue factor pathway inhibitor-2 in murine and human liver regulation during inflammation

Tissue factor pathway inhibitor-2 (TFPI-2) is a recently described serine proteinase inhibitor. Human and murine TFPI-2 share about 50% homology. The aim of this study was to investigate the cellular localization of human and murine TFPI-2 in the liver and the regulation of their expression during acute inflammation. Northern blot, in situ hybridization and studies on isolated hepatocytes demonstrated a high-level expression of TFPI-2 in murine hepatocytes. On the other hand, very little TFPI-2 mRNA expression could be detected in human liver. Studies with isolated human liver cells suggested that TFPI-2 expression in human liver was mainly observed in liver sinusoidal endothelial cells rather than hepatocytes. Liver murine TFPI-2 expression was greatly increased after lipopolysaccharide administration with a delayed kinetics as compared to alpha1-acid glycoprotein, a classical acute-phase reactant. Accordingly, studies with isolated cells showed that the increase in TFPI-2 transcripts occurred in non-hepatocytic cells. Moreover, the LPS response was abolished in mice with a hepatocyte-specific KO for the gp130 receptor, thus indicating that a mediator from hepatocytes is involved in the up-regulation of TFPI-2 in non-parenchymal cells. In conclusion, murine TFPI-2 is highly expressed in hepatocytes in the normal murine liver and is upregulated in non-parenchymal cells in the context of inflammation. The large difference in the level of liver expression of human and murine TFPI-2 suggests that despite significant sequence similarities, these proteins presumably have different functions in the two species.

Study of the effects of interferon a on several human hepatoma cell lines: analysis of the signalling pathway of the cytokine and of its effects on apoptosis and cell proliferation

BACKGROUND

Interferon alpha (IFNalpha), currently used for the treatment of chronic viral hepatitis, is also known to prevent the development of hepatocellular carcinoma (HCC), the mechanism of this action being still debatable.

AIMS

To study thoroughly in human hepatoma cell lines (HHL)--Hep3B, HepG2, HuH7, SKHep1, and Chang-Liver--submitted to rhIFNalpha, the signalling pathway of IFNalpha, the binding activity of the cytokine on specific gamma-activated sequence (GAS) and interferon-stimulated regulatory element (ISRE) nuclear sequences, and its effects on apoptosis and cell proliferation.

METHODS

The behaviour of signal transducer and activator of transcription (STAT)1, STAT2, p48(IRF9) and the binding of nuclear proteins were investigated by immunoblot and electro-mobility shift assay. Expression of some IFNalpha-dependent proteins--p21/(WAF1), inducible nitric oxide synthase, IRF1 and 2--were studied by immunoblot. Apoptosis and the cell cycle were studied by morphological and biochemical methods.

RESULTS

Transduction of INFalpha was unaltered, although there were some variations in the different HHL. Nuclear protein binding to GAS or ISRE showed that ISRE was mainly involved. Apoptosis did not occur. The cell cycle was slightly modified in HuH7. Three GAS- and/or ISRE-dependent proteins increased, suggesting that IFNalpha may have some biological effects on HHL.

CONCLUSIONS

The IFNalpha signalling pathway is functional in several HHL, but the cytokine has no apoptotic effect and a moderate anti-proliferative effect. This suggests that the preventive role of IFNalpha on HCC cannot be explained by an apoptotic and/or an anti-proliferative effect, but possibly by its action on several specific nuclear sequences that protect liver cells from transformation.

Terlipressin inhibits in vivo aortic iNOS expression induced by lipopolysaccharide in rats with biliary cirrhosis

In cirrhosis, lipopolysaccharide (LPS, a product of Gram-negative bacteria) in the blood may cause septic shock. LPS-elicited induction of arterial inducible nitric oxide synthase (iNOS) results in nitric oxide (NO)-induced vasodilation, which causes arterial hypotension and hyporeactivity to alpha(1)-adrenergic constrictors. In vitro studies have suggested that vasopressin inhibits iNOS expression in cultured vascular smooth muscle cells exposed to LPS. Thus, the aim of this study was to investigate the effects of terlipressin administration (a vasopressin analog) on in vivo LPS-induced aortic iNOS in rats with cirrhosis. LPS (1 mg/kg, intravenously) was administered followed by the intravenous administration of terlipressin (0.05 mg/kg, intravenously) or placebo 1 hour later. Arterial pressure was measured, and contractions to phenylephrine (an alpha(1)-adrenoceptor agonist), iNOS activity, and iNOS expressions (mRNA and protein) were investigated in isolated aortas. LPS-induced arterial hypotension and aortic hyporeactivity to phenylephrine were abolished in rats that received terlipressin. LPS-induced aortic iNOS activity and expression were suppressed in terlipressin-treated rats. In conclusion, in LPS-challenged rats with cirrhosis, terlipressin administration inhibits in vivo LPS-induced aortic iNOS expression. Terlipressin administration may be a novel approach for the treatment of arterial hypotension and hyporeactivity to alpha(1)-adrenergic constrictors in patients with cirrhosis and septic shock.

Transcriptional regulation of vascular endothelial growth factor by estradiol and tamoxifen in breast cancer cells: a complex interplay between estrogen receptors alpha and beta

Vascular endothelial growth factor (VEGF) is a potent angiogenic and prognostic factor for many tumors, including those of endocrine-responsive tissues such as the breast and uterus. Recent studies indicate that 17beta-estradiol (E(2)) modulates VEGF expression in breast and uterine cells, involving transcriptional activation through estrogen receptor (ER) alpha. However, molecular mechanisms of VEGF regulation mediated by the two ER subtypes and the potential role of ERbeta in the control of breast cancer angiogenesis have not yet been investigated. In transient transfection assays using the VEGF(-2275/+54) promoter-luciferase construct, E(2) (1 nM) increased transcription activity in MCF-7 cells (either untransfected or cotransfected with ERalpha) and it increased transcription activity in MDA-MB-231 cells cotransfected with ERalpha or ERbeta (1.8- and 2-fold induction, respectively). The positive effect was abolished when MCF-7 cells were treated with pure antiestrogen ICI 182,780 or the agonist/antagonist tamoxifen (1 micro M). To identify response elements involved in this transcriptional regulation, MCF-7 or MDA-MB-231 cells were transfected with several deletion constructs of the VEGF promoter. Deletion of 1.2-2.3 kb upstream to the transcription start in the VEGF promoter abrogated E(2)-dependent transcription in these cells. This region contains an imperfect estrogen-responsive element (ERE), ERE1520, and one activator protein 1 site. Transfection of MCF-7 cells (ERalpha) with the ERE1520-luciferase construct conferred transcriptional activity with 1 nM E(2) (1.9-fold induction). Also, the imperfect ERE formed a complex with ERalpha or ERbeta proteins in gel shift assay using MCF-7 or MDA-MB-231 nuclear extracts. In contrast to ERalpha, ERbeta could transactivate VEGF reporter construct in MDA-MB-231 cells, in the presence of E(2) or tamoxifen, suggesting different transactivational mechanisms between ERalpha and ERbeta in the presence of tamoxifen. Interestingly, E(2) inhibited VEGF transcription in MCF-7 cells transfected with ERbeta or MDA-MB-231 cells cotransfected with ERalpha and ERbeta, suggesting that heterodimerization of ERalpha/ERbeta has the ability to inhibit E(2)-induced VEGF expression in breast cancer cells. These results demonstrate that VEGF is a target gene for ERalpha and ERbeta in breast cancer cells; it remains to be determined whether ERalpha and ERbeta expression in breast biopsies correlates with VEGF expression and vascular density.

Activation of NF-kappa B, AP-1 and STAT transcription factors is a frequent and early event in human hepatocellular carcinomas

BACKGROUND/AIMS

Hepatitis B and C viruses, two inducers of hepatocarcinomas, have been shown to activate AP-1, NF-kappa B and STAT in vitro, but no detailed information on the activity of these transcription factors in vivo have been provided.

METHODS

We have measured the DNA binding activity of these transcription factors in the peri-tumoral and the tumoral parts of 15 primary liver cancers, of viral or non-viral etiologies, and in five hepatic metastases using electrophoretic mobility shift assays.

RESULTS

AP-1, NF-kappa B and STAT binding activities were increased in the peritumoral tissue, compared with histologically normal livers in 73, 87 and 70%, respectively, of the cases. A further activation of AP-1, NF-kappa B, but not STAT binding in the tumoral parts was detected in 40 and 80%, respectively, of the cases. A close correlation was found between JunD and c-Jun levels and AP-1 binding activity at the tumoral stage. By contrast, AP-1 and NF-kappa B binding activities were low or only slightly elevated in the peri-tumoral and the tumoral tissue of metastases.

CONCLUSIONS

Early activation of AP-1, NF-kappa B and STAT contributes probably to the acquisition of a transformed phenotype during hepatocarcinogenesis, whatever the etiology.

Overexpression of the mouse Fas gene in human Hep3B hepatoma cells overcomes their resistance to Fas-mediated apoptosis

BACKGROUND/AIMS

Fas-induced apoptosis is one of the main forms of apoptosis occurring in hepatocytes. We have previously demonstrated that the human hepatoma cell line Hep3B is resistant to Fas-mediated apoptosis. In this study, we investigated whether the human Fas receptor itself, or the Fas transduction pathway was responsible for the resistant phenotype.

METHODS

Clones of Hep3B cells overexpressing the mouse Fas gene (Hep3B(mfas)) were generated by transfection, and apoptosis was studied by (i) chromatin condensation and nuclear fragmentation, (ii) flow cytometry, (iii) DNA fragmentation and (iv) poly (ADP-ribose) polymerase cleavage.

RESULTS

Use of the species-specific and agonistic anti-mFas monoclonal antibody (JO2), showed that the mFas receptor was correctly routed to the plasma membrane of Hep3B(mfas) cells. Using the four above-mentioned criteria, we demonstrated that JO2 triggered mFas-mediated apoptosis of Hep3B(mfas), but not of Hep3B(pCi) cells (transfected with an empty vector).

CONCLUSIONS

Our data show (i) that the Fas signaling pathway can be completed when a functional mFas receptor is expressed in Hep3B cells, and thus, (ii) that the death-inducing signaling complex components and the effector caspases are functional in Hep3B cells. Moreover, they suggest that the Fas subunits are not pre-assembled at the cell membrane before receptor-ligand interaction.

Antral mucosa expresses functional leptin receptors coupled to STAT-3 signaling, which is involved in the control of gastric secretions in the rat

BACKGROUND & AIMS

Leptin is a circulating hormone that communicates the peripheral nutritional status to the hypothalamus, which controls food intake, energy expenditure, and body weight. This study characterizes leptin receptors and leptin-sensitive STAT proteins in the antrum and investigates the effects of leptin on gastric secretions.

METHODS

The effects of leptin on gastrin messenger RNA (mRNA), plasma gastrin, gastric acid in vivo in the rat, and on somatostatin and gastrin secretions by isolated antral cells were determined in vitro. Leptin receptors were investigated in isolated rat antral cells by reverse transcription-polymerase chain reaction and binding of [(125)I]-leptin studies. The effects of in vivo and in vitro leptin on transduction signal STAT proteins were investigated by immunoblotting antral extracts.

RESULTS

Peripheral injection of leptin inhibited in a dose-dependent manner, basal gastric secretion, gastrinemia, and mucosal gastrin mRNA in vivo. mRNAs encoding the long (Ob-Rb) and short (Ob-Ra) receptor forms were detected in rat antral mucosa, as were STAT-1, -3, and -5b immunoreactive proteins. Isolated antral cells specifically bound [(125)I]-leptin, and addition of leptin to these cells inhibited the release of somatostatin and increased the release of gastrin. These effects were associated with an increase in nuclear STAT-3 proteins in vitro and in vivo.

CONCLUSIONS

This study provides the first molecular evidence for the coexpression of leptin receptors and STAT-3 in antral mucosa. It provides further evidence for the involvement of leptin in the control of gastric secretions.

Functional cooperation between JunD and NF-kappaB in rat hepatocytes

AP-1 and NF-kappaB are rapidly activated during liver regeneration. Whether these parallel inductions have potential functional implications is not known. Isolated rat hepatocytes were stimulated with two mitogens, epidermal growth factor or hepatocyte growth factor and with tumor necrosis factor alpha, a cytokine involved in the liver regenerative response in vivo and a strong inducer of NF-kappaB. All three cytokines increased AP-1 and NF-kappaB binding to their cognate cis-element and induced a 2.5-fold activation of NF-kappaB-dependent transcription. Inactivation of AP-1 by TAM67, a dominant negative mutant of AP-1 drastically inhibited basal and cytokine-induced NF-kappaB transactivation. Overexpression of Jun D, but not of the other Jun or Fos proteins increased by threefold NF-kappaB transactivation. Functional cooperation between JunD and p65 was demonstrated in a simple Gal-hybrid system. Finally, a twofold decrease in NF-kappaB transactivation was found in hepatocytes isolated from JunD(-/-) mice compared with hepatocytes from JunD(+/+) mice. Altogether these data demonstrate a functional cooperation of p65 with JunD, a major constituent of AP-1 in normal hepatocytes.

Potentiation of Smad transactivation by Jun proteins during a combined treatment with epidermal growth factor and transforming growth factor-beta in rat hepatocytes. role of phosphatidylinositol 3-kinase-induced AP-1 activation

Cross-talk between Smad and mitogen-activated protein kinase pathways has been described recently, and evidence for Smad cooperation with AP-1 is emerging. Here we report that epidermal growth factor (EGF) potentializes transforming growth factor beta (TGF-beta)-induced Smad3 transactivation in rat hepatocytes, an effect abrogated by TAM-67, a dominant negative mutant of AP-1. Antisense transfection experiments indicated that c-Jun and JunB were involved in the synergistic effect, and endogenous c-Jun physically associated with Smad3 during a combined EGF/TGF-beta treatment. We next investigated which signaling pathway transduced by EGF was responsible for the Jun-induced synergism. Whereas inhibition of JNK had no effect, inhibition of the phosphatidylinositol-3' kinase (PI3-kinase) pathway by LY294002 or by expression of a dominant negative mutant of PI3-kinase reduced EGF/TGF-beta-induced Smad3 transcriptional activity. Transfection of an activated Ras with a mutation enabling the activation of the PI3-kinase pathway alone mimicked the EGF/TGF-beta potentiation of Smad3 transactivation, and TAM-67 abolished this effect, suggesting that the PI3-kinase pathway stimulates Smad3 via AP-1 stimulation. The EGF/TGF-beta-induced activation of Smad3 correlated with PI3-kinase and p38-dependent but not JNK-dependent phosphorylation of c-Jun. Since potentiation of a Smad-binding element-driven gene was also induced by EGF/TGF-beta treatment, this novel mechanism of Jun/Smad cooperation might be crucial for diversifying TGF-beta responses.

Differential effects of halothane and thiopental on surfactant protein C messenger RNA in vivo and in vitro in rats

BACKGROUND

Pulmonary surfactant is a complex mixture of proteins and phospholipids synthetized by alveolar type II cells. Volatile anesthetics have been shown to reduce surfactant phospholipid biosynthesis by rat alveolar type II cells. Surfactant-associated protein C (SP-C) is critical for the alveolar surfactant functions. Our goal was to evaluate the effects of halothane and thiopental on SP-C messenger RNA (mRNA) expression in vitro in rat alveolar type II cells and in vivo in mechanically ventilated rats.

METHODS

In vitro, freshly isolated alveolar type II cells were exposed to halothane during 4 h (1, 2, 4%) and 8 h (1%), and to thiopental during 4 h (10, 100 micrometer) and 8 h (100 micrometer). In vivo, rats were anesthetized with intraperitoneal thiopental or inhaled 1% halothane and mechanically ventilated for 4 or 8 h. SP-C mRNA expression was evaluated by ribonuclease protection assay.

RESULTS

In vitro, 4-h exposure of alveolar type II cells to thiopental 10 and 100 micrometer increased their SP-C mRNA content to 145 and 197%, respectively, of the control values. In alveolar type II cells exposed for 4 h to halothane 1, 2, and 4%, the SP-C mRNA content increased dose-dependently to 160, 235, and 275%, respectively, of the control values. In vivo, in mechanically ventilated rats, 4 h of halothane anesthesia decreased the lung SP-C mRNA content to 53% of the value obtained in control (nonanesthetized, nonventilated) animals; thiopental anesthesia increased to 150% the lung SP-C mRNA content.

CONCLUSIONS

These findings indicate that halothane and thiopental used at clinically relevant concentrations modulate the pulmonary SP-C mRNA content in rats. In vivo, the additive role of mechanical ventilation is suggested.

Stimulation of liver RNA and protein breakdown in endotoxemic rats: role of glucocorticoids

In systemic or localized acute inflammation, liver ribosomal RNA (rRNA) and protein contents increase. We first determined whether changes in RNA, more specifically rRNA, and protein breakdown rates were involved in the accumulation of both types of macromolecules 24 h after induction of endotoxemia. Liver RNA and protein contents were enhanced by 35 and 19%, respectively, in the endotoxemic rats. RNA and protein degradation rates measured during in situ cyclic perfusions of the livers were significantly higher in the endotoxemic rats than in the controls (42 and 46%, respectively). In order to check that the stimulation of RNA and protein degradation corresponded to an activation of the hepatocyte autophagic pathway, the fractional cytoplasmic volume (FCV) of autophagosomes, digestive autophagic vacuoles and dense bodies was measured by morphometry in electron microscopy. The FCV of the sum of these lysosomal structures was significantly increased in the endotoxemic rats. We next tried to identify the factor(s) responsible for the high breakdown rates. The increase in macromolecular degradation did not result from reduced portal amino acid supply. The effects of dexamethasone, interleukin-6, interleukin-1beta, and tumor necrosis factor alpha on RNA degradation were then investigated in primary cultures of hepatocytes isolated from control rats. Only dexamethasone stimulated RNA breakdown. Finally, pretreatment of endotoxemic rats with RU 38486, a glucocorticoid receptor antagonist, completely abolished the stimulation of RNA degradation observed in the sham-gavaged LPS-treated rats. Our data suggest an important role of glucocorticoids in the high levels of RNA and protein breakdown in endotoxemic rats.

Hepatocyte growth factor activates the AP-1 complex: a comparison between normal and transformed rat hepatocytes

BACKGROUND/AIMS

Stimulation of activator protein-1 (AP-1), a Fos/Jun complex, is a key event in the cell response to growth factors. We have investigated whether hepatocyte growth factor (HGF) induces differential AP-1 responses in normal and transformed rat hepatocytes, the 7777 cells.

METHODS

Primocultures of isolated hepatocytes or 7777 cells were stimulated with HGF. Gene expression was evaluated by ribonuclease protection assay and Western blot analysis. AP-1 DNA binding activity was measured by electrophoretic mobility shift assay. Identification of the proteins bound to the probes was made by supershift assays with specific antibodies. Cells were electroporated with plasmids containing an AP-1-dependent chloramphenicol acetyl transferase (CAT) gene, and CAT activity was measured 24 h after treatment with medium alone or HGF.

RESULTS

In both cell types, HGF triggered the same program of jun family mRNA activation, but distinct Fos/Jun proteins accumulated in the nucleus. HGF increased DNA-binding activity to the phorbol 12-O-tetradecanoate-13-acetate responsive element (TRE) in both cell types, but distinct TRE-binding proteins were recruited in the AP-1 dimers. HGF also increased consistently binding to a cAMP responsive element (CRE) in hepatocytes only. Finally, HGF triggered TRE- and CRE-dependent gene activations in hepatocytes but TRE-dependent gene activation alone in 7777 cells.

CONCLUSIONS

HGF-induced AP-1 activation leads to the formation of distinct dimers with different functional capacities in normal and transformed hepatocytes. These data suggest the importance of qualitative abnormalities of the AP-1 complex for the establishment or maintainance of a transformed phenotype.

Down-regulation of liver RNA breakdown by turpentine administration in the starved rat: autophagy and relevant factors

OBJECTIVE AND DESIGN

To determine whether the inhibition of RNA breakdown observed in ad libitum fed rats 24 h after turpentine administration still occurs in inflamed rats fasted for 24 h and to examine the mechanism and factors involved.

METHODS

RNA breakdown was measured during cyclic in situ perfusion of livers by the accumulation of [14C] cytidine after in vivo RNA labelling. Autophagic activity was determined by the morphometric analysis of lysosomal structures.

RESULTS

The decrease in RNA breakdown (53%) observed in the inflamed rats was accompanied by a 38% drop in the fractional cytoplasmic volume of initial and digestive autophagic vacuoles. Among amino acids, only the portal levels of glutamate were significantly enhanced by 83%. In vivo suppression of glucocorticoid activity using RU 38486 in inflamed rats did not affect the inhibition of RNA breakdown.

CONCLUSIONS

The results show that turpentine-induced inflammation in fasted rats inhibits RNA degradation as well as autophagy and that glucocorticoids do not seem to be involved.

Hepatocyte differentiation of WIF-B cells includes a high capacity of interleukin-6-mediated induction of alpha 1-acid glycoprotein and alpha 2-macroglobulin

Responsiveness to cytokine-mediated acute inflammatory stimuli of the highly differentiated and polarized WIF-B hybrid cell line was studied by measuring the induction of alpha 1-acid glycoprotein and alpha 2-macroglobulin mRNAs after interleukin-1, interleukin-6 and tumor necrosis factor-alpha treatments in the presence of dexamethasone. Compared with their Fao parent, WIF-B cells were 10 times more responsive to 24-h interleukin-6 induction regarding alpha 2-macroglobulin induction. At variance from the response measured in Fao cells, the late effects of interleukin-6 treatment confirmed the higher sensitivity of WIF-B cells to this cytokine as a 72-h treatment as 10 times more effective than a 24-h treatment at inducting alpha 1-acid glycoprotein mRNA. These findings highlight the hepatocyte differentiation of WIF-B cells compared with other hepatoma cell lines, with respect to the regulation of acute-phase protein gene expression. They also make WIF-B cells a convenient model to study the molecular effects of interleukin-6 in terms of transduction and/or transcription, and the many cross-talks that occur during the regulation of acute-phase protein gene expression.

Growth hormone inhibits rat liver alpha-1-acid glycoprotein gene expression in vivo and in vitro

The gene encoding alpha-1-acid glycoprotein (AGP), one of the major acute-phase proteins, is positively controlled at the transcriptional level by cytokines (interleukin-1 [IL-1], IL-6, and tumor necrosis factor alpha) and glucocorticoids. Here, we show that growth hormone (GH) treatment of isolated rat hepatocytes in vitro reduces AGP messenger RNA (mRNA) expression. AGP gene expression remained inducible by IL-1, IL-6, and phenobarbital (PB) in GH-treated hepatocytes. Interestingly, the repressive effect of GH on AGP gene expression was also observed in vivo: liver AGP mRNA content was strongly increased in hypophysectomized rats, and GH treatment of these animals led to a decrease in mRNA to levels lower than those in untreated control animals. Moreover, the inhibitory effect of GH mainly occurs at the transcriptional level and can be observed as little as 0.5 hours after GH adding in vitro to isolated hepatocytes. These results show negative regulation of AGP gene expression and strongly suggest that GH is a major endogenous regulator of constitutive AGP gene expression. Moreover, transfection assays showed that the region of the AGP promoter located at position -147 to -123 is involved in AGP gene regulation by GH. Furthermore, GH deeply modifies the pattern of nuclear protein binding to this region. GH treatment of hypophysectomized rats led to the release of proteins of 42 to 45 and 80 kd and to the binding of proteins of 48 to 50 and 90 kd.

Inducible expression of the alpha1-acid glycoprotein by rat and human type II alveolar epithelial cells

Alpha1-acid glycoprotein (AGP) is a major acute phase protein in rat and human. AGP has important immunomodulatory functions that are potentially important for pulmonary inflammatory response. The liver is the main tissue for AGP synthesis in the organism, but the expression of AGP in the rat lung has not been investigated. We show that AGP mRNA was induced in the lung of dexamethasone-, turpentine-, or LPS-treated rats, whereas AGP mRNA was not detected in the lung of control rats. In the lung of animals treated intratracheally with LPS, in situ hybridization showed that AGP gene expression was restricted to cells located in the corners of the alveolus, consistent with an alveolar type II (ATII) cell localization. The inducible expression of the AGP gene was confirmed in vitro with SV40 T2 cells and rat ATII cells in primary culture: maximal expression required the presence of dexamethasone. IL-1 and the conditioned medium of alveolar macrophages acted synergistically with dexamethasone. Rat ATII cells secreted immunoreactive AGP in vitro when stimulated with dexamethasone or with a combination of dexamethasone and the conditioned medium of alveolar macrophages. In vivo, in the human lung, we detected immunoreactive AGP in hyperplastic ATII cells, whereas we did not detect AGP in the normal lung. We conclude that AGP is expressed in the lung in cases of inflammation and that ATII cells are the main source of AGP in the lung.

Inducible Expression of the α1-Acid Glycoprotein by Rat and Human Type II Alveolar Epithelial Cells

α1-Acid glycoprotein (AGP) is a major acute phase protein in rat and human. AGP has important immunomodulatory functions that are potentially important for pulmonary inflammatory response. The liver is the main tissue for AGP synthesis in the organism, but the expression of AGP in the rat lung has not been investigated. We show that AGP mRNA was induced in the lung of dexamethasone-, turpentine-, or LPS-treated rats, whereas AGP mRNA was not detected in the lung of control rats. In the lung of animals treated intratracheally with LPS, in situ hybridization showed that AGP gene expression was restricted to cells located in the corners of the alveolus, consistent with an alveolar type II (ATII) cell localization. The inducible expression of the AGP gene was confirmed in vitro with SV40 T2 cells and rat ATII cells in primary culture: maximal expression required the presence of dexamethasone. IL-1 and the conditioned medium of alveolar macrophages acted synergistically with dexamethasone. Rat ATII cells secreted immunoreactive AGP in vitro when stimulated with dexamethasone or with a combination of dexamethasone and the conditioned medium of alveolar macrophages. In vivo, in the human lung, we detected immunoreactive AGP in hyperplastic ATII cells, whereas we did not detect AGP in the normal lung. We conclude that AGP is expressed in the lung in cases of inflammation and that ATII cells are the main source of AGP in the lung.

In vivo stimulation of polymeric Ig receptor transcytosis by circulating polymeric IgA in rat liver

Binding of human polymeric IgA ligand to its epithelial cell polymeric Ig receptor, pIgR, has been shown to stimulate pIgR apical transcytosis in an in vitro system, based on polarized confluent MDCK cells expressing rabbit pIgR. The present study aimed at testing whether such a stimulation also occurs in vivo. Transcytosis of pIgR was monitored by rat liver output of total secretory component (SC) into bile, measured by radial immunodiffusion as the sum of free SC and pIgA-bound SC. Whereas in the perfused rat liver system addition of pIgA to the perfusate showed no effect, i.v. injection of human and rat pIgA, but not of monomeric IgA nor PBS, in living rats significantly increased total bile SC output for more than 1 h. Furthermore, depletion of the normal pIgA level circulating in the liver before injecting more pIgA was not required to show the stimulation. Our data thus strongly suggest that stimulation of liver pIgR transcytosis by pIgA ligand binding is physiologically relevant, helping to quickly adjust pIgA transport into bile to increase circulating pIgA levels, without need for increased SC/pIgR synthesis.

Presence of distinct AP-1 dimers in normal and transformed rat hepatocytes under basal conditions and after epidermal growth factor stimulation

Activation of the transcriptional regulator AP-1, a dimeric complex formed of various combinations of Fos and Jun proteins, is a key step in the cellular response to mitogens. Because different dimers are believed to display different regulatory functions, we hypothesized that transformed cells that lack normal growth constraints might display AP-1 dimers that are different from those of normal cells. We therefore compared in primary and transformed rat hepatocytes (1) the composition of AP-1 dimers under basal conditions and (2) AP-1 induction by epidermal growth factor (EGF). Under basal conditions, AP-1 contained predominantly Jun homodimers in both cell types. However, whereas normal hepatocytes contained only JunD, both JunD and JunB were present in the AP-1 complex of 7777 cells. EGF treatment triggered almost identical programs of fos and jun gene activation at the messenger RNA (mRNA) level in both cell types, with an early accumulation of c-fos, c-jun, and junB mRNAs, but no change in junD mRNA levels. In both cell types, c-Fos and Fra-1 proteins increased after EGF treatment, but differences in the induction of Jun proteins were noted, with an increase of c-Jun in hepatocytes and an increase of JunB in 7777 cells. In both cell types, activation of AP-1 DNA binding activity by EGF was accompanied by the recruitment of Fra-1 into AP-1, detected earlier in 7777 cells than in hepatocytes, and with the transient appearance of c-Fos in 7777 cells only. Finally, EGF activated AP-1-dependent transcription in 7777 cells but not in hepatocytes. These data indicate important differences in the functional activity of AP-1 in transformed hepatocytes.

An improved digitonin-collagenase perfusion technique for the isolation of periportal and perivenous hepatocytes from a single rat liver: physiological implications for lobular heterogeneity

Morphological and functional heterogeneity of hepatocytes according to their position in the liver lobule has been known for many years. The digitonin-collagenase perfusion technique is widely used to study hepatocyte heterogeneity and has yielded reliable data. However, with this procedure, periportal (PP) or perivenous (PV) hepatocytes are isolated from different livers, allowing only comparison between cell populations issued from two separate animals. To overcome this drawback, we have modified this technique by perfusing the two main rat liver lobes of a single animal in succession. The procedure involved alternate clamping of the median and the left lateral lobes, restricting digitonin infusion to one lobe via the portal vein, and to the other via the caudal vena cava. Lobe exclusion during digitonin perfusion, and zonal restriction of digitonin-induced damage, were monitored using macroscopic and histological controls. We compared our results with previous data on PP and PV hepatocytes issued from two different livers using the conventional digitonin-collagenase perfusion technique. First, we found that the cellular sensitivity to angiotensin II, a calcium-mobilizing agonist, was 60% to 80% higher in PV than in PP hepatocytes, whereas, previously, no difference had been recorded. Second, we found that albumin messenger RNAs (mRNAs) were 35% more abundant in PP than in PV hepatocytes, whereas, previously, larger differences had been reported. Our results show that PP and PV hepatocytes may be isolated from a single liver using an improved digitonin-collagenase perfusion technique. Furthermore, we suggest that zonal differences can be artificially masked or amplified when comparing PP and PV cell populations from two different livers, indicating that it is preferable to use a single liver for accurate zonal comparisons between hepatocytes.

Inhibition of liver RNA breakdown during acute inflammation in the rat

Liver RNA- and protein-degradation rates were measured after the induction of acute inflammation in the rat. A preliminary study determined changes in hepatic RNA and protein content 12, 18 and 24 h after a turpentine oil injection. The RNA content in turpentine-treated rats compared with pair-fed animals increased significantly and sharply from 12 h (+ 11%) to 18 h (+ 32%) and slightly thereafter (+ 37% at 24 h). The liver protein content was significantly enhanced only at 24 h (+ 11%) in response to inflammation. RNA-degradation rates were determined in livers perfused cyclically in situ for 15 min by measuring the accumulation of radioactive cytidine in the medium 60 h after in vivo labelling of RNA by [5-3H]cytidine instead of [6-14C]orotic acid, the most commonly used radioactive marker. Several validation procedures showed that the method employed was a valid alternative to the use of radioactive orotic acid. RNA-degradation rates, which mainly reflect rRNA breakdown, were significantly lower in the turpentine-treated rats than in respective pair-fed animals at 18 and 24 h (57 and 45% decrease respectively). Proteolysis rates measured at 24 h together with RNA breakdown by valine accumulation in the perfusion medium were not modified after turpentine treatment. The main factors known to regulate RNA degradation (amino acids, insulin/glucagon ratio) were measured in the portal blood 24 h after induction of acute inflammation. Of the known regulatory amino acids, only glutamine and to a lesser extent methionine were increased in the turpentine-treated rats as compared with their pair-fed counterparts. The insulin/glucagon molar ratio was similar in both groups. In conclusion, the reduced breakdown of RNA, especially rRNA, is largely responsible for the accumulation of hepatic RNA during acute inflammation. This inhibition of RNA degradation could possibly be related to the increase in glutamine.

Effects of insulin, dexamethasone and cytokines on alpha 1-acid glycoprotein gene expression in primary cultures of normal rat hepatocytes

While the effects of insulin, dexamethasone and cytokines on alpha 1-acid glycoprotein gene expression have been investigated in various hepatoma cell lines, the individual and combined effects of these components on the expression of this gene have been rarely studied in cultured normal rat hepatocytes. In this cell model, we have shown that mRNA levels of alpha 1-acid glycoprotein were not decreased at least during the first 24 h of culture under basal conditions. During these short-term cultures, the expression of alpha 1-acid glycoprotein in normal hepatocytes showed a high degree of responsiveness to dexamethasone alone (20-fold increase) and to dexamethasone associated with various cytokines (interleukin-1 beta, interleukin-6 and tumor necrosis factor alpha) with a 40 to 100-fold increase depending on the cytokine. Insulin alone did not modify alpha 1-acid glycoprotein mRNA; however, this hormone exerted a positive effect (about 50% increase) in the presence of dexamethasone or dexamethasone with cytokines. These results indicate that the regulation of alpha 1-acid glycoprotein in cultured normal rat hepatocytes presents major differences when compared to reported observations in rat hepatoma cell lines.

Direct solution hybridization of guanidine thiocyanate-solubilized cells for quantitation of mRNAs in hepatocytes

The sensitivity of direct solution hybridization of hepatocytes solubilized in guanidium thiocyanate (GuSCN) for detecting alpha 1-acid glycoprotein and albumin mRNAs was studied. The sensitivity of detection was inversely correlated with the DNA concentration. Raising the hybridization temperature from 20 to 37 or 50 degrees C (with formamide) increased the hybridization efficiency three- to fourfold in cell lysates with a high DNA concentration (1 microgram/microliter), whereas the hybridization efficiency was already maximal at 20 degrees C in diluted samples. It was most important to normalize all hybridization reactions with an internal standard, such as sense mRNA, because of the great variation in hybridization efficiency from one cell preparation to another depending on the DNA concentration. Direct hybridization of GuSCN cell lysates labeled in vivo with [6-14C]orotic acid was more efficient than hybridizing equivalent amounts of purified [6-14C]-labeled RNA, perhaps because of greater mRNA integrity and/or better recoveries of mRNA in GuSCN cell lysates. Therefore, direct solution hybridization of GuSCN-solubilized hepatocytes, which avoids the problem of RNA purification, appears to be a rapid, sensitive, and reliable method for quantifying mRNA in hepatocytes.

Effects of nicotinamide on hepatocyte viability and secretion of albumin and alpha 1-acid glycoprotein by adult rat hepatocytes in primoculture. Comparison with dexamethasone and recombinant human interleukin-6

The effects of nicotinamide on hepatocyte viability and secretion of albumin and alpha 1-acid glycoprotein were studied in the absence or presence of dexamethasone and/or recombinant human interleukin-6 either after cell attachment (2 h) or after 24, 48, and 72 h of culture. The evolution of hepatocyte survival during the culture was appreciated by measurement of total DNA content. The secretion of albumin and alpha 1-acid glycoprotein was measured after a 4-h period following cell attachment or after 24, 48 and 72 h of culture. The important decrease of DNA content, mRNA levels and secretion of albumin and alpha 1-acid glycoprotein in control cultures after 2-3 days was not prevented by the addition of nicotinamide. In contrast, dexamethasone alone or with recombinant human interleukin-6 improved DNA content and albumin secretion with no additional effect of nicotinamide. The secretion of alpha 1-acid glycoprotein was largely induced by dexamethasone alone or dexamethasone and recombinant human interleukin-6. The increase of alpha 1-acid glycoprotein secretion was not modified by the addition of nicotinamide and averaged respectively 27- and 60-fold for dexamethasone alone and dexamethasone and recombinant human interleukin-6 after 48 h. These observations suggested that nicotinamide, at least in the conditions tested here, is unable to prevent alterations of hepatocyte viability and gene expression of cultured hepatocytes.

Glucagon administration in vivo stimulates hepatic RNA and protein breakdown in fed and fasted rats

Liver RNA and protein breakdown rates were measured simultaneously in fed and in 24 h-fasted rats during a short-term cyclic perfusion, 1 h after an intraperitoneal injection of glucagon or of saline. RNA was labelled in vivo by an intraperitoneal injection of [6-14C]orotic acid, 60 h before the start of the perfusion. The accumulation of radioactive cytidine and valine in the perfusion medium for 15 min was used to determine RNA breakdown and proteolysis respectively. The portal glucagon/insulin ratio was significantly higher in the fasted glucagon-treated rats than in their fed counterparts. Although glucagon administration significantly increased RNA and protein degradation rates in the fasted and in the fed groups, the effect was greater after 24 h of starvation. The relationship between these biochemical changes and the alterations of the hepatocyte lysosomal system was investigated by determining the fractional cytoplasmic volume of lysosomal structures (autophagic vacuoles and dense bodies) by morphometry in the fasted glucagon-treated rats and in their controls. Hyperlucagonaemia significantly enhanced the relative volume of autophagic vacuoles without affecting that of dense bodies. The results showed that hyperglucagonaemia induced in vivo stimulated both liver RNA and protein breakdown and that this effect was modulated by the nutritional status of the rats.

Biosynthesis and intracellular transport of a bile canalicular plasma membrane protein: studies in vivo and in the perfused rat liver

B10 is an integral glycoprotein of the plasma membrane that is exclusively localized to the canalicular (apical) domain in normal rat hepatocytes but may be expressed on the basolateral (sinusoidal and lateral) membrane in pathophysiological situations. To understand how B10 may be localized to the basolateral surface, we studied the biosynthesis and transport of this apical protein. In vivo pulse-chase experiments, followed by subcellular fractionation of the liver and immunoprecipitation, showed that B10 is first synthesized as a high-mannose form of 123 kD and then matured to a complex glycosylated form of 130 kD, which peaks in the Golgi apparatus after 15 min of chase and reaches the plasma membrane with a half-time of 30 to 45 min. Analysis of the protein in plasma membrane domain fractions showed that most of the newly synthesized molecule was localized in basolateral fractions after 30 min of chase and subsequently appeared in apical fractions. After 90 min of chase, most of the radiolabeled protein had reached its steady-state apical distribution. The same experiments performed in the perfused rat liver, in which the chase can be improved, gave similar results, except that the apical distribution of the radioactive molecule was attained more quickly. Thus B10, like all apical plasma membrane proteins studied so far in hepatocytes, is first transported to the basolateral surface and then reaches the membrane of the bile canaliculi. Alterations of the transcytotic step from the basolateral to the apical surfaces may result in abnormal basolateral localization.

Regulation of RNA degradation in cultured rat hepatocytes: effects of specific amino acids and insulin

The regulation of RNA degradation by specific amino acids and insulin was investigated in cultured rat hepatocytes from fed rats previously injected in vivo with [6-(14)C]orotic acid. The effects of three groups of amino acids were compared to those of a complete amino acid mixture. The first one consisted of the eight amino acids (leucine, proline, glutamine, histidine, phenylalanine, tyrosine, methionine, tryptophan) previously found to be particularly effective in the control of proteolysis. The two other groups were defined from our study with single additions of amino acids, one consisting of proline, asparagine, glutamine, alanine, phenylalanine, and leucine and the other including the latter group with serine, histidine, and tyrosine. The results showed that these three groups were able to strongly inhibit deprivation-induced RNA breakdown at one and ten times normal plasma concentrations but to a lower extent than the complete amino acid mixture. Six amino acids (proline, asparagine, glutamine, alanine, phenylalanine, leucine) inhibited individually RNA degradation by more than 20%. However, the deletions of proline, asparagine, glutamine, or alanine from the group of these six amino acids were not followed by a loss of inhibitory effect. On the contrary, an important loss of inhibition was observed when leucine and phenylalanine were deleted. Furthermore, only these two amino acids exhibited an additive inhibitory effect. Thus leucine and phenylalanine could be considered as important inhibitors of RNA breakdown in cultured rat hepatocytes. Finally, insulin which had no significant effect on RNA degradation in the absence of amino acids, was able to potentiate the inhibitory effect of different amino acid groups.

Responsiveness of RNA degradation to amino acids in cultured rat hepatocytes: Comparison with isolated rat hepatocytes

The role of amino acids in the regulation of RNA degradation was investigated in cultured hepatocytes from fed rats previously labeled in vivo with [6-14C]orotic acid. Rates of RNA degradation were determined between 42 and 48 h of culture from the release of radioactive cytidine in the presence of 0.5 mM unlabeled cytidine. The fractional rate was about 4.4 +/- 0.4%/h in the absence of amino acids (0x). The catabolism of RNA was decreased to basal level (1.5 +/- 0.3%/h) by the addition of amino acids at 10 times normal plasma concentration (10x). The inhibition of RNA degradation, expressed as percentage of maximal deprivation-induced response (0x minus 10x), averaged 60% at normal plasma levels of amino acids. The degree of responsiveness was greatly improved as compared to freshly isolated hepatocytes (20%) and was similar to the sensitivity previously observed with perfused livers. In cultured hepatocytes, the sensitivity of RNA degradation to amino acids was not affected by varying the volume of medium from 1 to 4 ml per dish. In freshly isolated hepatocytes, the inhibitory effect of amino acids was not modified by changing the cell density from 0.5 to 5 x 10(6) cells per ml. In the range of normal plasma concentration of amino acids, the low sensitivity of RNA degradation in isolated hepatocytes persisted with inhibition ranging from 10 to 20%. These findings suggest that the control of RNA degradation in both cultured and isolated hepatocytes is not affected by the total quantity of amino acids available in the medium, but their concentration is crucial. Electron microscopy observations and the inhibitory effect of 3-methyl-adenine in cultured rat hepatocytes partially confirmed the role of the lysosomal system in the increase of RNA degradation and its regulation by amino acids.

Rates of RNA degradation in isolated rat hepatocytes. Effects of amino acids and inhibitors of lysosomal function

1. RNA degradation in isolated rat hepatocytes was measured as the release of radioactive cytidine from fed rats previously labeled in vivo for 60 h with [6-14C]orotic acid. Rates were determined from the linear accumulation of [14C]cytidine between 30 and 120 min of incubation in the presence of 0.5 mM unlabeled cytidine to suppress reutilization. 2. In the absence of amino acids, rates of RNA degradation in isolated hepatocytes averaged 3.97%/h. A complete mixture of amino acids added at 10-20 times normal plasma concentration inhibited RNA degradation by 65-70%. However, at physiological concentrations of amino acids, RNA degradation in isolated rat hepatocytes was less responsive as compared to perfused rat livers. 3. Numerous and large autophagic vacuoles at various stages of digestion were identified throughout the cytoplasm of isolated hepatocytes after 2 h of incubation in the absence of amino acids. The addition of amino acids at 20 times normal plasma concentration abolished almost completely the appearance of autophagic vacuoles. Furthermore, prophylamine, which accumulates in lysosomes, suppressed RNA degradation by 65% and the inhibitor of autophagic vacuole formation, 3-methyladenine, inhibited 70-80% of the degradation. Taken together, these results strongly suggest a contribution of the lysosomal system in the increase of RNA degradation rates in isolated rat hepatocytes.

Influence of diets with different levels of protein and energy on liver albumin content in the rat

The influence of protein ingestion on liver albumin synthesis and albumin content was investigated in rats fed protein as a meal (90% casein) given apart from the other dietary components provided ad libitum. In this condition, protein ingestion rapidly stimulates liver total protein synthesis. Separately fed rats were studied 6 and 20 h after the protein meal. Control rats fed mixed diets containing 13 or 80% casein were killed either during the absorptive (night) or postabsorptive (light) periods. The ratio of hepatic albumin synthesis to total protein synthesis remained fairly constant (12-15%) in all groups, indicating that albumin synthesis paralleled total protein synthesis. Liver albumin content measured in microsomes by immunonephelometry was significantly higher in separately fed rats killed 6 h postmeal than in those killed after 20 h. In rats fed 13% casein, the liver albumin content remained high regardless of the time of killing. In rats fed 80% casein, the albumin content was higher during the absorptive period than during the postabsorptive period. Immunoperoxidase staining of the hepatocyte organelles involved in albumin synthesis, especially the Golgi apparatus, was more intense for separately fed rats killed 6 h postmeal than for those killed after 20 h. Livers of rats fed 13% casein also exhibited a pattern indicative of high hepatocyte albumin content, whereas livers of rats fed 80% casein contained less. These results show that, in separate feeding, wide circadian variations of albumin synthesis run parallel to changes in liver albumin content.

Improved recovery of rat liver fractions enriched in lysosomes by specific alteration of the sedimentation properties of mitochondria

A method for the preparation of lysosomes from rat liver is presented. The procedure requires only standard equipment and is completed within less than 3 h. Homogenization and differential centrifugation were performed at pH 7.4 in isotonic potassium phosphate-buffered sucrose medium. The addition of potassium phosphate, at the concentration used (10 mM), accelerated the sedimentation rate of mitochondria without altering that of lysosomes resulting in the decrease in the mitochondrial contamination of the final pellet. Further purification was achieved by isopycnic centrifugation in 45% isotonic Percoll performed in an angle rotor. Lysosomal fractions representing 51.5% of the original population were recovered over a density range of 1.09 to 1.15 g/ml. The most purified fraction (37-fold purified) contained 25.3% of lysosomal beta-N-acetylglucosaminidase, and only 0.9% of mitochondrial monoamine oxidase and 0.6% of peroxisomal urate oxidase original activities. It was practically devoid to endoplasmic reticulum contamination.

Activity of several enzymes of amino acid catabolism in the liver of rats fed protein as a meal

Rats having a protein-free diet available ad libitum were fed a daily casein meal at the beginning of either the light- or the dark-phase of the day. A control group received a mixed-diet ad libitum. In all three groups, daily food ingestion was the same and casein corresponded to 12% of total intake. Liver activities of alanine, aspartate, ornithine and tyrosine aminotransferase, ornithine decarboxylase and serine dehydratase were assessed. In mixed-fed controls, all activities were low. Tyrosine aminotransferase and ornithine decarboxylase exhibited clear circadian rhythms of low amplitude. Feeding casein as a concentrated meal had no effect on aspartate aminotransferase. It depressed alanine aminotransferase and serine dehydratase activities. Tyrosine aminotransferase and ornithine decarboxylase exhibited rapid and strong stimulatory responses but, within 12 hours, returned to levels similar to those observed in mixed-fed controls. Ornithine aminotransferase was increased in the group receiving the casein meal during the light phase. It is concluded that the capacity for amino acid catabolism remains low in separately-fed animals, and that only tyrosine and especially ornithine, which may become limiting for urea synthesis, are actively metabolized. Thus, when high fluxes of amino acids reach the liver following the absorption of the casein meal, more amino acids are available for incorporation into newly synthesized proteins.

Portal insulin and glucagon in rats fed proteins as a meal: immediate variations and circadian modulations

In adult rats, proteins fed as a meal apart from the remainder of the diet induce alterations of protein metabolism characterized by the simultaneous stimulation of protein synthesis and breakdown. These alterations occur in parallel with an acceleration of glycogenolysis. The purpose of this work was to investigate whether these metabolic changes are related to variations in portal insulin and glucagon levels or to insulin-glucagon balance. Portal hormone concentrations, aortic glycemia and aminoacidemia, liver glycogen contents were followed over a day-night cycle in rats adapted either to mixed feeding (10% protein) or to separate feeding (protein meal given 2 hours after the onset of the light phase). Insulin and glucagon were assayed by radioimmunoassay, glucagon with antibody K 964 specific for 3500 MW glucagon. During the 3 hours following the protein meal, the portal ratio of insulin to glucagon decreased; liver glycogenolysis and glucogenic amino acid catabolism were enhanced. This glucagonotropic and glucogenic response to a protein meal administered during daytime is consistent with the increase in protein turnover previously observed. Separate feeding did not alter the overall circadian pattern of portal insulinemia which rose at night but it did alter the overall circadian pattern of portal insulinemia which rose at night but it did alter that of portal glucagonemia by maintaining it at a low level during the nightly prandial period. No correlation could be evidenced between portal insulin concentrations and the aortic levels of any amino acid in either mixed-fed or separately-fed animals. Portal glucagonemia appeared to be weakly correlated with the aortic level of arginine in both experimental groups. In the separately fed group, highly significant correlation could be evidenced between portal insulin concentrations and the aortic levels of any amino acid in either mixed-fed or separately-fed animals. Portal glucagonemia appeared to be weakly correlated with the aortic level of arginine in both experimental groups. In the separately fed group, highly significant correlations were found between portal glucagonemia and aortic concentrations of the three branched and the two aromatic amino acids.

Regulation of protein synthesis and enzyme accumulation in the rat pancreas by amount and timing of dietary protein

A 24-hour study in rats evidenced a clear rhythmicity of both synthesis and storage of pancreatic hydrolases. Synthesis measured by incorporation of 3H leucine into proteins was maximal during the night, reaching 21.3 mg/g tissue at 2400 hours against 4.1 mg/g at 0900 hours. Amylase and chymotrypsinogen contents, on the contrary, were 2-fold higher during the day (resting period) than at night (feeding period), while trypsinogen did not vary significantly. The diametrical opposition between the variations in synthesis and enzyme contents shows that, during periods of active feeding, stimulated synthesis merely balances excretion, while during periods of spontaneous fasting, basal synthesis is greater than basal secretion resulting in a preprandial accumulation of hydrolases. The effect of dietary proteins was investigated by feeding them as a separate meal at different times of the day while providing a protein-free diet ad libitum. In this case the general pattern of synthesis was biphasic. Rates of protein synthesis increased rapidly 2- to 3-fold after the protein meal, while tissue amino acids concentrations dropped. This first peak was tentatively attributed to the action of digestive hormones released after protein ingestion. The second peak occurred 15-18 hours, later together with a rise in tissue amino-acids due to limited endogenous proteolysis. This suggests that digestive hormones and amino-acid supply act independently to stimulate the synthesis of hydrolases in the pancreas. The amount of enzyme stored depends on the timing of the protein meal with respect to the period of most intense feeding, i.e. on the timing of maximal synthesis with respect to maximal secretion.

Regulation of hepatic synthesis of proteins by the chronology of protein ingestion

Circadian variations in liver protein synthesis were were assessed in control rats fed a mixed 10% protein diet and in rats fed proteins as a separate meal either at 09:00 (SF 09) or at 21:00 (SF 21) and provided with a protein-free diet ad libitum. Protein synthesis was measured by incorporation of labelled leucine over a short period of time (15 min) at time-points regularly spaced over 24 h. In controls, the circadian variations observed were of moderate amplitude (from 2.75 mg/h per g at 09:00 to 5.77 mg/h per g at 06:00) correlated with increased protein and RNA contents of the liver. In separately fed animals ingestion of the protein meal triggered a 300% increase in protein synthesis within 1 h while the feeding pattern was unaltered. In the SF 09 group, high synthetic activity was not followed by an increase of hepatic protein content while hepatic urea concentrations were sharply increased and glucogenic amino acid pools were greatly depleted. It is suggested that the high influx of amino acids consecutive to the absorption of the dietary proteins is the key factor stimulating protein synthesis, while synchronisation with the energetic metabolism controls the degree of degradation. The possible involvement of variations in the insulin to glucagon ratio is discussed.