Interleukin-1 alpha suppresses gap junction-mediated intercellular communication in human endothelial cells

Gadolinium Chloride Restores the Function of the Gap Junctional Intercellular Communication between Hepatocytes in a Liver Injury

BACKGROUND

Gadolinium chloride (GdCl3) has been reported to attenuate liver injury caused by a variety of toxicants. Gap junctional intercellular communication (GJIC) is thought to be essential in controlling liver homeostasis and pathology. Here we evaluate the effects of GdCl3 on functional GJIC and connexin expression in mouse models and primary hepatocytes.

METHODS

Mice were administered GdCl3 intraperitoneally the day before a carbon tetrachloride (CCl4) injection or bile duct ligation (BDL) operation. Primary hepatocytes were treated with CCl4 or lipopolysaccharides (LPS), with or without GdCl3. A scrape loading/dye transfer assay was performed to assess the GJIC function. The expression of connexins was examined by real-time reverse transcription polymerase chain reaction (RT-PCR), western blot and immunofluorescent staining.

RESULTS

CCl4 treatment or the BDL operation led to the dysfunction of GJIC and a down-regulation of Cx32 and Cx26 in injured liver. GdCl3 administration restored GJIC function between hepatocytes by facilitating the transfer of fluorescent dye from one cell into adjacent cells via GJIC, and markedly prevented the decrease of Cx32 and Cx26 in injured liver. In primary hepatocytes, CCl4 or LPS treatment induced an obvious decline of Cx32 and Cx26, whereas GdCl3 pretreatment prevented the down-regulation of connexins. In vivo GdCl3 protected hepatocytes and attenuated the liver inflammation and fibrosis in liver injury mouse models.

CONCLUSION

GdCl3 administration protects functional GJIC between hepatocytes, and prevents the decrease of connexin proteins at mRNA and protein levels during liver injury, leading to the alleviation of chronic liver injury.

Immunomodulation by atorvastatin upregulates expression of gap junction proteins in coxsackievirus B3 (CVB3)-induced myocarditis

OBJECTIVE

To investigate the effect of atorvastatin on myocardial expression of gap junction proteins, connexins (Cxs), during coxsackievirus B3 (CVB3)-induced myocarditis.

METHODS

Viral myocarditis was induced in mice by inoculation with CVB3. Atorvastatin (5 or 10 mg kg(-1) day(-1)) or saline was administered by daily oral gavage from the day of induction of viral myocarditis to the day of sacrifice. Fourteen days after injection of CVB3, animals were sacrificed. Alterations in myocardial Cxs expression were examined by RT-PCR, immunoblot, and immunohistochemistry. Plasma levels of TNF-alpha and IFN-gamma were measured by ELISA.

RESULTS

Fourteen days after inoculation with CVB3, myocardial expression of Cx43 and Cx45 was significantly downregulated. Treatment with atorvastatin not only reduced the overproduction of TNF-alpha and IFN-gamma, but also enhanced the expression of Cx43 and Cx45, therefore attenuating myocardial injury and improving the survival rate of viral myocarditis.

CONCLUSION

This study shows for the first time that myocardial expression of Cxs is downregulated during CVB3-induced myocarditis and that immunomodulation by atorvastatin could restore the impaired gap junction channels and improve the outcome of viral myocarditis.

Opposite effects of interleukin-1alpha and transforming growth factor-beta2 induce stage-specific regulation of junctional adhesion molecule-B gene in Sertoli cells

In the mammalian testis, junctional adhesion molecule-B (JAM-B) is found at the blood-testis barrier between Sertoli cells and the apical ectoplasmic specializations between Sertoli and germ cells. The expression of JAM-B is tightly regulated to allow the transit of developing germ cells across the blood-testis barrier and the timely release of mature spermatids at stage VIII. In this study, the basal transcription of JAM-B in the mouse Sertoli cell line, MSC-1 cells, was examined. We found that the constitutive expression of JAM-B is carried out by the binding of specificity proteins (Sps), ETS domain transcription factor Elk-1 (Elk1), neuron-restrictive silencer factor (NRSF), and E2F transcription factor 3 (E2F3) to various cis-acting elements including TG interacting factor (TGIF), Elk-1, NRSF, and proximal Sp1 (pSp1) + E2F binding motifs. We also investigated the effects of two cytokines IL-1alpha and TGF-beta2 on JAM-B expression. IL-1alpha promotes JAM-B expression by facilitating the binding of Elk-1 to TGIF and pSp1 + E2F motifs in a p38-dependent manner, which leads to an additive effect on Sp1- and NRSF-mediated JAM-B transactivation. TGF-beta2 inhibits JAM-B transcription via the activation of mothers against decapentaplegic (Smad) proteins and activated Smads compete with specificity proteins (Sp1 and Sp3) for the TGIF motif, resulting in JAM-B repression. IL-1alpha and Smad3 expression have been reported to be stage specific. IL-1alpha is absent in the seminferous epithelium at stages VII-VIII, whereas a high level of nuclear Smad3 level is found at the same stages. This study shows for the first time that IL-1alpha and TGF-beta2 regulate JAM-B expression in an opposite manner, and in vitro data obtained herein provide some clues on how junctions are regulated in the testis.

Intercellular Communication in Atherosclerosis

Cell-to-cell communication is a process necessary for physiological tissue homeostasis and appears often altered during disease. Gap junction channels, formed by connexins, allow the direct intercellular communication between adjacent cells. After a brief review of the pathophysiology of atherosclerosis, we will discuss the role of connexins throughout the different stages of the disease.

Interferon-gamma inhibits intestinal restitution by preventing gap junction communication between enterocytes

BACKGROUND & AIMS

Necrotizing enterocolitis (NEC) is characterized by interferon-gamma (IFN-gamma) release and inadequate intestinal restitution. Because enterocytes migrate together, mucosal healing may require interenterocyte communication via connexin 43-mediated gap junctions. We hypothesize that enterocyte migration requires interenterocyte communication, that IFN impairs migration by impairing connexin 43, and that impaired healing during NEC is associated with reduced gap junctions.

METHODS

NEC was induced in Swiss-Webster or IFN(-/-) mice, and restitution was determined in the presence of the gap junction inhibitor oleamide, or via time-lapse microscopy of IEC-6 cells. Connexin 43 expression, trafficking, and localization were detected in cultured or primary enterocytes or mouse or human intestine by confocal microscopy and (35)S-labeling, and gap junction communication was assessed using live microscopy with oleamide or connexin 43 siRNA.

RESULTS

Enterocytes expressed connexin 43 in vitro and in vivo, and exchanged fluorescent dye via gap junctions. Gap junction inhibition significantly reduced enterocyte migration in vitro and in vivo. NEC was associated with IFN release and loss of enterocyte connexin 43 expression. IFN inhibited enterocyte migration by reducing gap junction communication through the dephosphorylation and internalization of connexin 43. Gap junction inhibition significantly increased NEC severity, whereas reversal of the inhibitory effects of IFN on gap junction communication restored enterocyte migration after IFN exposure. Strikingly, IFN(-/-) mice were protected from the development of NEC, and showed restored connexin 43 expression and intestinal restitution.

CONCLUSIONS

IFN inhibits enterocyte migration by preventing interenterocyte gap junction communication. Connexin 43 loss may provide insights into the development of NEC, in which restitution is impaired.

Connexins: new genes in atherosclerosis

Atherosclerosis, the main cause of death and disability in adult populations of industrialized societies, is a multifactorial progressive process involving a variety of pathogenic mechanisms. Our current view on the pathogenesis of the disease implies complex patterns of interactions between a dysfunctional endothelium, leukocytes, and activated smooth muscle cells in which cytokines and growth factors are known to play a crucial role. Apart from paracrine cell-to-cell signalling, a role for gap junction-mediated intercellular communication in the development of the disease has been recently suggested. Gap junction channels result from the docking of two hemichannels or connexons, formed by the hexameric assembly of connexins, and directly connect the cytoplasm of adjacent cells. In this review, we summarize existing evidence implicating connexins in atherosclerosis. Indeed, the expression pattern of vascular connexins is altered during atherosclerotic plaque formation. In addition, changes in connexin expression or gap junctional communication have been observed in vascular cells in vitro by disturbances in blood flow, cholesterol, inflammatory cytokines, and growth factors. Furthermore, genetically modifying connexin expression affects the course of the atherosclerotic process in mouse models of the disease. Finally, the involvement of connexins in treatment of atherosclerotic disease will be discussed.

Opposite regulation of connexin33 and connexin43 by LPS and IL-1α in spermatogenesis

The gap junction proteins, connexins (Cxs), are present in the testis, and among them, Cx43 play an essential role in spermatogenesis. In the present study, we investigated the testicular expression and regulation of another Cx, Cx33, previously described as a negative regulator of gap junction communication. Cx33 mRNA was present in testis and undetectable in heart, liver, ovary, and uterus. In the mature testis, Cx33 was specifically immunolocalized in the basal compartment of the seminiferous tubules, whereas Cx43 was present in both seminiferous tubule and interstitial compartments. During stages IX and X of spermatogenesis, characterized by Sertoli cell phagocytosis of residual bodies, Cx43 was poorly expressed within seminiferous tubules, while Cx33 signal was strong. To evaluate the role of phagocytosis in the control of Cx33 and Cx43 expression, the effect of LPS was analyzed in the Sertoli cell line 42GPA9. We show herein that phagocytosis activation by LPS concomitantly stimulated Cx33 and inhibited Cx43 mRNA levels. These effects appear to have been mediated through IL-1α, because the exposure of Sertoli cells to the IL-1 receptor antagonist partly reversed these effects. IL-1α enhanced and reduced, respectively, the levels of Cx33 and Cx43 mRNA in a time- and dose-dependent manner. These data reveal that Cx33 and Cx43 genes are controlled differently within the testis and suggest that these two Cxs may exert opposite and complementary effects on spermatogenesis.

Gap junctional communication in tissue inflammation and repair

Local injury induces a complex orchestrated response to stimulate healing of injured tissues, cellular regeneration and phagocytosis. Practically, inflammation is defined as a defense process whereby fluid and white blood cells accumulate at a site of injury. The balance of cytokines, chemokines, and growth factors is likely to play a key role in regulating important cell functions such as migration, proliferation, and matrix synthesis during the process of inflammation. Hence, the initiation, maintenance, and resolution of innate responses depend upon cellular communication. A process similar to tissue repair and subsequent scarring is found in a variety of fibrotic diseases. This may occur in a single organ such as liver, kidneys, pancreas, lung, skin, and heart, but fibrosis may also have a more generalized distribution such as in atherosclerosis. The purpose of this review is to summarize recent advances on the contribution of gap junction-mediated intercellular communication in the modulation of the inflammatory response and tissue repair.

Sepsis up-regulates the expression of connexin 40 in rat aortic endothelium

OBJECTIVE

A distinctive feature of sepsis is a pleiotropic modification of membrane protein expression in the vascular endothelium, associated with diminished endothelium-dependent relaxation (endothelial dysfunction). In cultured endothelial cells, inflammatory stimuli alter expression of connexins (Cx), proteins that make up the gap junctions responsible for intercellular communication. In the present study, we tested whether the polymicrobial sepsis induced by cecal ligation and perforation in the rat alters the expression of the connexins present in the vascular endothelium (i.e., Cx37, Cx40, and Cx43). We also examined a possible association between such changes and endothelial dysfunction in this model.

DESIGN

Animal study, with two parallel groups.

SETTING

Animal research facility.

SUBJECTS

One hundred four male adult Wistar rats.

INTERVENTIONS

Rats underwent either cecal ligation and perforation to induce sepsis or a sham operation and were killed after a variable time, mostly 24 hrs.

MEASUREMENTS AND MAIN RESULTS

Experiments designed to test for the impact of sepsis on connexin expression disclosed a three-fold increase in Cx40 messenger RNA and protein in the aorta, an effect that peaked at 24 hrs after cecal ligation and perforation, was specific to this connexin (i.e., levels of Cx37 and Cx43 did not vary), and was restricted to the aortic endothelium. Experiments designed to test the permeability of interendothelial gap junctions using the scrape-loading method did not show a change in function in the septic group. Finally, a time-course study was designed to test for a possible association of enhanced Cx40 expression with endothelial dysfunction. Endothelium-dependent relaxation was diminished in rings of aorta when harvested from septic rats before (6 hrs after surgery) but not at the time when enhanced Cx40 expression occurred (12 and 24 hrs).

CONCLUSION

In this experimental model, recovery from an early transient dysfunction of the aortic endothelium is associated with an enhanced expression of aortic endothelial Cx40.

The emperor wears no clothes in the field of carcinogen risk assessment: ignored concepts in cancer risk assessment

The following is a position paper challenging the paradigm that 'carcinogen = mutagen', and that the current rodent bioassay to predict risks to human cancers is relevant and useful. Specifically, we review current observations concerning carcinogenesis that might lead to another approach for assessing the identification of human carcinogenic hazards and the risk assessment that chemicals might pose. We give a brief review of the multistage and multimechanism process of cancer in a tissue that involves not only genotoxic but also epigenetic events, and the importance of stem and progenitor cells in the development of cancer. We focus on the often ignored 'epigenetic' effects of carcinogens and the role of cell communication systems in epigenetically altering gene expression that leads to an imbalance of cell proliferation, differentiation and apoptosis in a tissue that can contribute to the cancer process. To draw attention to the fact that the current paradigm and policy to test toxic chemicals is often misleading and incorrect, we discuss how oxidative stress, in spite of the DNA damaging data, most probably contributes to cancer at the epigenetic level. Additionally, we briefly review how this mutagenic concept has greatly diverted attention away from doing research on the lower molecular weight, non-genotoxic, polycyclic aromatic hydrocarbons (PAHs), and how these low molecular weight PAHs are etiologically more relevant to the disease potential of environmental mixtures such as cigarette smoke.

Decreased intercellular communication and connexin expression in mouse aortic endothelium during lipopolysaccharide-induced inflammation

The role of gap junctional intercellular communication during inflammatory processes is not well understood. In particular, changes in the expression and function of vascular endothelial connexins (gap junction proteins) in response to inflammatory agents has not been fully investigated. In this study, we used intercellular dye transfer methods to assess interendothelial communication in aortic segments isolated from mice treated with or without intraperitoneal lipopolysaccharide (LPS), a potent inflammatory mediator. LPS treatment resulted in a 49% decrease in endothelial dye coupling 18 h after injection. Western blots indicated that LPS treatment also caused a reduction in endothelial connexin40 (Cx40) levels to 33% of control levels. Connexin37 (Cx37) levels decreased only slightly after LPS treatment to 79% of control levels. We also examined endothelial communication in aortic segments isolated from Cx37-/- and Cx40-/- mice. LPS treatment caused a significantly greater decrease in dye transfer in endothelium isolated from Cx37-/- animals compared with endothelium from Cx40-/- animals (71 vs. 26% decrease). LPS injection caused a reduction in Cx40 levels in Cx37-/- endothelium, whereas LPS actually increased Cx37 levels in Cx40-/- endothelium. These results suggest that LPS mediates changes in endothelial gap junction-mediated communication, at least in part, through modulation of Cx40 and Cx37 levels.

Hypoxia-reoxygenation inhibits gap junctional communication in cultured human umbilical vein endothelial cells

We studied the change in gap junctional intercellular communication (GJIC) on human umbilical vein endothelial cells (HUVEC) under hypoxia-reoxygenation (H-R) conditions by the fluorescence redistribution after photobleaching (FRAP) method. Confluent HUVEC monolayers were exposed to hypoxia (pO2<0.1%) for 12 hours, and then were returned to normal atmospheric conditions for reoxygenation. Contrast microscopic observation showed no significant changes in the morphology of the HUVEC at any times after H-R. Reoxygenation following hypoxia caused time-dependent decrease in GJIC, that is, GJIC reduction was induced after 2 hours and reached maximum at 4-6 hours which recovered to normal levels after 18 hours. Oxidant sensitive fluorescence dye assay revealed that the generation of intracellular free radicals increased during the first 2 hours after reoxygenation. Hydroxyl radical scavengers (MCI-186, DMSO) and an iron chelator (deferoxamine) abolished the reduction of GJIC due to H-R. However, SOD, catalase and probucol were essentially inactive on this reduction. These data suggest that ischemia-reperfusion injury may be caused by a functional defect of GJIC induced by reactive oxygen radicals.

A new in vitro model for agonist-induced communication between microvascular endothelial cells

Microvascular endothelial cells (MECs) grown in Matrigel form capillary-like structures. We hypothesized that these "capillaries" better mimic communication properties of microvessels than conventional cell monolayers. MECs were isolated from the rat hindlimb skeletal muscle. Functional communication was tested by visualizing the spread of microinjected 6-carboxyfluorescein (CF) dye and by measuring a conducted change of membrane potential after micropipette application of 500 mM KCl or 10 mM adenosine triphosphate (ATP) on the capillary and monolayer. MECs grown under both conditions were dye-coupled, as demonstrated by the spread of CF injected into a single cell. The membrane potential of cells grown in capillaries (-59 +/- 5 mV) was significantly greater than that of cells grown in monolayers (-24 +/- 2 mV). KCl and ATP caused local depolarization (18 +/- 3 mV) and hyperpolarization (21 +/- 3 mV) in capillaries that yielded conducted 13 +/- 3 mV depolarization and 15 +/- 5 mV hyperpolarization at a 300-microm distal site, respectively. In monolayers, local and distal responses to agonists were 3- to 6-fold and 9- to 10-fold less, respectively, than the corresponding responses in capillaries. Cells grown under both conditions expressed connexin 43, as demonstrated by immunohistochemistry and Western blotting. We conclude that cells grown in capillaries yield substantially larger local and communicated responses than cells in monolayers and thus offer a more sensitive model for mechanistic studies of MEC communication.

Gap junctions in cells of the immune system: structure, regulation and possible functional roles

Gap junction channels are sites of cytoplasmic communication between contacting cells. In vertebrates, they consist of protein subunits denoted connexins (Cxs) which are encoded by a gene family. According to their Cx composition, gap junction channels show different gating and permeability properties that define which ions and small molecules permeate them. Differences in Cx primary sequences suggest that channels composed of different Cxs are regulated differentially by intracellular pathways under specific physiological conditions. Functional roles of gap junction channels could be defined by the relative importance of permeant substances, resulting in coordination of electrical and/or metabolic cellular responses. Cells of the native and specific immune systems establish transient homo- and heterocellular contacts at various steps of the immune response. Morphological and functional studies reported during the last three decades have revealed that many intercellular contacts between cells in the immune response present gap junctions or "gap junction-like" structures. Partial characterization of the molecular composition of some of these plasma membrane structures and regulatory mechanisms that control them have been published recently. Studies designed to elucidate their physiological roles suggest that they might permit coordination of cellular events which favor the effective and timely response of the immune system.

Gap junction modulation by extracellular signaling molecules: the thymus model

Gap junctions are intercellular channels which connect adjacent cells and allow direct exchange of molecules of low molecular weight between them. Such a communication has been described as fundamental in many systems due to its importance in coordination, proliferation and differentiation. Recently, it has been shown that gap junctional intercellular communication (GJIC) can be modulated by several extracellular soluble factors such as classical hormones, neurotransmitters, interleukins, growth factors and some paracrine substances. Herein, we discuss some aspects of the general modulation of GJIC by extracellular messenger molecules and more particularly the regulation of such communication in the thymus gland. Additionally, we discuss recent data concerning the study of different neuropeptides and hormones in the modulation of GJIC in thymic epithelial cells. We also suggest that the thymus may be viewed as a model to study the modulation of gap junction communication by different extracellular messengers involved in non-classical circuits, since this organ is under bidirectional neuroimmunoendocrine control.

Involvement of tyrosine kinase in the hypoxia/reoxygenation-induced gap junctional intercellular communication abnormality in cultured human umbilical vein endothelial cells

Vascular endothelial cells (EC), communicating with one another across gap junctions, are usually made dysfunctional by hypoxia and reoxygenation (H/R); however, very limited information exists regarding the effects of H/R on the endothelial gap junctions. We investigated whether H/R interferes with endothelial gap junctional intercellular communication (GJIC). After human umbilical vein EC had grown to confluence, they were exposed to hypoxia (pO2 < 0.1%) for 12-16 h and then returned to normal atmospheric conditions for reoxygenation. At 0-, 2-, 4-, 6-h reoxygenation, GJIC was detected by means of a fluorescence recovery after a photobleaching technique. The results demonstrated that a GJIC reduction (about 20% less than that under normoxia) was induced after 2 h of reoxygenation; after 4 h of reoxygenation, it began to recover (to about 10% less than that under normoxia); and after 6 h of reoxygenation, GJIC was restored to the normal level. Calphostin C (1 x 10(-7) mol/l), a specific protein kinase C inhibitor, partially inhibited the reduction in GJIC (resulting in a level about 10% less than that under normoxia), whereas the tyrosine kinase inhibitor genistein (10 micromol/L) completely blocked the reduction in GJIC. Vanadate (1.5 mmol/l), a tyrosine phosphatase inhibitor, amplified the inhibitory effect of H/R on GJIC (to about 40% less than that under normoxia). Immunofluorescence and immunoprecipitation showed that 2-h reoxygenation significantly stimulated tyrosine protein phosphorylation, and this phosphorylation event was obviously enhanced by vanadate. The results of Western blotting showed that the gap junctional protein connexin 43 (Cx43) was phosphorylated by H/R; moreover, immunoprecipitation demonstrated that 2-h reoxygenation induced a prominent increase of tyrosine phosphorylation of Cx43 compared with that under normoxia. These data indicate that H/R induces a transient endothelial GJIC dysfunction through the activation of tyrosine kinase and phosphorylation of tyrosine residues of Cx43.

Differential regulation of gap junctions by proinflammatory mediators in vitro

The development of inflammation is an important component of host defense against infection. The cellular and molecular processes underlying inflammation are well-studied, and it is known that cells of the blood vessel wall, such as endothelial cells and smooth muscle cells, play pivotal roles. Additionally, a wide variety of proinflammatory mediators have been defined, which coordinate the multicellular processes of inflammation. Knowledge of the potential role of blood vessel gap junctional intercellular communication (GJIC) in coordinating the inflammation process, however, is limited. In this study, we report that bacterial lipopolysaccharide (LPS), as well as the proinflammatory cytokines TNF-alpha and IL-1beta, selectively inhibit human myoendothelial GJIC in vitro without affecting GJIC between the respective homologous cell populations. This finding may represent a physiologically relevant component of the inflammatory response to infection. The work also provides some of the first clear evidence suggesting that a single eukaryotic cell can differentially regulate its GJIC between homologous and heterologous cell types in a simultaneous manner.

A mitosis-specific phosphorylation of the gap junction protein connexin43 in human vascular cells: biochemical characterization and localization

Western blotting studies revealed that connexin43 (Cx43), one of the major gap junction proteins in human vascular endothelial cells, is posttranslationally modified during mitosis. This mitosis-specific modification results in a Cx43 species that migrates as a single protein band and was designated Cx43(m). Cx43(m) was shown to be the result of additional Ser/Thr phosphorylation as indicated by: (a) the increased gel mobility induced by both alkaline phosphatase and the Ser/ Thr-specific protein phosphatase-2A (PP2A) and (b) the removal of virtually all (32)P(i) from Cx43(m) by PP2A. Immunofluorescent confocal microscopy of mitotic cells revealed that Cx43 is intracellularly located, while in nonmitotic cells Cx43 is located at regions of cell-cell contact. Dye coupling studies revealed that mitotic endothelial cells were uncoupled from each other and from nonmitotic cells. After cytokinesis, sister cells resumed cell coupling independent of de novo protein synthesis. The mitosis-specific phosphorylation of Cx43 correlates with the transient loss of gap junction intercellular communication and redistribution of Cx43, suggesting that a protein kinase that regulates gap junctions is active in M-phase.

PKC phosphorylation disrupts gap junctional communication at G0/S phase in clone 9 cells

Gap junctional communication during the progression of cell cycle from quiescent G0 to S phase was examined in cultured clone 9 rat liver cells. The transfer of scrape-loaded fluorescent dye was suppressed immediately after the stimulation of cell cycle progression in a synchronized cell population. Northern blot analysis showed that the temporal disturbance of gap junctional communication in cells passing from G0 to S phase did not result from transcriptional down-regulation of connexin 43. It was also found that the PKC inhibitor, calphostin C, was able to restore intercellular communication in serum stimulated cells. Data suggest a control mechanism by PKC mediated phosphorylation in the regulation of gap junction function which is vulnerable to cell cycling. The loss of gap junctional communication correlated with the increased phosphorylation of connexin 43 on serine residues in clone 9 cells.

Posttranscriptional regulation of connexin 32 expression in liver during acute inflammation

Gap junctions mediate the communication between adjacent cells in tissues. In the liver, connexin 32 (Cx32) subunits make up the predominating gap junctions. The expression of Cx32 gene has been observed to be down-regulated in response to inflammatory states and during liver regeneration. In the present study we attempt to elucidate the molecular mechanisms underlying the down-regulation of the Cx32 expression during acute inflammation. A decrease in the level of Cx32 mRNA in rat liver occurred between 3 and 6 h after intravenous administration of bacterial lipopolysaccharide (LPS), simultaneously with the induction of an acute inflammatory response characterized by an increase in the level for beta-fibrinogen and a reduction of phosphoenolpyruvate carboxykinase mRNA. The reduction in Cx32 steady-state mRNA levels appears to occur at the posttranscriptional level, since the rate of degradation of this message seems to be higher than the rate of transcription of the gene. Degradation of Cx32 mRNA was blocked by the administration of actinomycin D, but not by cycloheximide, prior to injection of LPS. The stabilization of Cx32 message by actinomycin D correlated with the preservation of Cx32 on the cell surface, which otherwise disappears after administration of LPS alone. These results suggest that cellular communication via gap junctions could be regulated at the level of gene expression, by a posttranscriptional mechanism, during acute inflammatory states.