Ischemia-induced STAT-1 expression and activation play a critical role in cardiomyocyte apoptosis

We show here that exposure of cardiac cells to simulated ischemia results in apoptosis and is accompanied by phosphorylation and increased expression and transcriptional activity of STAT-1. Similarly, interferon-gamma, which is known to induce STAT-1 activation, also induced apoptosis in cardiac cells. STAT-1-transfected cells were more susceptible to ischemia-induced cell death than cells transfected with a control plasmid lacking the STAT-1 coding sequence. Furthermore, an antisense STAT-1 vector reduced both ischemia- and overexpressed STAT-1-induced cell death in cardiac cells. Both STAT-1 overexpression and interferon-gamma treatment or exposure to ischemia activated the promoter of the pro-apoptotic caspase-1 gene in cardiomyocytes. Finally, ischemia/reperfusion also induced STAT-1 activation and caspase-1 processing in ventricular myocytes in the intact heart ex vivo. Immunofluorescent staining demonstrated an increase in STAT-1-positive staining in cardiomyocytes in response to ischemia/reperfusion that co-localized with terminal deoxynucleotidyl transferase dVTP nick end-labeling-positive apoptotic cells. These results suggest that STAT-1 plays a critical role in the regulation of ischemia/reperfusion-induced apoptosis in cardiac cells, acting at least in part via a caspase-1 activation-dependent pathway.

Urocortin protects against ischemic and reperfusion injury via a MAPK-dependent pathway

Urocortin (UCN) is a peptide related to hypothalamic corticotrophin-releasing hormone and binds with high affinity to corticotrophin-releasing hormone receptor-2beta, which is expressed in the heart. In this study, we report that UCN prevented cell death when administered to primary cardiac myocyte cultures both prior to simulated hypoxia/ischemia and at the point of reoxygenation after simulated hypoxia/ischemia. UCN-mediated cell survival was measured by trypan blue exclusion, 3'-OH end labeling of DNA (TUNEL), annexin V, and fluorescence-activated cell sorting. To explore the mechanisms that could be responsible for this effect, we investigated the involvement of MAPK-dependent pathways. UCN caused rapid phosphorylation of ERK1/2-p42/44, and PD98059, which blocks the MEK1-ERK1/2-p42/44 cascade, also inhibited the survival-promoting effect of UCN. Most important, UCN reduced damage in isolated rat hearts ex vivo subjected to regional ischemia/reperfusion, with the protective effect being observed when UCN was given either prior to ischemia or at the time of reperfusion after ischemia. This suggests a novel function of UCN as a cardioprotective agent that could act when given after ischemia, at reperfusion.

CRH-like peptides protect cardiac myocytes from lethal ischaemic injury

Simulated ischaemia causes both necrotic and apoptotic death of primary cultures of neonatal rat cardiac myocytes. Simulated ischaemia is associated with increased expression of urocortin mRNA and with the release of urocortin peptide into the medium. Exogenous urocortin is more potent than corticotropin releasing hormone (CRH) in protecting cardiac myocytes from necrotic and apoptotic death induced by ischaemia, and the cardioprotective effects of ischaemia-preconditioned media are abrogated by antagonists to the CRH family of peptides. Simulated ischaemia increases cardiac myocyte expression of CCAAT enhancer binding (C/EBP) transcription factors, and of the p65 subunit of NFkappaB, and reporter activity of a construct incorporating a fragment of the urocortin promoter containing a C/EBP consensus site is also enhanced by simulated ischaemia. The data suggest that ischaemia, acting partly through increased expression of C/EBP transactivators, increases expression of urocortin mRNA, which is rapidly translated to the mature form. The mature peptide is rapidly released, and exerts autocrine/paracrine protective effects through the cardiac CRH-R2 receptor which preferentially binds urocortin.

Quantitative assessment of cardiac myocyte apoptosis in tissue sections using the fluorescence-based tunel technique enhanced with counterstains

Apoptosis is a distinct form of cell death, induced, for example, by ischaemia/reperfusion injury, that results in characteristic alterations in cell morphology and fate. In tissue sections, the most commonly used technique to detect apoptosis is terminal deoxynucleotidyl transferase mediated nick end labelling (TUNEL) staining which labels the ends of DNA strand breaks characteristic of the apoptotic process. However, without the employment of additional staining, TUNEL is only a qualitative procedure that gives no information about the proportion of negative cells nor the cell type undergoing apoptosis. We have utilised propidium iodide (PI) as a counterstain to visualise TUNEL negative nuclei together with anti-desmin antibody in order to assess quantitatively apoptosis in specific cell types. The procedure has been evaluated in tissue sections from isolated perfused rat hearts subjected to ischaemia and reperfusion. Hearts were cross-sectioned into four 2.5 mm thick slices which were fixed in 4% formaldehyde and embedded in paraffin. Serial sections (5 microns) were cut, dewaxed and pretreated by incubation with trypsin at 37 degrees C for 30 min. After the employment of the TUNEL assay, sections were labelled with anti-desmin antibody, counterstained with PI and finally examined by confocal fluorescent microscopy. Apoptosis was not seen in sections from hearts subjected to ischaemia alone nor in control hearts. After 35 min of ischaemia the percentages of TUNEL positive cells were very low both in myocytes (0.1%) and in non-myocytes (0.3%). In ischaemic-reperfused hearts, the number of TUNEL positive cells was only significantly higher in vascular cells (44+/-5%) and cardiac myocytes (6+/-2%). This simple method therefore allows quantification of apoptosis in myocytic and non-myocytic cells in tissue sections. Use of alternative immunohistochemical markers would permit adaptation of the method to the quantitative assessment of apoptosis in other tissues.

Interleukin-10 activates heat-shock protein 90beta gene expression

Elevated levels of the cytokine interleukin-10 (IL-10) have been reported in patients with active systemic lupus erythematosus (SLE). Any role for IL-10 in the pathogenesis of SLE is likely to involve the activation of expression of specific genes within its target cells. We have previously reported elevated levels of the 90 000 MW heat-shock protein (hsp 90) and autoantibodies to hsp 90 in patients with SLE. Recent studies have shown that the cytokine IL-6 activates hsp 90 gene expression via specific transcription factors that include STAT-3 (signal transducer and activator of transcription 3). In view of the known role of STAT proteins in IL-10 signalling pathways, we have investigated the effect of IL-10 on hsp 90 gene expression. Here we report that IL-10 enhances the expression of hsp 90 in both a human hepatoma cell line (HepG2) stably expressing the human IL-10 receptor and peripheral blood mononuclear cells (PBMC). In reporter gene assays IL-10 is able to activate both the hsp 90alpha and hsp 90beta promoters directly. Furthermore, a short region of the hsp 90beta promoter which is activated in response to IL-10, contains a STAT-3 binding site. This element but not a mutant derivative unable to bind STAT-3, is able to confer a response to IL-10 on a heterologous promoter. These results may be understood in terms of the shared signalling mechanisms of IL-10 and IL-6 and provide evidence of a role for IL-10 in the overexpression of hsp 90 in SLE, with possible pathological consequences.

Signal transducer and activator of transcription-1 and heat shock factor-1 interact and activate the transcription of the Hsp-70 and Hsp-90beta gene promoters

We have previously demonstrated that interleukin-6 (IL-6) increases the levels of the heat shock protein 90 (Hsp-90) and activates the Hsp-90beta promoter via the IL-6-activated transcription factors NF-IL6 and signal transducer and activator of transcription-3 (STAT-3). Here, we show that interferon-gamma (IFN-gamma) treatment increases the levels of Hsp-70 and Hsp-90 and also enhances the activity of the Hsp-70 and Hsp-90beta promoters with these effects being dependent on activation of the STAT-1 transcription factor by IFN-gamma. These effects were not seen in a STAT-1-deficient cell line, indicating that IFN-gamma modulates Hsp induction via a STAT-1-dependent pathway. The effect of IFN-gamma/STAT-1 was mediated via a short region of the Hsp-70/Hsp-90 promoters, which also mediates the effects of NF-IL6 and STAT-3 and can bind STAT-1. This region also contains a binding site for the stress-activated transcription factor HSF-1. We show that STAT-1 and HSF-1 interact with one another via a protein-protein interaction and produce a strong activation of transcription, which is in contrast to our previous finding that STAT-3 and HSF-1 antagonize one another. To our knowledge this is the first report of HSF-1 interacting directly via a protein-protein interaction with another transcription factor. Such protein-protein interactions and the binding of a number of different stress and cytokine-activated transcription factors to a short region of the Hsp-90 and Hsp-70 gene promoters are likely to play a very important role in Hsp gene activation by non-stressful stimuli and the integration of these responses with the stress response of these genes.

Heat shock proteins delivered with a virus vector can protect cardiac cells against apoptosis as well as against thermal or hypoxic stress

Over expression of heat shock proteins (hsps) by transfection of plasmid constructs in vitro and in transgenic animals in vivo can protect primary cardiac cells from subsequent exposure to severe thermal or hypoxic stress. Here we show that such protection can also be achieved by over-expressing the hsps using herpes simplex virus (HSV) vectors capable of efficient gene delivery in vivo. Moreover, the convenience and high efficiency of this system has allowed us to show, for the first time, that over-expression of hsp27 or hsp70 can protect cardiac cells against three different apoptosis-inducing stimuli as well as against thermal or hypoxic stress whereas hsp56 has no protective effect. The potential therapeutic use of inducing the over-expression of specific hsps in cardiac cells in vivo using pharmacological or gene therapy procedures is discussed.

The regulation of heat shock proteins and their role in systemic lupus erythematosus

OBJECTIVES

After a serendipitous suggestion, it was established that a significant subset of patients with systemic lupus erythematosus (SLE) overexpress the 90-kD heat shock protein (Hsp90). In this review, we have analyzed our own data and that of others, to explore the link between Hsp90 and SLE.

METHODS

We performed a detailed literature review focusing on the potential role of Hsp in the etiopathogenesis of SLE.

RESULTS

Data are discussed showing surface expression of this Hsp in patients with lupus, a similar overexpression in the splenocytes of MRL/Ipr mice before the onset of disease, the detection of antibodies to Hsp90 in a proportion of both lupus patients and lupus-prone mice, and most recently, an analysis of the transcription factors that regulate the production of this protein and the influence of key cytokines on these factors.

CONCLUSIONS

These observations provide a model to show how a protein with key physiological roles in healthy individuals may, on occasion, become the target of an autoimmune attack with clinical consequences recognized in both mouse and human. Given that up to now, other heat shock proteins are not targeted in a similar fashion, the specificity of these responses is remarkable.

Elevation of IL-6 in transgenic mice results in increased levels of the 90 kDa heat shock protein (hsp90) and the production of anti-hsp90 antibodies

Treatment of human peripheral blood lymphocytes (PBL) in vitro with the cytokine interleukin-6 (IL-6) induces increased levels of the 90 kDa heat shock protein (hsp90). Hsp90 levels are also elevated in PBLs of human patients with systemic lupus erythematosus (SLE) and in MRL/lpr mice with autoimmune disease. Although IL-6 is elevated in both these situations it has not been shown that it is involved in stimulating elevation of hsp90 levels in vivo. Here we show directly that the elevation of IL-6 in vivo either in mice transgenic for the IL-6 gene or in knock-out mice lacking a functional gene for the transcription factor C/EBP beta (NF-IL-6) does indeed result in elevated hsp90 levels. This overexpression is associated with the specific production of autoantibodies to hsp90 in these mice which is also observed in SLE patients and MRL/1pr mice. Hence IL-6 is likely to play a critical role in the regulation of hsp90 levels both in autoimmune disease states and potentially in normal cells in vivo. In turn the elevated levels of hsp90 produced in autoimmune diseases are likely to be responsible for the observed production of anti-hsp90 autoantibodies.

Cardiotrophin-1 induces heat shock protein accumulation in cultured cardiac cells and protects them from stressful stimuli

Cardiotrophin-1 (CT-1) was originally identified as a molecule capable of inducing cardiac hypertrophy. We show here that treatment of cultured neonatal cardiocytes with CT-1 induces enhanced synthesis of the heat shock proteins hsp70 and hsp90, with hsp70 levels being enhanced three-fold and hsp90 levels being enhanced seven-fold. Such CT-1-treated cells are protected against subsequent exposure to severe thermal or ischaemic stress, as assayed both by measures of total cell death, such as trypan blue exclusion and LDH release, and by measures of apoptosis, such as propidium-iodide-staining and TUNEL-labelling. Hence, CT-1 can induce the protective hsps and protect cardiac cells from diverse stresses.

Expression and protective effects of urocortin in cardiac myocytes

Reverse transcription PCR showed that mRNA encoding the CRH-like molecule, urocortin, is expressed in a rat cardiac myocyte cell line and in primary cultures of cardiac myocytes. Identity of the amplified with the published sequence was established by restriction mapping and direct sequencing. Expression of urocortin mRNA was increased 12-18 h after thermal injury. Urocortin peptide protected cardiac myocytes from cell death induced by hypoxia. The data suggest that urocortin is an endogenous cardiac myocyte peptide which modulates the cellular response to stress.

The nuclear factor interleukin-6 (NF-IL6) and signal transducer and activator of transcription-3 (STAT-3) signalling pathways co-operate to mediate the activation of the hsp90beta gene by interleukin-6 but have opposite effects on its inducibility by heat shock

The levels of the 90 kDa heat-shock protein (hsp90) and the activity of the hsp90beta gene promoter are increased in response to treatment by interleukin (IL)-6. The hsp90beta gene promoter contains binding sites for the transcription factors nuclear factor IL-6 (NF-IL6) and signal transducer and activator of transcription 3 (STAT-3), which are activated respectively by the mitogen-activated-protein-kinase and Jak-kinase pathways following IL-6 treatment. Both these factors can activate the hsp90 promoter and have a strong synergistic effect on its activity, which appears to be critical for IL-6-mediated activation of the promoter. Interestingly, the two factors interact differently with the heat-shock factor (HSF) and a heat-shock stress. Thus STAT-3 reduces the stimulatory effect of heat shock whereas NF-IL6 enhances it. When applied together, heat shock and IL-6 produce only weak activation of the hsp90 promoter compared with either stimulus alone, indicating that the inhibitory effect of STAT-3 on HSF predominates under these conditions. In contrast, IL-1, which activates only the NF-IL6 pathway, synergizes with heat shock to produce strong activation of hsp90. These effects are discussed in terms of the multiple stimuli that may regulate the hsp90 promoter in unstressed cells and their interaction with its stress-mediated activation.

C/EBP activates the human corticotropin-releasing hormone gene promoter

The purpose of these studies was to identify whether transcription factors, associated with cytokine signalling, affected promoter activity of the corticotropin releasing hormone (CRH) gene. Fragments of a 3.6 kb sequence of the human CRH gene promoter were amplified by PCR and ligated upstream of a CAT reporter. These constructs were transfected into a variety of cell lines, either alone or together, with transcription factor expression vectors. Basal activity of a 3070 bp CRH promoter fragment was only seen in neuronal and lymphoblastoid cell lines. Promoter activity was increased by the transcription factors C/EBPbeta (NF-IL6) and more strongly, by C/EBPdelta (NF-IL6beta). Increased CRH promoter activity following phorbol ester treatment was inhibited by a dominant negative NF-IL6 mutant, showing that the effects of phorbol ester were principally mediated by C/EBP. Moreover, the inverse changes in the expression of CRH in the hypothalamus and spleens of arthritic rats were paralleled by similar inverse changes in NF-IL6beta expression in these organs. These data show that some transcription factors associated with cytokine signalling can also activate the CRH promoter.

Interleukin 6 activates heat-shock protein 90 beta gene expression

The levels of the cytokine interleukin-6 (IL-6) and the heat-shock protein hsp90 have both been reported to be elevated in patients with active systemic lupus erythematosus (SLE). We show that hsp90 protein accumulates to increased levels in both HuH7 hepatoma cells and peripheral blood mononuclear cells (PBMCs) treated with IL-6. In PBMCs this effect occurs without induction of the other hsps, paralleling the specific elevation of hsp90 in SLE. IL-6 is able to activate the hsp90 gene promoter directly; this activation can also be achieved by overexpressing either of the transcription factors NF-IL-6 or NF-IL-6 beta whose synthesis is induced by IL-6 treatment. Hence the induction of hsp90 protein accumulation by IL-6 is likely to be dependent on the enhanced activity of the hsp90 beta gene promoter produced by increased levels of NF-IL-6 and/or NF-IL-6 beta. These effects are discussed in terms of the role of hsp90 in the normal immune system and the mechanism of its activation in patients with SLE.

Total body zinc depletion and its relationship to the development of hyperprolactinemia in chronic renal insufficiency

Modulation of free plasma zinc levels has been implicated in the increase in plasma prolactin levels seen in patients with chronic renal insufficiency (CRI). The relative importance of this mechanism in comparison to others, however, has not been elucidated. Zinc equilibrium between plasma and red blood cells is partly dependent upon red blood cell carbonic anhydrase (CA). In the present paper, we have investigated the interrelationships among total plasma zinc, leukocyte zinc, prolactin, and erythrocyte CA in patients with CRI. Uremic patients were shown to have significantly increased levels of plasma prolactin and erythrocyte CA activity when compared to normal controls. Moreover, red blood cell CA total concentration and isoenzyme-I and-II levels, as well as plasma zinc were found to be significantly decreased in uremic patients in comparison to normal controls. In patients with CRI, a negative correlation was demonstrated between erythrocyte CA catalytic activity and plasma zinc, as well as between plasma zinc and plasma prolactin levels. Moreover, leukocyte zinc content, which is a reliable indicator of total body zinc stores, was found to be significantly decreased in uremic patients when compared to normal controls. A strong negative correlation between leukocyte zinc content and plasma prolactin levels was documented in CRI patients. Our results suggest that alterations in erythrocyte CA levels, enzymatic activity or isoenzyme profile are most probably mechanistically and etiologically unrelated to the high plasma prolactin levels in CRI patients. Contrariwise, depletion of total body zinc stores, rather than redistribution of this trace metal among extracellular compartments, may represent one of the major contributing mechanisms leading to uremic hyperprolactinemia.

The ARP-1 orphan receptor represses steroid-mediated stimulation of human placental lactogen gene expression

Studies were performed to determine whether ARP-1, which is an orphan receptor of the steroid receptor superfamily, inhibits basal activity of the human placental lactogen (hPL) promoter and the increase in hPL promoter activity in response to the receptors for thyroid hormone (TR) and retinoic acid (RAR). Co-transfection of an ARP-1 expression vector into BeWo choriocarcinoma cells, along with an expression vector containing 1.2 kb of the hPL promoter coupled to a CAT reporter gene, resulted in a dose-dependent inhibition of basal CAT activity. In addition, ARP-1 inhibited the stimulation of CAT activity by RAR alpha and TR beta expression vectors. Mobility shift assays demonstrated that ARP-1 binds specifically to a composite steroid response element on the hPL promoter that confers retinoic acid and T3 responsiveness. The results implicate an inhibitory role for ARP-1 in the regulation of hPL gene expression and strongly suggest that hPL gene expression is regulated, at least in part, by the interaction of stimulatory and inhibitory members of the steroid receptor superfamily.

Ontogeny of the expression and regulation of interleukin-6 (IL-6) and IL-1 mRNAs by human trophoblast cells during differentiation in vitro

During human placental differentiation, mononuclear cytotrophoblast cells fuse and differentiate into syncytiotrophoblast cells. Although syncytiotrophoblast cells have been shown to express interleukin-1 alpha (IL-1 alpha), IL-1 beta and IL-6, the pattern of expression of these cytokines during placental differentiation is unknown. We have examined the expression of IL-1 alpha, IL-1 beta and IL-6 mRNA during differentiation of cytotrophoblast cells in culture. IL-1 alpha, IL-1 beta and IL-6 mRNA levels were determined by semiquantitative reverse transcription-PCR analysis using glyceraldehyde phosphate dehydrogenase as an internal control. All three cytokine mRNA levels decreased markedly during trophoblast differentiation. After 6 days in culture, when almost all the cytotrophoblast cells had fused and differentiated into syncytiotrophoblast cells, the amounts of IL-1 alpha, IL-1 beta and IL-6 mRNA were decreased by 87.1, 72.1 and 60.9% respectively. Exogenous IL-6 had differential effects on cytokine mRNA expression. When added to placental cultures during the first 6 days of culture, IL-6 markedly inhibited IL-6, IL-1 alpha and IL-1 beta mRNA expression. However, when added to the cells during days 6-9 of culture, when most of the cells were syncytiotrophoblast cells, IL-6 stimulated IL-1 alpha and IL-1 beta mRNA expression. The results of these studies indicate that IL-1 alpha, IL-1 beta and IL-6 mRNA expression decreases markedly during cytotrophoblast differentiation in vitro and that the regulation of trophoblast cytokine mRNA levels changes during differentiation.

Identification of a composite steroid hormone response element on the human placental lactogen promoter

Three regions of the human placental lactogen (hPL) promoter that contain several half-site motifs that closely resemble the responsive elements for thyroid hormone (TR), all trans retinoic acid (RAR) and 1,25 dihydroxyvitamin D3 (VDR) have been identified and characterized. Transfection studies in BeWo choriocarcinoma cells indicate that site A (nt -979 to -954) is responsive to RAR alpha but not TR beta. Site B (nt -1140 to -1170) is responsive to both RAR alpha and TR beta, and site C (nt -550 to -580) is not responsive to either RAR alpha or TR. These findings, together with the observation that placental cells express retinoid receptors and TRs, strongly suggest a role for these receptors in the regulation of the hPL gene. Site B on the hPL promoter is able to integrate the responses to RA and T3 through a single element.

Retinoic acid and thyroid hormone regulate placental lactogen expression in human trophoblast cells

In this study, we have demonstrated that retinoic acid (RA) and thyroid hormone (T3) stimulate the synthesis and release of human placental lactogen (hPL), one of the major secretory products of syncytiotrophoblast cells. Enzymatically, dispersed trophoblast cells from term placentas exposed continuously to RA (0.5 microM) and T3 (0.1 microM) for 5 days released significantly more hPL than control cells after 3 days of exposure (P < 0.001 in each instance). On days 4 and 5, the amounts of hPL released by cells exposed to RA and T3 were approximately 3- and 5-fold higher than those in control cells, respectively. The stimulation by both RA and T3 was dose dependent and was accompanied by stimulation of hPL messenger RNA levels. RA and T3 caused 3.5- and 5.6-fold increases, respectively, in chloramphenicol acetyltransferase activity in BeWo choriocarcinoma cells transfected transiently with a 2.3-kilobase (kb) fragment of the hPL promoter (-2300 to 2 basepairs) coupled to a chloramphenicol acetyltransferase reporter gene. Deletion construct analysis of the hPL promoter (2.3, 1.2, and 0.5 kb) indicated that the T3- and RA-responsive elements are localized -0.5 to -1.2 kb up-stream from the transcriptional start site (+1), where several consensus RA- and T3-responsive element sites are present. These results indicate that RA and T3 stimulate the synthesis and release of hPL by a mechanism involving hPL gene transcription and further support a role for these steroids in placental function.

The nuclear factor NF-IL6 activates human placental lactogen gene expression

Transient transfection studies using deletion mutants of the hPL promoter indicate that the DNA elements for NF-IL6 responsiveness are located between -2.3 to -1.1 kb. Subsequent transfection studies using a hPL promoter fragment containing the region between -1376 to -1088 bp ligated to a heterologous SV40 CAT vector (NF-IL6/hPL-CAT) demonstrated that the NF-IL6/hPL-CAT construct is responsive to NF-IL6. Mobility shift assays using nuclear extracts from BeWo choriocarcinoma cells overexpressing NF-IL6 demonstrated specific binding of the extracts to a labeled oligonucleotide probe to this region of the hPL promoter. These studies therefore strongly suggest that the effect of IL-6 on hPL gene expression is mediated, at least in part, by the binding of NF-IL6 to a region of the hPL promoter that contains three NF-IL6 responsive elements.

Regulation of human placental lactogen expression by 1,25-dihydroxyvitamin D3

The human placenta synthesizes 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] and expresses the vitamin D receptor (VDR), but the roles of 1,25-(OH)2D3 and the VDR in placental physiology are poorly understood. In this study, we have demonstrated that 1,25-(OH)2D3 stimulates the synthesis and release of human placental lactogen (hPL), one of the major secretory products of syncytiotrophoblast cells. Enzymatically dispersed trophoblast cells from term placentas exposed continuously to 1,25-(OH)2D3 (0.1, 6, and 37 microM) for 5 days released significantly more hPL than control cells after the third day of exposure. On days 4 and 5, the amounts of hPL released by cells exposed to 1,25-(OH)2D3 were 2.54- and 4.14-fold that of control cells (P < 0.001 in each instance). The stimulation by 1,25-(OH)2D3 was dose dependent and was accompanied by stimulation of hPL messenger RNA levels. Transient transfection studies of BeWo choriocarcinoma cells transfected with hPL promoter constructs coupled to the chloramphenicol acetyltransferase reporter gene indicated that the stimulation of hPL expression is due at least in part to stimulation of hPL gene expression. Deletion analysis studies of the hPL promoter indicated that a region between -500 to -1200 basepairs is necessary for 1,25-(OH)2D3 responsiveness. Analysis of this region shows a consensus vitamin D response element (VDRE) DNA-binding site of a direct repeat motif separated by three bases. Ligation of this placental VDRE site into a heterologous chloramphenicol acetyltransferase vector caused 1,25-(OH)2D3 responsiveness. Moreover, mobility shift assays demonstrated binding of VDR to placental VDRE. These results indicate that 1,25-(OH)2D3 stimulates the synthesis and release of hPL by a mechanism involving hPL gene transcription and support a role for vitamin D and the VDR in placental function.

Interleukin-6 stimulates placental lactogen expression by human trophoblast cells

Interleukin-6 (IL-6) stimulates the release of hCG from syncytiotrophoblast cells, but the effects of IL-6 and other cytokines on the release of placental lactogen (hPL) are unknown. To determine the effect of IL-6 on hPL release, we exposed an enriched fraction of trophoblast cells (prepared by the isopycnic centrifugation of enzymatically dispersed term placenta) continuously to IL-6 (500 U/ml) for up to 6 days. The amounts of hPL released by the IL-6-exposed cells during days 3 and 6 were 177.6 +/- 2.4% and 267.5 +/- 12.6% that of control cells, respectively (P < 0.0001 in each instance). In addition, the hPL messenger RNA (mRNA) contents of the IL-6-exposed cells after 3 and 6 days of exposure were 2.2- and 4.7-fold that of control cells. The stimulatory effect of IL-6 on hPL release and hPL mRNA levels was dose dependent, with a minimal effective dose of 50 U/ml. IL-1 beta, which is known to stimulate IL-6 production by human trophoblast cells, also stimulated dose-dependent increases in hPL release and hPL mRNA levels. IL-6 (500 U/ml) had no effect on trophoblast differentiation, but stimulated a 20-fold increase in hPL promoter activity in BeWo choriocarcinoma cells transfected transiently with a plasmid containing 2.3 kilobases of the hPL promoter coupled to the chloramphenicol acetyltransferase gene. In addition, BeWo cells exposed to IL-6 (500 U/ml) for 3 and 6 days contained 2.4- and 3.2-fold more hPL mRNA levels than control cells. Because placental macrophages and syncytiotrophoblast cells release IL-6, these results strongly suggest an autocrine/paracrine role for IL-6 in the regulation of hPL release. The increase in hPL release appears to be due at least in part to an increase in hPL gene expression.