Tobias G. Poehlmann

Trophoblast invasion: the role of intracellular cytokine signalling via signal transducer and activator of transcription 3 (STAT3)

Trophoblast cells display a very unique capability: they physiologically invade into the surrounding tissue. This capability is widely associated with tumours, and, indeed, the invasive behaviour of both is rather similar. The imposing difference is that trophoblast cell invasion is temporally and locally controlled in contrast to unlimited tumour invasion. It initiates immediately after embryo implantation into the endometrium. Parallel to tumours, trophoblasts secrete proteases, such as matrix metalloproteinases, which dissolve the extracellular matrix and the surrounding tissue. Thereby, these proteases prepare and allow true invasion of trophoblasts. The invasive capacities of trophoblasts are positively and negatively regulated by numerous cytokines including leukaemia inhibitory factor (LIF), interleukin-6, hepatocyte growth factor, granulocyte macrophage-colony stimulating factor and others. They interact via specific receptors with the trophoblast cells, in which they activate intracellular signalling cascades. These will then induce expression of invasion relevant genes. One of these signalling pathways is the Janus kinase/signal transducers and activators of transcription (STAT) pathway. Especially phosphorylated STAT3 enhances invasiveness of tumours and trophoblast cells, where it is mainly activated by LIF. One of its most efficient physiological antagonists is suppressor of cytokine signalling 3. The balance of these two intracellular molecules seems to be a key regulator of tumour and trophoblast invasion.

Signal Transduction in Trophoblast Invasion

During the first trimester of pregnancy, well-differentiated primary cells of the placenta known as trophoblast cells grow in an invasive and destructive fashion similar to malignancies, but limited in space and time. The comparison of trophoblast cells with their malignant counterpart, human choriocarcinoma cells, offers an attractive model to understand the origin or development of malignant growth. Several cytokines and growth factors are known to influence trophoblast migration (e.g. EGF, IGF-2, HGF), proliferation (e.g. leptin, HGF, GM-CSF) and/or invasion (e.g. leukemia inhibitory factor, LIF), each factor utilizing at least one pathway for intracellular signaling in the trophoblast. Two pathways that are crossed especially often mediate the signals of these factors and are simultaneously well established in terms of tumor invasion: the Janus kinase-signal transducers and activators of transcription (Jak-Stat) and receptor-associated tyrosine kinase-mitogen-activated protein kinase (RTK-MAPK) pathways. These two pathways are detrimental for reproduction in general, and in part for placenta development, as a series of knockout experiments demonstrate. Aspects of each pathway are also implicated to be involved in trophoblast invasion, e.g. STAT3 is constitutively activated in invasive first trimester trophoblast cells, and activated ERK is detectable in intermediate trophoblast cells, an invasive phenotype. Interaction at several intersection points between the pathways has been described in several cell systems so that the same would seem to be possible in trophoblast cells. In this review, some of the possible areas of interaction are alluded to.

Progesterone-Induced Blocking Factor Activates STAT6 via Binding to a Novel IL-4 Receptor

Progesterone-induced blocking factor (PIBF) induces Th2-dominant cytokine production. Western blotting and EMSA revealed phosphorylation as well as nuclear translocation of STAT6 and inhibition of STAT4 phosphorylation in PIBF-treated cells. The silencing of STAT6 by small interfering RNA reduced the cytokine effects. Because the activation of the STAT6 pathway depends on the ligation of IL-4R, we tested the involvement of IL-4R in PIBF-induced STAT6 activation. Although PIBF does not bind to IL-4R, the blocking of the latter with an Ab abolished PIBF-induced STAT6 activation, whereas the blocking of the IL-13R had no effect. PIBF activated suppressor of cytokine signaling-3 and inhibited IL-12-induced suppressor of cytokine signaling-1 activation. The blocking of IL-4R counteracted all the described effects, suggesting that the PIBF receptor interacts with IL-4R α-chain, allowing PIBF to activate the STAT6 pathway. PIBF did not phosphorylate Jak3, suggesting that the γ-chain is not needed for PIBF signaling. Confocal microscopic analysis revealed a colocalization and at 37°C a cocapping of the FITC PIBF-activated PIBF receptor and PE anti-IL-4R-labeled IL-4R. After the digestion of the cells with phosphatidylinositol-specific phospholipase C, the STAT6-activating effect of PIBF was lost, whereas that of IL-4 remained unaltered. These data suggest the existence of a novel type of IL-4R composed of the IL-4R α-chain and the GPI-anchored PIBF receptor.

Interleukin-11 increases invasiveness of JEG-3 choriocarcinoma cells by modulating STAT3 expression

Amongst the interleukin-6 (IL-6) family of cytokines, leukemia inhibitory factor (LIF) has been shown to promote trophoblast invasion and proliferation. In the present study interleukin-11 (IL-11), another member of the IL-6 family, was investigated for its role in regulating invasion, migration and proliferation of JEG-3 choriocarcinoma cells. JEG-3 cells, like extra villous trophoblast (EVT), express mRNA transcripts encoding IL-11 and IL-11 receptor-alpha (IL-11Ralpha). Treatment of JEG-3 cells with IL-11 led to an increase in invasion across Matrigel extracellular matrix without an increase in proliferation. There was a dose-dependent increase in activation of STAT3 under the influence of IL-11 with maximum Tyr705 phosphorylation by 10min. In addition, treatment of JEG-3 cells with IL-11 for 24h led to an increase in expression of unphosphorylated STAT1 and STAT3. Analysis of the nuclear fraction showed an increased localization of STAT3 following IL-11 treatment while STAT1 was absent. Silencing the expression of STAT3 by siRNA caused a 25% reduction in invasion compared to control cells, however this was not significant. Furthermore, treatment of STAT3-silenced JEG-3 cells with IL-11 led to a significant increase in invasion compared to STAT3-silenced cells without cytokine, but this was not significant compared to non-transfected control cells. Silencing the expression of gp130 but not of IL-6R abrogated the increase in invasiveness of JEG-3 cells following IL-11 treatment. In conclusion, activation and upregulation of STAT3 appears to be critical for the IL-11-mediated increase in invasiveness of JEG-3 cells.

Inhibition of term decidual NK cell cytotoxicity by soluble HLA-G1

Objectives  Soluble (s)HLA‐G1 is produced by trophoblast cells. Aim was to analyze the capacities and mechanisms of sHLA‐G1 to regulate interleukin (IL)‐2‐induced cytotoxicity of natural killer (NK) cells from human deciduas.

Role of regulatory and angiogenic cytokines in invasion of trophoblastic cells.

Citation Dubinsky V, Poehlmann TG, Suman P, Gentile T, Markert UR, Gutierrez G. Role of regulatory and angiogenic cytokines in invasion of trophoblastic cells. Am J Reprod Immunol 2010; 63: 193–199

Signal Transducer and Activator of Transcription 3 (STAT3) and Suppressor of Cytokine Signaling (SOCS3) Balance Controls Cytotoxicity and IL-10 Expression in Decidual-Like Natural Killer Cell Line NK-92

Citation Braunschweig A, Poehlmann TG, Busch S, Schleussner E, Markert UR. Signal transducer and activator of transcription 3 (STAT3) and suppressor of cytokine signaling 3 (SOCS3) balance controls cytotoxicity and IL‐10 expression in decidual‐like natural killer cell line NK‐92. Am J Reprod Immunol 2011; 66: 329–335

ORIGINAL ARTICLE: Role of Regulatory and Angiogenic Cytokines in Invasion of Trophoblastic Cells

Citation Dubinsky V, Poehlmann TG, Suman P, Gentile T, Markert UR, Gutierrez G. Role of regulatory and angiogenic cytokines in invasion of trophoblastic cells. Am J Reprod Immunol 2010; 63: 193–199

Inhibition of HLA-G Production in JEG-3 Choriocarcinoma Cells by RNA Interference

Human leukocyte antigen‐G (HLA‐G) plays a major role in escape of trophoblast cells from maternal cytotoxicity. Unless its malignant transformation, Jeg‐3 choriocarcinoma cell line maintained the capacity of HLA‐G production. For the analysis of function and mechanisms of HLA‐G‐induced immune regulation, a human cellular model with suppressed HLA‐G would be very helpful. RNA interference (RNAi) is a very elegant method for this approach, but the design of appropriate oligonucleotide sequences may provide difficulties. We designed oligonucleotides to interfere exclusively with HLA‐G mRNA, which were applied at different concentrations to 50% confluent Jeg‐3 cells. After 36 hr, the HLA‐G content in Jeg‐3 cells was analyzed by Western blots. Applying the described RNAi method and oligonucleotides the cellular content of HLA‐G was dose‐dependently reduced as assessed in several independent Western blots. This method provides a tool for extensive investigation of HLA‐G functions in vitro and in vivo.

ORIGINAL ARTICLE: Selective Downregulation of Phosphoinositide 3‐Kinase alpha in Leukocytes During Pregnancy

Problem  During pregnancy, it is crucially important that the mother’s immune system tolerates the developing embryo. Although a number of mechanisms of immunological tolerance have been described, little is known about intracellular signaling events, causing a decrease in the mother’s leukocyte activity.