Susann Busch

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.

mTOR mediates human trophoblast invasion through regulation of matrix-remodeling enzymes and is associated with serine phosphorylation of STAT3

The intracellular signaling molecule mammalian target of rapamycin (mTOR) is essential for cell growth and proliferation. It is involved in mouse embryogenesis, murine trophoblast outgrowth and linked to tumor cell invasiveness. In order to assess the role of mTOR in human trophoblast invasion we analyzed the in vitro invasiveness of HTR-8/SVneo immortalized first-trimester trophoblast cells in conjunction with enzyme secretion upon mTOR inhibition and knockdown of mTOR protein expression. Additionally, we also tested the capability of mTOR to trigger signal transducer and activator of transcription (STAT)-3 by its phosphorylation status. Rapamycin inhibited mTOR kinase activity as demonstrated with a lower phosphorylation level of the mTOR substrate p70 S6 kinase (S6K). With the use of rapamycin and siRNA-mediated mTOR knockdown we could show that cell proliferation, invasion and secretion of matrix-metalloproteinases (MMP)-2 and -9, urokinase-like plasminogen activator (uPA) and its major physiological uPA inhibitor (PAI)-1 were inhibited. While tyrosine phosphorylation of STAT3 was unaffected by mTOR inhibition and knockdown, serine phosphorylation was diminished. We conclude that mTOR signaling is one major mechanism in a tightly regulated network of intracellular signal pathways including the JAK/STAT system to regulate invasion in human trophoblast cells by secretion of enzymes that remodel the extra-cellular matrix (ECM) such as MMP-2, -9, uPA and PAI-1. Dysregulation of mTOR may contribute to pregnancy-related pathologies caused through impaired trophoblast invasion.

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.

The Rheb switch 2 segment is critical for signaling to target of rapamycin complex 1.

The small GTPase Rheb is a positive upstream regulator of the target of rapamycin (TOR) complex 1 in mammalian cells and can bind directly to TOR complex 1. To identify the regions of the Rheb surface most critical for signaling to TOR complex 1, we created a set of 26 mutants wherein clusters of 1-5 putative solvent-exposed residues were changed to alanine, ultimately changing 65 residues distributed over the entire Rheb surface. The signaling function of these mutants was assessed by their ability, in comparison to wild type Rheb, to restore the phosphorylation of S6K1(Thr389) when expressed transiently in amino acid-deprived 293T cells. The major finding is that two mutants situated in the Rheb switch 2 segment, Y67A/I69A and I76A/D77A, exhibit a near total loss of function, whereas extensive replacement of the switch 1 segment and other surface residues with alanines causes relatively little disturbance of Rheb rescue of S6K1 from amino acid withdrawal. This is surprising in view of the minimal impact of guanyl nucleotide on Rheb switch 2 configuration. The loss of function Rheb switch 2 mutants are well expressed and exhibit partial agonist function in amino acid-replete cells. They are unimpaired in their ability to bind GTP or mammalian (m)TOR in vivo or in vitro, and the mTOR polypeptides retrieved with these inactive Rheb mutants exhibit kinase activity in vitro comparable with mTOR bound to wild type Rheb. We conclude that Rheb signaling to mTOR in vivo requires a Rheb switch 2-dependent interaction with an element other than the three known polypeptide components of TOR complex 1.

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

Reproductive immunology - An update

Pregnancy is one of the most challenging experiences for the immune system. It entails the confrontation and cooperation of maternal cells with allogeneic (sperm) and semi-allogeneic (fetal) cells and factors. On the one hand, it must actively acquire a specific tolerance towards the foreign cells and organism (the fetus) to avoid harming reactions, while recognizing the very same to support and control their development and growth. On the other hand, the immune system simultaneously may not reduce its capability to defend mother and fetus from microorganisms and pathogens. Almost all branches of the immune system are claimed to react and adapt in order to fulfill these complex duties. In this review, current knowledge concerning the most important cellular and soluble immunological components in the decidua is presented. Special regards are made to decidual NK, T and dendritic cells as well as to trophoblast cells, representing the fetal counterpart of most bilateral interactions. Furthermore, the role and functions of soluble factors, including HLA-G, PIBF, IDO and a variety of cytokines, are described.

Erratum: Reproductive immunology - An update (Transfusion Medicine and Hemotherapy (2006) 33 (474-485))

a Placenta-Labor, Abteilung für Geburtshilfe, Friedrich-Schiller-Universität Jena, Germany bInmunología, Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires / IDEHU, Argentina c PsychoNeuroImmunologisches Labor, Biomedizinisches Forschungszentrum Charité, Campus Virchow, Universitätsmedizin Berlin, dFrauenklinik, Universität Würzburg, Germany e Reproductive and Tumor Immunology, Research Group of the Hungarian Academy of Sciences, Department of Medical Microbiology and Immunology, Pecs University, Medical School, Pecs, Hungary

1141636674 Differential serine and tyrosine phosphorylation of Signal Transducer and Activator of Transcription 3 (STAT3) in Jeg-3 choriocarcinoma cell lines

Background:  Signal Transducer and Activator of Transcription 3 (STAT3) is an intracellular signalling molecule, which is used by several cytokines, including leukemia inhibitory factor (LIF), epithelial growth factor (EGF), and interleukin‐6 (IL‐6). It induces a variety of gene transcripts and cell functions. In trophoblast cells and in tumor cells, its tyrosine phosphorylation is directly linked to their invasiveness. The regulation and function of STAT3 serine phosphorylation is still widely unclear.