Background and purpose: Endothelins (ETs) and their G protein-coupled receptors exert key physiological functions during normal and aberrant placental development. Trophoblast cells mediate the contact between the embryo and the mother, by establishing a transient organ, the placenta. Choriocarcinoma cells display many of the biochemical and morphological characteristics of in utero invasive trophoblast cells and may therefore be used as a suitable model to study epithelial tumour progression of foetal-derived cells. Experimental approach: The present study aimed at investigating ET receptor-mediated activation of the mitogen-activated protein kinase (MAPK) pathway in human choriocarcinoma. Key results: Both JAR and Jeg-3 choriocarcinoma cell lines expressed ET receptor subtype B (ET B ) but not ET A receptor transcripts. ET B receptor engagement by ET-1 and ET-3 resulted in a similar time-and concentration-dependent phosphorylation of p42/44 MAPK, also known as extracellular regulated kinase 1/2. Using specific pharmacological antagonists/inhibitors, we showed that ET-1/-3-mediated signal transduction by the ET B receptor is transmitted via G i -and G q -dependent pathways through activation of the Src (G i ) and protein kinase C (G q ) axis that converge at Ras/Raf, leading to downstream activation of p42/44. On a functional level, ET B engagement and subsequent phosphorylation of p42/44 resulted in enhanced transcription of the immediate early response genes c-fos and c-jun, a process commonly assumed to be mediated by the ET A receptor, and increased cell growth and relative cell area. Conclusions and implications: As human choriocarcinoma cells secrete ETs, pharmacological antagonism of ETs and/or ET B receptor-mediated signal transduction could represent a likely target therapy for choriocarcinoma.

Research highlights► Chlorinated HDL promotes expression of heme oxygenase-1 (HO-1) in endothelial cells. ► Expression involves p42/44 MAPK and activation of transcription factor Egr-1. ► EMSA demonstrates induction of Egr-1 DNA binding activity. ► Immunocytochemistry shows translocation of Egr-1 to the nucleus. ► Silencing of p42/44 MAPK and Egr-1 impairs HO-1 expression to baseline levels.

Lysophosphatidic acid (LPA), a naturally occurring bioactive phospholipid, mediates a multitude of (patho)physiological events including activation of mitogen-activated protein kinases (MAPKs). As LPA may induce cellular reponses in human osteosarcoma, the present study aimed at investigating expression of various LPA receptors, LPA-mediated activation of MAPK via G-protein coupling, and expression of early response genes in a cellular model for human osteosarcoma. We show that MG-63 cells express three members of the endothelial differentiation gene (Edg) family of G-protein coupled receptor transcripts (LPA1–3) but only two (LPA4/5) out of three members of the non-Edg family LPA receptor transcripts. Stimulation of MG-63 cells with LPA or synthetic LPA receptor agonists resulted in p42/44 MAPK phosphorylation via LPA1–LPA3 receptors. Using pharmacological inhibitors, we show that LPA-mediated phosphorylation of p42/44 MAPK by LPA receptor engagement is transmitted by Gαi-dependent pathways through the Src family of tyrosine kinases. As a consequence, a rapid and transient upregulation of the zinc finger transcription factor early growth response-1 (Egr-1) was observed. Egr-1 expression was strictly mediated via Gαi/Src/p42/44 MAPK pathway; no involvement of the Gαq/11/PLC/PKC or the PLD/PI3 kinase/Akt pathways was found. LPA-induced expression of functional Egr-1 in MG-63 cells could be confirmed by electrophoretic mobility shift assay. LPA-induced Egr-1 upregulation was accompanied by a time-dependent decrease of periostin (previously called osteoblast-specific factor 2), a cell adhesion protein for pre-osteoblasts. Silencing of LPA1 and/or Egr-1 in MG-63 cells reversed LPA-mediated suppression of periostin. We here demonstrate a crosslink between Egr-1 and periostin in cancer cells, in particular in human osteosarcoma.