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Localization and regulation of mRNA transcripts encoding activin receptors in human placental trophoblast cells Chen, Victor


There is increasing evidence to suggest that activin can function as an autocrine/paracrine regulator in various tissues, including the reproductive system. At the cellular level, activin acts via a family of activin receptor (ActR) subtypes which includes two type I (ActRI and ActRLB) and two type II (II and ILB) receptors. The role of activin in the human placenta is not clearly understood. In this study, the detection of inlubin/activin subunit and ActRI mRNA were examined in first trimester cytotrophoblasts, term cytotrophoblasts, extravillous trophoblast (EVT) cells, immortalized extravillous trophoblast (LEVT) cells, JEG-3 cells, decidual tissue, and decidual cells. Regulation of ActRI mRNA levels was also studied in LEVT cells using competitive polymerase chain reaction (cPCR). With the exception of JEG-3 cells, ActRILB mRNA was detected in all cell populations, mRNA transcripts encoding inhibina, inhibinRA, inhibinpB, ActRI, ActRII and ActRILB were detected in the whole cell populations. However, ActRLB mRNA could not be detected in all cell populations. With Northern blot hybridization analysis, it was found that the ActRI mRNA level was greatest in first trimester EVT cells followed in decreasing order of first trimester cytotrophoblasts, JEG-3 cells and term cytotrophoblasts. An internal standard of ActRI cDNA for cPCR was constructed for the precise quantitation of the ActRI mRNA levels in LEVT cells. The ActRI mRNA accumulation was stimulated in a dose-dependent manner by activin-A with a maximal effect three times that of control culture at a dose of 10 ng/ml activin-A. The time course of the activin-A effects on ActRI mRNA levels showed an early response with the maximal increase at 6 hours. The effects of follistatin, an activin binding protein, with and without the concomitant presence of activin-A, were also examined. Follistatin had no effect on ActRI mRNA levels in the absence of activin- A. Co-treatment of activin-A and follistatin demonstrated the blocking effect of follistatin on activin-A with dose dependent manner. This study provides evidence for the first time that activin-A and follistatin modulate the ActRI mRNA levels in an autocrine/paracrine manner in human placental trophoblast cells.

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