Inhibin subunits, follistatin and activin receptors in the human teratocarcinoma cell line Tera-2

TGFβ Family Signaling Pathways in Pluripotent and Teratocarcinoma Stem Cells' Fate Decisions: Balancing Between Self-Renewal, Differentiation, and Cancer

The transforming growth factor-β (TGFβ) family factors induce pleiotropic effects and are involved in the regulation of most normal and pathological cellular processes. The activity of different branches of the TGFβ family signaling pathways and their interplay with other signaling pathways govern the fine regulation of the self-renewal, differentiation onset and specialization of pluripotent stem cells in various cell derivatives. TGFβ family signaling pathways play a pivotal role in balancing basic cellular processes in pluripotent stem cells and their derivatives, although disturbances in their genome integrity induce the rearrangements of signaling pathways and lead to functional impairments and malignant transformation into cancer stem cells. Therefore, the identification of critical nodes and targets in the regulatory cascades of TGFβ family factors and other signaling pathways, and analysis of the rearrangements of the signal regulatory network during stem cell state transitions and interconversions, are key issues for understanding the fundamental mechanisms of both stem cell biology and cancer initiation and progression, as well as for clinical applications. This review summarizes recent advances in our understanding of TGFβ family functions in naїve and primed pluripotent stem cells and discusses how these pathways are involved in perturbations in the signaling network of malignant teratocarcinoma stem cells with impaired differentiation potential.

Regulation of endometrial adenocarcinoma cell proliferation by Activin-A and its modulation by 17beta-estradiol

A role for activins in regulating cellular transformation is suggested by the alpha-inhibin knockout mouse in which development of gonadal tumors is associated with elevated activin levels. It was the purpose of the current study to determine whether activin had similar actions on endometrial cell lines, specifically on a well differentiated estrogen-responsive endometrial adenocarcinoma cell line (ISH) and estrogen-unresponsive cells (HEC-50) obtained from a poorly differentiated endometrial adenocarcinoma. Activin was secreted by both adenocarcinoma cell lines. Using reverse transcription-PCR, messenger RNA type I and type II activin receptor subtypes were detected in both cell lines: expression of IB and IIB was approximately three- to fourfold greater in ISH cells than in HEC-50 cells, while activin receptor IA and IIA messenger RNA levels were approximately equal in both cell lines. Activin treatment (30-300 ng/ml) caused a dose- and time-dependent inhibition of ISH cells proliferation and resulted in a significant decrease in Bcl-2 protein and mRNA levels. No difference was observed in Bax expression. There was no significant effect of activin when the cultures of ISH cells were exposed to 17beta-estradiol. In contrast, activin showed a weak, but significant, mitogenic effect on HEC-50 cells without modifications in Bax and Bcl-2 mRNA and protein levels. The results demonstrate that activin is a regulator of endometrial cancer cell growth. 17beta-Estradiol may promote resistance of estrogen-responsive endometrial cancer cells to the growth-retarding effects of activin and one of the mechanisms might be a down-regulation of the activin receptors.

Regulation of cell proliferation, apoptosis, and carcinogenesis by activin

The aim of this review is to provide insight into the molecular mechanisms by which activin A modulates cell proliferation, apoptosis, and carcinogenesis in vitro and in vivo. Activin A, a member of the TGFbeta superfamily, has various effects on diverse biological systems, including cell growth inhibition in many cell types. However, the mechanism(s) by which activin exerts its inhibitory effects are not yet understood. This review highlights activin's effects on activin receptors and signaling pathway, modulation of activin signaling, and regulation of cell proliferation and apoptosis by activin. Based on the experiences of all the authors, we emphasized cell cycle inhibitors such as p16 and p21 and regulators of apoptosis such as p53 and members of the bcl-2 family. Aside from activin's inhibition of cell proliferation and enhancement of apoptosis, other newly developed methods for molecular studies of apoptosis by activin were briefly presented that support the role of activin as an inhibitor of carcinogenesis and cancer progression. These methods include subtractive hybridization based on covalent bonding, a simple and accurate means to determine molecular profile of as few as 20 cells based on an RNA-PCR approach, and a messenger RNA-antisense DNA interference phenomenon (D-RNAi), resulting in a long-term gene knockout effects.

Teratocarcinomas and human embryology: pluripotent human EC cell lines. Review article

The histogenesis of germ cell tumours (GCT) reflects the normal processes of gametogenesis, fertilisation and subsequent embryonic cell differentiation. Understanding the mechanisms that control the differentiation of embryonal carcinoma (EC) cells into a variety of embryonic and extraembryonic cell types is pertinent to understanding the progression of GCT. EC cells also provide a tool for analysing the mechanisms that control differentiation during embryonic development, and particularly the mechanisms that control differentiation along alternative cell line, NTERA2, into neurones and other cell types in response to agents such as retinoic acid, HMBA and the bone morphogenetic proteins. We have also compared the pluripotent NTERA2 EC cells with other human EC cell lines that exhibit a much reduced capacity for cell differentiation. A variety of genes are activated during NTERA2 differentiation. In particular we have identified a novel human member of the wnt family. This wnt gene is activated following retinoic acid induction of differentiation but is later down-regulated as the cells mature into neurones and other cell types. We have also observed expression of genes belonging to the Frizzled family, which is likely to include genes encoding receptors for the wnt gene products. Thus in the NTERA2 system, genes pertinent to regulating cell differentiation during embryonic development are activated and appear to play a role in modulating how these pluripotent human EC cells differentiate.

Human testicular germ cell tumours express inhibin subunits, activin receptors and follistatin mRNAs

Germ cell development is influenced by activin and inhibin, which are produced by Sertoli cells. Activin also affects differentiation of mouse embryonal carcinoma cells, which, to a certain extent, resemble the embryonal carcinoma component of germ cell tumours. Therefore, the expression of inhibin/activin subunits, of activin receptors and of the activin-binding protein follistatin was studied in testicular germ cell tumours, using RNAase protection assays. Testicular germ cell tumours of adolescents and adults (TGCTs) and spermatocytic seminomas expressed activin type I and type II receptors (ActRI and ActRII respectively). Seminomas expressed significantly lower levels of ActRIIA (P<0.05, Mann-Whitney U-test) and higher levels of ActRIA (P<0.05) and ActRIB (P<0.05) compared with non-seminomas. All tumours expressed inhibin beta-subunit transcripts, which are a prerequisite for activin synthesis. Non-seminomas contained significantly higher levels of the inhibin betaA subunit (P<0.001) compared with seminomas. No activin betaC subunit transcripts could be demonstrated by RNAase protection. Inhibin alpha-subunit expression was absent in the spermatocytic seminomas, in six out of nine seminomas and in 10 out of 11 non-seminomas. Follistatin was expressed predominantly in non-seminomas and spermatocytic seminomas. This expression of activin type I and type II receptors in combination with expression of inhibin beta-subunits indicates that activin may act as a para- or autocrine factor in the regulation of growth and differentiation of tumours of human germ cells.