Role of estrogen in regulation of cellular differentiation: A study using human placental and rat Leydig cells

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Abstract

Estrogen classically is recognized as a growth-promoting hormone. Recent evidence suggests that estrogens are also involved in a wide variety of cellular and physiological functions involving the central nervous system, immune system, cardiovascular system and bone homeostasis. Our studies in cytotrophoblasts and BeWo cells, demonstrated that 17β-estradiol induces terminal differentiation of placental trophoblasts directly and this differentiation is coupled with an increased production of TGFβ1, which, in turn, affects telomerase activity and telomerase associated components at the level of hTERT. Furthermore, using rats treated in vivo with either EDS or estradiol and in vitro Leydig cell cultures, we proposed that 17β-estradiol mediated down-regulation of collagen IV α4 expression could be one of the possible mechanisms for the inhibition of progenitor Leydig cell proliferation. In this review, we summarize the results from both the model systems, the human placental cytotrophoblast and rat Leydig cells to conclude that 17β-estradiol has a unique stage-specific role in differentiation.

Introduction

Traditionally, estrogen is considered to be a mitogenic hormone, and several cancers in human females are estrogen dependent. Thus, anti-estrogens have found a place in therapy for cancer. It is known that exposure to estrogens can influence the risk of cancer in the main target organs, breast, endometrium and ovary, during different phases of a woman's life (Persson, 2000). In men, estrogen is considered as one of the hormonal risk factors in the development of benign prostatic hyperplasia and prostate cancer although the evidence for the possible role of estrogen in prostate cancer has come largely from epidemiological and experimental studies (Harkonen and Makela, 2004). Recent evidence suggests that, in addition to the traditional role of estrogen in tumorogenesis, estrogens are also involved in a wide variety of cellular and physiological functions, involving the central nervous system (Korol, 2004, Li and Shen, 2005), immune system (Lang, 2004), cardiovascular system (Zhu et al., 2004) and bone homeostasis (Gennari et al., 2005).

Recently, we proposed that E2, classically recognized as a growth-promoting hormone, has a distinct, novel role in human trophoblastic differentiation (Rama et al., 2004). Similarly, we hypothesized a role for 17β-estradiol-mediated down-regulation of Col IV α4 expression could be one of the possible mechanisms for inhibition of progenitor Leydig cell proliferation (Anbalagan and Rao, 2004). In this review, we summarize the results from both model systems, the placental cytotrophoblast and Leydig cells, which permit us to conclude that 17β-estradiol has a very unique role in differentiation, in a stage-specific fashion.

Section snippets

Estrogens and female reproduction

Placentation is the pinnacle of reproductive evolution and a great evolutionary pressure favors hemochorial placenta (Carter and Enders, 2004), where the trophoblasts are in direct contact with maternal blood, as in humans. Two distinct pathways of differentiation lead to the formation of two distinct trophoblastic cells: the extravillous trophoblast which is engaged in remodeling the endometrium during pregnancy, its vasculature and the villous syncytiotrophoblast which is involved in

E2-induced terminal differentiation in placental trophoblast and BeWo cell lines

With a view to elucidate the mechanism of action of 17β-estradiol during placentation, we employed two in vitro model systems. In the first model, cytotrophoblasts isolated from human term placentae were allowed to spontaneously differentiate in DMEM-HG containing 20% FCS. In the second model system, BeWo human choriocarcinoma cells were induced to differentiate following addition of either 10 μM Forskolin (Rama and Rao, 2001) or 10 ng/ml recombinant human TGFβ1 (Rama et al., 2003) or 10 μM E2 (

E2 governs TGFβ1 expression in differentiating trophoblastic cells

A significant increase in TGFβ1 at the transcriptional level, with a parallel increase in TGFβ1 protein level, was observed in BeWo cells treated with 10 μM E2. This suggests that E2-induced trophoblastic differentiation is coupled with increased production of TGFβ1. At this juncture, it is interesting to recall our earlier observations that TGFβ1, on its own, can bring about terminal differentiation in these cells (Rama et al., 2001, Rama et al., 2003). Therefore, it was important to determine

Effects of TGFβ1 on telomerase activity and telomerase associated components

In TGFβ1-treated (10 ng/ml) BeWo choriocarcinoma cells a decrease in telomerase (TR) activity and a decrease in expression of only hTERT along with cellular differentiation were noted. These results confirm the observations that correlate down-regulation of TR with cell differentiation (Koyanagi et al., 2000, Yu et al., 2004). Further, TGFβ1 down-regulates expression of hTERT at the mRNA level (Rama et al., 2001). TGFβ1-induced suppression of hTERT gene expression could represent an important

E2 regulates cell cycle proteins during placental differentiation

Human trophoblastic BeWo cells cultured in the presence of 10 μM 17β-estradiol for 72–96 h had a significant loss in transcript levels of Cyclin A2 in addition to an appreciable down-regulation in the level of protein expression of Cyclin E. There are two known isoforms of Cyclin E, 52 kDa and 50 kDa in size (McKenzie et al., 1998). Though human trophoblastic cells were found to predominantly express the larger isoform (i.e. the 52 kDa protein), we could find that both isoforms are down-regulated by

Estrogens and male reproduction

The role of estrogen and ER in male reproduction has been of interest since the production of estrogen was first reported in the male reproductive system by Staffieri et al. (1965). Estrogens are produced by male gonads and accessory reproductive tissues, and the presence of ERα and ERβ has been described in testis, prostate, efferent ducts and penis (Bodker et al., 1999, Makela et al., 2000, Salmi et al., 2001, Dietrich et al., 2004). Male mice lacking estrogen receptor-α, i.e. ERKO mice, are

Leydig cells and estrogen

Synthesis of steroid hormones and production of spermatozoa are two essential functions of the mammalian testis. Normal testicular development and maintenance of spermatogenesis are controlled by gonadotrophins and testosterone whose effects are modulated by locally produced factors, including estrogens (Carreau et al., 2003). While testis is a target organ for the actions of estrogens, they have a dramatic influence, usually inhibitory, on Leydig cell function (Abney, 1999). However, the

Acknowledgements

The authors wish to thank Council of Scientific and Industrial Research, Department of Science and Technology, Department of Biotechnology, Indian Council of Medical Research, Govt. of India, and Mellon and CONRAD Foundation, USA, for financial assistance. One of the authors (A. Jagannadha Rao) is thankful to Council of Scientific and Industrial Research, Govt. of India, for award of Council of Scientific and Industrial Research Emeritus Scientist Fellowship.

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