Hormonal regulation of proliferation in two populations of rabbit endometrial cells in culture

Histological and ultrastructural regulation in rabbit endometrial explants by estrogen in serum-free culture

A repertoire of hormonal signals including estrogen regulate the growth, differentiation, and functioning of diverse target tissues, including the ovary, the mammary gland, and skeletal tissue. A serum-free culture system derived from rabbit endometrium explants has been devised and is reported here to explore estrogen action in vitro. The system involves aseptically harvesting the uterus from a virgin rabbit, dissecting the endometrium, explanting it into 1- to 2-mm(3) pieces weighing approximately 1-2 mg each, and incubating these pieces in serum-free Medium-199. The culture is carried out for a period of 4 d in a humidified CO(2) incubator at 37 degrees C with 5% CO(2). The effect of extraneously added estrogen (1 microg/ml) was investigated by histological and ultrastructural procedures. It was observed that estrogen could induce specific changes, such as abundant mitochondria, rough endoplasmic reticulum, golgi complex, and intracellular collagen deposition, in both the epithelial and the fibroblast cell components of the explanted tissue. The study, therefore, indicates that the proposed system is an ideal tool for exploring and demonstrating estrogen responsiveness under in vitro conditions.

Progesterone therapy for endometrial carcinoma reduces cell proliferation but does not alter apoptosis

BACKGROUND

Although the anticancer effects of progesterone therapy for patients with endometrial carcinoma are widely acknowledged, a detailed assessment of the resultant morphologic alterations in tumor tissue kinetics has hitherto been lacking.

METHODS

Biopsy and hysterectomy specimens of 14 endometrial carcinomas (endometrioid-type) before and during progesterone therapy were studied to clarify changes in apoptosis and cell proliferation and their relation to morphologic alterations. The extent of squamous differentiation within tumor lesions was also examined.

RESULTS

In the good-response group, tumor cells took on characteristics of normal endometrial gland cells in the secretory phase. A positive correlation between reduction in the mitotic index and the degree of morphologic alterations during hormone therapy was observed, but the frequency of apoptotic cells did not vary. In both the good-response and poor-response groups, development or enlargement of squamous areas was observed, in comparison with the initial biopsy specimens.

CONCLUSIONS

These results suggest that prolonged progesterone administration can suppress cell proliferation in endometrial carcinomas through tumor cell differentiation without altering apoptosis, resulting in a shift in tissue kinetics toward a relative predominance of cell deletion. In addition, increases in the occurrence of squamous areas within tumors do not always appear to be related to treatment efficacy.

Cell cycle expression of estrogen receptors determined by image analysis on human breast cancer cells in vitro and in vivo

We have investigated, by image analysis, the cell cycle expression of estrogen receptors (ER) on MCF-7 cell line and on MCF-7 xenografts. The results demonstrate, in vitro as well as in vivo, an increase of ER concentration during the G0/G1-phase, followed by a decrease during the S-phase until the late S-phase where a rapid increase was noted. These results confirm that estrogens are involved in the DNA synthesis since ER is expressed in vivo at a maximal level in the late G1. In presence of saturating concentrations of 17 beta-estradiol, the mean ER concentration in G0/G1 phase is significantly decreased compared with the control cells cultured in estrogen-deprived medium. This indicates that 17 beta-estradiol down-regulates ER preferentially in the G0/G1 phase. These data suggest that ER in S and G2/M phases is unable to interact with its ligand. Consequently, estrogens may have no effects on the entry of cells in mitosis. Finally, after long-term tamoxifen treatment of MCF-7 xenografts, a tamoxifen-resistant tumor was developed which was characterized by a change in the profile of ER concentration during the G0/G1 phase. In conclusion, it is possible that the differences in cell cycle distribution of ER could be correlated with different phenotypes of breast cancer and also with different clinical phases of tumoral evolution. However, it remains to be known what is the clinical significance of the ER cell cycle expression in relation to tumor aggressiveness and survival.

Morphological and immunohistochemical differentiation patterns of rabbit uterine epithelium in vitro

We describe morphological and immunohistochemical changes of uterine epithelium from immature rabbits in vitro in response to hormonal treatments, using a matrix-coated semipermeable filter. These investigations were compared to in vivo studies of uterine epithelium from immature rabbits treated with estrogen and/or progesterone. In vitro, polarization of the epithelium seems to be best developed under progesterone dominance, and the pattern of cell organelles is similar to those seen in vivo. Two types of apical protrusions could be observed in cultures treated with progesterone, some shaped like domes, containing cell organelles, and some irregular in shape with small lucent vesicles. Both types of apical differentiation are typical for the in vivo situation. In vitro, estrogen leads to a more pseudostratified growth pattern of the cells. They develop apical protrusions with big vesicles probably containing mucin, as in vivo. Treatment with both steroid hormones leads to a heterogeneous response of the uterine epithelial cells in culture, some cells responding more to the estrogen, others to the progesterone whereas in vivo the progesterone-dominant features are obvious. Immunohistochemistry of uteroglobin in monensin-treated cultures gives evidence for uteroglobin secretion in all cultures, but to a lesser extent in the untreated, and this is strongly increased in cultures treated with estrogen and progesterone. These results correspond to observations made in vivo. This in vitro cell culture method seems therefore to provide a useful model for investigating the regulatory mechanisms of sexual steroid hormones and the cell biology of uterine receptivity.

Growth factors in the uterus: steroidal regulation and biological actions

Rapid progress has been made within the last 5-6 years in characterizing polypeptide growth factors in uterine tissues and fluids. There is convincing evidence that their synthesis and/or secretion is regulated by steroid hormones. The possibility that these growth factors play a central role in growth and development of the uterus or placenta is suggested by the presence of their receptors on uterine or placental cells and their stimulatory effects on these cells in vitro. Since growth factors interact synergistically and also have non-mitogenic functions, the presence of a variety of these factors in the uterus suggests that they probably regulate various aspects of uterine function through complex autocrine and paracine pathways. However, experimental models need to be designed that will permit a more detailed analysis of the actual role of these factors in utero. Fruitful approaches may be to administer neutralizing antibodies or blocking peptides so as to antagonize uterine growth factor action, or to develop appropriate transgenic animals. These and other lines of study should help us to understand the role of growth factors in development of the immature uterus, growth of the placenta or gravid uterus, repair and angiogenesis of the endometrium, and uterine pathology.

Proliferation and differentiation of mouse uterine epithelial cells in primary serum-free culture: estradiol-17 beta suppresses uterine epithelial proliferation cultured on a basement membrane-like substratum

The effects of different substrata and estradiol-17 beta (E2) on proliferation and differentiation of mouse uterine epithelial cells was examined in a serum-free primary culture system. When cultured on rat-tail collagen gels, the epithelial cells rapidly increased in number to form a simple squamous cell layer that exhibited a relatively undifferentiated state (a few short microvilli, no secretory granules, and poorly developed endoplasmic reticulum). Addition of E2 into the culture medium did not affect the proliferation of epithelial cells on collagen gel. Uterine epithelial cells grown on a reconstituted basement membrane-like substratum (Matrigel) formed a simple columnar/cuboidal cell layer exhibiting fully developed characteristics (many long microvilli, many secretory granules, and fully developed endoplasmic reticulum). Examination of epithelial proliferation by counting substratum-attached cell number revealed only a slow increase in cell growth on Matrigel, and E2 did not significantly affect it. However, measurement of proliferating cells by labeling cells with 5-bromo-2'-deoxyuridine revealed that cells on Matrigel were replicating and that E2 (10(-7) to 10(-11) M) actually significantly suppressed epithelial proliferation. However, there was not an effect of E2 on total cell number, indicating that the cells in control medium replicate faster and detach more readily from the substratum than those in E2-supplemented medium on Matrigel. Thus, it is probable that E2 significantly reduces the rate of cell detachment from the substratum, which may mimic the in vivo condition where significant decrease in apoptosis or cell death is induced by E2.

Rabbit endometrium in organ culture: morphological evidence for progestational differentiation in vitro

This communication describes conditions for long-term organotypic culture of rabbit endometrium allowing progesterone-induced transformation, as typical for early pregnancy, to continue in vitro. This system appears to compare favorably with in vitro models so far proposed for the study of hormonal control of uterine function or for the investigation of cell-biological aspects of embryo implantation. The specific aim in the presented system is to provide approximate normal epithelium-stroma interrelationships. Fragments of endometrium consisting of epithelium and stroma were obtained during early pseudopregnancy and cultured on a gyratory shaker. Morphology was investigated by light microscopy, transmission and scanning electron microscopy. During the first two days the epithelium grows over the exposed stroma regenerating a complete epithelial lining. No central necrosis is found in the stroma for up to 6 days, and the tissue keeps its organotypic architecture although certain morphological differences can be observed between regenerated versus original epithelium. In the regenerating portion a stage-specific cell differentiation and the reformation of a basal lamina are missing. Progesterone substitution preserves cell morphology and allows to maintain, in vitro, the stage-specific pattern of cell organelles. Most characteristic is the induction of extensive fusion of epithelial cells. These large symplasms are comparable in size and structure to those formed in pregnancy in the implantation chamber in vivo. Only the superficial parts of the original (not the regenerated) epithelium are capable of progesterone-induced large-scale fusion. This organotypical culture system appears to be of potential value for in vitro studies on hormone action and on endometrial receptivity for embryo implantation.

Effect of phorbol ester on prostaglandin regulation of proliferation in rabbit endometrial cells

We have proposed that two of the endogenously synthesized endometrial prostaglandins, prostaglandin F2 alpha (PGF2 alpha) and prostaglandin E1 (PGE1), play a regulatory role in growth control of the endometrium. PGF2 alpha increases DNA synthesis and PGE1 inhibits that effect. Primary cultures of rabbit endometrial cells were used here to examine the effects of the tumor-promoting, diacylglycerol mimicking, phorbol ester, 12-O-tetradecanoyl phorbol-13-acetate (TPA), on the prostaglandin control of cell proliferation. TPA treatment of these cultures results in: a decrease in control levels of proliferation and complete inhibition by TPA of PGF2 alpha stimulated DNA synthesis; a reduction in [3H]PGF2 alpha binding with short term treatment but an increase to above control binding level with long term treatment; an inhibition of the normal PGF2 alpha stimulated inositol polyphosphate synthesis; and a small increase in accumulation of PGF2 alpha in the culture media. Furthermore, in this culture system, TPA does not down regulate [3H]PGE1 binding; it does not alter the normal PGE1 stimulation of cAMP synthesis; and it has no effect on the normal endogenous PGE1 synthesis by these cultures. The above results are consistent with our previous observations that PGF2 alpha works through the intracellular messengers inositol polyphosphate/diacylglycerol whereas PGE1 works through cAMP.

A role for prostaglandins in estrogen growth regulation

Several lines of evidence support the theory that estrogen increases prostaglandin F2 alpha (PGF2 alpha) receptor number and amplifies the intracellular response to the uterine mitogen, PGF2 alpha, in primary cultures of rabbit endometrium. It is proposed here that estrogen induction of growth in target tissues may be mediated through prostaglandins. Determination of prostaglandin receptor status and prostaglandin levels in estrogen dependent tumors could be of importance as diagnostic tools. The use of prostaglandin synthesis inhibitors and/or antagonists in the therapy of these tumors should be considered.

Requirement for prostaglandin F2 alpha in 17 beta-estradiol stimulation of DNA synthesis in rabbit endometrial cultures

We have hypothesized that two of the endogenously synthesized endometrial prostaglandins (PGs), prostaglandin F2 alpha (PGF2 alpha), and prostaglandin E1 (PGE1), play a regulatory role in growth control of the rabbit endometrium. PGF2 alpha increases DNA synthesis and PGE1 inhibits that effect. Primary cultures of rabbit endometrial cells were used to examine the possible role of these PGs in the mechanism of action of 17 beta-estradiol on DNA synthesis. Towards this end, binding, second messenger and DNA synthesis experiments were performed. 17 beta-estradiol stimulation resulted in a time dependent (optimal: approximately 6 h) and 17 beta-estradiol concentration dependent (optimal: approximately 10(-7) M 17 beta-estradiol in phenol red-containing medium) increase in [3H]PGF2 alpha binding. Scatchard type analysis of the binding data revealed an increase in receptor number while the receptor affinity for [3H]PGF2 alpha remained the same as in the control treated cultures. This 17 beta-estradiol stimulated increase in PGF2 alpha receptor allowed a suboptimal concentration of PGF2 alpha (10(-9) M) to increase intracellular levels of inositol polyphosphates, while by itself this concentration of PGF2 alpha caused no significant change in intracellular inositol polyphosphate levels. 17 beta-estradiol, alone among the several studied steroid hormones, could increase [3H]PGF2 alpha binding. Proliferation studies revealed that, in these primary cultures of rabbit endometrium, 17 beta-estradiol could increase DNA synthesis but not in the presence of indomethacin, unless PGF2 alpha was added to the medium at a concentration (10(-10) M) near or above what is normally accumulated in the medium by these cultures. In the absence of 17 beta-estradiol stimulation, addition of these same low concentrations of PGF2 alpha had no effect on DNA synthesis. Apparently, through its effect on the PGF2 alpha receptor, 17 beta-estradiol enhances the PGF2 alpha stimulated DNA synthesis response approximately 100 fold. The DNA synthesis induced by 17 beta-estradiol can be inhibited by PGE1, as can PGF2 alpha-induced DNA synthesis. We propose that 17 beta-estradiol may be mediating its mitogenic effect through an alteration of the prostaglandin agonist:antagonist control of proliferation in rabbit endometrial cultures. In addition we suggest that, if 17 beta-estradiol acts to increase PGF2 alpha, receptors as part of its mode of action, this may be of importance in other tissues possessing both prostaglandin and 17 beta-estradiol receptors.

Regulation of inositol phosphate levels by prostaglandins in cultured endometrial cells

Stimulation of cultured rabbit endometrial cells by one of the rabbit endometrial cell culture proliferation factors, prostaglandin F2 alpha (PGF2 alpha), resulted in a very rapid increase in the intracellular levels of [3H]-inositol triphosphate (IP3), [3H]-inositol biphosphate (IP2), and [3H]-inositol monophosphate (IP1) in cells prelabeled with [3H]-inositol. These increases in inositol phosphate levels were detected in periods of stimulation as short as 30 seconds, reached a maximum by 1 1/2-2 min and declined to control levels by 6-10 min. The stimulation was dose-dependent with maximal increases observed near 10(-6) M PGF2 alpha. The cholinergic agent, carbachol, also led to time and dose-independent increases in IP3. Lithium, cadmium, silver, copper, and zinc ions had no effect either on the breakdown of IP3 or on the accumulation of IP1. In contrast, vanadate at 10(-6) or 10(-5) M did lead to a decrease in the breakdown of IP1 and a concomitant increase in IP1, IP2, and IP3. PGF2 alpha was found previously to induce an increase in rabbit endometrial cell DNA synthesis which was inhibited by concomitant or prior addition of prostaglandin E1 (PGE1). PGE1, in a dose-dependent manner, was found to inhibit the observed IP3 increase by PGF2 alpha at 1 1/2 min of stimulation. PGF2 alpha treated and control cultures did not differ in cAMP or cGMP levels, cellular 45Ca uptake, nor cellular 22Na uptake. We propose that IP3 may be one of the intracellular messenger(s) synthesized following the treatment of rabbit endometrial cell cultures with the proliferation agent PGF2 alpha and that it may play a crucial role with cAMP in growth regulation.

Evidence for soluble factors regulating cell death and cell proliferation in primary cultures of rabbit endometrial cells grown on collagen

Primary cultures of rabbit endometrial cells grown on collagen substrates exhibit cyclic changes in DNA content throughout extended periods of culture. These cycles are characterized by periods of significant increases and decreases in the DNA content of the cultures or number of cells present, yet through the entire duration of culture there is no net change in the total DNA. The rates of cell proliferation and cell death change through time in culture with the same periodicity as the changes in DNA. Neither changes in the rate of cell proliferation nor the rate of cell death alone are sufficient to account for the changes in DNA. Rather, there appears to be a feedback mechanism operating between cell proliferation and cell death such that when one increases, the other increases concomitantly in order to maintain a homeostasis in total culture mass. This homeostasis appears to be mediated by a soluble cell proliferation factor (CPF) and a cell death factor (CDF) produced by the cells. CPF and CDF may be obtained from either conditioned media or cultured cell extracts. These biological activities are heat and trypsin sensitive. The major mode of cell death in these cultures appears to be apoptosis or programmed cell death, characteristic of renewing epithelia. The data suggest that this tissue culture model system represents a renewing cell population containing stem cells and their progeny, whose total growth is strictly regulated by CPF and CDF. As such, it provides a model system in which to study homeostasis and how it may be altered in hyperplasia and neoplasia, as well as its regulation by hormones.

Prostaglandin F2 alpha and E1 regulation of proliferation in primary cultures of rabbit endometrial cells

The study of growth of endometrial cells is of importance in reproductive biology. Several factors and hormones are thought to play important roles in the control of growth. Prostaglandin F2 alpha (PGF2 alpha) causes an increase in both tritiated thymidine ([3H]Tdr) incorporation into DNA and in the cell number of primary cultures of rabbit endometrial cells cultured in a serum-free, chemically defined media. Prostaglandins F1 alpha, E1, E2, A2, and B2 and arachidonic acid (all tested at 10(-7) M) do not affect [3H]Tdr incorporation as compared to control cultures. The increase in [3H]Tdr incorporation into DNA in response to PGF2 alpha stimulation is concentration-dependent (optimal approximately 3 X 10(-7) M) and is seen starting approximately 9 hr poststimulation. Both prostaglandin E1 (PGE1) and prostaglandin E2 (PGE2), but not PGs F1 alpha, I2, A2, B2, their parent molecules, or related molecules, antagonize and can completely block the PGF2 alpha-induced increase in [3H]Tdr incorporation into DNA. This antagonism is seen both when the cells are pretreated with PGE1 prior to the PGF2 alpha stimulation and when the cells are exposed to both PGE1 and PGF2 alpha simultaneously. Exogenously added 8-Br-cAMP mimics the PGE1 antagonism of PGF2 alpha. The PGF2 alpha-induced increase in [3H]Tdr incorporation is not synergistic, antagonistic, or additive with the [3H]Tdr incorporation increase in response to either estradiol-17 beta or epidermal growth factor. The specific effect of PGF2 alpha on primary culture endometrial cell growth and its antagonism by PGE1, PGE2, and 8-Br-cAMP are new findings.

Binding and second messengers of prostaglandins F2 alpha and E1 in primary cultures of rabbit endometrial cells

Several factors and hormones are thought to play a role in the growth control of endometrial cells. We have shown that prostaglandin F2 alpha (PGF2 alpha) is a growth factor for primary cultures of rabbit endometrial cells grown in serum-free, chemically defined medium and that prostaglandin E1 (PGE1) antagonizes the PGF2 alpha induction of growth (Orlicky et al., 1986). [3H]PGF2 alpha binds to whole cells in a time (optimal approximately 30 min)- and temperature-dependent (optimal 37 degrees C), disassociable (90% disassociable within 30 min), saturable (Kd1 = 4.9 X 10(-8) M, n1 = 1.2 X 10(5) molecules/cell; Kd2 = 2.6 X 10(-7) M, n2 = 3.0 X 10(5) molecules/cell), and specific manner. [3H]PGE1 binds in a time-dependent (optimal 25 min), disassociable (90% disassociable within 10 min), saturable (Kd = 6.4 X 10(-8) M, n = 1.2 X 10(5) molecules/cell), and specific manner. This specific binding of [3H]PGF2 alpha and [3H]PGE1 is down-regulatable by prior treatment of the cultures with unlabeled ligand, and up-regulatable by prior treatment of the cultures with indomethacin to inhibit endogenous PG synthesis. Proteolytic enzyme treatment for 2 min reduces the specific binding of PGF2 alpha by 75%. PGE1 stimulates intracellular cAMP synthesis and accumulation in a time (optimal 10 min)- and concentration (half-maximal stimulation at 10(-6) M)-dependent manner but has no effect on intracellular cGMP. PGF2 alpha has no effect on either intracellular cAMP or cGMP in this system. We describe here for the first time the analysis at a biochemical level of the interaction between two prostaglandins, antagonistic to each other in terms of growth regulation.

Regulation of cultured rat vaginal epithelial cells by 17 beta-estradiol and progesterone

We have previously described a technique to obtain short-term cultures of epithelial cells from Wistar rat vaginae. In order to improve the efficiency and life span of these cultures, in the present study we have cultured the vaginal cells with lethally irradiated 3T3 cell feeder layers. Under this condition, cells can grow for several weeks while retaining epithelial characteristics and can eventually be subcultured. The proliferative effect of the ovarian hormones in these cultures was studied using two different approaches, [Methyl-3H]Thymidine (3HTdr) incorporation and increase in cell number. Both assays indicated a proliferative effect of 17 beta-estradiol and progesterone at physiological concentrations. This proliferative effect was also shown in feeder layer-free cultures, ruling out an indirect effect through the mesodermal cells. The capacity of the hormones to modify terminal differentiation in the culture was also studied, using colony stratification as an indicator of differentiation. Progesterone and fetal calf serum had an inhibitory effect on terminal differentiation, whereas 17 beta-estradiol induced a stimulatory action. This culture model allowed us to show a direct effect of the ovarian hormones on vaginal cells in vitro and seems to be a useful model to study hormone-cell interactions in vitro.

Induction of DNA synthesis in cultured rabbit uterine cells by estradiol and inhibition of the estrogen response

Addition of 17 beta-estradiol to primary cultures of rabbit uterine cells resulted in the induction of DNA synthesis. This phenomenon is present only in cells cultured at low density. Culture medium taken from high density cultures inhibited it, suggesting that those cells produce a soluble estrogen-inhibiting factor.

A developmental view of endometrial hyperplasia and carcinoma based on experimental research

On the basis of experimental research, using rabbit uterine epithelium as a model, it is postulated that human endometrial hyperplasia or carcinoma may be due to derangement of intrinsic growth mechanisms such as cell proliferation, migration, loss and differentiation. Ovarian hormones, estrogen inhibitor or amplifying factors, prostaglandins, stroma-epithelial interactions, proteolytic activity and hormone receptors, all regulate the described intrinsic growth mechanisms, and their excess or lack could result in altered growth patterns. It is also proposed that different types of endometrial carcinoma could result from neoplastic transformation of cells at different stages of differentiation. Since cells at those stages could respond to various hormones in different ways, it would seem of therapeutic value to know the cell of origin in each type of endometrial carcinoma.

Decrease of estrogen receptors induced by 17 beta-estradiol and progesterone in cultured rabbit endometrial cells

A whole cell technique to measure estradiol receptors in cultured rabbit endometrial cells is described. The estradiol receptors measured appear to be composed of at least two components: one component has high affinity but low capacity, while the other component has low affinity but high capacity. Using the assay, the effects of estradiol and progesterone pretreatment were examined on the estradiol receptor levels. It was found that both of the hormones decreased the number of estrogen receptors in the cultured cells. The finding that estradiol decreased its own receptors was unexpected and its possible relevance is discussed.