Further studies on the regulation of cultured rabbit endometrial cells by diethylstilbestrol and progesterone

Coordinated regulation of apoptosis and cell proliferation by transforming growth factor beta 1 in cultured uterine epithelial cells

Cell and tissue growth is regulated through a complex interplay of stimulatory and inhibitory signals. We describe two biological actions of transforming growth factor beta 1 (TGF-beta 1) in primary cultures of rabbit uterine epithelial cells: (i) inhibition of cell proliferation and (ii) a concomitant increase in cells undergoing apoptosis (programmed cell death). It is proposed that proliferation and apoptosis together comprise normal cell 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.

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.

Normal human endometrium in cell culture. I. Separation and characterization of epithelial and stromal components in vitro

Separation of human endometrium into its epithelial and stromal components has been achieved through collagenase digestion and has permitted a study of these two cell populations under specific experimental culture conditions. The stromal cell populations showed a progesterone response, were easily handled in culture, and displayed a limited in vitro life span typical of human diploid fibroblasts. In contrast, epithelium only survived in short-term primary culture and showed no clear hormone response. High-density epithelial cultures remained viable for longer periods in culture. Comparisons between resurfacing endometrial epithelial cells in vivo and epithelial cells migrating from explants in vitro suggested that this initial epithelial migration in vitro was the counterpart of the repair response in vivo.

Hormonal regulation of cultured rabbit endometrial cells

A technique for culturing primary explants of rabbit endometrial cells in chemically defined medium has been developed. Diethylstilbestrol and natural estrogens were found to increase the rate of DNA initiation while progesterone had the opposite effect. Ultrastructural studies revealed that with estrogens, the cultures had the appearance of rapidly dividing cells having large euchromatic nuclei and prominent nucleoli, with aboundant free ribosomes in the cytoplasm. On the other hand, progesterone induced the formation of large multinucleated cells and also converted the cells to a more secretory type. When the cultures appear secretory, a protein called blastokinin (uteroglobin) is believed secreted. We have found that cultured cells synthesize blastokinin and progesterone is necessary for its continuous synthesis. The cultures were found to have receptors for the ovarian hormones and these receptors exhibited saturation kinetics. The dissociation constants for the receptors were also determined. A hypothetical model for the hormonal regulation of cell proliferation and differentiation is proposed.