Mode of Estrogen Action on Cell Proliferative Kinetics in CAMA-1 Cells. I. Effect of Serum and Estrogen

Abstract

Both serum and estrogen affect cell proliferation in CAMA-1 cells. Their effects on cell cycle kinetics are being investigated with partially synchronized cells following 48 hours of serum deprivation. By comparing the growth kinetics of synchronized (serum-deprived) cells with asynchronized (normal-fed) cells, we observed that there was a delay of cell proliferation for approximately 25 hr for synchronized cells and that estrogen only induced cell proliferation in serum-supplemented culture. A serum protein (RPF), precipitated by ammonium sulfate, dialyzed in 3,500 daltons cut off membrane and reconstituted in culture medium, was shown to stimulate cell proliferation in a dose-related manner. In the absence of RPF, estrogen had no effect on cell growth and S-phase formation in serum-free medium, but significantly induced cell growth in the presence of RPF. Experiments conducted with a synchronized cell population showed that estrogen increased the proportion of G1 phase cells to enter S phase, shortened the G1 phase duration, and ultimately increased the proportion of mitotic cells per cycle. Collectively, these results show that (a) estrogen effects of cell proliferation in vitro requires a serum component, a "G1/S-promoting factor" and (b) estrogen-induced tumor growth is a result of an accelerated rate of G1/S transition and an increased number of dividing cells per cycle. The knowledge of the interaction of estrogen with the G1/S promoting factor on cell growth is of both fundamental and therapeutic importance.

Mode of estrogen action on cell proliferation in CAMA‐1 cells: II. Sensitivity of G1 phase population

“…Estrogen-induced cell proliferation cannot take place without first allowing the cells at this stage to be exposed to E2. This finding confirms our previous report that, when CAMA-1 cells were arrested at the early G1 phase by serum deprivation [4], E2 elicited a stimulatory effort to early G1 phase cells, resulting in promoting more and faster exit of these cells to S phase. During serum deprivation, synchronized cells had a lengthy G1 phase.…”

“…During this phase, each cell undergoes a single random process with constant probability per unit time that takes it into the S phase. Results from this study and a previous report [4] that indicate that E2 shortens G1 duration and increases the Gl/S transition correspond well with this model; that is, E2 alters the probability of cells entering into DNA synthesis without an apparent effect on the rates of other periods of the cycle.…”

“…Such studies can best be achieved with synchronized populations. In this study and in a previous study [4], we have successfully demonstrated that the three methods of cell synchronization used for CAMA-1 cells, namely, dThd block at Gl/S boundary, nocodazole arrest at G2/M boundary, and serum deprivation at early G1 phase [4], are of particular value in monitoring E2 effects on the cell cycle kinetics and in testing the sensitivity of the different cell phases to estrogen stimulation or inhibition. Our result shows that the cell-proliferating property of E2 lies mainly in promoting GI to S phase transition, ie, shortening of the G1 duration, and causes more and faster turnover of E2-stimulated cells per cell cycle.…”

“…Employing an in vitro model with the human mammary adenocarcinoma cell line CAMA-1, we demonstrated that 170-estradiol (E2) stimulates cell proliferation in a dose-related manner [2,3]. The E2-induced cell growth requires the presence of serum [2,4]. We reported that E2 increases cell yield, shortens the population doubling time [2], and increases other biochemical parameters [5,6] in an asynchronous population.…”

Attenuation of Estrogen Receptor α (ERα) Signaling by Selenium in Breast Cancer Cells via Downregulation of ERα Gene Expression

“…What is demonstrated here for the first time in estrogen-dependent breast cancer cells is a novel component of the overall antiproliferative effect of MSA; the inhibition of ER signaling. Estrogens are important mitogenic signals for the growth of breast cancers, and have been shown to induce G 1 /S transition in breast cancer cells [25] by control of several key cellcycle regulators (for ref see [26]). In addition to inducing cellular proliferation, estrogens increase cell survival by upregulating the antiapoptotic factor bcl-2 [27] and downregulating several proapoptotic factors [28].…”