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Department of Obstetrics and Gynecology, University of British Columbia, Vancouver, British Columbia, Canada V6H 3V5
Address all correspondence and requests for reprints to: Peter C. K. Leung, Ph.D., Department of Obstetrics and Gynecology, University of British Columbia, 2H-30, 4490 Oak Street, Vancouver, British Columbia, Canada V6H 3V5. E-mail: peleung{at}interchange.ubc.ca
In the present study, we investigated the expression of estrogen
receptors (ER
and ERß) in human ovarian surface epithelial (hOSE)
cells and the ovarian cancer cell line, OVCAR-3, and provided novel
evidence that estrogen may have a growth regulatory effect in these
cells. Expression levels of ER
messenger RNA (mRNA) were 1.5-fold
higher in OVCAR-3 cells than in hOSE cells, as revealed by
semiquantitative RT-PCR and Southern blot analysis. A significant
increase (3.3-fold) in ERß mRNA levels was observed in OVCAR-3 cells
compared with hOSE cells. In parallel with mRNA levels, expression
levels of ER
and ERß proteins were also higher in OVCAR-3 cells
compared with hOSE cells. We recently proposed that GnRH and its
receptor may have an autocrine role in hOSE and ovarian cancer cells.
To determine whether estrogen regulates GnRH and GnRH receptor (GnRHR),
hOSE and OVCAR-3 cells were treated with various concentrations of
17ß-estradiol for 24 h. Expression levels of GnRH and GnRHR mRNA
were examined using quantitative and competitive RT-PCR, respectively.
Treatment with 17ß-estradiol induced a significant down-regulation of
GnRH mRNA in OVCAR-3 cells, but not in hOSE cells and of GnRHR mRNA in
both hOSE and OVCAR-3 cells. Tamoxifen, an estrogen antagonist,
prevented the effects of 17ßestradiol, suggesting that estradiol
action is mediated via the ER. Finally, the effect of estrogen on the
growth of hOSE and OVCAR-3 cells was investigated. The cells were
treated with various concentrations of 17ß-estradiol, and the
proliferative index of cells was measured using
[3H]thymidine incorporation and DNA fluorometric assays.
17ß-Estradiol stimulated the growth of OVCAR-3 cells in a dose- and
time-dependent manner. In contrast, 17ß-estradiol failed to stimulate
the growth of hOSE cells. As estrogen down-regulated GnRH and GnRHR
mRNA, we investigated whether estrogen treatment blocks the growth
inhibitory effect of a GnRH agonist in OVCAR-3 and hOSE cells. Cells
were treated with 17ß-estradiol (10-7
M) together with (D-Ala6)-GnRH
(10-7 M), and the proliferative
index of cells was measured. Pre- or cotreatment of cells with
17ß-estradiol significantly attenuated the growth inhibitory effect
of the GnRH agonist in OVCAR-3 cells, whereas no effect of
17ß-estradiol treatment was observed in hOSE cells. To our knowledge,
these results provide the first demonstration of a potential
interaction between the estradiol/ER and GnRH/GnRHR systems, which may
be important in the growth regulation of normal and neoplastic hOSE
cells.
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