Document Detail

Oestradiol is a potent mitogen and modulator of GnRH signalling in alphaT3-1 cells: are these effects causally related?
MedLine Citation:
PMID:  10607935     Owner:  NLM     Status:  MEDLINE    
GnRH acts via phospholipase C (PLC) activating G-protein coupled receptors to stimulate secretion of gonadotrophins from gonadotrophs. These cells are also regulated by gonadal steroids, which act centrally to influence GnRH secretion, and peripherally to modulate GnRH action. We have shown that oestradiol can stimulate proliferation and modulate GnRH-stimulated [(3)H]inositol phosphate ([(3)H]IP(x)) accumulation (used as a measure of PLC activity) in a gonadotroph-derived cell line (alphaT3-1). Here we show that when alphaT3-1 cells were incubated in medium with 2% foetal calf serum (FCS), [(3)H]thymidine incorporation was not stimulated by oestradiol but was reduced to <2% of control by the oestrogen antagonist, raloxifene. The inhibitory effect of 10 or 1000 nM raloxifene was reversed competitively by oestradiol. A similar pattern of effects was seen when effects of oestradiol and raloxifene on the proportion of cells in the S-phase of the cell cycle (as measured by flow cytometry of propidium iodide-labelled cells) and on oestrogen receptor activity (as measured by trans-activation of the oestrogen-response elements in the vitellogenin promoter) were quantified. In addition, RT-PCR revealed expression of alpha and beta (but not beta2) subtypes of oestrogen receptors. Thus, oestrogen is an essential mitogen for alphaT3-1 cells, its mitogenic effect is oestrogen receptor mediated and is associated with a marked alteration of cell cycle distribution, and the full extent of these effects are best revealed in the presence of raloxifene. Using this strategy, we found that cells cultured for 4 days with 10 nM raloxifene expressed GnRH receptors (K(d) for (125)I-buserelin 4.33 nM) and that their activation by GnRH caused a concentration-dependent increase in [(3)H]IP(x) (in cells labelled with [(3)H]inositol) and inositol 1,4,5 trisphophate (in unlabelled cells). Addition of 10 nM oestradiol (to overcome receptor blockade by raloxifene) reduced GnRH receptor number by 31% but increased maximal effects on [(3)H]IP(x) and Ins(1,4,5)P(3) approximately 4-fold. The effects of oestradiol on GnRH receptor number and signalling were not, however, mimicked by culture for 2 days in medium with 10% FCS and the S-phase blocker, thymidine (15 mM). This treatment increased the proportion of cells in the S-phase 2- to 3-fold but did not alter GnRH receptor number or signalling. Other treatments which altered cell cycle transition (hydroxyurea, colcemid, methotrexate) also failed to alter GnRH receptor number or signalling and no correlation was seen between GnRH receptor number or GnRH-stimulated [(3)H]IP(x) accumulation and the proportion of cells in the S-phase or G2/M-phases of the cell cycle. Thus, oestradiol has pronounced effects on GnRH signalling, proliferation and cell cycle distribution in alphaT3-1 cells, but these trophic effects do not underlie the modulation of GnRH signalling.
B Williams; A N Brooks; T C Aldridge; W D Pennie; R Stephenson; C A McArdle
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  The Journal of endocrinology     Volume:  164     ISSN:  0022-0795     ISO Abbreviation:  J. Endocrinol.     Publication Date:  2000 Jan 
Date Detail:
Created Date:  2000-05-01     Completed Date:  2000-05-01     Revised Date:  2006-11-15    
Medline Journal Info:
Nlm Unique ID:  0375363     Medline TA:  J Endocrinol     Country:  ENGLAND    
Other Details:
Languages:  eng     Pagination:  31-43     Citation Subset:  IM    
Division of Medicine, University of Bristol, Bristol, UK.
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MeSH Terms
Cell Cycle*
Cell Line
Estradiol / pharmacology*
Estrogen Antagonists / pharmacology
Flow Cytometry
Gonadotropin-Releasing Hormone / metabolism*,  pharmacology
Inositol 1,4,5-Trisphosphate / metabolism
Pituitary Gland / drug effects*,  metabolism
Raloxifene / pharmacology
Receptors, LHRH / metabolism
Signal Transduction / drug effects*
Thymidine / pharmacology
Reg. No./Substance:
0/Estrogen Antagonists; 0/Receptors, LHRH; 33515-09-2/Gonadotropin-Releasing Hormone; 50-28-2/Estradiol; 50-89-5/Thymidine; 84449-90-1/Raloxifene; 85166-31-0/Inositol 1,4,5-Trisphosphate

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