SHORT-TREM AND LONG-TERM ESTRADIOL TREATMENT INHIBITS GROWTH AND ALTERS EXPRESSION OF P21(WAF1 CIP1) IN AN ENDOMETRIAL ADENOCARCINOMA CELL-LINE LACKING FUNCTIONAL P53/

Oestrogen is assumed to play a significant role in cell cycle regulati on of cells expressing the oestrogen receptor, although its mechanism of action is not yet well defined. To examine this, a mutant p53-expre ssing human endometrial adenocarcinoma cell line of the oestradiol-inh ibited growth phenotype was treated with oestradiol for 2 weeks (short -term) and 6 months (long-term). With short-term treatment, cells were treated with increasing doses of oestradiol. The highest dose, 1 mu M , was used in the long-term interval. The influence of the hormone on growth, proliferation and expression of some cell cycle and apoptosis- related proteins was evaluated. In cells treated for 2 weeks, there wa s a dose-dependent inhibition of both growth and proliferation with a significant decrease in labelling index (LI) and S-phase fraction (SPF ) and a simultaneous increase in the fraction of cells in G0/G1. Exten ding the oestradiol treatment to 6 months showed further growth retard ation and decreased proliferation with cells accumulating in G0/G1. An alysis of the expression of p21(WAF1/Cip1) showed a nearly 2-fold incr ease after 2 weeks treatment with 1 mu M oestradiol, which was also ob served after long-term treatment without any further increase in prote in levels. Expression of the anti-apoptotic protein bcl-2 was not affe cted after short-term treatment but decreased significantly after 6 mo nths treatment compared to control cells. Our results suggest the exis tence of a p53-independent pathway of oestradiol regulation of growth and proliferation in this human endometrial adenocarcinoma, resulting in accumulation of cells in G0/G1 through p21(WAF1/Cip1) induction and , after prolonged treatment, downregulation of bcl-2 protein. (C) 1997 Published by Elsevier Science Ltd.