Roles of antiestrogen binding sites in human endometrial cancer cells

Abstract

Estrogen-noncompatible antiestrogen binding sites (AEBS) as well as estrogen receptors (ER), and the growth-inhibitory effect of tamoxifen were investigated in two human endometrial cancer cell lines, IK-90 and HEC-IA cells. IK-90 cells contained specific AEBS, but no ER was found in these cells. Scatchard plot analysis of AEBS in 12,000 g supernatant from IK-90 cells showed a high affinity binding site for tamoxifen ( K d :5.6 ± 1.0nM) with the maximum binding site of 457 ± 47 fmol/mg protein. However, no measurable ER or AEBS was found in HEC-IA cells. The effect of tamoxifen on the growth of cells was found to be identical in both cell lines; the addition of 10 μ M tamoxifen to culture medium was cytocidal whereas tamoxifen at lower concentrations (1 nM-1μM) did not significantly affect the growth of both IK-90 and HEC-IA cells. These results demonstrate for the first time the presence of AEBS in human endometrial cancer cells. The present results also suggest that AEBS does not play a fundamental role in mediating the growth:inhibitory effect of tamoxifen in endometrial cancer cells.