Tritiated actinomycin-D staining method: a valuable tool to study oestrogen receptor-induced modifications of...

Exposure at 4 degrees C of purified cell nuclei from uterus and hormone-sensitive mammary cancer to their own cytosol preincubated with oestradiol produced a significant increase in their ability to bind [3H] actinomycin D (3H-AMD). This increase did not occur under conditions preventing the transfer of the oestrogen-receptor into the cell nucleus, nor in cancer cell nuclei devoid of oestrogen-receptors. Uterine cytosol preincubated with the strong antioestrogen 4-hydroxytamoxifen did not modify the 3H-AMD binding capacity of the uterine nuclei but significantly suppressed the increase induced by oestradiol. Moreover, ultrastructural study of tumour nuclei revealed that the oestradiol receptor-induced increase was associated with a marked chromatin dispersion. These results strongly suggest that the 3H-AMD staining method is a valuable tool for the assessment of oestrogen receptor-induced modifications of transcriptional activity in normal and pathological tissue as well.