Loss of X-chromatin and X-chromosome activation in HeLa cells.

Activation of second X-chromosome by the action of estradiol-17 beta was studied with HeLa cells. The incidence of X-chromatin in estrogen-treated cells decreased remarkably from 55% to 6%. Further, heavy incorporation of 3H-uridine occurred in the X-chromatin bodies of the treated cells while no such labelling was observed in controls. There was also a manifold increase in the activity of the enzyme G-6-PD in steroid-treated cells, and this increase in enzyme activity could be inhibited by addition of actinomycin D. A nonestrogenic steroid such as testosterone had no effect on these parameters. These observations do indicate activation of second X-chromosome of HeLa cells by estradiol-17 beta.