HORMONAL-REGULATION OF DE NOVO PYRIMIDINE SYNTHESIS AND UTILIZATION IN HUMAN-BREAST CANCER-CELLS IN TISSUE-CULTURE

  • 1 January 1983
    • journal article
    • research article
    • Vol. 43  (10) , 4681-4690
Abstract
The hormonal regulation of pyrimidine synthesis and utilization is examined in the estrogen-responsive MCF-7 human breast cancer cell line. [14C]Acetate is used as a novel marker in assaying the incorporation of pyrimidine nucleotides derived through de novo synthesis into DNA. Technical verification of the validity of this tracer in DNA synthesis is presented. The experimental conditions permitting extrapolation from radioactivity incorporated into DNA to pmol of DNA synthesized/unit of time are discussed. Estrogen administration increases the incorporation of [14C] acetate into DNA, and this effect is most evident after 36 of exposure to hormone. Treatment with the antiestrogen tamoxifen produces substantial reductions in the rate of incorporation of [14C]acetate into DNA. Incorporation correlates well with net rates of DNA synthesis, as measured by 32Pi incorporation into DNA. Concomitant administration of thymidine in concentrations in excess of 10-7 M partially relieves tamoxifen inhibition of net DNA synthesis following 18-32 h of estrogen treatment. Activity of de novo enzymes such as carbamylphosphate synthetase, aspartate transcarbamylase, orotidine pyrophosphorylase, and orotidine decarboxylase also varies with hormone treatment. All characteristically increase following estrogen treatment of decrease after tamoxifen administration. Changes in de novo pyrimidine synthesis after hormone treatment apparently are directly linked to hormone-induced alterations in the activity of specific enzymes in the de novo pathway.