Figure 4.

Estrogen may stimulate the pentose phosphate pathway. Estrogen can enter cells and bind to estrogen receptors (ESR) so that it can be delivered to the nucleus as a complex to stimulate a cascade biochemical reactions. (A) Once the pentose phosphate pathway is activated, the de novo biosynthesis of nucleotides can largely supply the materials (DNA and RNA) for cell proliferation. (B) When G6PD activity is inhibited with 6-AN, E2-ESR can promote the expression of G6PD without stimulating the de novo biosynthesis of nucleotides; the cells cannot proliferate, or may even reduce their growth rate to preserve sufficient energy for cell survival.