Cell cycle dependent oscillatory expression of estrogen receptor-α links Pol II elongation to neoplastic transformation

Decades of studies provided a detailed view of the mechanism of estrogen receptor-alpha (ER alpha) regulated gene transcription and the physio-pathological relevance of the genetic programs controlled by this receptor in a variety of tissues. However, still limited is our knowledge on the regulation of ER alpha synthesis. Preliminary observations showed that the expression of ER alpha is cell cycle regulated. Here, we have demonstrated that a well described polymorphic sequence in the first intron of ER alpha (PvuII and XbaI) has a key role in regulating the ER alpha content in cycling cells. We have shown that the RNA Pol II (Pol II) elongation is blocked at the polymorphic site and that the proto-oncogene c-MYB modulates the release of the pausing polymerase. It is well known that the two SNPs are associated to an increased risk, progression, survival and mortality of endocrine-related cancers, here we have demonstrated that the c-MYB-dependent release of Pol II at a specific phase of the cell cycle is facilitated by the px haplotype, thus leading to a higher ER alpha mitogenic signal. In breast cancer, this mechanism is disrupted when the hormone refractory phenotype is established; therefore, we propose this oscillator as a novel target for the development of therapies aimed at sensitizing breast cancer resistant to hormonal treatments. Because PvuII and XbaI were associated to a broad range physio-pathological conditions beside neoplastic transformation, we expect that the ER alpha oscillator contributes to the regulation of the estrogen signal in several tissues.