Roscovitine, a selective CDK inhibitor, reduces the basal and estrogen-induced phosphorylation of ER-α in human ER-positive breast cancer cells

J Cell Biochem. 2011 Mar;112(3):761-72. doi: 10.1002/jcb.23004.

Abstract

Roscovitine (ROSC), a selective cyclin-dependent kinase (CDK) inhibitor, arrests human estrogen receptor-α (ER-α) positive MCF-7 breast cancer cells in the G(2) phase of the cell cycle and concomitantly induces apoptosis via a p53-dependent pathway. The effect of ROSC is markedly diminished in MCF-7 cells maintained in the presence of estrogen-mimicking compounds. Therefore, we decided to examine whether ROSC has any effect on the functional status of the ER-α transcription factor. Exposure of MCF-7 cells to ROSC abolished the activating phosphorylation of CDK2 and CDK7 in a concentration and time-dependent manner. This inhibition of site-specific modification of CDK7 at Ser164/170 prevented phosphorylation of RNA polymerase II and reduced basal phosphorylation of ER-α at Ser118 in non-stimulated MCF-7 cells (resulting in its down-regulation). In MCF-7 cells, estrogen induced strong phosphorylation of ER-α at Ser118 but not at Ser104/Ser106. ROSC prevented this estrogen-promoted activating modification of ER-α. Furthermore, we sought to determine whether the activity of ROSC could be enhanced by combining it with an anti-estrogen. Tamoxifen (TAM), a selective estrogen receptor modulator (SERM), affected breast cancer cell lines irrespective of their ER status. In combination with ROSC, however, it had a different impact, enhancing G(1) or G(2) arrest. Our results indicate that ROSC prevents the activating phosphorylation of ER-α and that its mode of action is strongly dependent on the cellular context. Furthermore, our data show that ROSC can be combined with anti-estrogen therapy. The inhibitory effect of TAM on ER-negative cancer cells indicates that SERMs crosstalk with other steroid hormone receptors.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antineoplastic Agents / pharmacology*
  • Antineoplastic Agents, Hormonal / pharmacology
  • Breast Neoplasms / metabolism*
  • Breast Neoplasms / pathology
  • Cell Cycle / drug effects
  • Cell Proliferation / drug effects
  • Cell Survival / drug effects
  • Cyclin-Dependent Kinases / antagonists & inhibitors*
  • Dichlororibofuranosylbenzimidazole / pharmacology
  • Drug Synergism
  • Enzyme Inhibitors / pharmacology
  • Estradiol / pharmacology
  • Estrogen Receptor alpha / metabolism*
  • Estrogens / pharmacology
  • Female
  • Humans
  • Neoplasms, Hormone-Dependent / metabolism*
  • Neoplasms, Hormone-Dependent / pathology
  • Phosphorylation
  • Purines / pharmacology*
  • RNA Polymerase II / metabolism
  • Roscovitine
  • Tamoxifen / pharmacology
  • Tumor Suppressor Protein p53 / metabolism

Substances

  • Antineoplastic Agents
  • Antineoplastic Agents, Hormonal
  • Enzyme Inhibitors
  • Estrogen Receptor alpha
  • Estrogens
  • Purines
  • Tumor Suppressor Protein p53
  • Tamoxifen
  • Roscovitine
  • Estradiol
  • Dichlororibofuranosylbenzimidazole
  • Cyclin-Dependent Kinases
  • RNA Polymerase II