Fiskus W, Ren Y, Mohapatra A, Bali P, Mandawat A, Rao R, Herger B, Yang Y, Atadja P, Wu J, Bhalla K

The molecular chaperone heat shock protein (hsp)-90 maintains estrogen receptor (ER)-alpha in an active conformation, allowing it to bind 17beta-estradiol (E2) and transactivate genes, including progesterone receptor (PR)-beta and the class IIB histone deacetylase HDAC6. By inhibiting HDAC6, the hydroxamic acid analogue pan-HDAC inhibitors (HA-HDI; e.g., LAQ824, LBH589, and vorinostat) ...

Read More

induce hyperacetylation of the HDAC6 substrates alpha-tubulin and hsp90. Hyperacetylation of hsp90 inhibits its chaperone function, thereby depleting hsp90 client proteins. Here, we determined the effect of HA-HDIs on the levels and activity of ERalpha, as well as on the survival of ERalpha-expressing, estrogen-responsive human breast cancer MCF-7 and BT-474 cells.Following exposure to HA-HDIs, hsp90 binding, polyubiquitylation levels, and transcriptional activity of ERalpha, as well as apoptosis and loss of survival, were determined in MCF-7 and BT-474 cells.Treatment with HA-HDI induced hsp90 hyperacetylation, decreased its binding to ERalpha, and increased polyubiquitylation and depletion of ERalpha levels. HA-HDI treatment abrogated E2-induced estrogen response element-luciferase expression and attenuated PRbeta and HDAC6 levels. Exposure to HA-HDI also depleted p-Akt, Akt, c-Raf, and phospho-extracellular signal-regulated kinase-1/2 levels, inhibited growth, and sensitized ERalpha-positive breast cancer cells to tamoxifen.These findings show that treatment with HA-HDI abrogates ERalpha levels and activity and could sensitize ERalpha-positive breast cancers to E2 depletion or ERalpha antagonists.

Date: Aug. 15, 2007

View in: Pubmed Google Scholar

116041