Hsp90 chaperone facilitates E2F1/2-dependent gene transcription in human breast cancer cells

The growth factor-stimulated cell cycle progression is regulated by the coordinated functions of cyclins and cyclin-dependent kinases. CDKs phosphorylate Rb, and hyperphosphorylated Rb disassociate from E2F. Hsp90 facilitates the functional stabilization of E2F and, thus, E2F-dependent gene transcription. The 17AAG treatment disassociates E2F from Hsp90, resulting in its proteasomal degradation. RGFP966 treatment acetylates Hsp90, and acetylated Hsp90 is functional incompetent and fails to interact with E2F. Therefore, inhibition of HDAC3 and Hsp90 interferes with the E2F-dependent gene transcription, thus favors cell cycle inhibition. [Display omitted] •Hsp90 interacts with E2F1/2 transcription factors.•Interfering with Hsp90 chaperoning functions interfere with E2F stability and nuclear accumulation.•Hsp90-dependent E2F regulation appeared to be specific to cancer cells.•Hsp90 interaction with E2F is affected by its acetylation by HDAC3. The 90 kDa heat shock protein, Hsp90, is involved in the conformational stabilization and functional maturation of diverse cancer-promoting proteins. To date, more than 300 Hsp90 clients have identified, suggesting that Hsp90 plays a central role in deciding cancer cell fate. In this study, we present the nuclear functions of Hsp90 in regulating the E2F-dependent gene transcription. We show that the conformation specific Hsp90 inhibitor, 17AAG decreases the total cellular E2F levels more selectively in cancer cells than transformed cells. With the help of coimmunoprecipitation experiments, we show that Hsp90 interacts with E2F1 and E2F2 in cancer cells, whereas in transformed cells, only E2F1 interacts with Hsp90. Retention of E2F2 in the nucleus of cancer cells upon MG132 combination with 17AAG has suggested that Hsp90 is required for E2F2 stability and function. The HDAC6 inhibitor tubacin treatment did not interfere with E2F1/2 stability and nuclear accumulation. However, the HDAC3 inhibitor, RGFP966 treatment, decreased nuclear E2F1/2 and its target gene expression. The nuclear accumulation of E2F1 and E2F2 upon cell cycle inhibition correlated with decreased acetylated Hsp90. We expose the nuclear functions of Hsp90 in facilitating the cell cycle progression through stabilizing E2F1/2.