Inhibition Effect Of Histone Deacetylase Inhibitor FK228 On Prostate Cancer Cells

Introduction Prostate cancer is currently the most frequently diagnosed and the second death causing cancer in male tumor. Although initially sensitive to androgen withdrawal, most prostate cancer can manage to survive and progress to an androgen refractory state for which no successful therapy exists to date. One approach to this dilemma might be to target the very machinery that allow cancer cells to adapt so successfully to environmental stress. FK228, a potent histone deacetylase inhibitor (HDACI), is a potential target in this regard. Recent studies have found that in addition to causing histone acetylation, FK228 can also acetylate heat shock protein (HSP) 90, a critical chaperone participating in multi-signal transduction pathways vital for tumor cell growth. As a result the chaperone complexes destabilized and the client proteins were degraded.Objective In the present study we investigated the antitumor effect of FK228 on LNCaP prostate cancer cell line. Since the androgen receptor (AR) plays a pivotal role in prostate cancer, we then investigated the changes of AR after drug treatment. In addition, key signaling molecules such as HER2, Akt, Raf-1 were assayed. Finally we determined whether acetylation of HSP90 was associated with its chaperone function with AR.Methods Proliferation of LNCaP cells exposed to FK228 was detected by MTT assay. Cell apoptosis was assayed by Hoechst 33342 nuclei staining as well as cleaved PARP expression. Western blot was used to analyze a panel of HSP90 client proteins expression. Semi-quantitative RT-PCR was used to assay the transactivation ability of AR to target gene such as prostate specific antigen. Co-immunoprecipitation followed by western blot was used to analyze the protein-protein interaction.Results FK228 exposure caused G2/M cell cycle arrest as well as apoptotic cell death. FK228 treatment increased HSP90 acetylation and abrogated AR-HSP90 binding. HSP90 client proteins, such as AR, HER2, Raf-1, cdk4, and Akt were depleted by FK228 both in a dose and time- dependent manner. Consistent with AR depletion, a dramatic decrease of androgen-induced PSA geneactivation could be observed. However, MG132, a reversible proteasome inhibitor, could almost completely restore the AR expression decreased by FK228.Conclusions FK228 exhibits significant antitumor effect against LNCaP cell line. FK228 treatment increased HSP90 acetylation and decreased AR-HSP90 binding, followed by the AR degradation through the proteasome pathway. To our knowledge, this is the first report that FK228 decreased the AR through modulation of HSP90 acetylation. Taken together, our results suggest that the antitumor activity of FK228 may be mediated, at least in part, by acetylating HSP90 and destabilization of HSP90 client proteins in LNCaP cell line, thus providing a novel mechanism for HDACI to inhibit prostate cancer cell proliferation.