Histone Deacetylase Inhibitor Downregulation of bcl-xl Gene Expression Leads to Apoptotic Cell Death in Mesothelioma

Abstract

It has been shown that mesothelioma expresses the antiapoptotic protein BCL-XL, but not BCL-2, rendering bcl-xl gene expression a potential therapeutic target. Sodium butyrate (NaB) is a histone deacetylase inhibitor capable of alteration of bcl-2 family protein expression in other tumor types. Mesothelioma cell lines (REN, I-45) were exposed to NaB, and viability (colorimetric assay) and apoptosis (TUNEL, Hoescht staining, flow cytometry) were evaluated. Effects on bcl-2 family protein, fas-fas ligand, and caspases were examined by Western blot analysis and functional assay. An RNase assay evaluated bcl-2 family messenger RNA (mRNA) expression. Overexpressing BCL-XL mesothelioma clones were created by plasmid transfer. Cells were sensitive to NaB at low IC(50) (REN, 0.3 mM; I-45, 1 mM) and demonstrated apoptosis (percentage of cells below G1 phase by flow cytometry [sub-G1]: REN, 38.5%; I-45, 30.9%). A significant decrease in BCL-XL protein expression was noted with BAK, BAX, and BCL-2 unchanged, and this was corroborated at the transcriptional level with selectively decreased bcl-xl mRNA production after sodium butyrate exposure. Fas expression and fas-fas ligand sensitivity were unchanged. Caspases demonstrated low-level activation. Stable overexpressing BCL-XL clones were proportionally resistant to the NaB effect. This study suggests that mesothelioma cells are sensitive to the induction of apoptosis related to the attenuation of antiapoptotic bcl-xl gene and protein expression. Additional study of the therapeutic benefit of targeting bcl-xl gene expression in mesothelioma is warranted.

A bipartite butyrate‐responsive element in the human calretinin (CALB2) promoter acts as a repressor in colon carcinoma cells but not in mesothelioma cells

“…Before this time point, proliferation was similar or even slightly increased in butyrate-treated cells of mesothelial origin. While the addition of butyrate to colon cancer cells induces morphological changes from a pavement-like appearance of untreated cells to a more flattened morphology with a larger nucleus and clear cytoplasm, butyrate-treated MeT-5A cells showed cell swelling, rounding and detachment from the culture dishes typical for cell death and also signs of apoptosis were detected (e.g., pycnotic fragmented nuclei) as described before in the mesothelioma cell lines REN and I-45 [Cao et al, 2001]. In MeT-5A cells treated with ''tolerable'' doses of butyrate (1 and 2 mM), expression levels of CR were essentially unchanged.…”

“…On the other hand, such a physiological signaling role in cells of mesothelial origin appears rather unlikely, however it cannot be entirely excluded. Nonetheless, butyrate was previously shown to increase cell death in mesothelioma cells by decreasing the levels of the anti-apoptotic protein BCL-XL [Cao et al, 2001].…”

Sensitization of osteosarcoma cells to death receptor-mediated apoptosis by HDAC inhibitors through downregulation of cellular FLIP

“…29,32 On the contrary, we did not observe changes in Fas and Bcl-X L expression following treatment of OST, U-2 OS, and HeLa cells with FR901228 (Figure 3b). The difference between previous reports and our results may be due to cell type-specific effects.…”

Histone Deacetylase (HDAC) Inhibition as a Novel Treatment for Diabetes Mellitus

“…Several links between Bcl-2 proteins and HDACi have been found primary in models of cancer where high concentrations of HDACi are used to induce apoptosis in cancer cells. In transformed cells, HDACi operates via the proapoptotic Bcl-2 proteins Bim (155), Bid (156) and Bax (157), which are upregulated, processed or translocated to the mitochondrial membrane, respectively, while expression of the antiapoptotic Bcl-2 protein Bcl-X L is downregulated (158). The effects of lower HDACi concentrations used in inflammatory diseases on the regulation of the Bcl-2 protein family and an effect of HDACi on cytokine-induced activation of the intrinsic apoptotic pathway in β cells are yet to be examined.…”