title: c-Myc overexpression sensitizes Bim-mediated Bax activation for apoptosis induced by histone deacetylase inhibitor suberoylanilide hydroxamic acid (SAHA) through regulating Bcl-2/Bcl-xL expression.
abstract: Overexpression of the oncogene c-Myc sensitizes many apoptotic signals through the activation of mitochondrial apoptosis pathway. However, the underling mechanism has not been clearly defined. Here, we investigated the effect of c-Myc expression on histone deacetylase inhibitor suberoylanilide hydroxamic acid (SAHA)-induced apoptosis in rat fibroblast cells possessing various c-Myc levels. In Rat 1a cells overexpressing c-Myc, SAHA-induced enhanced the cell death response relative to the parental cells; whereas Rat 1a cells lacking c-Myc were refractory to SAHA treatment. We demonstrated that SAHA selectively induced the expression of pro-apoptotic BH3-only protein Bim, leading to Bax activation in c-Myc-expressing cells. Where c-Myc was absent, Bim, despite its induction by SAHA, failed to activate Bax and was unable to induce apoptosis. These results indicate that c-Myc is dispensable for Bim induction by SAHA, but is required for subsequent Bax activation. We further show that the expression levels of anti-apoptotic Bcl-2/Bcl2-xL were much elevated in Myc-null cells compared with the c-Myc-expressing cells; furthermore, depletion of Bcl-2/Bcl-xL in these cells restored the ability of SAHA to induce apoptosis by enhancing Bax activation. These data indicate that SAHA induces apoptosis through Bim-triggered Bax activation and that c-Myc regulates this process by modulating Bcl-2/Bcl-xL. Our results provide novel insight into the mechanism whereby Myc sensitizes the apoptotic signals; furthermore, our data suggest that cancer cells with deregulated Myc might be more sensitive to SAHA treatment.
authors.affiliation: Laboratory of Molecular Pharmacology, Genome Institute of Singapore, Genome Building, #02-01, 60 Biopolis Street, Singapore 138672, Singapore.
authors.forename: Xia
authors.initials: X
authors.lastname: Jiang
authors.forename: Ying Hung
authors.initials: YH
authors.lastname: Tsang
authors.forename: Qiang
authors.initials: Q
authors.lastname: Yu
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D051017:Apoptosis Regulatory Proteins / Q000235:genetics / Q000378:metabolism*; D000072224:Bcl-2-Like Protein 11; D015153:Blotting, Western; D002460:Cell Line; D005434:Flow Cytometry; D015870:Gene Expression / Q000187:drug effects; D056572:Histone Deacetylase Inhibitors; D006877:Hydroxamic Acids / Q000494:pharmacology*; D047468:Immunoprecipitation; D008565:Membrane Proteins / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics / Q000378:metabolism; D016271:Proto-Oncogene Proteins c-myc / Q000235:genetics / Q000378:metabolism*; D034622:RNA Interference; D051381:Rats; D020133:Reverse Transcriptase Polymerase Chain Reaction; D000077337:Vorinostat; D051028:bcl-2-Associated X Protein / Q000235:genetics / Q000378:metabolism; D051020:bcl-X Protein / Q000235:genetics / Q000378:metabolism
chemical_list: D051017:Apoptosis Regulatory Proteins; D000072224:Bcl-2-Like Protein 11; C494813:Bcl2l1 protein, rat; C000606778:Bcl2l11 protein, rat; D056572:Histone Deacetylase Inhibitors; D006877:Hydroxamic Acids; D008565:Membrane Proteins; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D016271:Proto-Oncogene Proteins c-myc; D051028:bcl-2-Associated X Protein; D051020:bcl-X Protein; D000077337:Vorinostat