title: Amino acid starvation induces reactivation of silenced transgenes and latent HIV-1 provirus via down-regulation of histone deacetylase 4 (HDAC4).
abstract: The epigenetic silencing of exogenous transcriptional units integrated into the genome represents a critical problem both for long-term gene therapy efficacy and for the eradication of latent viral infections. We report here that limitation of essential amino acids, such as methionine and cysteine, causes selective up-regulation of exogenous transgene expression in mammalian cells. Prolonged amino acid deprivation led to significant and reversible increase in the expression levels of stably integrated transgenes transcribed by means of viral or human promoters in HeLa cells. This phenomenon was mediated by epigenetic chromatin modifications, because histone deacetylase (HDAC) inhibitors reproduced starvation-induced transgene up-regulation, and transcriptome analysis, ChIP, and pharmacological and RNAi approaches revealed that a specific class II HDAC, namely HDAC4, plays a critical role in maintaining the silencing of exogenous transgenes. This mechanism was also operational in cells chronically infected with HIV-1, the etiological agent of AIDS, in a latency state. Indeed, both amino acid starvation and pharmacological inhibition of HDAC4 promoted reactivation of HIV-1 transcription and reverse transcriptase activity production in HDAC4(+) ACH-2 T-lymphocytic cells but not in HDAC4(-) U1 promonocytic cells. Thus, amino acid deprivation leads to transcriptional derepression of silenced transgenes, including integrated plasmids and retroviruses, by a process involving inactivation or down-regulation of HDAC4. These findings suggest that selective targeting of HDAC4 might represent a unique strategy for modulating the expression of therapeutic viral vectors, as well as that of integrated HIV-1 proviruses in latent reservoirs without significant cytotoxicity.
authors: Center for Translational Genomics and Bioinformatics,  San Raffaele Scientific Institute, Ospedale San Raffaele, 20132 Milan,  Italy.
authors: Ilaria
authors: I
authors: Palmisano
authors: Giulia
authors: G
authors: Della Chiara
authors: Rosa Lucia
authors: RL
authors: D'Ambrosio
authors: Claudia
authors: C
authors: Huichalaf
authors: Paola
authors: P
authors: Brambilla
authors: Silvia
authors: S
authors: Corbetta
authors: Michela
authors: M
authors: Riba
authors: Rosanna
authors: R
authors: Piccirillo
authors: Sergio
authors: S
authors: Valente
authors: Giorgio
authors: G
authors: Casari
authors: Antonello
authors: A
authors: Mai
authors: Filippo
authors: F
authors: Martinelli Boneschi
authors: Davide
authors: D
authors: Gabellini
authors: Guido
authors: G
authors: Poli
authors: Maria Vittoria
authors: MV
authors: Schiaffino
mesh_terms: D016117:Albinism, Ocular / Q000378:metabolism; D019175:DNA Methylation; D015536:Down-Regulation; D005136:Eye Proteins / Q000378:metabolism; D015971:Gene Expression Regulation, Enzymologic; D015967:Gene Expression Regulation, Viral; D020868:Gene Silencing; D015497:HIV-1 / Q000235:genetics*; D006367:HeLa Cells; D006655:Histone Deacetylases / Q000096:biosynthesis* / Q000235:genetics*; D006801:Humans; D008562:Membrane Glycoproteins / Q000378:metabolism; D011401:Promoter Regions, Genetic; D011533:Proviruses / Q000235:genetics; D012097:Repressor Proteins / Q000096:biosynthesis* / Q000235:genetics*; D015533:Transcriptional Activation; D019076:Transgenes; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism; D014443:Tyrosine / Q000737:chemistry
chemical_list: D005136:Eye Proteins; C095276:GPR143 protein, human; D008562:Membrane Glycoproteins; D012097:Repressor Proteins; D014409:Tumor Necrosis Factor-alpha; D014443:Tyrosine; C400300:HDAC4 protein, human; D006655:Histone Deacetylases