Maintenance of integrated proviral gene expression requires Brm, a catalytic subunit of SWI/SNF complex.
We show here that murine leukemia virus-based retrovirus vector transgene expression is rapidly silenced in human tumor cell lines lacking expression of Brm, a catalytic subunit of the SWI/SNF chromatin remodeling complex, even though these vectors can successfully enter, integrate, and initiate transcription. We detected this gene silencing as a reduction in the ratio of cells expressing the exogenous gene rather than a reduction in the average expression levels, indicating that down-regulation occurs in an all-or-none manner. Retroviral gene expression was protected from silencing and maintained in Brm-deficient host cells by exogenous expression of Brm but not BRG1, an alternative ATPase subunit in the SWI/SNF complex. Introduction of exogenous Brm to these cells suppressed recruitment of protein complexes containing YY1 and histone deacetylase (HDAC) 1 and 2 to the 5'-long terminal repeat region of the integrated provirus, leading to the enhancement of acetylation of specific lysine residues in histone H4 located in this region. Consistent with these observations, treatment of Brm-deficient cells with HDAC inhibitors but not DNA methylation inhibitors suppressed retroviral gene silencing. These results suggest that the Brm-containing SWI/SNF complex subfamily (trithorax-G) and a complex including YY1 and HDACs (Polycomb-G) counteract each other to maintain transcription of exogenously introduced genes.
Mizutani
Taketoshi
T
Division of Host-Parasite Interaction, Department of Microbiology and Immunology, Institute of Medical Science, University of Tokyo, 4-6-1 Shirokanedai, Minato-ku, Tokyo 108-8639, Japan.
Ito
Taiji
T
Nishina
Mitsue
M
Yamamichi
Nobutake
N
Watanabe
Akiko
A
Iba
Hideo
H
D000306:Adrenal Cortex Neoplasms; D000818:Animals; D002277:Carcinoma; D002289:Carcinoma, Non-Small-Cell Lung; D002843:Chromatin / Q000378:metabolism; D029721:Drosophila Proteins; D005260:Female; D017353:Gene Deletion; D015967:Gene Expression Regulation, Viral; D015723:Gene Library; D020868:Gene Silencing; D005822:Genetic Vectors; D006801:Humans; D009052:Leukemia Virus, Murine / Q000235:genetics*; D008175:Lung Neoplasms; D051379:Mice; D012516:Osteosarcoma; D021122:Protein Subunits; D016601:RNA-Binding Proteins; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017412:Ribonucleoprotein, U1 Small Nuclear / Q000378:metabolism; D014157:Transcription Factors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic; D014407:Tumor Cells, Cultured; D002583:Uterine Cervical Neoplasms; D014721:Vesicular stomatitis Indiana virus / Q000235:genetics
D002843:Chromatin; D029721:Drosophila Proteins; D021122:Protein Subunits; D016601:RNA-Binding Proteins; D011994:Recombinant Proteins; D017412:Ribonucleoprotein, U1 Small Nuclear; C084011:SMARCA2 protein, human; C499503:Smarca2 protein, mouse; D014157:Transcription Factors; C089969:snf protein, Drosophila