title: Differential control of retrovirus silencing in embryonic cells by proteasomal regulation of the ZFP809 retroviral repressor.
abstract: Replication of the murine leukemia viruses is strongly suppressed in mouse embryonic stem (ES) cells. Proviral DNAs are formed normally but are then silenced by a large complex bound to DNA by the ES cell-specific zinc-finger protein ZFP809. We show here that ZFP809 expression is not regulated by transcription but rather by protein turnover: ZFP809 protein is stable in embryonic cells but highly unstable in differentiated cells. The protein is heavily modified by the accumulation of polyubiquitin chains in differentiated cells and stabilized by the proteasome inhibitor MG132. A short sequence of amino acids at the C terminus of ZFP809, including a single lysine residue (K391), is required for the rapid turnover of the protein. The silencing cofactor TRIM28 was found to promote the degradation of ZFP809 in differentiated cells. These findings suggest that the stem cell state is established not only by an unusual transcriptional profile but also by unusual regulation of protein levels through the proteasomal degradation pathway.
authors.affiliation: Department of Biological Sciences, Columbia University Medical Center, Columbia University, New York, NY 10032.
authors.forename: Cheng
authors.initials: C
authors.lastname: Wang
authors.affiliation: Department of Biochemistry and Molecular Biophysics, Columbia University Medical Center, Columbia University, New York, NY 10032; spg1@cumc.columbia.edu.|Department of Microbiology and Immunology, Columbia University Medical Center, Columbia University, New York, NY 10032.|Howard Hughes Medical Institute, Columbia University Medical Center, Columbia University, New York, NY 10032.
authors.forename: Stephen P
authors.initials: SP
authors.lastname: Goff
mesh_terms: D000818:Animals; D045744:Cell Line, Tumor; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D005786:Gene Expression Regulation; D020868:Gene Silencing; D057809:HEK293 Cells; D054884:Host-Pathogen Interactions; D006801:Humans; D051379:Mice; D008979:Moloney murine leukemia virus / Q000235:genetics* / Q000502:physiology; D000066450:Mouse Embryonic Stem Cells / Q000378:metabolism* / Q000821:virology; D041681:NIH 3T3 Cells; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D011485:Protein Binding; D011533:Proviruses / Q000235:genetics / Q000502:physiology; D012190:Retroviridae / Q000235:genetics / Q000502:physiology; D000076183:Tripartite Motif-Containing Protein 28 / Q000235:genetics / Q000378:metabolism
chemical_list: D004268:DNA-Binding Proteins; C541321:ZFP809 protein, mouse; D000076183:Tripartite Motif-Containing Protein 28; D046988:Proteasome Endopeptidase Complex
keywords: embryonic stem cells; proteasome; retrovirus; transcriptional repressor