title: Transformation by E1A oncoprotein involves ubiquitin-mediated proteolysis of the neuronal and tumor repressor REST in the nucleus.
abstract: The adenovirus early region 1A (E1A) protein promotes cell immortalization and transformation by mediating the activities of key cellular regulators. The repressor element 1-silencing transcription factor (REST), which is a major neuronal and tumor suppressor, was previously found mainly in the cytoplasm rather than in the nuclei of adenovirus-transformed rodent cells (22). We now demonstrate that the loss of REST in the nucleus is due to its rapid degradation by the ubiquitin-proteasome system. Only nuclear REST, but not its cytoplasmic counterpart, was ubiquitinated and degraded. REST degradation was blocked by the ubiquitination inhibitor PYR-41 and the proteasome inhibitor MG-132 but not by the nuclear export inhibitor leptomycin B. REST degradation required both of its two C-terminal degrons that are recognized by the ubiquitin ligase SCF(β-TrCP), since deletion or mutation of either degron eliminated degradation. Importantly, E1A was shown to mediate REST ubiquitination and degradation by upregulating β-TrCP. Knockdown of E1A in virus-transformed cells reduced both β-TrCP and ubiquitination of nuclear REST. In contrast, when expressed in HeLa cells, E1A enhanced the degradation of nuclear REST. Reconstitution of REST in virus-transformed cells negatively affected E1A-mediated cell proliferation and anchorage-independent growth. These data strongly indicate that E1A stimulates ubiquitination and proteolysis of REST in the nucleus, thereby abolishing the tumor suppressor functions of REST.
authors.affiliation: Department of Microbiology, School of Dental Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA.
authors.forename: Hancheng
authors.initials: H
authors.lastname: Guan
authors.forename: Robert P
authors.initials: RP
authors.lastname: Ricciardi
mesh_terms: D017500:Adenovirus E1A Proteins / Q000235:genetics / Q000378:metabolism*; D000258:Adenovirus Infections, Human / Q000378:metabolism / Q000821:virology*; D000260:Adenoviruses, Human / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D002467:Cell Nucleus / Q000378:metabolism*; D002472:Cell Transformation, Viral; D006367:HeLa Cells; D006801:Humans; D051379:Mice; D041681:NIH 3T3 Cells; D009474:Neurons / Q000378:metabolism* / Q000821:virology; D046988:Proteasome Endopeptidase Complex / Q000235:genetics / Q000378:metabolism; D059748:Proteolysis; D012097:Repressor Proteins / Q000378:metabolism*; D025801:Ubiquitin / Q000378:metabolism*; D054875:Ubiquitination; D000099229:RE1-Silencing Transcription Factor
chemical_list: D017500:Adenovirus E1A Proteins; D046988:Proteasome Endopeptidase Complex; D012097:Repressor Proteins; D025801:Ubiquitin; D000099229:RE1-Silencing Transcription Factor