title: Nuclear membrane protein LAP2beta mediates transcriptional repression alone and together with its binding partner GCL (germ-cell-less).
abstract: LAP2beta is an integral membrane protein of the nuclear envelope involved in chromatin and nuclear architecture. Using the yeast two-hybrid system, we have cloned a novel LAP2beta-binding protein, mGCL, which contains a BTB/POZ domain and is the mouse homologue of the Drosophila germ-cell-less (GCL) protein. In Drosophila embryos, GCL was shown to be essential for germ cell formation and was localized to the nuclear envelope. Here, we show that, in mammalian cells, GCL is co-localized with LAP2beta to the nuclear envelope. Nuclear fractionation studies reveal that mGCL acts as a nuclear matrix component and not as an integral protein of the nuclear envelope. Recently, mGCL was found to interact with the DP3alpha component of the E2F transcription factor. This interaction reduced the transcriptional activity of the E2F-DP heterodimer, probably by anchoring the complex to the nuclear envelope. We demonstrate here that LAP2beta is also capable of reducing the transcriptional activity of the E2F-DP complex and that it is more potent than mGCL in doing so. Co-expression of both LAP2beta and mGCL with the E2F-DP complex resulted in a reduced transcriptional activity equal to that exerted by the pRb protein.
authors.affiliation: Pediatric Hemato-Oncology Department, Division of Hematology, Chaim Sheba Medical Center, Tel-Hashomer and the Sackler School of Medicine, Tel-Aviv University, Israel.
authors.forename: E
authors.initials: E
authors.lastname: Nili
authors.forename: G S
authors.initials: GS
authors.lastname: Cojocaru
authors.forename: Y
authors.initials: Y
authors.lastname: Kalma
authors.forename: D
authors.initials: D
authors.lastname: Ginsberg
authors.forename: N G
authors.initials: NG
authors.lastname: Copeland
authors.forename: D J
authors.initials: DJ
authors.lastname: Gilbert
authors.forename: N A
authors.initials: NA
authors.lastname: Jenkins
authors.forename: R
authors.initials: R
authors.lastname: Berger
authors.forename: S
authors.initials: S
authors.lastname: Shaklai
authors.forename: N
authors.initials: N
authors.lastname: Amariglio
authors.forename: F
authors.initials: F
authors.lastname: Brok-Simoni
authors.forename: A J
authors.initials: AJ
authors.lastname: Simon
authors.forename: G
authors.initials: G
authors.lastname: Rechavi
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002289:Carcinoma, Non-Small-Cell Lung / Q000378:metabolism; D002352:Carrier Proteins / Q000502:physiology; D018797:Cell Cycle Proteins; D002875:Chromosomes / Q000737:chemistry; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D004330:Drosophila; D029721:Drosophila Proteins; D050684:E2F Transcription Factors; D006801:Humans; D007340:Insulinoma / Q000378:metabolism; D036341:Intercellular Signaling Peptides and Proteins; D008175:Lung Neoplasms; D046911:Macromolecular Substances; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism*; D051379:Mice; D008969:Molecular Sequence Data; D009685:Nuclear Envelope / Q000737:chemistry / Q000378:metabolism*; D009687:Nuclear Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D010179:Pancreas / Q000166:cytology / Q000378:metabolism; D021381:Protein Transport / Q000502:physiology; D012441:Saccharomyces cerevisiae; D017385:Sequence Homology; D014157:Transcription Factors / Q000378:metabolism*; D014158:Transcription, Genetic / Q000502:physiology; D014407:Tumor Cells, Cultured / Q000378:metabolism
chemical_list: D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; C117145:DP-interacting protein, mouse; D029721:Drosophila Proteins; D050684:E2F Transcription Factors; C471550:Gcl protein, mouse; D036341:Intercellular Signaling Peptides and Proteins; D046911:Macromolecular Substances; D008565:Membrane Proteins; D009687:Nuclear Proteins; D014157:Transcription Factors; C076187:gcl protein, Drosophila; C093413:lamina-associated polypeptide 2