title: Fe65, a ligand of the Alzheimer's beta-amyloid precursor protein, blocks cell cycle progression by down-regulating thymidylate synthase expression.
abstract: The functions of the Alzheimer's beta-amyloid precursor protein (APP) and of its complex with the adaptor protein Fe65 are still unknown. We have demonstrated that Fe65 is also a nuclear protein and APP functions as an extranuclear anchor, thus preventing Fe65 nuclear translocation. According to this finding, it was also demonstrated that Fe65 could play a role in the regulation of transcription. In the present paper we show that the overexpression of Fe65 prevents G(1) --> S cell cycle progression of serum-stimulated fibroblasts and that the contemporary overexpression of APP abolishes this effect of Fe65. The overexpression of Fe65 completely abolishes the activation of a key S phase gene, the thymidylate synthase (TS) gene, driven by the transcription factor LSF/CP2/LBP1 (LSF). This phenomenon is observed only in experimental conditions leading to the accumulation of Fe65 in the nucleus. Similarly, the two other members of the Fe65 protein family, Fe65L1 and Fe65L2, have been found to translocate into the nucleus and to prevent the activation of the TS gene promoter induced by LSF. Two results support the hypothesis that the inhibitory effect of Fe65 on cell cycle progression in fibroblasts is the result of the inhibition of TS gene expression: (i) Fe65 overexpression, but not Fe65 and APP co-expression, prevents the accumulation of endogenous TS upon the exposure of cells to serum, and (ii) thymidine addition to the culture medium completely overcomes the growth arrest caused by Fe65. In neuronal PC12 cells, the overexpression of Fe65 or of Fe65L1 and Fe65L2 blocks cell cycle, as observed in fibroblasts, but thymidine supplementation to culture medium does not revert this block, thus suggesting that Fe65 proteins induce in neuronal cells a gene expression program different from that activated in fibroblasts.
authors.affiliation: Dipartimento di Biochimica e Biotecnologie Mediche, Università di Napoli Federico II, 80131 Napoli, Italy.
authors.forename: Paola
authors.initials: P
authors.lastname: Bruni
authors.forename: Giuseppina
authors.initials: G
authors.lastname: Minopoli
authors.forename: Tiziana
authors.initials: T
authors.lastname: Brancaccio
authors.forename: Maria
authors.initials: M
authors.lastname: Napolitano
authors.forename: Raffaella
authors.initials: R
authors.lastname: Faraonio
authors.forename: Nicola
authors.initials: N
authors.lastname: Zambrano
authors.forename: Ulla
authors.initials: U
authors.lastname: Hansen
authors.forename: Tommaso
authors.initials: T
authors.lastname: Russo
mesh_terms: D000595:Amino Acid Sequence; D016564:Amyloid beta-Protein Precursor / Q000378:metabolism*; D000818:Animals; D001483:Base Sequence; D002453:Cell Cycle / Q000502:physiology*; D002460:Cell Line; D017931:DNA Primers; D015536:Down-Regulation / Q000502:physiology*; D006801:Humans; D008024:Ligands; D051379:Mice; D008969:Molecular Sequence Data; D009419:Nerve Tissue Proteins / Q000378:metabolism / Q000502:physiology*; D009687:Nuclear Proteins / Q000378:metabolism / Q000502:physiology*; D011401:Promoter Regions, Genetic; D013940:Thymidylate Synthase / Q000235:genetics*
chemical_list: C091042:APBB1 protein, human; D016564:Amyloid beta-Protein Precursor; C486243:Apbb1 protein, mouse; D017931:DNA Primers; D008024:Ligands; D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; D013940:Thymidylate Synthase