title: The expression of B23 and EGR1 proteins is functionally linked in tumor cells under stress conditions.
abstract: BACKGROUND
  The nucleolus is a multi-domain enriched with proteins involved in ribosome biogenesis, cell cycle and apoptosis control, viral replication and differentiation of stem cells. Several authors have suggested a role for the nucleolus also in malignant transformation. We have recently demonstrated that under specific circumstances the transcriptional factor EGR1 is shuttled to the nucleolus where it functions as a negative regulator of RNA polymerase I. Since this activity is hampered in ARF -/- cells, and ARF transcription is regulated by EGR1 while the turnover of ARF protein is under the control of B23, we speculated that some sort of cooperation between EGR1 and B23 might also exist.
  
  
  RESULTS
  In this work we identified a canonical EGR1 binding site on the B23 promoter through experiments of transactivation and in vitro DNA binding assay. We then found that the levels of B23 expression are directly correlated with those of EGR1, and that this correlation applies to several cellular types and to different stress conditions. Furthermore, we showed that EGR1 stability and accumulation within the nucleolus is in turn regulated by B23 through proteasome involvement, similarly to ARF turnover.
  
  
  CONCLUSIONS
  Our results highlight EGR1 as a regulator of B23 expression actively playing within the newly discovered nucleolar B23-ARF-EGR1 network.
authors.affiliation: Department of Medico-Surgical Sciences and Biotechnologies, University of Rome Sapienza, Corso della Repubblica 79, 04100, Latina, Italy. donatella.ponti@uniroma1.it.
authors.forename: Donatella
authors.initials: D
authors.lastname: Ponti
authors.affiliation: Division of Thoracic Surgery, Department of Medical-Surgical Science and Translational Medicine, University Sapienza, S. Andrea Hospital, via di Grottarossa 1035, 00189, Rome, Italy. daniela.bastianelli@uniroma1.it.
authors.forename: Daniela
authors.initials: D
authors.lastname: Bastianelli
authors.affiliation: Department of Medico-Surgical Sciences and Biotechnologies, University of Rome Sapienza, Corso della Repubblica 79, 04100, Latina, Italy. p.rosa@uniroma1.it.
authors.forename: Paolo
authors.initials: P
authors.lastname: Rosa
authors.affiliation: Department of Medico-Surgical Sciences and Biotechnologies, University of Rome Sapienza, Corso della Repubblica 79, 04100, Latina, Italy. luca.pacini@uniroma1.it.
authors.forename: Luca
authors.initials: L
authors.lastname: Pacini
authors.affiliation: Division of Thoracic Surgery, Department of Medical-Surgical Science and Translational Medicine, University Sapienza, S. Andrea Hospital, via di Grottarossa 1035, 00189, Rome, Italy. mohsen.ibrahim@uniroma1.it.
authors.forename: Mohsen
authors.initials: M
authors.lastname: Ibrahim
authors.affiliation: Division of Thoracic Surgery, Department of Medical-Surgical Science and Translational Medicine, University Sapienza, S. Andrea Hospital, via di Grottarossa 1035, 00189, Rome, Italy. erinoangelo.rendina@uniroma1.it.
authors.forename: Erino Angelo
authors.initials: EA
authors.lastname: Rendina
authors.affiliation: Department of Medico-Surgical Sciences and Biotechnologies, University of Rome Sapienza, Corso della Repubblica 79, 04100, Latina, Italy. giuseppe.ragona@uniroma1.it.
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Ragona
authors.affiliation: Department of Medico-Surgical Sciences and Biotechnologies, University of Rome Sapienza, Corso della Repubblica 79, 04100, Latina, Italy. antonella.calogero@uniroma1.it.
authors.forename: Antonella
authors.initials: A
authors.lastname: Calogero
mesh_terms: D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D051766:Early Growth Response Protein 1 / Q000235:genetics / Q000378:metabolism*; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D051379:Mice; D018345:Mice, Knockout; D008969:Molecular Sequence Data; D009369:Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000503:physiopathology; D009687:Nuclear Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D000090243:Nucleophosmin; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D013312:Stress, Physiological
chemical_list: D051766:Early Growth Response Protein 1; C486109:Egr1 protein, mouse; C000715570:Npm1 protein, mouse; D009687:Nuclear Proteins; D000090243:Nucleophosmin