title: High mobility group A1 is a molecular target for MYCN in human neuroblastoma.
abstract: High mobility group A1 (HMGA1) is an architectural transcription factor and a putative protoncogene. Deregulation of its expression has been shown in most human cancers. We have previously shown that the expression of the HMGA family members is deregulated in neuroblastoma cell lines and primary tumors. On retinoic acid (RA) treatment of MYCN-amplified neuroblastoma cell lines, HMGA1 decreases with a kinetics that strictly follows MYCN repression. In addition, MYCN constitutive expression abolishes HMGA1 repression by RA. Here we explored the possibility that HMGA1 expression might be sustained by MYCN in amplified cells. Indeed, MYCN transfection induced HMGA1 expression in several neuroblastoma cell lines. HMGA1 expression increased in a transgene dose-dependent fashion in neuroblastoma-like tumors of MYCN transgenic mice. In addition, it was significantly more expressed in MYCN-amplified compared with MYCN single-copy primary human neuroblastomas. MYCN cotransfection activated a promoter/luciferase reporter containing a 1,600 bp region surrounding the first three transcription start sites of the human HMGA1 and eight imperfect E-boxes. By heterodimerizing with its partner MAX, MYCN could bind to multiple DNA fragments within the 1,600 bp. Either 5' or 3' deletion variants of the 1,600 bp promoter/luciferase reporter strongly decreased luciferase activity, suggesting that, more than a single site, the cooperative function of multiple cis-acting elements mediates direct HMGA1 transactivation by MYCN. Finally, HMGA1 repression by RNA interference reduced neuroblastoma cell proliferation, indicating that HMGA1 is a novel MYCN target gene relevant for neuroblastoma tumorigenesis.
authors.affiliation: Department of Experimental Medicine and Pathology, University La Sapienza, Rome, Italy. giuseppe.giannini@uniroma1.it
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Giannini
authors.forename: Fabio
authors.initials: F
authors.lastname: Cerignoli
authors.forename: Massimiliano
authors.initials: M
authors.lastname: Mellone
authors.forename: Isabella
authors.initials: I
authors.lastname: Massimi
authors.forename: Cinzia
authors.initials: C
authors.lastname: Ambrosi
authors.forename: Christian
authors.initials: C
authors.lastname: Rinaldi
authors.forename: Carlo
authors.initials: C
authors.lastname: Dominici
authors.forename: Luigi
authors.initials: L
authors.lastname: Frati
authors.forename: Isabella
authors.initials: I
authors.lastname: Screpanti
authors.forename: Alberto
authors.initials: A
authors.lastname: Gulino
mesh_terms: D000818:Animals; D048708:Cell Growth Processes / Q000235:genetics; D045744:Cell Line, Tumor; D002648:Child; D005784:Gene Amplification; D017930:Genes, Reporter; D024003:HMGA Proteins / Q000096:biosynthesis / Q000235:genetics*; D006801:Humans; D008156:Luciferases / Q000096:biosynthesis / Q000235:genetics; D051379:Mice; D008822:Mice, Transgenic; D000071447:N-Myc Proto-Oncogene Protein; D009447:Neuroblastoma / Q000235:genetics* / Q000378:metabolism; D009687:Nuclear Proteins / Q000235:genetics*; D015513:Oncogene Proteins / Q000235:genetics*; D011401:Promoter Regions, Genetic; D034622:RNA Interference; D015533:Transcriptional Activation; D014162:Transfection
chemical_list: D024003:HMGA Proteins; C459801:MYCN protein, human; D000071447:N-Myc Proto-Oncogene Protein; D009687:Nuclear Proteins; D015513:Oncogene Proteins; D008156:Luciferases