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See detailNucleolin binds specifically to an AP-1 DNA sequence and represses AP1-dependent transactivation of the matrix metalloproteinase-13 gene.
Samuel, Shaija; Twizere, Jean-Claude ULg; Beifuss, Katherine K et al

in Molecular Carcinogenesis (2008), 47(1), 34-46

Transcriptional regulation via activator protein-1 (AP-1) protein binding to AP-1 binding sites within gene promoter regions of AP-1 target genes plays a key role in controlling cellular invasion ... [more ▼]

Transcriptional regulation via activator protein-1 (AP-1) protein binding to AP-1 binding sites within gene promoter regions of AP-1 target genes plays a key role in controlling cellular invasion, proliferation, and oncogenesis, and is important to pathogenesis of arthritis and cardiovascular disease. To identify new proteins that interact with the AP-1 DNA binding site, we performed the DNA affinity chromatography-based Nucleotide Affinity Preincubation Specificity TEst of Recognition (NAPSTER) assay, and discovered a 97 kDa protein that binds in vitro to a minimal AP-1 DNA sequence element. Mass spectrometric fragmentation sequencing determined that p97 is nucleolin. Immunoblotting of DNA affinity-purified material with anti-nucleolin antibodies confirmed this identification. Nucleolin also binds the AP-1 site in gel shift assays. Nucleolin interacts in NAPSTER with the AP-1 site within the promoter sequence of the metalloproteinase-13 gene (MMP-13), and binds in vivo in chromatin immunoprecipitation assays in the vicinity of the AP-1 site in the MMP-13 promoter. Overexpression of nucleolin in human HeLa cervical carcinoma cells significantly represses AP-1 dependent gene transactivation of a minimal AP-1 reporter construct and of an MMP-13 promoter reporter sequence. This is the first report of nucleolin binding and transregulation at the AP-1 site. [less ▲]

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See detailYB-1 represses AP1-dependent gene transactivation and interacts with an AP-1 DNA sequence.
Samuel, Shaija; Twizere, Jean-Claude ULg; Bernstein, Lori R

in Biochemical Journal (2005), 388(Pt 3), 921-8

Involvement of the AP-1 (activator protein-1) transcription factor has been demonstrated previously in the regulation of cell proliferation and cell-cycle progression, in the control of cell migration ... [more ▼]

Involvement of the AP-1 (activator protein-1) transcription factor has been demonstrated previously in the regulation of cell proliferation and cell-cycle progression, in the control of cell migration, invasion and metastasis, and in signal transduction, stress responsiveness, DNA replication and DNA repair. YB-1 (Y-box-binding protein-1) has also been implicated in many of these processes. However, the mechanism by which YB-1 mediates these processes is poorly understood. In the present study, we report that overexpression of a transfected gene encoding YB-1 in human HeLa cervical carcinoma cells significantly represses the transactivation of a minimal AP-1 reporter construct in response to the tumour promoter PMA. YB-1 also represses mRNA expression and PMA-induced promoter transactivation of the endogenous AP-1 target gene encoding matrix metalloproteinase-12 (metalloelastase). YB-1 transrepression of both the minimal and matrix metalloproteinase-12 promoter reporter constructs is dependent on the AP-1 sequence. To identify new nuclear proteins that bind specifically to the AP-1 DNA-binding site, we devised a DNA-affinity-chromatography-based assay termed NAPSTER (nucleotide-affinity preincubation specificity test of recognition) and discovered a 49 kDa protein from human cancer cells that binds in a sequence-specific manner to the AP-1 DNA sequence. By tandem MS fragmentation sequencing analyses we determined that p49 is a YB-1. Immunoblotting of the NAPSTER-purified p49 protein using anti-YB-1 antibodies confirmed YB-1 binding to the AP-1 DNA sequence, as did gel mobility-supershift assays using YB-1 antibodies. This is the first report of YB-1 transrepression and interaction at the AP-1 DNA-binding site. [less ▲]

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See detailInteraction of retroviral Tax oncoproteins with tristetraprolin and regulation of tumor necrosis factor-alpha expression.
Twizere, Jean-Claude ULg; Kruys, Veronique; Lefebvre, Laurent et al

in Journal of the National Cancer Institute (2003), 95(24), 1846-59

BACKGROUND: The Tax oncoproteins are transcriptional regulators of viral expression involved in pathogenesis induced by complex leukemogenic retroviruses (or delta-retroviruses, i.e., primate T-cell ... [more ▼]

BACKGROUND: The Tax oncoproteins are transcriptional regulators of viral expression involved in pathogenesis induced by complex leukemogenic retroviruses (or delta-retroviruses, i.e., primate T-cell leukemia viruses and bovine leukemia virus). To better understand the molecular pathways leading to cell transformation, we aimed to identify cellular proteins interacting with Tax. METHODS: We used a yeast two-hybrid system to identify interacting cellular proteins. Interactions between Tax and candidate interacting cellular proteins were confirmed by glutathione S-transferase (GST) pulldown assays, co-immunoprecipitation, and confocal microscopy. Functional interactions between Tax and one interacting protein, tristetraprolin (TTP), were assessed by analyzing the expression of tumor necrosis factor-alpha (TNF-alpha), which is regulated by TTP, in mammalian cells (HeLa, D17, HEK 293, and RAW 264.7) transiently transfected with combinations of intact and mutant Tax and TTP. RESULTS: We obtained seven interacting cellular proteins, of which one, TTP, was further characterized. Tax and TTP were found to interact specifically through their respective carboxyl-terminal domains. The proteins colocalized in the cytoplasm in a region surrounding the nucleus of HeLa cells. Furthermore, coexpression of Tax was associated with nuclear accumulation of TTP. TTP is an immediate-early protein that inhibits expression of TNF-alpha at the post-transcriptional level. Expression of Tax reverted this inhibition, both in transient transfection experiments and in stably transfected macrophage cell lines. CONCLUSION: Tax, through its interactions with the TTP repressor, indirectly increases TNF-alpha expression. This observation is of importance for the cell transformation process induced by leukemogenic retroviruses, because TNF-alpha overexpression plays a central role in pathogenesis. [less ▲]

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