title: Identification of a co-activator that links growth factor signalling to c-Jun/AP-1 activation.
abstract: The AP-1 transcription factor c-Jun is essential for cellular proliferation in many cell types, but the molecular link between growth factors and c-Jun activation has been enigmatic. In this study we identify a previously uncharacterized RING-domain-containing protein, RACO-1 (RING domain AP-1 co-activator-1), as a c-Jun co-activator that is regulated by growth factor signalling. RACO-1 interacted with c-Jun independently of amino-terminal phosphorylation, and was both necessary and sufficient for c-Jun/AP-1 activation. Growth factor-mediated stimulation of AP-1 was attributable to MEK/ERK-dependent stabilization of RACO-1 protein. Stimulation of the MEK/ERK pathway strongly promoted Lys 63-linked ubiquitylation of RACO-1, which antagonized Lys 48-linked degradative auto-ubiquitylation of the same Lys residues. RACO-1 depletion reduced cellular proliferation and decreased expression of several growth-associated AP-1 target genes, such as cdc2, cyclinD1 and hb-egf. Moreover, transgenic overexpression of RACO-1 augmented intestinal tumour formation triggered by aberrant Wnt signalling and cooperated with oncogenic Ras in colonic hyperproliferation. Thus RACO-1 is a co-activator that links c-Jun to growth factor signalling and is essential for AP-1 function in proliferation.
authors.affiliation: Mammalian Genetics Laboratory, Cancer Research UK London Research Institute, Lincoln's Inn Fields Laboratories, 44, Lincoln's Inn Fields, London WC2A 3PX, UK.
authors.forename: Clare C
authors.initials: CC
authors.lastname: Davies
authors.forename: Atanu
authors.initials: A
authors.lastname: Chakraborty
authors.forename: Filippo
authors.initials: F
authors.lastname: Cipriani
authors.forename: Katharina
authors.initials: K
authors.lastname: Haigh
authors.forename: Jody J
authors.initials: JJ
authors.lastname: Haigh
authors.forename: Axel
authors.initials: A
authors.lastname: Behrens
mesh_terms: D000818:Animals; D002453:Cell Cycle; D002460:Cell Line; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D011905:Genes, ras / Q000235:genetics; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins / Q000378:metabolism*; D007414:Intestinal Neoplasms / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D008239:Lysine / Q000378:metabolism; D020935:MAP Kinase Signaling System; D051379:Mice; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism; D041681:NIH 3T3 Cells; D010766:Phosphorylation; D011485:Protein Binding; D016755:Proto-Oncogene Proteins c-jun / Q000378:metabolism*; D015398:Signal Transduction; D018808:Transcription Factor AP-1 / Q000378:metabolism*; D014157:Transcription Factors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D025801:Ubiquitin / Q000378:metabolism; D054875:Ubiquitination
chemical_list: D036341:Intercellular Signaling Peptides and Proteins; D016755:Proto-Oncogene Proteins c-jun; D018808:Transcription Factor AP-1; D014157:Transcription Factors; D025801:Ubiquitin; D020929:Mitogen-Activated Protein Kinase Kinases; D008239:Lysine