title: CSN5/JAB1 suppresses the WNT inhibitor DKK1 in colorectal cancer cells.
abstract: The COP9 signalosome (CSN) is a multi-protein complex that is highly conserved in eukaryotes. Due to its regulatory impact on processes such as cell cycle, DNA damage response and apoptosis, the CSN is essential for mammalian cells. One of the best-studied functions of the CSN is the deNEDDylation of cullin-RING ligases (CRLs) via its catalytically active subunit CSN5/JAB1, thereby triggering the degradation of various target proteins. CSN5 was found to be overexpressed in many human cancer entities, including colon adenocarcinoma. Overactivation of WNT signaling is known as a key step in colon cancer development. Recently, we found that depletion of CSN5 in colorectal cancer (CRC) cells affects WNT signaling by downregulation of β-catenin. To investigate changes in gene expression associated with the CSN5 knockdown, we performed a microarray using cDNA from the CRC cell line SW480. We found the WNT ligand WNT6 and the WNT inhibitors DKK1 and DKK4 differentially regulated in CSN5 knockdown cells. DKK1 expression and DKK1 protein levels depended on CSN5 in different CRC cell lines. In addition, DKK1 secretion was increased following CSN5 knockdown, affecting WNT signaling in SW480 cells. Consequently, blocking of secreted DKK1 in cell-conditioned media abolished β-catenin downregulation in SW480 cells, while treatment with recombinant DKK1 mimicked the CSN5 knockdown effect. Furthermore, knockdown of DKK1 was able to rescue the proliferative deficiency of CSN5 knockdown cells. We conclude that downregulation of WNT signaling in colorectal cancer cells resulting from CSN5 knockdown is mediated, at least in part, by elevated DKK1 secretion. Moreover, experiments with the NEDDylation inhibitor MLN-4924 indicated that DKK1 expression is regulated by a so far unidentified repressor, the stability of which could be controlled by a CSN-regulated CRL.
authors.affiliation: Institute of Biochemistry and Molecular Cell Biology, Uniklinik RWTH Aachen, RWTH Aachen University, Pauwelsstraße 30, 52074 Aachen, Germany; Clinic of General, Visceral and Transplantation Surgery, Molecular Tumor Biology, Uniklinik RWTH Aachen, RWTH Aachen University, Pauwelsstraße 17, 52074 Aachen, Germany. Electronic address: sjumpertz@ukaachen.de.
authors.forename: Sandra
authors.initials: S
authors.lastname: Jumpertz
authors.affiliation: Institute of Biochemistry and Molecular Cell Biology, Uniklinik RWTH Aachen, RWTH Aachen University, Pauwelsstraße 30, 52074 Aachen, Germany. Electronic address: thomas.hennes@rwth-aachen.de.
authors.forename: Thomas
authors.initials: T
authors.lastname: Hennes
authors.affiliation: Department of Translational Research, Institute for Stroke and Dementia Research, Klinikum der Universität München, Ludwig-Maximilians-University, 81377 Munich, Germany. Electronic address: yaw.asare@med.uni-muenchen.de.
authors.forename: Yaw
authors.initials: Y
authors.lastname: Asare
authors.affiliation: Institute of Biochemistry and Molecular Cell Biology, Uniklinik RWTH Aachen, RWTH Aachen University, Pauwelsstraße 30, 52074 Aachen, Germany; Howard Hughes Medical Institute and Department of Developmental Biology, Stanford University School of Medicine, Stanford, CA 94305, USA. Electronic address: anke.schuetz@rwth-aachen.de.
authors.forename: Anke K
authors.initials: AK
authors.lastname: Schütz
authors.affiliation: Institute of Biochemistry and Molecular Cell Biology, Uniklinik RWTH Aachen, RWTH Aachen University, Pauwelsstraße 30, 52074 Aachen, Germany; Department of Vascular Biology, Institute for Stroke and Dementia Research, Klinikum der Universität München, Ludwig-Maximilians-University, 81377 Munich, Germany; Munich Cluster for Systems Neurology (SyNergy), 81377 Munich, Germany. Electronic address: juergen.bernhagen@med.uni-muenchen.de.
authors.forename: Jürgen
authors.initials: J
authors.lastname: Bernhagen
mesh_terms: D000075686:COP9 Signalosome Complex / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D045744:Cell Line, Tumor; D015179:Colorectal Neoplasms / Q000378:metabolism / Q000473:pathology; D003517:Cyclopentanes / Q000494:pharmacology; D015536:Down-Regulation / Q000187:drug effects; D045325:HCT116 Cells; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism*; D047908:Intracellular Signaling Peptides and Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D010447:Peptide Hydrolases / Q000235:genetics / Q000378:metabolism*; D011743:Pyrimidines / Q000494:pharmacology; D034622:RNA Interference; D012333:RNA, Messenger / Q000378:metabolism; D034741:RNA, Small Interfering / Q000378:metabolism; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000235:genetics / Q000494:pharmacology; D051153:Wnt Proteins / Q000235:genetics / Q000378:metabolism; D060449:Wnt Signaling Pathway / Q000187:drug effects; D051176:beta Catenin / Q000378:metabolism
chemical_list: D003517:Cyclopentanes; C501126:DKK1 protein, human; C442333:DKK4 protein, human; D036341:Intercellular Signaling Peptides and Proteins; D047908:Intracellular Signaling Peptides and Proteins; D011743:Pyrimidines; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D011994:Recombinant Proteins; C490674:WNT6 protein, human; D051153:Wnt Proteins; D051176:beta Catenin; D010447:Peptide Hydrolases; C501488:COPS5 protein, human; D000075686:COP9 Signalosome Complex; C539933:pevonedistat
keywords: COP9 signalosome/CSN; CSN5/JAB1; Colorectal cancer; DKK1; MLN-4924; WNT signalling pathway