COPS2 (COP9 constitutive photomorphogenic homolog subunit 2 (Arabidopsis))

2009-09-01   Susanne Jennek , Florian Kraft , Aria Baniahmad 

Institute of Human Genetics, Anthropology, Jena University Hospital, Kollegiengasse 10, 07743 Jena, Germany




Atlas Image
The CSN2 gene is localized on chromosome 15q21.2 (top panel). A homologous sequence is located on chromosome 9q33.2 (not shown).The gene structure highlights intron/exon arrangement, whereas red boxes display coding sequence (CDS) and grey the untranslated regions. The lower panel exhibits the CSN2/Alien cDNA. The green boxes indicate the 13 exons and the black line below illustrates the coding sequences CDS. The grey box in isoform 2 highlights the additional inserted 21bp stretch which is specific for this splice variant. Differential functions of these isoforms are not yet known. The italic numbers illustrate the base pairs.


The promoter region of CSN2 contains 4 NF-kB binding sites. Binding to these sites activates the transcription of CSN2 gene. Deletion of the C terminus of NF-kB abrogates the ability to induce CSN2 gene expression (Wu et al., 2009).
Furthermore, CSN2/Alien gene expression in vivo is activated by thyroid hormone receptor (TR) and thyroid hormone suggesting a regulatory feedback mechanism between TR and CSN2/Alien expression (Tenbaum et al., 2003).


Atlas Image
Schematic structure of the CSN2 protein (modified according to Akiyama et al., 2003). The N-terminal region contains a region for interaction with DAX-1/NiF3l1 (aa 1-275). The central part of the protein includes the nuclear localization signal (NLS), a leucine zipper (LZ) domain and a corepressor region (CR) which contains an I/LXXI/VI motif. The C-terminal region contains a PCI domain, might be used for interaction between CSN subunits (reviewed in: Wei and Deng, 2003). The numbers represent the amino acids (aa).


Three isoforms are known:
  • CSN2 short/Alien a: 305 amino acids (aa); 36 kDa protein.
  • CSN2 long 1/Alien b1: 443 aa; 51.6 kDa protein.
  • CSN2 long 2/Alien b2: 450 aa; 52.4 kDa protein.

    CSN2 activity can be regulated through phosphorylation and dephosphorylation (Kapelari et al., 2000).

  • Expression

    Mouse Csn2 is widely expressed in embryonic, fetal and adult tissues (Schaefer et al., 1998). Several mRNA levels have been described in mice: 1,8 kb ; 2,2 kb ; 4 kb and 6 kb (Schaefer et al.,1998; Altincicek et al., 2000; Tenbaum et al., 2003).


    CSN2 is localized in both the cytoplasm and the nucleus, predominantly being localized in the nucleus (Schaefer et al., 1998; Dressel et al., 1999; Tenbaum et al., 2003).


    CSN2 short/Alien a acts as a corepressor for nuclear hormone receptors (NHR). Originally in mammalians, Alien was identified as an interacting protein of the thyroid hormone receptor (TR) in a ligand-sensitive manner (Lee et al., 1995). Moreover, Alien enhances TR-mediated gene silencing through its autonomous silencing function (Dressel et al., 1999). Additionally, the vitamin D receptor (VDR), the androgen receptor (AR) and the orphan receptor DAX-1 can also interact with Alien. Functionally Alien enhances gene silencing mediated by these nuclear receptors (Altincicek et al., 2000; Polly et al., 2000; Moehren et al., 2007). Notably, Alien seems to lack interaction with retinoid X receptor (RXR), retinoid acid receptor (RAR), estrogen receptor (ER), glucocorticoid receptor (GR) and germ cell nuclear factor (GCNF) (Dressel et al., 1999; Fuhrmann et al., 2000; reviewed in: Papaioannou et al., 2007).

    Also, corepression function was identified by CSN2 short/Alien a for transcription factors involved in cell cycle regulation and DNA repair such as several members of the E2F transcription factor family (Escher et al., 2007; reviewed in: Papaioannou et al., 2007). Alien is recruited to the E2F1 gene promoter repressing endogenous E2F1 gene expression in vivo. The data also suggest that Alien inhibits transactivation of E2F1, a positive regulator of cell cycle progression. In line with this, Alien represses cell cycle progression. Remarkably, the inhibition of E2F1-mediated transactivation is independent of retinoblastoma protein pRB (Tenbaum et al., 2007). pRB represses E2F1 transcriptional activation. It is not yet known whether Alien is able to substitute pRB function during cell cycle progression (Tenbaum et al., 2007). Furthermore, a direct interaction between Alien and pRB is detected. Interestingly, a pRB-mutant lacking silencing function also lacks interaction with CSN2 short/Alien (Escher et al., 2007).

    In addition, Alien interacts with the highly conserved chromatin associated tumor suppressor proteins Inhibitor of growth 1 (p33-ING1b) and 2 (p33-ING2) in vivo and both p33ING1b and p33ING2 are known to induce premature cellular senescence. It is shown that p33ING proteins enhance Alien-mediated gene silencing (Fegers et al., 2007).

    The recruitment of HDAC-activity is one mechanism by which Alien realizes its corepression functions (Dressel et al., 1999). However, it is suggested that Alien exhibits both HDAC-dependent and -independent options for gene repression (reviewed in: Papaioannou et al., 2007). Moreover, CSN2 short/Alien a interacts with nucleosome assembly protein 1 (NAP1) in vivo and in vitro regulating its activity through enhancing NAP1-mediated nucleosome assembly on DNA and thereby leading to gene repression (Eckey et al., 2007).

    The CSN2 long/Alien b isoform is an essential part of the COP9 signalosome (CSN) complex which is highly conserved in eukaryotes and consists of eight subunits (reviewed in: Wie et al., 2008). The CSN complex plays a central role in the regulation of degradation of multiple proteins through the ability to de-neddylate cullin, which enables the association of cullin with CAND1, a negative regulator of the cullin-based E3 ubiquitin ligases (reviewed in: von Arnim, 2003; reviewed in: Wolf et al., 2003; Chamovitz, 2009; Wu et al., 2009). A role for CSN2 long/Alien b is suggested by the interaction between CSN2 and subunits of the 26S proteasome was already shown (Huang et al., 2005). The promoter region of the Csn2 gene contains NF-kB binding sites like other CSN subunits. Accordingly, these members of the CSN complex are regulated by NF-kB. Snail, a transcription factor, which is a part of the TGF-b pathway and is involved in inflammatory-triggered migration, invasiveness and metastasis of tumor cells, is stabilized by the induction of the CSN complex via NF-kB (Wu et al., 2009). There are also COP9 subcomplexes with yet unknown functions (reviewed in: Wei et al, 2008).

    Interaction of COP9 via CSN2 with p53 in tumors can raise the stability of p53, the most important protein involving in a variety of essential tumor suppressive functions and induction of cellular senescence. But in contrast to Snail, the lower turnover does not lead to an increase in transcription activity and therefore neither to an increased p21 expression nor to cell cycle arrest (Leal et al., 2008).

    Moreover, CSN2 protein interacts physically with the anaphase-promoting complex (APC/C), a major regulator of the cell cycle and affects specifically its stability (Kob et al., 2008).


    CSN2 is a highly conserved protein from humans to Drosophila (Dressel et al., 1999). CSN2 has homologies in any multicellular organism including plants. It is over 60% identical between animal and plant counterparts (Wei and Deng, 2003; Schwechheimer, 2004).

    Originally, the name Alien was given to a gene in the Drosophila genome with an unknown function (Goubeaud et al., 1996). It shares high homologies with Thyroid hormone receptor-interacting protein 15 (TRIP15), a mammalian protein (Lee et al.,1995; Dressel et al., 1999).



    So far natural occurring point mutations of CSN2 in association with cancer and other disease were not yet described.

    Implicated in

    Entity name
    Human tumors
    Aberrant expression of CNS2/Alien seems to be associated with human tumors. CSN2 expression is lost in several human tumors. In thyroid tumors the loss of CSN2 is at least 50% (Leal et al., 2008). Moreover, high percentages of reduction (15-30%) of CSN2 mRNA level were observed in tumors of pancreas, breast, ovary, kidney, uterus und rectum (Leal et al., 2008).
    It was shown by quantitative analysis that the CSN2 expression is reduced up to 50% in tumors of prostate, lung and colon (Leal et al., 2008).


    Pubmed IDLast YearTitleAuthors
    125221002003The role of transcriptional corepressor Nif3l1 in early stage of neural differentiation via cooperation with Trip15/CSN2.Akiyama H et al
    107130762000Interaction of the corepressor Alien with DAX-1 is abrogated by mutations of DAX-1 involved in adrenal hypoplasia congenita.Altincicek B et al
    193053902009Revisiting the COP9 signalosome as a transcriptional regulator.Chamovitz DA et al
    102070621999Alien, a highly conserved protein with characteristics of a corepressor for members of the nuclear hormone receptor superfamily.Dressel U et al
    173393342007The nucleosome assembly activity of NAP1 is enhanced by Alien.Eckey M et al
    173309492007Various members of the E2F transcription factor family interact in vivo with the corepressor alien.Escher N et al
    179298522007The tumor suppressors p33ING1 and p33ING2 interact with alien in vivo and enhance alien-mediated gene silencing.Fegers I et al
    117029492001Mouse germline restriction of Oct4 expression by germ cell nuclear factor.Fuhrmann G et al
    88174531996The Drosophila gene alien is expressed in the muscle attachment sites during embryogenesis and encodes a protein highly conserved between plants, Drosophila and vertebrates.Goubeaud A et al
    160457612005Consequences of COP9 signalosome and 26S proteasome interaction.Huang X et al
    109038622000Electron microscopy and subunit-subunit interaction studies reveal a first architecture of COP9 signalosome.Kapelari B et al
    195359052009Regulation of the anaphase-promoting complex by the COP9 signalosome.Kob R et al
    179683252008Cellular senescence bypass screen identifies new putative tumor suppressor genes.Leal JF et al
    77769741995Two classes of proteins dependent on either the presence or absence of thyroid hormone for interaction with the thyroid hormone receptor.Lee JW et al
    181749162007The coregulator Alien.Papaioannou M et al
    108778392000VDR-Alien: a novel, DNA-selective vitamin D(3) receptor-corepressor partnership.Polly P et al
    155718082004The COP9 signalosome (CSN): an evolutionary conserved proteolysis regulator in eukaryotic development.Schwechheimer C et al
    175705422007Alien inhibits E2F1 gene expression and cell proliferation.Tenbaum SP et al
    145705712003The COP9 signalosome.Wei N et al
    194110702009Stabilization of snail by NF-kappaB is required for inflammation-induced cell migration and invasion.Wu Y et al
    146472952003The COP9 signalosome: an assembly and maintenance platform for cullin ubiquitin ligases?Wolf DA et al
    146119492003On again-off again: COP9 signalosome turns the key on protein degradation.von Arnim AG et al

    Other Information

    Locus ID:

    NCBI: 9318
    MIM: 604508
    HGNC: 30747
    Ensembl: ENSG00000166200


    dbSNP: 9318
    ClinVar: 9318
    TCGA: ENSG00000166200


    Gene IDTranscript IDUniprot

    Expression (GTEx)



    PathwaySourceExternal ID
    Vesicle-mediated transportREACTOMER-HSA-5653656
    Membrane TraffickingREACTOMER-HSA-199991
    DNA RepairREACTOMER-HSA-73894
    Nucleotide Excision RepairREACTOMER-HSA-5696398
    Global Genome Nucleotide Excision Repair (GG-NER)REACTOMER-HSA-5696399
    DNA Damage Recognition in GG-NERREACTOMER-HSA-5696394
    Transcription-Coupled Nucleotide Excision Repair (TC-NER)REACTOMER-HSA-6781827
    Formation of TC-NER Pre-Incision ComplexREACTOMER-HSA-6781823
    Clathrin-mediated endocytosisREACTOMER-HSA-8856828
    Cargo recognition for clathrin-mediated endocytosisREACTOMER-HSA-8856825

    Protein levels (Protein atlas)

    Not detected


    Pubmed IDYearTitleCitations
    179683252008Cellular senescence bypass screen identifies new putative tumor suppressor genes.24
    270175212016Apolipoprotein A-1 binding protein promotes macrophage cholesterol efflux by facilitating apolipoprotein A-1 binding to ABCA1 and preventing ABCA1 degradation.16
    173393342007The nucleosome assembly activity of NAP1 is enhanced by Alien.13
    194009512009Analysis of the role of COP9 Signalosome (CSN) subunits in K562; the first link between CSN and autophagy.10
    151733822004The highly conserved region of the co-repressor Sin3A functionally interacts with the co-repressor Alien.9
    179298522007The tumor suppressors p33ING1 and p33ING2 interact with alien in vivo and enhance alien-mediated gene silencing.3
    181749162007The coregulator Alien.3
    195359052009Regulation of the anaphase-promoting complex by the COP9 signalosome.3
    269426992016DDA1 promotes stage IIB-IIC colon cancer progression by activating NFκB/CSN2/GSK-3β signaling.3
    150625752003Mixed lineage kinase 2 enhances trans-repression of Alien and nuclear receptors.2


    Susanne Jennek ; Florian Kraft ; Aria Baniahmad

    COPS2 (COP9 constitutive photomorphogenic homolog subunit 2 (Arabidopsis))

    Atlas Genet Cytogenet Oncol Haematol. 2009-09-01

    Online version: