High impact information on COP9

• Therefore COP9, together with COP8 and COP11, defines a novel signaling step in mediating light control of plant development [1].
• Thus, the COP9 signalosome may play an important role in mediating E3 ubiquitin ligase-mediated responses [2].
• COP10 is part of a nuclear protein complex and capable of directly interacting with both COP1 and the COP9 signalosome [3].
• A multifaceted role of the COP9 signalosome in cell-signaling processes is hinted at by its associated novel kinase activity, as well as the involvement of its subunits in regulating multiple cell-signaling pathways and cell-cycle progression [4].
• Moreover, our study reveals a cellular process whereby auxin induces and Rac GTPases mediate the recruitment of nucleoplasmic Aux/IAAs into proteolytically active nuclear protein bodies, into which components of the SCF(TIR1), COP9 signalosome, and 26S proteasome are also recruited [5].

Biological context of COP9

• COP9: a new genetic locus involved in light-regulated development and gene expression in arabidopsis [6].
• This adult-lethal phenotype indicates that the COP9 locus also plays a critical role for normal development of the light-grown plant [6].
• These properties imply that the mutation in the COP9 locus uncouples the light/dark signals from morphogenesis and light-regulated gene expression [6].
• Molecular cloning of subunit 4 of the complex revealed that it is a proteasome-COP9 complex-eIF3 domain protein encoded by a gene that maps to chromosome 5, near the chromosomal location of the cop8 and fus4 mutations [7].
• No proteins homologous to COP9 signalosome components were identified in the Saccharomyces cerevisiae genome, suggesting that the COP9 signalosome is specific for multi-cellular differentiation [13] [8].

Anatomical context of COP9

• We have also developed an Arabidopsis protoplast immunolocalization assay and demonstrated that the COP9 complex is localized in the nucleus and that its nuclear localization is not affected by light conditions or tissue types [9].
• Purification of the COP9 signalosome from porcine spleen, human cell lines, and Arabidopsis thaliana plants [10].

Associations of COP9 with chemical compounds

• Here, we show that plants with reduced COP9 signalosome levels had decreased auxin response similar to loss-of-function mutants of the E3 ubiquitin ligase SCFTIR1 [2].
• The COP9 signalosome interacts physically with SCF COI1 and modulates jasmonate responses [11].
• COP1, another COP/DET/FUS protein, is itself not a subunit of the COP9 signalosome [12].
• The Arabidopsis inositol 1,3,4-trisphosphate 5/6 kinase, AtItpk-1, is involved in plant photomorphogenesis under red light conditions, possibly via interaction with COP9 signalosome [13].

Physical interactions of COP9

• The COP9 signalosome interacts with SCF UFO and participates in Arabidopsis flower development [14].

Other interactions of COP9

• Epistatic analyses with the long hypocotyl hy1, hy2, hy3, hy4, and hy5 mutations suggested that these three loci, similar to COP1 and COP9, act downstream of both phytochromes and a blue light receptor, and probably HY5 as well [15].
• Thus, we conclude that COP8 encodes subunit 4 of the COP9 signalosome [7].
• Evidence for FUS6 as a component of the nuclear-localized COP9 complex in Arabidopsis [9].
• Here, we report the identification of two apparently redundant genes, AJH1 and AJH2, that encode a subunit of the COP9 complex [16].
• Our data provide evidence that DET1, COP1, and COP9 most likely act as negative regulators of several sets of genes, not just those involved in light-regulated seedling development [17].

Analytical, diagnostic and therapeutic context of COP9

• Both COP9 and FUS6 cofractionated into identical high molecular mass fractions in an analytical gel filtration assay, and neither was found in its monomeric form [9].
• In order to reveal the developmental function of the COP9 signalosome in animals, we have isolated Drosophila melanogaster genes encoding eight subunits of the COP9 signalosome, and have shown by co-immunoprecipitation and gel-filtration analysis that these proteins are components of the Drosophila COP9 signalosome [8].
• Indirect immunofluorescence studies suggested that the mammalian COP9 complex is largely nuclear localized [18].

References