title: CgIκB3, the third novel inhibitor of NF-kappa B (IκB) protein, is involved in the immune defense of the Pacific oyster, Crassostrea gigas.
abstract: Inhibitor of NF-κB (IκB), the important regulator of NF-κB/Rel signaling pathway, plays the crucial role in immune response of both vertebrates and invertebrates. Here, a novel homologue of IκB was cloned from Crassostrea gigas, and designated as CgIκB3. The complete CgIκB3 cDNA was 1282 bp in length, including a 942 bp open reading frame (ORF), a 51 bp 5' UTR and a 289 bp 3' UTR. The ORF encodes a putative protein of 313 amino acids with a predicted molecular weight of approximately 34.7 kDa. Sequence analysis reveals that CgIκB3 contains a conserved degradation motif but with only five ankyrin repeats. Neither a PEST domain nor a C-terminal casein kinase II phosphorylation site was identified through either alignment or bioinformatic prediction. Phylogenetic analysis suggested that CgIκB3 shares common ancestor with CgIκB1 rather CgIκB2, and theoretically it may originate from one duplication event prior to divergence of CgIκB1 and CgIκB2. Tissue expression analyses demonstrated that CgIκB3 mRNA is the most abundant in gills and heart. The expression following PAMP infection showed that CgIκB3 was significantly up-regulated in a similar pattern when challenged with LPS, HKLM or HKVA, respectively. Moreover, similar to CgIκB1 and CgIκB2, CgIκB3 can also inhibit Rel dependent NF-κB activation in HEK293 cells in a dose-dependent manner. In summary, these findings suggest that CgIκB3 can be as the functional inhibitor of NF-κB/Rel and involved in the host defense of C. gigas. The discovery of the third IκB emphasizes the complexity and importance of the regulation on NF-κB activation.
authors.affiliation: Key Laboratory of Tropical Marine Bio-resources and Ecology and Guangdong Provincial Key Laboratory of Applied Marine Biology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China; Graduate School of the Chinese Academy of Sciences, Beijing 100049, China; Guangdong Key Laboratory of Laboratory Animals, Guangdong Laboratory Animals Monitoring Institute, Guangzhou, China.
authors.forename: Fengjiao
authors.initials: F
authors.lastname: Xu
authors.affiliation: Key Laboratory of Tropical Marine Bio-resources and Ecology and Guangdong Provincial Key Laboratory of Applied Marine Biology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China; South China Sea Bio-Resource Exploitation and Utilization Collaborative Innovation Center, Guangzhou 510275, China.
authors.forename: Jun
authors.initials: J
authors.lastname: Li
authors.affiliation: Key Laboratory of Tropical Marine Bio-resources and Ecology and Guangdong Provincial Key Laboratory of Applied Marine Biology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China; South China Sea Bio-Resource Exploitation and Utilization Collaborative Innovation Center, Guangzhou 510275, China.
authors.forename: Yuehuan
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: School of Biological Science and Technology, Qiongzhou University, Sanya 572022, China.
authors.forename: Xiaomei
authors.initials: X
authors.lastname: Li
authors.affiliation: Key Laboratory of Tropical Marine Bio-resources and Ecology and Guangdong Provincial Key Laboratory of Applied Marine Biology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China; South China Sea Bio-Resource Exploitation and Utilization Collaborative Innovation Center, Guangzhou 510275, China. Electronic address: yzhang@scsio.ac.cn.
authors.forename: Yang
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: Key Laboratory of Tropical Marine Bio-resources and Ecology and Guangdong Provincial Key Laboratory of Applied Marine Biology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China; South China Sea Bio-Resource Exploitation and Utilization Collaborative Innovation Center, Guangzhou 510275, China.
authors.forename: Zhiming
authors.initials: Z
authors.lastname: Xiang
authors.affiliation: Key Laboratory of Tropical Marine Bio-resources and Ecology and Guangdong Provincial Key Laboratory of Applied Marine Biology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China; South China Sea Bio-Resource Exploitation and Utilization Collaborative Innovation Center, Guangzhou 510275, China. Electronic address: carlzyu@scsio.ac.cn.
authors.forename: Ziniu
authors.initials: Z
authors.lastname: Yu
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D049896:Crassostrea / Q000235:genetics* / Q000276:immunology* / Q000378:metabolism; D006434:Hemocytes / Q000276:immunology* / Q000378:metabolism; D020672:I-kappa B Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D008969:Molecular Sequence Data; D016328:NF-kappa B / Q000235:genetics / Q000378:metabolism; D009928:Organ Specificity; D000069452:Pathogen-Associated Molecular Pattern Molecules / Q000494:pharmacology; D010802:Phylogeny; D016415:Sequence Alignment; D015398:Signal Transduction
chemical_list: D020672:I-kappa B Proteins; D016328:NF-kappa B; D000069452:Pathogen-Associated Molecular Pattern Molecules
keywords: CgIκB3; Crassostrea gigas; Gene duplication; Immune defense; Rel/NF-κB