IKKε-like plays an important role in the innate immune signaling of the Pacific oyster (Crassostrea gigas)

IxB-related kinase epsilon (IKK epsilon) plays a crucial role in the activation of nuclear factor kappa B (NF-kappa B) by phosphorylating inhibitor of NF-kappa B (I kappa B) and in the regulation of interferon (IFN) gene expression by phosphorylating IFN regulatory factors (IRFs). In this study, we cloned an IKK epsilon homologue cDNA (designated as CgIKK epsilon-like) from the Pacific oyster, Crassostrea gigas. The full 2896-bp cDNA sequence comprised a 2163-bp open reading frame (ORF) encoding 720 amino acids. CgIKK epsilon-like is ubiquitously expressed, and its mRNA levels in hemocytes after poly I:C, V. alginolyticus, or OsHV-1 mu Var challenge were analyzed by real-time PCR. Compared to that in the control, CgIKK epsilon-like mRNA expression levels were significantly increased at 3 h and peaked at 6 h after OsHV-1 mu Var challenge; no obvious changes were observed in expression levels until 24 h after either V. alginolyticus or poly I:C challenge, reaching a maximum at 24 h (p < 0.01) and then rapidly decreasing. CgIKK epsilon-like transfection into human cell lines induced NF-kappa B and ISRE activation, while transfection with CgIKK epsilon-like deletion mutants abolished NF-kappa B and ISRE reporter gene activation. Additionally, CgIKK epsilon-like could interact with CgTBK1 and could form homodimers strongly, which may be critical for the immune signaling transduction. Last but not least, we found that CgIKK epsilon-like may increase CgI kappa Bs phosphorylation and could interact with CgIRF8. Together, these results suggest that CgIKK epsilon-like could respond to pathogenic infection, participate in the immune signal transduction and activate NF-kappa B and ISRE reporter genes. Thus, CgIKK epsilon-like could play an important role in the oyster immune system.