Characterization of the black carp TRAF6 signaling molecule in innate immune defense

Tumor necrosis factor receptor-associated factor 6 (TRAF6) plays a vital role in the innate immune response of higher vertebrates. To elucidate its function in teleost fish, TRAF6 homologue of black carp (Mylopharyngodon piceus) has been cloned and characterized in this study. Black carp TRAF6 (bcTRAF6) transcription in Mylopharyngodon piceus fin (MPF) cells was up-regulated in response to both poly (I:C) treatment and viral infection, but was suppressed by LPS stimulation. bcTRAF6 migrated around 72 KDa in immunoblot analysis and was identified as a cytosolic protein suggested to be associated with vesicles scattering in the cytoplasm. Reporter assay demonstrated that NF-κB instead of IFN was activated by bcTRAF6; and EPC cells expressing bcTRAF6 presented the same cytopathic effect (CPE) ratio to that of control cells. When co-expressed with bcMAVS, bcTRAF6 was redistributed and overlapped with the subcellular location of bcMAVS. It was interesting that bcMAVS mediated the IFN induction was up-regulated by low input of bcTRAF6 but down-regulated by high input of bcTRAF6. Taken together, the data generated in this paper supported the conclusion that bcTRAF6 associated with bcMAVS and was recruited into bcMAVS mediated signaling during host innate immune response.