Molecular characterization of tumor necrosis factor receptor-associated factor 6 (TRAF6) in pearl oyster Pinctada martensii

Tumor necrosis factor receptor-associated factor 6 (TRAF6) is a key signaling adaptor molecule for tumor necrosis factor receptor superfamily and Toll-like receptor/interleukin-1 receptor family members. It signals the upstream receptors and is involved in a wide range of biological functions, such as immunity and bone metabolism. In this report, the TRAF6 gene from the pearl oyster Pinctada martensii (designated as PmTRAF6) was identified and characterized. The obtained full-length PmTRAF6 cDNA was 2273 bp, containing a 5'-untranslated region (UTR) of 297 bp, a 3'-UTR of 128 bp with a 42-bp poly (A) tail, and an open reading frame of 1848 bp that encoded 616-amino acid residues. The deduced protein sequence of PmTRAF6 contained a conserved TRAF family motif including a RING-type zinc finger, two TRAF-type zinc fingers, and a coiled-coil region followed by one meprin and TRAF homology domain. Multiple-sequence alignment indicated that TRAF6 was highly conserved among species, and PmTRAF6 showed 53% sequence identity to Azumapecten farreri and Mizuhopecten yessoensis. Furthermore, an amino acid sequence containing a low-complexity region was inserted in the TRAF6s from mollusk. Quantitative real-time polymerase chain reaction analysis demonstrated that PmTRAF6 was constitutively expressed in all tissues studied, with the most abundant mRNA expression in hepatopancreas and gill in P. martensii. After lipopolysaccharide stimulation, the expression of PmTRAF6 mRNA was dramatically upregulated. These results suggested that the obtained PmTRAF6 was a member of the TRAF6 family and perhaps involved in the innate immune response of pearl oyster.