Cloning and characterization of cDNAs for two distinct tumor necrosis factor receptor superfamily genes from Japanese flounder Paralichthys olivaceus

Tumor necrosis factor receptor (TNFR) superfamily regulates diverse biologic functions, including cell proliferation, differentiation, and survival, in addition to providing costimulatory signals for programmed cell death or apoptosis. In this study, cDNA fragments for two distinct TNFR homologues were obtained from a Japanese flounder, Paralichthys olivaceus, cDNA library. Full-length cDNAs of TNFR-1 and TNFR-2 homologues were obtained by using these cDNA fragments as probes. The cDNA for the Japanese flounder TNFR-1 homologue predicts a peptide of 395 amino acids that is 35% identical to the extracellular region of mouse TNFR-1, whereas the cDNA of the Japanese flounder TNFR-2 homologue predicts a peptide of 483 amino acids that is 40% identical to the extracellular region of human TNFR-2. The cytoplasmic domain contains a sequence that has the consensus motif of the death domain of the Japanese flounder TNFR-1 homologue. In a healthy fish, the mRNAs of both TNFR homologues were predominantly expressed in leukocytes, kidney, gill, and spleen. Expression of the Japanese flounder TNFR-1 homologue was induced in peripheral blood lymphocytes (PBLs) after stimulation with LPS (500 microg/ml) for 1 h, and TNFR-2 homologue was strongly induced in PBLs after stimulation with Con A (50 microg/ml) and PMA (0.35 microg/ml) for 3 h. The different expression patterns of the two distinct TNFR homologues may be critical in determining whether binding with TNF-alpha or TNF-beta have activating, proliferative, or apoptotic effects on target cells.