Cloning and functional characterization of the p65 subunit of NF-κB from olive flounder (Paralichthys olivaceus)

NF-κB is a master transcription factor found in almost all cell types that responds to diverse cellular stimuli by activating the expression of stress response genes, including immune-related genes. cDNA encoding the p65 subunit of olive flounder (Paralichthys olivaceus) NF-κB (Po-p65) was isolated through an EST analysis of an olive flounder cDNA library, a screen of BAC library, and rapid amplification of cDNA ends (RACE). The cDNA for Po-p65 encodes a polypeptide 626 amino acids in length containing a well-conserved Rel-homology domain (RHD). The primary sequence of Po-p65 showed strong homology with p65 from perch and zebrafish (82.7 and 64.4%, respectively), and shared 43.4–42.1% homology with p65 from other species, including mammals, while the N-terminal RHD of Po-p65 showed strong identity (95.6–67.8%) with that of other species. Po-p65 mRNA expression was detected in all flounder tissues examined. The over-expression of full-length Po-p65 (Po-p65f), but not of a Po-p65 C-terminus deletion mutant (Po-p65ΔC), stimulated κB element-driven reporter (κB-luc) activity in a dose-dependent manner and regulated the expression of p65 target genes, including TNF-α and IκB-α, in HINAE olive flounder cells. Po-p65f translocated to the nucleus following stimulation with poly I:C in HINAE cells. Together, these results suggest that Po-p65 is evolutionarily and functionally conserved in flounder and mammals and may provide clues to the detailed molecular mechanism(s) underlying immune response regulation in flounder.