NF-κB p65 modulates the promoter activity of large yellow croaker (Larimichthys crocea) interleukin-2.

Interleukin-2 (IL-2) plays pivotal roles in immune regulation, particularly in T cell-mediated adaptive immunity. Precise control of IL-2 transcription is therefore essential for proper immune function. Although the regulation of mammalian IL-2 has been well characterized, the molecular mechanisms governing IL-2 expression in teleost remain poorly understood. Here, we identified and characterized the 5' flanking region of the large yellow croaker (Larimichthys crocea, Lc) IL-2, which contains many putative conserved binding sites of transcription factors critical in regulating IL-2 expression, such as NFAT, NF-κB, AP-1, Oct1, FoxP3. Functional assays demonstrated that this region could drive the expression of EGFP and luciferase, suggesting it is the LcIL-2 promoter. Its activity could be specifically induced by T cell activators (PHA, Con-A, CI, and PMA) but not innate immune stimuli. The LcNF-κB p65 could enhance the promoter activity of LcIL-2 in a dose-dependent manner, while mutations in NF-κB binding site of LcIL-2 promoter significantly impaired this activation. Chromatin immunoprecipitation further confirmed the direct binding of LcNF-κB p65 to the LcIL-2 promoter. Moreover, deletion of C-terminal conserved domains (CRs) in LcNF-κB p65 impaired its transactivation function. These findings elucidate an evolutionarily conserved yet distinct NF-κB-mediated regulatory mechanism for IL-2 expression in teleost, providing new insights into the molecular basis of fish adaptive immunity.