IFN-γ up-regulates kappa opioid receptors (KOR) on murine macrophage cell line J774

In this study we examined basal and IFN-γ-regulated expression of kappa opioid receptors (KOR) on cells of a murine macrophage cell line, J774. Basal KOR expression was found both at transcriptional and protein levels. KOR protein was predominantly located intracellular (86.4 ± 12.9% positive cells; n = 4), and only in minority of J774 cells (9.1 ± 6.4% positive cells; n = 4) on plasma membranes, as revealed by Fluorescence-Activated Cell Sorter (FACS) analysis and immunocytochemistry. Proinflammatory cytokine IFN-γ up-regulated KOR expression both at transcriptional (up to 24 times) and protein levels (up to 4.2 times). KOR expressed on J774 cells was functionally active as its ligation with Dynorphin-A(1-17) (100 nM and 1 μM) triggered phosphorylation of ERK1/2. Involvement of KOR in the Dynorphin-A(1-17)-induced triggering of ERK1/2 phosphorylation is suggested since truncated Dynorphin-A(2-17), which does not bind to KOR, was ineffective. Collectively, we have shown for the first time that cells of J774 cell line constitutively express functionally active KOR, which triggers signalization via ERK1/2 phosphorylation and which could be up-regulated by proinflammatory IFN-γ. The data may be relevant for better understanding of the role of KOR and their endogenous ligand Dynorphin-A in regulation of inflammatory and immune responses.