Norepinephrine inhibits the cytotoxicity of NK92‑MI cells via the β2‑adrenoceptor/cAMP/PKA/p‑CREB signaling pathway

Norepinephrine (NE) can regulate natural killer (NK) cell activity, but the mechanism remains unclear. In the present study the roles of adrenergic receptors (ARs) in inhibiting NK92‑MI cells‑mediated cytotoxicity by NE were investigated. To examine the effect of NE on NK92‑MI cytotoxicity, a lactate dehydrogenase‑release cytotoxicity assay was used to determine the cytotoxicity of NK92‑MI cells against K562 cells. To evaluate the possible function of the α, β1 and β2 AR in mediating NE‑induced effects, NK92‑MI cells were pre‑incubated with phenol‑amine, CGP20712A and ICI118551 prior to stimulation by NE. To evaluate the role of cyclic adenosine monophosphate (cAMP)‑protein kinase A (PKA) signaling pathway in the inhibitory effect on cytotoxicity of NK92‑MI cell by NE, NK92‑MI cells were pre‑incubated with PKA inhibitor Rp‑8‑Br‑cAMP prior to stimulation by NE. It was demonstrated that NE decreased cytotoxicity and downregulated the expression of perforin, granzyme B and interferon (IFN)‑γ of NK92‑MI cells in a dose‑dependent manner. Blocking NE functional receptors by ARs antagonists, particularly of β2 AR antagonist, suppressed the inhibitory effect of NE on cytotoxicity and expression of perforin, granzyme B, IFN‑γ of NK92‑MI cells significantly. Blockade of β2 AR in NE treated NK92‑MI cells resulted in a reduction of the expression of phosphorylated (p)‑cAMP‑responsive element‑binding protein (CREB) and intracellular cAMP concentration. Inhibiting the activity of PKA by Rp‑8‑Br‑cAMP in NE treated NK92‑MI cells resulted in increased cytotoxicity. The results of the present study suggest that NE can inhibit cytotoxicity and expression of perforin, granzyme B, IFN‑γ of NK92‑MI cell mainly via the β2‑AR/cAMP/PKA/p‑CREB signaling pathway.