Norepinephrine activates NF-κB transcription factor in cultured rat pineal gland.

Abstract Aims The circadian rhythm in mammalian pineal melatonin secretion is modulated by norepinephrine (NE) released at night. NE interaction with β 1 -adrenoceptors activates PKA that phosphorylates the transcription factor CREB, leading to the transcription and translation of the arylalkylamine- N -acetyltransferase (AANAT) enzyme. Several studies have reported the interplay between CREB and the nuclear factor-κB (NF-κB) and a circadian rhythm for this transcription factor was recently described in the rat pineal gland. In this work we studied a direct effect of NE on NF-κB activation and the role played by this factor on melatonin synthesis and Aanat transcription and activity. Main methods Cultured rat pineal glands were incubated in the presence of two different NF-κB inhibitors, pyrrolidine-dithiocarbamate or sodium salicylate, and stimulated with NE. Melatonin content was quantified by HPLC with electrochemical detection. AANAT activity was measured by a radiometric assay and the expression of Aanat mRNA was analyzed by real-time PCR. Gel shift assay was performed to study the NF-κB activation in cultured rat pineal glands stimulated by NE. Key findings Our results showed that the p50/p50 homodimer of NF-κB is activated by NE and that it has a role in melatonin synthesis, acting on Aanat transcription and activity. Significance Here we present evidence that NF-κB is an important transcription factor that acts, directly or indirectly, on Aanat transcription and activity leading to a modulation of melatonin synthesis. NE plays a role in the translocation of NF-κB p50/p50 homodimer to the nucleus of pinealocytes, thus probably influencing the nocturnal pineal melatonin synthesis.