Inhibition of Nuclear Factor-Kappa B Sensitises Anterior Pituitary Cells to Tumour Necrosis Factor-α- and Lipopolysaccharide-Induced Apoptosis

Nuclear factor-kappa B (NF-kappa B), an important pro-inflammatory factor, is a crucial regulator of cell survival. Both lipopolysaccharide (LPS) and tumour necrosis factor (TNF)-alpha activate NF-kappa B signalling. Oestrogens were shown to suppress NF-kappa B activation. Oestrogens exert a sensitising action to pro-apoptotic stimuli such as LPS and TNF-alpha in anterior pituitary cells. In the present study, we show by western blotting that 17 beta-oestradiol (E-2) decreases TNF-alpha-induced NF-kappa B/p65 and p50 nuclear translocation in primary cultures of anterior pituitary cells from ovariectomised (OVX) rats. Also, the in vivo administration of E-2 decreases LPS-induced NF-kappa B/p65 and p50 nuclear translocation. To investigate whether the inhibition of NF-kappa B pathway sensitises anterior pituitary cells to pro-apoptotic stimuli, we used an inhibitor of NF-kappa B activity, BAY 11-7082 (BAY). BAY, at a concentration that fails to induce apoptosis, has permissive action on TNF-alpha-induced apoptosis of lactotrophs and somatotrophs from OVX rats, as assessed by terminal deoxynucleotidyl transferase dUTP nick end labelling (TUNEL). Pharmacological inhibition of NF-kappa B signalling enhances E-2-sensitising effect to TNF-alpha-induced apoptosis in lactotrophs but not in somatotrophs. In vivo administration of BAY allowed LPS-induced apoptosis in anterior pituitary cells from OVX rats (determined by fluorescence activated cell sorting). Furthermore, LPS-induced expression of Bcl-xL in pituitaries of OVX rats is decreased by E-2 administration. Our results show that inhibition of the NF-kappa B signalling pathway sensitises anterior pituitary cells to the pro-apoptotic action of LPS and TNF-alpha. Because E-2 inhibits LPS- and TNF-alpha-activated NF-kappa B nuclear translocation, the present study suggests that E-2 sensitises anterior pituitary cells to TNF-alpha- and LPS-induced apoptosis by inhibiting NF-kappa B activity.