Inhibition of nuclear factor-kappa B sensitises anterior pituitary cells to tumour necrosis factor-α- and lipopolysaccharide-induced apoptosis

Nuclear factor-kappa B (NF-κB), an important pro-inflammatory factor, is a crucial regulator of cell survival. Both lipopolysaccharide (LPS) and tumour necrosis factor (TNF)-α activate NF-κB signalling. Oestrogens were shown to suppress NF-κB activation. Oestrogens exert a sensitising action to pro-apoptotic stimuli such as LPS and TNF-α in anterior pituitary cells. In the present study, we show by western blotting that 17β-oestradiol (E(2)) decreases TNF-α-induced NF-κB/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-κB/p65 and p50 nuclear translocation. To investigate whether the inhibition of NF-κB pathway sensitises anterior pituitary cells to pro-apoptotic stimuli, we used an inhibitor of NF-κB activity, BAY 11-7082 (BAY). BAY, at a concentration that fails to induce apoptosis, has permissive action on TNF-α-induced apoptosis of lactotrophs and somatotrophs from OVX rats, as assessed by terminal deoxynucleotidyl transferase dUTP nick end labelling (TUNEL). Pharmacological inhibition of NF-κB signalling enhances E(2)-sensitising effect to TNF-α-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-κB signalling pathway sensitises anterior pituitary cells to the pro-apoptotic action of LPS and TNF-α. Because E(2) inhibits LPS- and TNF-α-activated NF-κB nuclear translocation, the present study suggests that E(2) sensitises anterior pituitary cells to TNF-α- and LPS-induced apoptosis by inhibiting NF-κB activity.