Involvement of NFkappaB signaling pathway in the proapoptotic action of estrogens in the anterior pituitary gland

G. EIJO; S. ZARATE; G. JAITA; J. FERRARIS; M. L. MAGRI; D. RADL; V.ZALDIVAR,; V. BOTI; D. PISERA; A. SEILICOVICH

Boston

Congreso; 93º Annual Meeting of the Endocrine Society; 2011

Nuclear Factor kappa B (NFkB), a transcription factor activated by several stimuli including TNF-á and lipopolysaccharide (LPS), induces the expression of genes involved in cell survival. Activation of estrogen receptors mediates the inhibition of the NF B pathway in various cell types. Since in anterior pituitary (AP) cells, estrogens exert a sensitizing effect to proapoptotic stimuli, we investigated whether the estrogenic action involves inhibition of this pathway. We determined the effect of 17â-estradiol (E2) on NF B/p65 and p50 nuclear translocation in primary cultures of AP cells from ovariectomized (OVX) rats. As determined by Western blot, E2 decreased TNF-á-induced NFkB/p65 and p50 translocation in cultured AP cells. E2 administration (200 mg/kg for 2 days) to OVX rats reduced LPS-induced activation of NF B/p65 and p50 in the anterior pituitary gland as well as Bcl-xL expression (C: 1.0 ± 0.0, LPS: 1.4 ± 0.1, E2: 1.2 ± 0.1, E2+LPS: 1.2 ± 0.1; p< 0.01; ANOVA). To investigate whether inhibition of the NFkB pathway sensitizes AP cells to proapoptotic stimuli, the cells were incubated with BAY 11-7082 (Bay), an inhibitor of NF B pathway. In the presence of Bay at a concentration that does not induce apoptosis (1 µM), TNF-á increased the percentage of TUNEL positive-lactotropes (C: 3.8%, TNF-á: 4.1%, Bay: 3.6%, Bay + TNF-á: 17.5%; p< 0.01;chi2) and somatotropes (C: 3.8%, TNF-á: 3.6%, Bay: 3.4%, Bay + TNF-á: 7.5%; p<0.01;chi2) from OVX rats. E2 enhanced the sensitizing action of Bay in TNF-á-induced apoptosis of lactotropes (TNF-á: 4.1%, Bay + TNF-á: 17.2%, E2 + TNF-á : 15.7%, Bay + E2 + TNF-á: 37.8%; p<0.01;chi2) but not of somatotropes. LPS administration also increased the percentage of apoptosis in AP cells when OVX rats were treated with Bay (5 mg/Kg) (V: 9.2 ± 0.9, LPS: 10.4 ± 0.6, Bay: 8.9 ± 0.5, Bay + LPS: 19.9 ± 0.3; p<0.01; ANOVA). These results suggest that E2 sensitizes AP cells to proapoptotic stimuli by decreasing the activity of the NFkB pathway. Additive effects of E2 and Bay suggest that additional mechanisms contribute to TNF-á-induced apoptosis in lactotropes