Nerve growth factor regulates dopamine D(2) receptor expression in prolactinoma cell lines via p75(NGFR)-mediated activation of nuclear factor-kappaB.

Two groups of prolactinoma cell lines were identified. One group (responder) expresses both D(2) dopamine receptors and an autocrine loop mediated by nerve growth factor (NGF) and one group (nonresponder) lacks both D(2) receptors and NGF production. D(2) receptor expression in these cell lines is dependent on NGF. Indeed, NGF inactivation in responder cells decreases D(2) receptor density, while NGF treatment induces D(2) receptor expression in nonresponders. Here we show that inactivation of p75(NGFR), but not of trkA, resulted in D(2) receptor loss in responder cells and prevented D(2) receptor expression induced by NGF in the nonresponder. Analysis of nuclear factor-kappaB (NF-kappaB) nuclear accumulation and binding to corresponding DNA consensus sequences indicated that in NGF-secreting responder cells, but not in nonresponders, NF-kappaB is constitutively activated. Moreover, NGF treatment of nonresponder cells induced both nuclear translocation and DNA binding activity of NF-kappaB complexes containing p50, p65/RelA, and cRel subunits, an effect prevented by anti-p75(NGFR) antibodies. Disruption of NF-kappaB nuclear translocation by SN50 remarkably impaired D(2) receptor expression in responder cells and prevented D(2) gene expression induced by NGF in nonresponders. These data indicate that in prolactinoma cells the effect of NGF on D(2) receptor expression is mediated by p75(NGFR) in a trkA-independent way and that NGF stimulation of p75(NGFR) activates NF-kappaB, which is required for D(2) gene expression. We thus suggest that NF-kappaB is a key transcriptional regulator of the D(2) gene and that this mechanism may not be confined to pituitary tumors, but could also extend to other dopaminergic systems.