A Role of p75 in NGF-Mediated Down-Regulation of the A_2A Adenosine Receptors in PC12 Cells

Abstract

Nerve growth factor (NGF) induces differentiation of the rat pheochromocytoma clone (PC12) by activating the high affinity receptor, p140^trkA, linked to mitogen-activated protein kinase. While the physiological role of the low affinity NGF receptor (p75) has not been clearly defined, this receptor promotes activation of nuclear factor (NF) κB in Schwann cells. PC12 cells express the A_2A adenosine receptor (AR), whose expression is significantly decreased by NGF treatment. In this study, we determined whether TrkA or p75 is involved in NGF-mediated regulation of A_2AAR expression. NGF treatment decreased A_2AAR in a time-dependent manner, with maximal effects observed by 1 day, and continued down-regulation of the receptor for up to 3 days in the presence of NGF. The decrease in A_2AAR was associated with a more delayed decrease in the steady-state levels of the A_2AAR mRNA. Down-regulation of the A_2AAR at 1 day was mimicked by activators of NFκB, such as H₂O₂, and ceramide, and was attenuated by the inhibitor pyrrolidine dithiocarbamate or following transient transfection of PC12 cells with a dominant negative IκBα mutant. Moreover, NGF stimulated nuclear accumulation of p65 subunits of NFκB (but not p50 subunits) in PC12 cells, as determined by electrophoretic mobility shift assays and by Western blotting. In contrast, inhibition of TrkA by AG879 or of TrkA-dependent mitogen-activated protein kinase mitogen-activated protein kinase kinase with PD98059 blocked PC12 cell differentiation without affecting A_2AAR down-regulation, suggesting dissociation between these two phenomena. Taken together, these data provide strong support for the involvement of the p75/NFκB pathway in NGF-mediated down-regulation of A_2AAR in PC12 cells.