Adenosine A2A receptor mRNA regulation by nerve growth factor is TrkA-, Src-, and Ras-dependent via extracellular regulated kinase and stress-activated protein kinase/c-Jun NH2-terminal kinase

We have shown previously that nerve growth factor (NGF) down-regulates adenosine A(2A) receptor (A(2A)AR) mRNA in PC12 cells, To define cellular mechanisms that modulate A(2A)AR expression, A(2A)AR mRNA and protein levels were examined in three PC12 sublines: i) PC12nnr5 cells, which lack the high affinity NGF receptor TrkA, ii) srcDN2 cells, which overexpress kinase-defective Src, and iii) 17.26 cells, which overexpress a dominant-inhibitory Ras, In the absence of functional TrkA, Src, or Ras, NGF-induced down-regulation of A(2A)AR mRNA and protein was significantly impaired. However, regulation of A(2A)AR expression was reconstituted in PC12nnr5 cells stably transfected with TrkA. Whereas NGF stimulated the mitogen-activated protein kinases p38, extracellular regulated kinase 1 and 2 (ERK1/ERK2), and stress-activated protein kinase/c-Jun NH2-terminal kinase (SAPK/JNK) in PC12 cells, these kinases were activated only partially or not at all in srcDN2 and 17.26 cells. Inhibiting ERK1/ERK2 with PD98059 or inhibiting SAPK/JNK by transfecting cells with a dominant-negative SAPK beta/JNK3 mutant partially blocked NGF-induced down-regulation of A(2A)AR expression in PC12 cells, In contrast, inhibiting p38 with SB203580 had no effect on the regulation of A(2A)AR mRNA and protein levels. Treating SAPK beta/JNK3 mutant-transfected PC12 cells with PD98059 completely abolished the NGF-induced decrease in A(2A)AR mRNA and protein levels, These results reveal a role for ERK1/ERK2 and SAPK/JNK in regulating A(2A)AR expression.