Delta opioid receptors expressed by stably transfected jurkat cells signalthrough the map kinase pathway in a ras-independent manner

Delta opioid receptors (DOR) are G-protein coupled 7-transmembrane receptor s (GPCR), expressed by thymic and splenic T cells, that modulate interleuki n (IL)-2 production and proliferation in response to concanavalin A or cyos slinking the TCR. Mitogen-activated protein kinases (MAPKs) are involved in mediating intracellular responses to TCR crosslinking. In addition, MAPKs can be activated by signaling cascades that are initiated by the release of G-proteins from GPCRs. To determine whether DORs expressed by T cells sign al through the MAPKs, extracellular-regulated kinases (ERKs) 1 and 2, two d elta opioid peptides, deltorphin and pD-Ala(2),D-Leu(5)]-enkephalin (DADLE) , were studied in Jurkat cells that had been stably transfected with DOR (D OR-Ju.1). These peptides rapidly and dose-dependently induced ERK phosphory lation; pretreatment with naltrindole (NTI), a selective DOR antagonist, ab olished this. Pertussis toxin (PTX) also inhibited phosphorylation, indicat ing the involvement of the G(i/o) proteins. Herbimycin A, a protein tyrosin e kinase (PTK) inhibitor, reduced the DADLE-induced ERK phosphorylation by 68%. ERK phosphorylation was inhibited by Bisindolylmaleimide 1 (GF109203X) , an inhibitor of PKC. and by pretreatment with PMA prior to DADLE. A GTP/G DP exchange assay was used to assess the potential role of Ras in the pathw ay leading to ERK phosphorylation; DADLE failed to stimulate GTP/GDP exchan ge in comparison to PMA. Additional studies showed that DADLE stimulated an increase in cfos mRNA; this was reduced by the inhibitor of MAPK/ERK kinas e (MEK). PD98059. Therefore, in DOR-Ju.1 cells, DOR agonists stimulate ERK phosphorylation in a Ras independent and PKC-dependent manner; PTKs appear to be involved. MAPKs mediate the increase in cfos mRNA induced by DOR agon ists. (C) 1999 Elsevier Science B.V. All rights reserved.