Dopamine D-2 receptor activation causes mitogenesis via p44/42 mitogen-activated protein kinase in opossum kidney cells

This study was conducted to determine the expression of dopamine D-2-like r eceptors in opossum kidney (OK) cells and to examine the potential role of these receptors in mitogenesis. First, the presence of D-2-like receptor bi nding sites in OK cell membranes was demonstrated by radioligand binding. u sing [H-3]spiperone. The D-2-like receptor subtypes expressed in OK cells w ere subsequently demonstrated, by Western blotting, to be D-2, D-3, and D-4 receptors. OK cells were stimulated with bromocriptine. (+/-)-2-(N-phenyle thyl-N-propyl)amino-5-hydroxytetralin hydrochloride. (R)-(+)-2-dipropylamin o-7-hydroxy-1,2,3,4-tetrahydronaphthalene hydrobromide. or PD 168,077 malea te (D-2-like, D-2, D-3, and D-4 receptor agonists. respectively), and mitog enesis was measured as a function of [H-3]thymidine incorporation. It was o bserved that, whereas bromocriptine and (R)-(+/-)-2-(N-phenylethyl-N-propyl )amino-5-hydroxytetralin hydrochloride produced increases in [H-3]thymidine incorporation, (R)-(+)-2-dipropylamino-7-hydroxy- 1,2,3,4-tetrahydronaphth alene hydrobromide and PD 168.077 maleate did not produce such an effect, i ndicating the involvement of D-2 receptors in the mitogenic response. Pertu ssis toxin and PD 98059 blocked the mitogenesis caused by bromocriptine, su ggesting a role for G(i) or G(o) proteins and p44/42 mitogen-activated prot ein kinase (MAPK), respectively. Furthermore. it was observed that bromocri ptine produced a time-dependent increase in the phosphorylation (activation ) of p44/42 MAPK, which was blocked by domperidone, pertussis toxin, or PD 98059. Therefore. this study demonstrates that, although OK cells express D -2, D-3, and D-4 receptors, activation of only D-2 receptors causes mitogen esis via phosphorylation of p44/42 MAPK. Furthermore, the cellular mechanis ms contributing to D-2 receptor-mediated phosphorylation of p44/42 MAPK see m to involve the tyrosine kinase, phosphatidylinositol-3-kinase. and protei n kinase C pathways. It is likely that bromocriptine and other preferential D-2 receptor agonists might provide protection against ischemic reperfusio n injury in renal proximal tubular cells, by increasing the survival rates for ischemic cells.