Mitogen-activated protein kinases in rat brain neuronal cultures are activated by angiotensin II type 1 receptors and inhibited by angiotensin II type 2 receptors

Neurons cultured from neonatal rat hypothalamus and brainstem contain many angiotensin II (Ang II) type 2 (AT(2)) receptors, and we previously determined that activation of these sites elicited a stimulation of serine/threonine phosphatase 2A (PP2A). Here, we have investigated the effects of Ang II on neuronal mitogen-activated protein (MAP) kinases, potential targets for PP2A. Using in-gel kinase assays and immunoprecipitation analyses we have shown that Ang II (10 nM(-1) mu M) elicits significant increases in p44(MAPK) (Erk1) and p42(MAPK) (Erk2) activities in cultured neurons, mediated via Ang II type 1 (AT(1)) receptors. This stimulatory effect of Ang II on Erk1 and Erk2 activities was potentiated by blockade of AT(2) receptors with (S)-1-[4-(dimethylamino)-3-methylphenyl]methyl-5-(diphenylacetyl)-4,5,6,7-tetrahydro-1H-imidazo[4,5-C]pyridine-6-carboxylic acid (PD 123319, 1 mu M). Furthermore, the AT(2) receptor agonist N-alpha-nicotinoyl-Tyr-Lys-(N-alpha CBZ-Arg)-His-Pro-Ile-OH (CGP42112A) (10-50 nM) caused significant decreases in neuronal Erk1 and Erk2 activities, which were abolished by PD 123319 (1 mu M) and by the PP2A inhibitor okadaic acid (3 nM). This indicates that AT(1) and AT(2) receptors have opposite actions on Erb1 and Erk2 activities in neonatal neurons. Since MAP kinases are involved in the regulation of growth/differentiation and apoptosis, our data may provide an intracellular basis for modulatory effects of Ang II receptors on these processes.