Mitogenic signaling via endogenous kappa-opioid receptors in C6 glioma cells: Evidence for the involvement of protein kinase C and the mitogen-activated protein kinase signaling cascade

As reports on G protein-coupled receptor signal transduction mechanisms con tinue to emphasize potential differences in signaling due to relative recep tor levels and cell type specificities, the need to study endogenously expr essed receptors in appropriate model systems becomes increasingly important . Here we examine signal transduction mechanisms mediated by endogenous K-o pioid receptors in C6 glioma cells, an astrocytic model system. We find tha t the kappa-opioid receptor-selective agonist U69,593 stimulates phospholip ase C activity, extracellular signal-regulated kinase 1/2 phosphorylation, PYK2 phosphorylation, and DNA synthesis. U69,593-stimulated extracellular s ignal-regulated kinase 1/2 phosphorylation is shown to be upstream of DNA s ynthesis as inhibition of signaling components such as pertussis toxin-sens itive G proteins, L-type Ca2+ channels, phospholipase C, intracellular Ca2 release, protein kinase C, and mitogen-activated protein or extracellular signal-regulated kinase kinase blocks both of these downstream events. In a ddition, by overexpressing dominant-negative or sequestering mutants, we pr ovide evidence that extracellular signal-regulated kinase 1/2 phosphorylati on is Ras-dependent and transduced by G(beta gamma) subunits. In summary, w e have delineated major features of the mechanism of the mitogenic action o f an agonist of the endogenous kappa-opioid receptor in C6 glioma cells.