PKC-δ and CaMKII-δ2 mediate ATP-dependent activation of ERK1/2 in vascular smooth muscle

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Abstract
ATP, a purinergic receptor agonist, has been shown to be involved in vascular smooth muscle (VSM) cell DNA synthesis and cell proliferation during embryonic and postnatal development, after injury, and in atherosclerosis. One mechanism that ATP utilizes to regulate cellular function is through activation of ERK1/2. In the present study, we provide evidence that ATP-dependent activation of ERK1/2 in VSM cells utilizes specific isoforms of the multifunctional serine/threonine kinases, PKC, and Ca2+/calmodulin-dependent protein kinase II (CaMKII) as intermediates. Selective inhibition of PKC-δ activity with rottlerin, or adenoviral overexpression of kinase-negative PKC-δ, attenuated the ATP- and phorbol 12,13-dibutyrate (PDBu)-stimulated ERK1/2 activation. Inhibition of PKC-α activity with Gö-6976, or adenoviral overexpression of kinase-negative PKC-α, was ineffective. Alternatively, treatment with KN-93, a selective inhibitor of CaMKII activation, or adenoviral overexpression of kinase-negative CaMKII-δ2, inhibited ATP-dependent activation of ERK1/2 but had no effect on PDBu- or PDGF-stimulated ERK1/2. In addition, adenoviral overexpression of dominant-negative ras (Ad.HA-RasN17) partially inhibited the ATP- and PDBu-induced activation of ERK1/2 and blocked ionomycin- and EGF-stimulated ERK1/2, and inhibition of tyrosine kinases with AG-1478, an EGFR inhibitor, or the src family kinase inhibitor PP2 attenuated ATP-stimulated ERK1/2 activation. Taken together, these data indicate that PKC-δ and CaMKII-δ2 coordinately mediate ATP-dependent transactivation of EGF receptor, resulting in increased ERK1/2 activity in VSM cells.

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