Regulation of inhibitory pratein-κB and monocyte chemoattractant protein-1 by angiotensin II type 2 receptor-activated Src homology protein tyrosine phosphatase-1 in fetal vascular smooth muscle cells

Abstract

In the present study we examined the effects of angiotensin II (Ang II) type 2 (AT2) receptor stimulation on AT1 receptor-mediated monocyte chemoattractant protein-1 (MCP-1) expression and the possible mechanisms of AT2 receptor-mediated signaling in cultured rat fetal vascular smooth muscle cells, which express both AT1 and AT2 receptors. Ang II stimulation Induced MCP-1 mRNA expression as well as an increase in nuclear factor-κB (NF-κB) binding to the corresponding cis DNA element of the MCP-1 promoter region and a decrease in the cytosolic inhibitory protein-κB (IκB) protein level via AT 1 receptor stimulation, whereas stimulation of the AT2 receptor decreased Ang II-induced MCP-1 expression, NF-κB DNA binding, and IκB degradation, suggesting that activation of the AT2 receptor attenuated AT1 receptor-mediated MCP-1 expression via a decrease in NF-κB DNA binding and an increase in IκB stability. Moreover, we demonstrated that AT2 receptor stimulation attenuated TNFα-mediated NF-κB activation and MCP-1 expression. A tyrosine phosphatase inhibitor, orthovanadate, attenuated the AT2 receptor-mediated increase in IκB protein. Moreover, we observed that two IκB subunits (IκBα and IκBβ) were tyrosine-phosphorylated after Ang II stimulation. Transfection of a dominant-negative Src homology protein tyrosine phosphatase-1 mutant into vascular smooth muscle cells inhibited the AT2 receptor-mediated increase in IκB, leading to a significant increase in AT1 receptor-induced NF-κB activation and MCP-1 expression. Taken together, our results demonstrated that AT2 receptor stimulation attenuated MCP-1 expression via IκB stabilization, and Src homology protein tyrosine phosphatase-1 might play a critical role in the transcriptional regulation of MCP-1 expression through the control of IκB protein stability.