B‐Myb regulates the A2B adenosine receptor in vascular smooth muscle cells

Abstract

The A_2B adenosine receptor (A_2BAR) has been described to control various vascular functions, including inhibition of smooth muscle cell proliferation. Here, we sought to understand the regulation of A_2BAR gene expression in aortic vascular smooth muscle cells (VSMCs), with a focus on the proliferation phase. Assays with A_2BAR‐β‐gal aortic VSMCs, in which the endogenous A_2BAR gene promoter drives the expression of prokaryotic β‐galactosidase (β‐gal) instead of the endogenous A_2BAR gene, show that β‐gal expression is upregulated when the cells are induced to exit from cell cycle arrest. Similarly, the level of A_2BAR mRNA is upregulated in proliferating primary aortic VSMCs. In search of related mechanisms, it was noted that the A_2BAR gene promoter contains several putative binding sites for the proliferation‐inducing transcription factor, B‐Myb. Using a clone of the 5′ region upstream of the mouse A_2BAR gene linked to a reporter gene, B‐Myb site deletion mutants were generated. It was determined that B‐Myb upregulates the A_2BAR gene promoter, and specific promoter binding sites were identified as functional. In accordance, B‐Myb also elevates endogenous A_2BAR mRNA and receptor activity, and this activity decreases cell proliferation. Our data are novel in that they show that this proliferation‐inhibiting A_2BAR is itself an inducible receptor regulated by B‐Myb. J. Cell. Biochem. 103: 1962–1974, 2007.