Interferon Regulatory Factor-1 Up-regulates Angiotensin II Type 2 Receptor and Induces Apoptosis

Abstract

The expression of the angiotensin II type 2 (AT 2 ) receptor is developmentally and growth regulated. In cultured R3T3 cells, expression of this receptor is markedly induced at the confluent state and with serum deprivation. In this study we demonstrated that the removal of serum from culture media resulted in the induction of apoptosis in these cells and the addition of angiotensin II further enhanced apoptosis. We have previously identified an interferon regulatory factor (IRF) binding motif in the mouse AT 2 receptor gene promoter region. In this report, we observed that serum removal increased IRF-1 expression, with a rapid and transient decrease of IRF-2. To prove that the changes in IRFs after serum removal mediated apoptosis and up-regulated AT 2 receptor, we transfected antisense oligonucleotides for IRF-1 or IRF-2 into R3T3 cells and observed that IRF-1 antisense oligonucleotide attenuated apoptosis and abolished the up-regulation of AT 2 receptor. IRF-2 antisense oligonucleotide pretreatment did not affect the onset of apoptosis after serum removal; instead, it increased AT 2 receptor binding and enhanced angiotensin II-mediated apoptosis. Taken together, these results suggest that increased IRF-1 after serum starvation contributes to the induction of apoptosis and that increased IRF-1 up-regulates the AT 2 receptor expression after serum starvation, resulting in enhanced angiotensin IImediated apoptosis.Angiotensin II (Ang II) 1 exerts various actions in its diverse target tissues controlling vascular tone, hormone secretion, tissue growth, and neuronal activities. Most of the known effects of Ang II in adult tissues are mediated by the Ang II type 1 (AT 1 ) receptor. Recently, a second receptor subtype known as AT 2 receptor has been cloned by us and others (1, 2). The AT 2 receptor is abundantly and widely expressed in fetal tissues, but present only in at limited levels in adult tissues such as adrenal medulla, specific brain regions, uterine myometrium, heart, and atretic ovarian follicles (3-8). The highly abundant expression of this receptor during embryonic and neonatal growth and quick disappearance after birth has led to the suggestion that this receptor is involved in growth, development, and/or differentiation. Our studies using in vivo gene transfer of the rat AT 2 receptor into an injured rat carotid artery have demonstrated an attenuation of neointimal hyperplasia resulting from AT 2 receptor transgene overexpression (9), and Stoll et al. (10) also demonstrated that the antiproliferative actions of the AT 2 receptor offset the growth promoting effects mediated by the AT 1 receptor.Greater than 99.9% of the ovarian follicles present at birth undergo atresia, an event dependent on apoptosis or "programmed cell death." Interestingly, AT 2 receptor expression is tightly associated with ovarian follicular atresia (3,8). AT 2 receptor is also abundantly expressed in immature brain and some specific regions of the brain (5, 6). Approximately half of the neurons produced during embryogenesis di...

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