Activation of intracellular angiotensin AT(2) receptors induces rapid cell death in human uterine leiomyosarcoma cells

The presence of angiotensin type 2 (AT(2)) receptors in mitochondria and their role in NO generation and cell aging were recently demonstrated in various human and mouse non-tumour cells. We investigated the intracellular distribution of AT(2) receptors including their presence in mitochondria and their role in the induction of apoptosis and cell death in cultured human uterine leiomyosarcoma (SK-UT-1) cells and control human uterine smooth muscle cells (HutSMC). The intracellular levels of the AT(2) receptor are low in proliferating SK-UT-1 cells but the receptor is substantially up-regulated in quiescent SK-UT-1 cells with high densities in mitochondria. Activation of the cell membrane AT(2) receptors by a concomitant treatment with angiotensin II and the AT(1) receptor antagonist, losartan, induces apoptosis but does not affect the rate of cell death. We demonstrate for the first time that the high-affinity, non-peptide AT(2) receptor agonist, Compound 21 (C21), penetrates the cell membrane of quiescent SK-UT-1 cells, activates intracellular AT2 receptors and induces rapid cell death; approximately 70% of cells died within 24 h. The cells, which escaped cell death, displayed activation of the mitochondrial apoptotic pathway, i.e. down-regulation of the Bcl-2 protein, induction of the Bax protein and activation of caspase-3. All quiescent SK-UT-1 cells died within 5 days after treatment with a single dose of C21. C21 was devoid of cytotoxic effects in proliferating SK-UT-1 cells and in quiescent HutSMC. Our results point to a new, unique approach enabling the elimination non-cycling uterine leiomyosarcoma cells providing that they over-express the AT(2) receptor.