Effect of angiotensin AT2 receptor on cell differentiation and apoptosis in leiomyosarcoma, endothelial cells and PC12W cells

There is evidence indicating that Ang II interferes with a number of cellular processes in various cells. To explore the role of AT1 and AT2 receptors for the proliferation and growth of the human leiomyosarcoma (SK-UT-1), the effects of Ang II on the proliferation, differentiation and apoptosis in this cells line were studied. RT-PCR analysis revealed that SK-UT-1 cells express both AT1 and AT2 receptors. Activation of neither receptor subtype did alter 3H-thymidine incorporation and the number of cells. However, stimulation of AT2 receptors up-regulated mRNA and protein levels of smooth muscle cell differentiation markers, SM22 and calponin. Activation of the AT2 receptor in SK-UT-1 cells also induced apoptosis which was detectable 36 or 48 hours post receptor stimulation. These results can be interpreted as an effort of Ang II acting on the AT2 receptor to antagonise proliferation of tumor cells, to promote their differentiation or to induce apoptosis. Further experiments were designed to study the signal transduction pathways involved in the AT2 receptor-induced differentiation of coronary endothelial cells (CEC) and PC12W cells. In CEC, AT2 receptor stimulation induced zincfinger homoeodomain enhancer binding protein(Zfhep) mRNA expression. Zfhep mRNA up-regulation could only be detected when the AT1 receptor was inhibited, demonstrating a negative-regulatory influence of AT1 receptors on AT2-receptor mediated actions. The induction of Zfhep indicates that the AT2 receptor may play a role in the orchestration of intracellular events associated with embryonic development or differentiation. Data presented in the third part of this thesis also demonstrate that Ang II, via activation of AT2 receptors, can stimulate cell differentiation in PC12W cells by NO-related and cGMP-dependent mechanisms through up-regulation of eNOS mRNA level. The effect is independent on bradykinin activation. These results identify some intracellular components of the signaling pathways activated by the AT2 receptor involved in the proposed function of this receptor in the development, regeneration and differentiation