Regulation of blood pressure by the type 1A angiotensin II receptor gene.

The renin-angiotensin system plays a critical role in sodium and fluid homeostasis. Genetic or acquired alterations in the expression of components of this system are strongly implicated in the pathogenesis of hypertension. To specifically examine the physiological and genetic functions of the type 1A receptor for angiotensin II, we have disrupted the mouse gene encoding this receptor in embryonic stem cells by gene targeting. Agtr1A(-/-) mice were born in expected numbers, and the histomorphology of their kidneys, heart, and vasculature was normal. AT1 receptor-specific angiotensin II binding was not detected in the kidneys of homozygous Agtr1A(-/-) mutant animals, and Agtr1A(+/-) heterozygotes exhibited a reduction in renal AT1 receptor-specific binding to approximately 50% of wild-type [Agtr1A(+/+)] levels. Pressor responses to infused angiotensin II were virtually absent in Agtr1A(-/-) mice and were qualitatively altered in Agtr1A(+/-) heterozygotes. Compared with wild-type controls, systolic blood pressure measured by tail cuff sphygmomanometer was reduced by 12 mmHg (1 mmHg = 133 Pa) in Agtr1A(+/-) mice and by 24 mmHg in Agtr1A(-/-) mice. Similar differences in blood pressure between the groups were seen when intraarterial pressures were measured by carotid cannulation. These studies demonstrate that type 1A angiotensin II receptor function is required for vascular and hemodynamic responses to angiotensin II and that altered expression of the Agtr1A gene has marked effects on blood pressures.

Expression of the fms-like tyrosine kinase 4 gene becomes restricted to lymphatic endothelium during development.

We have recently cloned the human fms-like tyrosine kinase 4 gene FLT4, whose protein product is related to two vascular endothelial growth factor receptors FLT1 and KDR/FLK1. Here the expression of FLT4 has been analyzed by in situ hybridization during mouse embryogenesis and in adult human tissues. The FLT4 mRNA signals first became detectable in the angioblasts of head mesenchyme, the cardinal vein, and extraembryonally in the allantois of 8.5-day postcoitus (p.c.) embryos. In 12.5-day p.c. embryos, the FLT4 signal decorated developing venous and presumptive lymphatic endothelia, but arterial endothelia were negative. During later stages of development, FLT4 mRNA became restricted to vascular plexuses devoid of red cells, representing developing lymphatic vessels. Only the lymphatic endothelia and some high endothelial venules expressed FLT4 mRNA in adult human tissues. Increased expression occurred in lymphatic sinuses in metastatic lymph nodes and in lymphangioma. Our results suggest that FLT4 is a marker for lymphatic vessels and some high endothelial venules in human adult tissues. They also support the theory on the venous origin of lymphatic vessels.

The glucocorticoid receptor type II complex is a target of the HIV-1 vpr gene product.

The vpr gene of human immunodeficiency virus type 1 (HIV-1) encodes a 15-kDa virion-associated protein that functions as a regulator of cellular processes linked to the HIV life cycle. We report the interaction of a 41-kDa cytosolic viral protein R interacting protein 1 (Rip-1) with Vpr in vitro. Rip-1 displays a wide tissue distribution, including relevant targets of HIV infection. Vpr protein induced nuclear translocation of Rip-1, as did glucocorticoid receptor (GR)-II-stimulating steroids. Importantly, Vpr and Rip-1 coimmunoprecipitated with the human GR as part of an activated receptor complex. Vpr complementation of a vpr mutant virus was also mimicked by GR-II-stimulating steroids. Vpr and GR-II actions were inhibited by mifepristone, a GR-II pathway inhibitor. Together these data directly link the activity of the vpr gene product to the glucocorticoid steroid pathway and provide a biochemical mechanism for the cellular and viral activity of Vpr, as well as suggest that a unique class of antivirals, which includes mifepristone (RU486), may influence HIV-1 replication.