[Renin: structure and expression regulation of the gene, biosynthesis, and cellular pathways of secretion]

The renin angiotensin system plays a major role in the control of blood pressure and electrolyte balance. It consists of a cascade of proteolytic cleavages leading to the biologically active angiotensin II (AII). Renin acts on angiotensinogen to yield angiotensin I (AI). AI is a prohormone and must be cleaved to the octapeptide AII by the action of the angiotensin I converting enzyme. Application of recombinant DNA technology has made possible the cloning of the renin gene and its cDNA which has provided newer insights into the regulation of renin gene expression, biosynthesis, and secretion. The information gained from such molecular biology techniques may contribute importantly to the efforts in the development of an effective renin inhibitor for the treatment of hypertension. The mouse and rat renin gene contains nine exons separated by eight intervening sequences, in contrast the human renin gene contains ten exons separated by nine introns. However, the renin gene of the three species spans 12 kb approximately. In its 5' flanking region, major control elements are present which include promotors and enhancers as well as regulatory elements such as estrogen and glucocorticoid receptor sites, and cAMP induction sequences. The combined action of these elements will result in tissue specific expression and regulation of the gene. In addition to the control at the gene expression level, renin is also regulated at the post-translational and secretory levels. The translational product of renin mRNA is preprorenin, which is cotranslationally cleaved to prorenin, an inactive precursor of renin. The majority of the new synthesized human prorenin is constitutively secreted. However, prorenin is also processed intracellularly and converted to the mature single chain active renin which is stored in secretory granules. Active renin is released by a regulated mechanism which can be stimulated by cAMP and other secretagogues. Studies are under way to examine the responses of renin gene expression, biosynthesis and secretion to various physiological conditions and to determine if there are alterations in the structure and expression of the renin gene that may be involved in the development of clinical and experimental hypertension.