ANGIOTENSINOGEN GENE-EXPRESSION IS STIMULATED BY THE CAMP-RESPONSIVE ELEMENT-BINDING PROTEIN IN OPOSSUM KIDNEY-CELLS

It has been reported previously that the addition of isoproterenol or forskolin stimulates the expression of the angiotensinogen (ANG) gene in opossum kidney (OK) 27 cells, an OK cell line with a fusion gene co ntaining the 5'-flanking regulatory sequence of the rat ANG gene fused with a human growth hormone (hGH) gene as a reporter, pOGH (ANG N-149 8/+18), permanently integrated into their genomes. To investigate whet her the effect of isoproterenol or forskolin on the expression of the ANG gene is mediated via the nuclear 43-kD cAMP-responsive element bin ding protein (CREB), OK 27 cells were transiently transfected with an expression plasmid containing the cDNA for the 43-kD CREB (pRSV/CREB). The level of expression of the pOGH (ANG N-1498/+18) in OK 27 cells w as estimated by the amount of immunoreactive hGH secreted into the cul ture medium. Transfection of pRSV/CREB alone stimulated the expression of pOGH (ANG N-1498/+18). The addition of isoproterenol or forskolin further enhanced the stimulatory effect of pRSV/CREB on the expression of pOGH (ANG N-1498/+8). The enhancing effect of isoproterenol was in hibited by the presence of propranolol (an inhibitor of beta-adrenocep tors) and (R)-p-adenosine 3'5'-cyclic monophospho-orthioate (Rp)-cAMP (an inhibitor of cAMP-dependent protein kinase A1 and II). Transfectio n of pRSV/CREB had no effect on the expression of thymidine kinase gro wth hormone in OK 13 cells, an OK cell line with a fusion gene contain ing the promoter/enhancer DNA sequence of the viral thymidine-kinase g ene fused with an hGH gene as a reporter, thymidine kinase growth horm one, permanently integrated into their genomes. These studies demonstr ate that isoproterenol stimulates the expression of ANG gene via the c AMP-dependent protein kinase A and probably via the interaction of the 43-kD CREB with the 5'-flanking region of the ANG gene. Our data indi cate that the nuclear 43-kD CREB may have a modulatory role on the exp ression of the ANG gene in OK cells.