EFFECT OF GLUCOSE ON THE EXPRESSION OF THE ANGIOTENSINOGEN GENE IN OPOSSUM KIDNEY-CELLS

To investigate whether D(+)-glucose has a stimulatory effect on the ex pression of the angiotensinogen (Ang) gene in opossum kidney (OK) cell s, we used OK cells with a fusion gene containing various lengths of t he 5'-flanking regulatory sequence of the rat Ang gene fused with the human growth hormone (hGH) gene as a reporter, stably integrated into their genomes. The level of expression of the fusion gene was quantifi ed by the amount of immunoreactive-human growth hormone (IR-hGH) secre ted into the medium. The addition of D(+)-glucose stimulated the expre ssion of pOGH (Ang N-1498/+18) in OK 27 cells in a dose-dependent mann er (5 to 25 mM), whereas the addition of D-mannitol, L-glucose and 2-d eoxy-D-glucose (25 mM) had no effect. The stimulatory effect of D(+)-g lucose (25 mM) was blocked by the presence of staurosporine or H7 (an inhibitor of protein kinase C) or U73122 (an inhibitor of phospholipas e C and A(2)) but not blocked by the presence of Rp-cAMP (an inhibitor of cAMP-dependent protein kinase A). The addition of D(+)-glucose (25 mM) also stimulated the expression of pOGH (Ang N-960/+18) and pOGH ( Ang N-688/+18) in OK 960 and OK 688 cells, respectively. it had no sti mulatory effect, however, on the expression of pOGH (Ang N-280/+18) an d pOGH (Ang N-35/+18) in OK 280 and OK 35 cells, respectively. The add ition of D(+)-glucose also had no effect on the expression of pTKGH in OK 13 cells, an OK cell line, into which had been stably integrated a fusion gene, pTKGH containing the promoter/enhancer DNA sequence of t he viral thymidine-kinase (TK) gene fused with a human growth hormone gene as a reporter. These studies demonstrate that the stimulatory eff ect of high D(+)-glucose concentration (25 mM) on the expression of th e angiotensinogen-growth hormone fusion genes in OK cells is mediated via the 5'-flanking region of the angiotensinogen gene and the protein kinase C signal transduction pathway. Our data indicate that a high g lucose concentration may activate the renin-angiotensin system in the renal proximal tubular cells.