Atrial natriuretic peptide stimulates the expression of transforming growth factor-beta in cultured murine mesangial cells: relationship to suppression of proliferation.

Atrial natriuretic peptide (ANP) is a growth suppressor for a variety of different cell types including cultured mesangial cells. This study examined the effects of ANP on the expression and synthesis of transforming growth factor-beta (TGF-beta) in a cultured murine mesangial cell line (MMC). Full-length rat ANP as well as 8-bromo-cGMP, but not ring-deleted ANP analogues, induced, in a dose-dependent manner, TGF-beta 1 mRNA expression in MMC. Moreover, full-length ANP and 8-bromo-cGMP stimulated the synthesis and release of TGF-beta 1 into cell culture supernatants as measured by a specific enzyme-linked immunosorbent assay and mink cell bioassay. The induction of TGF-beta 1 by 10(-6) M ANP and 10(-4) M 8-bromo-cGMP for 24 h was also documented by western blotting of MMC culture supernatants. However, transient transfection studies in MMC with three different murine TGF-beta 1 reporter gene constructs revealed only little stimulation of activity after ANP treatment, suggesting that posttranscriptional activation may mainly contribute to TGF-beta mRNA induction. Functional studies demonstrated that the ANP-mediated inhibition of mitosis, induced by 5% fetal calf serum, is partly abolished in the presence of a neutralizing anti-TGF-beta 1-3 antibody. In addition, the antiproliferative effects of exogenous 8-bromo-cGMP are also attenuated by anti-TGF-beta 1-3 antibody. These findings indicate that ANP stimulates TGF-beta expression in MMC and that the antiproliferative effects of ANP in this cell line may be mediated, at least to some extent, by the endogenous induction of TGF-beta. An increase in intracellular cGMP is most likely the mediator of this TGF-beta 1 induction. Considering the fibrogenic effects of TGF-beta, these findings may be important in the development of glomerulosclerosis in situations with an increase in local or systemic ANP.