Regulation of endothelin production and secretion in cultured collecting duct cells by endogenous transforming growth factor-beta

Confluent cultures of two renal collecting duct cell lines (M-1 and mIMCD-K2 cells derived from cortical and inner medullary collecting ducts, respectively) express endothelin, (ET(1)), transforming growth factor-beta (TGF beta; both TGF beta 1 and TGF beta 2), and both types of the TGF beta receptor. Experiments were performed to test whether endogenous TGF beta may be a paracrine modulator of ET(1) expression in these cells. Treatment of M-1 and mIMCD-K2 cells with TGF beta 2 antisense oligodeoxynucleotides (ODN) significantly reduced ET(1) messenger RNA (mRNA) and ET secretion (as well as TGF beta 2 mRNA) in a concentration-dependent manner, whereas control ODN were without significant effects. To produce ET inhibition, antisense ODN had to be present in the basolateral medium, whereas its sole presence in the apical medium was without effect. In addition, a pan-specific TGF beta antibody caused a significant reduction of ET(1) mRNA expression and ET(1) secretion. M-1 cells were found to express high levels of the mRNA for plasminogen activator of both tissue and urokinase types. Addition of the nonspecific serine protease inhibitor aprotinin (50 mu g/ml) to the medium for 24 h significantly reduced the secretion of ET(1). These results suggest that secretion of endogenous TGF beta, at least in part activated by the plasminogen/plasmin system, participates in the regulation of ET(1) synthesis and secretion by collecting duct cell lines.