INDUCTION OF FIBRONECTIN GENE-EXPRESSION BY TRANSFORMING GROWTH FACTOR-BETA-1 IS ATTENUATED IN BRONCHIAL EPITHELIAL-CELLS BY ADP-RIBOSYLTRANSFERASE INHIBITORS

Transforming growth factor-beta (TGF-beta) exerts on several effects on cultured airway epithelial cells including inhibition of proliferation and stimulation of fibronectin gene expression. ADP-ribosylation is one potential regulatory mechanism of gene expression by TGF-beta. We tested this possibility by exposing cultured bovine bronchial epithelial cells to the chemical inhibitor of ADP-ribosyl transferase enzymes, 3-aminobenzamide (3-AB) and, for comparison, 3-aminobenzoic acid (3-ABA), which is structurally similar to 3-AB but which does not inhibit ADP-ribosyl transferases. Exponential cell growth rate (1.2 doublings/day) or cellular morphology observed by phase contrast microscopy were not affected by 3 mM 3-AB or 3-ABA. Neither compound antagonized inhibition of cell division or induction of squamous morphology by TGF-beta-1. In contrast, the sixfold stimulation of fibronectin production by exposure of cells to 30 pM TGF-beta-1 for 48 h was reduced by 50% in the presence of 3 mM 3-AB, whereas 3 mM 3-ABA had no effect. The antagonistic effect was augmented by administration of 3-AB 24 h prior to induction by TGF-beta-1. Northern blot hybridization analyses demonstrated that 3-AB, but not 3-ABA, attenuated the induction of fibronectin mRNA by TGF-beta-1 by up to 50%. These observations may implicate a role of cellular ADP-ribosylation in the regulation of some gene expression by TGF-beta.