Inactivation of platelet-derived growth factor-BB following modification by ADP-ribosyltransferase

1 Arginine-specific ADP-ribosyltransferase (ART1) is expressed on the surfa ce of a number of cell types, and catalyses the transfer of ADP-ribose from NAD(+) to target proteins. We investigated whether extracellular proteins such as growth factors may serve as substrates for this enzyme, with subseq uent alteration in their biological activity. Experiments were performed wi th rat skeletal muscle membranes and V79 Chinese hamster lung fibroblasts w ith doxycycline-inducible expression of human ART. 2 From a panel of growth factors, platelet-derived growth factor-BB (PDGF-B B) was found to be the best substrate for ART1, whereas the structural homo logue PDGF-AA was not a substrate. Under conditions of maximum labelling 5 mot ADP-ribose was incorporated per mot of PDGF-BB. 3 Purified (ADP-ribosyl)-PDGF-BB did not stimulate a mitogenic or chemotact ic response in human pulmonary smooth muscle cells. and showed a reduced ca pacity to bind to PDGF receptors in competition binding experiments., when compared to unmodified PDGF-BB. 4 PDGF-dependent [H-3-methyl]-thymidine incorporation was measured in the A RT1-transfected fibroblast cell line at physiological concentrations of PDG F-BB, and without addition of extracellular NAD(+). Fibroblasts expressing human ART1 at the cell surface showed reduced mitogenic responses to PDGF-B B, but not to PDGF-AA. This loss of mitogenic response in cells expressing ART1 activity was reversed by the addition of agmatine (an ART1 substrate). 5 In conclusion, we propose that PDGF-BB-dependent signalling may be regula ted by posttranslational modification of the growth factor by ART1 at the c ell surface. This has been demonstrated in membranes of rat skeletal muscle , and the reaction confirmed in ART1-transfected fibroblasts.