Differentiation of 3T3‐L1 pre‐adipocytes induced by inhibitors of poly(ADP‐ribose) polymerase and by related noninhibitory acids

To analyze a possible involvement of ADP-ribosylation reactions in 3T3-L1 pre-adipocyte differentiation. ADP-ribosyltransferase activities is permeabilized cells as well as endogenous amounts of protein-bound mono- and poly(ADP-ribose) residues were determined. Also, in vivo labeling with [3H]adenosine of ADP-ribose residues linked to high-mobility-group (HMG) proteins was performed. As an additional probe, the effects of ADP-ribosylation inhibitors and non-inhibitory analogs were studied. Basal and total poly(ADP-ribose) polymerase activities markedly increased prior to the appearance of the differentiation marker glycerol-3-phosphate dehydrogenase. Despite these apparent changes in activity, however, neither protein-bound poly(ADP-ribose) residue nor mono(ADP-ribosyl) groups in histones, nor the NAD content, changed significantly under these conditions. Furthermore, although HMG protein-associated [3H]ADP-ribose was reduced in differentiating [3H]adenosine-labeled cells, the data suggest altered precursor pool labeling rather than a specific decrease in ADP-ribosylated HMG proteins. Non-participation of ADP-ribosylation reactions in 3T3-L1 differentiation is further supported by experiments with inhibitors and non-inhibitory analogs. Benzamide at 0.3-3 mM per se without effect on differentiation, was able to induce specific gene expression when combined with insulin (10(-12)-10(-7) M). Similar effects were seen with benzoate as well as with nicotinamide, 3-aminobenzamide and their corresponding acids. The data indicate that benzamide and analogs have profound effects on chromatin functions that are not mediated by ADP-ribosylation reactions.