Abstract
The effects of adenosine diphosphate (ADP) ribosylation inhibitors on hematopoietic growth factor-induced proliferation were examined. Significant inhibition of interleukin-3 (IL-3), colony-stimulating factor 1, and lung conditioned media-induced clonal agar growth of normal murine hematopoietic cells by 10 mmol/L nicotinamide (NAM), 10 mmol/L 3-aminobenzamide (3AB), and 5 mmol/L N1-methylnicotinamide (1MN) was noted. Nicotinic acid, a related compound that does not inhibit ADP ribosylation, failed to inhibit the growth factor-mediated proliferation. NAM (10 mmol/L), 3AB (10 mmol/L), and 1MN (5 mmol/L) also prevented IL-3 and phorbol ester-stimulated 3H-thymidine incorporation into the IL-3-responsive FDC-P1 cell line. Exposure of FDC-P1 cells to 10 mmol/L NAM led to a significant decrease in nuclear poly-(ADP-ribose) levels. Exposure of FDC-P1 cells to 5 mmol/L 1MN did not affect the interaction of the phorbol ester receptor, protein kinase-C (PK-C), with the cell membrane as determined by assay of phorbol ester binding in cytosol and membrane preparations. Nor did it affect the catalytic activity of PK-C as determined by assaying the in vitro phosphorylation of histone H1 by cytosolic kinase preparations from FDC-P1 as well as EL4 thymoma cells. 1MN markedly enhanced the inhibitory effects of phorbol esters on DNA synthesis of EL4 cells even at concentrations (1.25 mmol/L) that had no effects on DNA synthesis in the absence of phorbol esters. Our findings demonstrate that (a) active ADP ribosylation inhibitors interfere with growth factor-induced proliferation of murine hematopoietic cells and (b) the inhibition occurs at a step that follows the activation and translocation of PK-C and is more closely linked to DNA synthesis.
Keloid fibroblasts are refractory to inhibition of DNA synthesis by phorbol esters. Altered response is accompanied by reduced sensitivity to prostaglandin E2 and altered down-regulation of phorbol ester binding sites.
