Extracellular cyclic ADP-ribose increases intracellular free calcium concentration and stimulates proliferation of human hemopoietic progenitors

Cyclic ADP-ribose (cADPR) is a universal second messenger that regulates ma ny calcium-related cellular events by releasing calcium from intracellular stores. Since these events include enhanced cell proliferation and since th e bone marrow harbors both ectoenzymes that generate cADPR from NAD(+) (CD3 8 and BST-1), we investigated the effects of extracellular cADPR on human h emopoietic progenitors (HP). Exposure of HE to 100 mu M cADPR for 24 h indu ced a significant increase in colony output (P<0.01) and colony size (P<0.0 03). A horizontal expansion of HP, as demonstrated by a markedly increased replating efficiency in semisolid medium (up to 700 times compared to contr ols), was also observed, indicating that cADPR priming can affect cell grow th for multiple generations over several weeks after exposure. Influx of ex tracellular cADPR into the cells was demonstrated, and a causal relationshi p between the functional effects and the increase of intracellular free cal cium concentration induced by cADPR on HP was established through the use o f specific antagonists. Similar effects on HP were produced by nanomolar co ncentrations of the nonhydrolyzable cADPR analog 3-deaza-cADPR, These data demonstrate that extracellular cADPR behaves as a cytokine enhancing the pr oliferation of human HP, a finding that may have biomedical applications fo r the ex vivo expansion of hemopoietic cells.-Podesta, M., Zocchi, E., Pitt o, A, Usai, C., Franco, L., Bruzzone, S., Guida, L., Bacigalupo, A., Scadde n, D. T., Walseth, T. F., De Flora, A., Daga, A Extracellular cyclic ADP-ri bose increases intracellular free calcium concentration and stimulates prol iferation of human hemopoietic progenitors.