Accumulation of cyclic ADP-ribose measured by a specific radioimmunoassay in differentiated human leukemic HL-60 cells with all-trans-retinoic acid.

Cyclic adenosine diphosphoribose (cADPR) is a novel candidate for the mediator of Ca2+ release from intracellular Ca2+ stores. The formation of this cyclic nucleotide is catalyzed by not only Aplysia ADP-ribosyl cyclase but also an ecto-form enzyme of NAD+ glycohydrolase (NADase), which was previously identified as all-trans-retinoic acid (RA)-inducible CD38 in human leukemic HL-60 cells. In the present study, we developed a radioimmunoassay specific for cADPR, by which more than 100 fmol of cADPR could be detected without any interference by other nucleotides. The possible involvement of CD38 in the formation of cellular cADPR was investigated with the radioimmunoassay method. A marked increase in cellular cADPR was accompanied by all-trans-RA-induced differentiation of HL-60 cells. Moreover, a high level of cellular cADPR was observed in other leukemic cell lines, in which CD38 mRNA was expressed. Thus, CD38, which was initially identified as an NADase, appeared to be responsible for the formation of cellular cADPR.