Mode of action of erythropoietin (Epo) in an Epo-dependent murine cell line. I. Involvement of adenosine 3',5'-cyclic monophosphate not as a second messenger but as a regulator of cell growth.

A subclone of the interleukin 3 (IL-3)-dependent murine cell line DA-1 was recently established, and its growth found to be dependent on erythropoietin (Epo) as well as on IL-3. This subclone, named DA-1ER, has been used to study the mechanisms of action of these two growth factors, though most especially of Epo. In the present study, the involvement of adenosine 3',5'-cyclic monophosphate (cAMP) in the growth of DA-1ER cells was analyzed. In initial experiments, cAMP levels in cells stimulated with either recombinant Epo or recombinant IL-3 were monitored. The results showed that no significant changes in cellular cAMP levels had occurred. The cAMP-enhancing agents, N6-2'-o-dibutyryl-adenosine 3',5'-cyclic monophosphate (dbcAMP), 3-isobutyl-1-methyl-xanthine (IBMX), and cholera toxin (CT) were then applied to DA-1ER cells to see whether they could induce cell growth, but none of them was effective. The data indicated that cAMP was not the so-called second messenger for Epo or IL-3. The regulatory effects of cAMP on Epo- and IL-3-stimulated cell growth were next examined. It was found that whereas Epo-stimulated growth was markedly inhibited by cAMP-enhancing agents, IL-3-stimulated growth was relatively resistant and inhibited only by high doses of these agents. These data suggested that cAMP could play different roles in the same cells, depending on which growth factors were applied, and that it finely regulated proliferation and differentiation of multireceptor-bearing hematopoietic precursor cells.