Enhanced ability of myelopoietins, dual receptor agonists for human IL-3 and g-csf receptors and the IL-3 receptor agonist, daniplestim, to suppress apoptosis and stimulate cytokine-inducible gene expression

The chimeric receptor agonists, myelopoietins (MPOs), bind and activate the human IL-3 and G-CSF receptors while daniplestim binds the human IL-3 receptor with 20-fold higher affinity than native IL-3. In CFU assays using human bone marrow-derived CD34+ cells, MPOs demonstrated a greater increase in the numbers of CFUs compared to the coaddition of native IL-3 & G-CSF. We have investigated how MPOs and daniplestim stimulate growth and prevent apoptosis using Annexin V/propidium iodide binding, alteration in mitochondrial membrane potential, TUNEL assays, and DNA laddering in the OCI-AML and AML-193 cell lines. MPOs prevented apoptosis more effectively than IL-3 or G-CSF or the co-addition of IL-3 & G-CSF. The expression of apoptosis- and cytokine-regulated genes was examined by RT-PCR. Bcl-XL and Oncostatin M were detected at 2-4 fold higher levels in OCI-AML cells treated with MPOs than cells treated with the co-addition of IL-3 & G-CSF. These cDNAs were detected in 10-fold lower levels in cytokine-deprived cells. Furthermore, IL-3 and daniplestim differed in their abilities to induce LIF expression: native IL-3 induced LIF expression, while daniplestim did not. These results suggest that MPOs inhibit apoptosis more efficiently than the co-addition of IL-3 and G-CSF and induced expression of Bcl-XL and Oncostatin M in cytokine-responsive cell lines.