DPP4 truncated GM-CSF and IL-3 manifest distinct receptor-binding and regulatory functions compared with their full-length forms.

Dipeptidylpeptidase 4 (DPP4/CD26) enzymatically cleaves select penultimate amino acids of proteins, including colony-stimulating factors (CSFs), and has been implicated in cellular regulation. To better understand the role of DPP4 regulation of hematopoiesis, we analyzed the activity of DPP4 on the surface of immature blood cells and then comparatively assessed the interactions and functional effects of full-length (FL) and DPP4 truncated (T) factors (T-granulocyte-macrophage-CSF (T-GM-CSF)) and T-interleukin-3 (T-IL-3)) on both in vitro and in vivo models of normal and leukemic cells. T-GM-CSF and -IL-3 had enhanced receptor binding, but decreased CSF activity, compared with their FL forms. Importantly, T-GM-CSF and -IL-3 significantly, and reciprocally, blunted receptor binding and myeloid progenitor cell proliferation activity of both FL-GM-CSF and -IL-3 in vitro and in vivo. Similar effects were apparent in vitro using cluster-forming cells from patients with acute myeloid leukemia regardless of cytogenetic or molecular alterations and in vivo using animal models of leukemia. This suggests that DPP4 T-molecules have modified binding and functions compared with their FL counterparts and may serve regulatory roles in normal and malignant hematopoiesis.