Enkephalin Is a Growth Factor for Biphenotypic Leukemias

Abstract

Though some leukemia cells are recently recognized to have ectoenzymes, their role is still unclear. We investigated whether enkephalin (Enk), a substrate of both neutral endopeptidase (NEP : CD 10) and aminopeptidase N (APN : CD 13), had an effect on cell growth. ³H-Thymidine incorporation and MTT assay showed that in cell lines of biphenotypic leukemia that had both activities of NEP and APN, ³H-thymidine uptake and cell growth increased with Enk, whereas acute lymphoblastic and non-lymphoblastic leukemia cell lines did not. Inhibition of APN activity suppressed proliferation. There was no Ca mobilization. These data suggest that Enk is one of the growth factors for some leukemias, that the cell growth pathway requires that it be cleaved by APN and that it is independent of Ca mobilization.