Characterization and partial purification of CD34(+) progenitor cell ecto-phosphatidic acid phosphohydrolase

Phosphatidic acid and its hydrolysis product, diacylglycerol, play potentia lly vital roles as extracellular messengers in numerous cellular systems an d may play a key role in regulating hematopoiesis. In this study, we descri be an ecto-phosphatidic acid phosphohydrolase that potentially regulates ce llular responses to phosphatidic acid on bone marrow derived human hematopo ietic progenitors. We partially purified hematopoietic progenitor ecto-PAPa se using a novel in-gel phosphatase assay and then characterized the enzyme on phenotypically defined subpopulations of hematopoietic CD34(+) progenit ors isolated by flow cytometry. The most pronounced PAPase activity was con fined to uncommitted CD34(+)/CD38(+) hematopoietic progenitors, which lacke d the expression of other lineage-associated antigens. We conclude that hem atopoietic progenitor cells at various stages of maturation possess a poten t ecto-PAPase, an enzyme well positioned to regulate progenitor cell growth and differentiation induced by phosphatidic acid and related lipids.