STAGE-SPECIFIC EXPRESSION OF P2Y RECEPTORS, ECTO-APYRASE, AND ECTO-5'-NUCLEOTIDASE IN MYELOID LEUKOCYTES

The expression of P2 purinergic receptor subtypes in leukocytes varies with both lineage and developmental stage. Given the recent identific ation and cloning of at least seven distinct G protein-coupled ATP rec eptor subtypes (P2Y family), we investigated P2Y receptor subtype expr ession during myeloid cell differentiation. We observed that KG-1 myel oblasts express P2Y(1) but not P2Y(2) receptors (previously termed P-2 U receptors), whereas later myeloid progenitors, including HL-60 promy elocytes and THP-1 monocytes, expressed P2Y(2) but not P2Y(1) receptor s. In KG-1 cells, significant activation of Ca2+ mobilization by P2Y(1 ) receptors was only observed after preincubation with potato apyrase, an exogenous ATPase. This indicated that P2Y(1) receptors are desensi tized in KG-1 cells by autocrine mechanisms that may involve enhanced release of endogenous nucleotides and/or decreased expression of cell- surface ectonucleotidases. We compared the levels of ecto-apyrase acti vity and expression in KG-1 myeloblasts and HL-60 promyelocytes. Extra cellular ATP was rapidly metabolized by HL-60 but not by KG-1 cells. R everse transcription-polymerase chain reaction analysis indicated that mRNA for CD39 (cluster of differentiation), an identified ecto-apyras e, was present in HL-60 but not KG-1 cells. Ecto-apyrase activity was modestly increased with differentiation of myeloid progenitors with ei ther phorbol 12-myristate 13-acetate (PMA) or dibutyryl adenosine 3',5 '-cyclic monophosphate (DBcAMP). Differentiation of HL-60 cells with P MA, but not DBcAMP, strongly induced ecto-5'-nucleotidase activity and CD73 mRNA expression. These observations indicate that signal transdu ction by extracellular ATP in myeloid leukocytes can be regulated by d evelopmentally programmed changes in the expression of P2Y receptor su btypes and multiple ectonucleotidases.