ADENOSINE METABOLISM DURING PHORBOL-MYRISTATE ACETATE-MEDIATED INDUCTION OF HL-60 CELL DIFFERENCE - CHANGES IN EXPRESSION PATTERN OF ADENOSINE KINASE, ADENOSINE-DEAMINASE, AND 5'-NUCLEOTIDASE

Adenosine has potent immunosuppressive activity. Since the source of a denosine and the mechanism of its release in the immune system is larg ely unknown and may vary according to cell type, we have evaluated the relationship between adenosine metabolism and the enzymatic activitie s and mRNA levels of adenosine-metabolizing enzymes in myeloid and lym phoid cell lines. Induction of HL-60 cell differentiation along the ma crophage lineage by PMA resulted in a reduction in the activities of a denosine deaminase (ADA), adenosine kinase (AK), and inosine monophosp hate-specific cytosolic 5'-nucleotidase and an elevation of ecto-5'-nu cleotidase (ecto-5'-NT). These changes were accompanied by an elevatio n of ecto-5'-NT mRNA and a decrease in ADA and AK mRNAs in a time-depe ndent fashion. Comparison of AK and ADA mRNA levels in several other l eukemic cell lines revealed generally similar responses to PMA with mu ch stronger suppression in immature T cells than in B cells. The metab olism of adenosine either through phosphorylation (AK) or deamination (ADA) was reduced in PMA-stimulated cells. Furthermore, the cumulative changes in enzyme expression resulted in a 2.5-fold increase in intra cellular adenosine formation in PMA-stimulated cells. The inhibition o f AK by 5'-iodotubercidin further increased adenosine formation by 6-f old over that in untreated cells. In accord with the increase in ecto- 5'-NT activity, extracellular AMP dephosphorylation increased dramatic ally, but there was no increase in extracellular ATP degradation. Thes e results indicate that a coordinated shift in adenosine-metabolizing enzyme levels during PMA-induced HL-60 cell differentiation is accompa nied by a decrease in adenosine uptake and an increase in adenosine re lease.