Changes in the activities and gene expressions of poly(ADP-ribose) glycohydrolases during the differentiation of human promyelocytic leukemia cell line HL-60.

The metabolism of poly(ADP-ribose) is known to play important roles in the nuclear function of the mammalian cells. In this study, changes in the activities and gene expressions of poly(ADP-ribose) glycohydrolases (PARG) in HL-60 cells treated with 12-O-tetradecanoyl-phorbol-13-acetate (TPA) or a PARG inhibitor, tannic acid, were investigated. Nuclear PARG activities of HL-60 cells treated with TPA were reduced to 30-40% of the activity in untreated cells at 24 h, while PARG activities in the cytoplasm remained unchanged. The transient decrease in the nuclear PARG activity by TPA treatment was accompanied by differentiation as measured by the nitroblue tetrazolium (NBT) reducing activity and adhesion to the culture dishes. In the presence of H7, an inhibitor of protein kinase C (PKC), both the decrease in nuclear PARG activity and the induction of differentiation by TPA treatment were suppressed. On the other hand, treatment with tannic acid caused the nuclear PARG activity to decrease continuously while the NBT reducing activity increased, but no morphological differentiation to macrophage-like cells was apparent. In order to analyze PARG gene expression, we isolated the human PARG cDNA by the RT-PCR technique. RT-PCR analysis revealed that TPA treatment leads to a reduction in the PARG gene expression prior to the phenotypic expression of macrophage-like cell differentiation, which was diminished by the presence of H7. Also, PARG gene expression was reduced by tannic acid treatment. These results provide the first evidence that a transient decrease in nuclear PARG activity is important for the onset of differentiation of HL-60 cells to macrophage-like cells.