CELL-CYCLE PHASE-DEPENDENT EFFECT OF RETINOIC ACID ON THE INDUCTION OF GRANULOCYTIC DIFFERENTIATION IN HL-60 PROMYELOCYTIC LEUKEMIA-CELLS - EVIDENCE FOR SPHINGANINE POTENTIATION OF RETINOIC ACID-INDUCED DIFFERENTIATION

The efficiency of retinoic acid (RA)-induced differentiation was dependent on the position of HL-60 cells in the cell cycle. Our results demonstrated that cells at the G1/S border were more efficiently induced to differentiate by short exposure to RA than cells at other phases of the cell cycle. Synchronization of cells in G1/S phase by aphidicolin (APH) or mimosine (MIMO) increased the sensitivity of cells to RA short exposure treatment. Pretreatment with sphinganine (SP), a protein kinase C (PKC) inhibitor, potentiated RA-induced cell differentiation. By cell cycle analysis, SP was found to block the cell progression through the G1/S phase. Consequently, cells accumulated in the G1/S phase of the cell cycle. The present data therefore suggest a possible mechanism of action of SP to enhance RA-induced differentiation.