ALKALINE-PHOSPHATASE ACTIVITY DURING SPHINGANINE POTENTIATION OF RETINOIC ACID-INDUCED DIFFERENTIATION OF HUMAN PROMYELOCYTIC LEUKEMIA-CELLLINE, HL-60

Sphinganine (SP) pre-treatment potentiated the retinoic acid (RA)-indu ced (4-96h exposures) differentiation and increase of alkaline phospha tase (ALP) activity. A higher percentage of SP pre-treated cells in RA exposures resembled mature myelocytes or granulocytes; greater increa se in ALP activity was observed. In cells exposed to RA alone for only a period of 24h, the ALP activity could still increase and reach a si milar maximum ALP activity (8.5-10.0 units/mg protein) at 48h as it wa s under continuous RA treatment. In all cells with longer exposures (2 4-96h) to RA, SP pre-treatment increased ALP activity to more or less the same higher maximum (14.0-15.5 units/mg protein). SP, added 24h be fore or concomitantly, but not 24 nor 48h after the addition of RA, co uld potentiate the RA-induced differentiation and increase of ALP acti vity.