COORDINATED DOWN-REGULATION OF BCL-2 AND BAX EXPRESSION DURING GRANULOCYTIC AND MACROPHAGE-LIKE DIFFERENTIATION OF THE HL-60 PROMYELOCYTIC LEUKEMIA-CELL LINE

The bcl-2 protein suppresses apoptosis and the bax protein opposes the cytoprotective effect of bcl-2, A decrease in bcl-2 levels has been i mplicated in the induction of apoptosis during the terminal differenti ation of HL60 myeloid leukaemia cells. We show here that bax protein a lso declined with a time course similar to the downregulation of bcl-2 following treatment of HL60 with phorbol myristate acetate (PMA), dim ethyl sulphoxide (DMSO) or retinoic acid (RA), Decreased bcl-2 protein expression in induced cells was associated with downregulation of its mRNA. By contrast, the decrease in bax occurred by a post-transcripti onal mechanism. Co-ordinate downregulation of bcl-2 and bax proteins m ay fine-tune the induction of apoptosis during cellular differentiatio n.