Differentiating agents regulate cathepsin B gene expression in HL-60 cells

We utilized HL-60 cells as a model system to examine the regulation of ctsb gene expression by differentiating agents. Inducers of monocytic different iation [phorbol ester (PMA), calcitriol (D-3), and sodium butyrate (NaB)] a nd inducers of granulocytic differentiation [all-trans retinoic acid (RA) a nd 9-cis retinoic acid (9-cis RA)] increase ctsb mRNA levels in a dose-depe ndent manner as determined by Northern blot hybridization, Dg and retinoids exert additive effects, suggesting that these agents act in part through d istinct pathways, Actinomycin D decay experiments indicate that D-3, NaB, R A, and 9-cis RA do not alter mRNA stability. In contrast, PMA markedly incr eases the half-life of ctsb mRNA. In transient transfection assays, PMA. an d NaB both stimulate transcription of the luciferase reporter gene placed u nder the control of ctsb promoter fragments. Thus, inducers of HL-60 cell d ifferentiation can regulate the expression of the ctsb gene at both transcr iptional and posttranscriptional levels.