REGULATION OF THE EXPRESSION OF GALACTOSIDE-BINDING LECTIN DURING HUMAN MONOCYTIC DIFFERENTIATION

The widely distributed hL-31 (CBP35, epsilonBP, mL-34, L-29, Mac-2) is a Ca2+-independent galactoside-binding lectin which functions as a re ceptor on mammalian cells for glycoproteins containing poly-N-acetylla ctosamine side chains. Little is known about the regulation of its exp ression. The human promyelocytic leukemia cell line, HL-60, was used t o determine whether expression of hL-31 (Mac-2) correlated with macrop hage/monocyte differentiation. Nondifferentiated HL-60 cells and HL-60 cells grown in the presence of 1.24 muM retinoic acid expressed only trace amounts of hL-31. In contrast, both hL-31 transcripts and protei n were detected at 8 h after addition of 17 nm 12-O-tetradecanoylphorb ol-13-acetate and reached maximal levels at 24 h. Addition of actinomy cin D along with 12-O-tetradecanoylphorbol-13-acetate blocked accumula tion of hL-31 mRNA. In contrast, addition of actinomycin D to 12-O-tet radecanoylphorbol-13-acetate-treated HL-60 cells that had already accu mulated high levels of hL-31 mRNA did not cause significant reduction in RNA levels until 6-8 h had elapsed. Since increased hL-31 expressio n was not associated with an increase in transcriptional activity of t he hL-31 gene, these results suggest that hL-31 expression is regulate d at the posttranscriptional level, at least in part, by stabilization of its mRNA. The results also indicate that the processes leading to increased hL-31 expression in HL-60 cells may be specific to different iation along the monocyte/macrophage pathway.