Regulation of the expression of galactoside-binding lectin during human monocytic differentiation

The widely distributed hL-31 (CBP35, epsilon BP, mL-34, L-29, Mac-2) is a Ca(2+)-independent galactoside-binding lectin which functions as a receptor on mammalian cells for glycoproteins containing poly-N-acetyllactosamine side chains. Little is known about the regulation of its expression. The human promyelocytic leukemia cell line, HL-60, was used to determine whether expression of hL-31 (Mac-2) correlated with macrophage/monocyte differentiation. Nondifferentiated HL-60 cells and HL-60 cells grown in the presence of 1.24 microM retinoic acid expressed only trace amounts of hL-31. In contrast, both hL-31 transcripts and protein were detected at 8 h after addition of 17 nM 12-O-tetradecanoylphorbol-13-acetate and reached maximal levels at 24 h. Addition of actinomycin D along with 12-O-tetradecanoylphorbol-13-acetate blocked accumulation of hL-31 mRNA. In contrast, addition of actinomycin D to 12-O-tetradecanoylphorbol-13-acetate-treated HL-60 cells that had already accumulated high levels of hL-31 mRNA did not cause significant reduction in RNA levels until 6-8 h had elapsed. Since increased hL-31 expression was not associated with an increase in transcriptional activity of the hL-31 gene, these results suggest that hL-31 expression is regulated 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 differentiation along the monocyte/macrophage pathway.