We have used differential display polymerase chain reaction to identify genes that are upregulated after retinoic acid (RA) treatment of human myeloblastic HL-60 cells. Three of the cDNAs cloned hybridized to RA- inducible transcripts on Northern blots, one of which was shown to encode sequences for monocyte chemoattractant protein-1 (MCP-1), a recently described cytokine that is chemotactic for monocytes but not for neutrophils. Nuclear run-on analysis indicated that the upregulation of the MCP-1 gene occurs at the transcriptional level in HL-60 cells. MCP-1 transcript levels also increased after RA treatment of the NB4 acute promyelocytic cell line. MCP-1 transcripts were undetectable in freshly isolated neutrophils by Northern analysis or reverse transcription-polymerase chain reaction but were readily detectable in neutrophils after incubation in media at 37 degrees C for 20 hours, suggesting that an activation event can lead to MCP-1 expression in neutrophils. Immunocytochemistry confirmed the presence of MCP-1 protein in activated neutrophils. This is the first report that the MCP-1 gene is RA-responsive in myeloid cell lines and is expressed in neutrophils. MCP-1 expression by activated neutrophils may play an important role in attracting monocytes to the site of tissue damage or infection.

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