The CD18(￥a-subunit of integrin) is essential for expression of structural and functional CD11/CD18(￥a/￥a-subunit) complexes on the cell surface, and myeloperoxidase plays a role in the bacteriocidal action of granulocytes. Effects on CD18 and myeloperoxidase genes expression have been investigated during TPA-induced differentiation of HL-60 cells. CD18 mRNA was induced at 24 hr and myeloperoxidase mRNA was rapidly reduced at 12 hr. The level of CD18 mRNA was induced and myeloperoxidase was reduced in proportion to concentration of TPA. TPA-induced CD18 mRNA was slightly decreased and myeloperoxidase mRNA was no effect in cells treated with cycloheximide, respectively. On the other hand CD18 mRNA was completely reduced by actinomycin D pretreatment. TPA-dependent stimulation of CD18 gene and repression of myeloperoxidase gene were completely restored by staurosporin pretreatment. These results suggest that phosphorylation of a protein is a crucial step for the induction of CD18 mRNA and the repression of myeloperoxidase during TPA-induced differentiatian of HL-60.
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