Expression of the myeloid-specific leukocyte integrin gene CD11d during macrophage foam cell differentiation and exposure to lipoproteins.

The leukocyte integrin gene CD11d is expressed predominantely on subsets of the myelomonocytic lineage (myeloid cells), particularly on macrophage foam cells and splenic red pulp macrophages. Its expression pattern clearly differs from myeloid-specific leukocyte integrins CD11b and CD11c and the leukocyte-specific integrin CD11a. Although the functions of CD11d have not been determined in any detail, its expression in these cell types suggests that it may play a role in the atherosclerotic process. To better understand how this gene is regulated, the steady-state level of CD11d mRNA in differentiating bone marrow CD34+CD38- cells, peripheral blood monocytes, and monocytic cell lines was assessed by Northern blot analysis and RT-PCR and compared with those of CD11a, CD11b, and CD11c. Expression of CD11d occurs early in CD34+CD38- cells, rises, and then decreases, in contrast to the expression of the other leukocyte integrins. Expression of CD11d reappears in peripheral blood monocytes differentiating to macrophage foam cells. Oxidized lipoproteins (OxLDL) and acetylated lipoproteins (AcLDL) failed to upregulate CD11d following differentiation of peripheral blood monocytes or the monocytic cell line HL60. However, when both OxLDL and AcLDL were present during differentiation, CD11d was further upregulated. This suggests that expression of CD11d is coordinately regulated with expression of LDL receptors and the development of the foam cell. Site-directed mutagenesis of the -100 to -20 region of the CD11d promoter revealed transcription factor binding sites essential for expression of this gene. Decoy oligonucleotides to the -100 to -20 region taken up by CD34+CD38- cells block their differentiation into myeloid colonies. This suggests that one or more transcription factors that regulate CD11d also are essential for myeloid differentiation, and that the CD11d promoter may be used as a model gene to identify transcription factors essential for myeloid cell differentiation.