CD43 gene expression is mediated by a nuclear factor which binds pyrimidine-rich single-stranded DNA

CD43 is a leukocyte-specific surface molecule which plays an important role both in adhesion and signal transduction, We have identified a site spanni ng nucleotides +18 to +39 within the human CD43 gene promoter which in vitr o is hypersensitive to cleavage by nuclease S1. Repeats of this region are sufficient to activate expression of a heterologous promoter in CD43-positi ve cell lines. Two nuclear factors, PyRo1 and PyRo2, interact with the hype rsensitive site. PyRo1 is a single-stranded DNA-binding protein which binds the pyrimidine-rich sense strand. Mutation analysis demonstrates that the motif TCCCCT is critical for PyRo1 interaction. Replacement of this motif w ith the sequence CATATA abolishes PyRo1 binding and reduces expression of t he CD43 promoter by 35% in Jurkat T lymphocytic cells and by 52% in the pre -erythroid/pre-megakaryocytic cell line K562. However, this same replacemen t failed to affect expression in U937 monocytic cells or in CEM T lymphocyt ic cells. PyRo1, therefore, exhibits cell-specific differences in its funct ional activity. Further analysis demonstrated that PyRo1 not only interacts with the CD43 gene promoter but also motifs present within the promoters o f the CD11a, CD11b, CD11c and CD11d genes. These genes encode the a subunit s of the beta 2 integrin family of leukocyte adhesion receptors, Deletion o f the PyRo1 binding site within the CD11c gene reduced promoter activity in T lymphocytic cells by 47%. However, consistent with our analysis of the C D43 gene, the effect of this same deletion within U937 monocytic cells was less severe. That PyRo1 binds preferentially to single-stranded DNA and seq uences within the CD43 and CD11 gene promoters suggests that expression of these genes is influenced by DNA secondary structure.