REGULATION OF MOUSE COLONY-STIMULATING FACTOR-I GENE PROMOTER ACTIVITY BY AP1 AND CELLULAR NUCLEIC ACID-BINDING PROTEIN

Macrophage colony-stimulating factor (M-CSF; CSF-1) is a member of a c omplex network of cytokines that regulate monocytic cell development a nd activity, It is produced in nearly all organs by cell types commonl y found in connective tissue, including fibroblasts and monocytes, Whe ther different cell types share common or have divergent mechanisms fo r regulating CSF-1 gene expression is not known. To address this quest ion, the identity of cis-acting elements and cognate trans-acting fact ors was characterized in a region of the CSF-1 promoter known to be mo re active in monocytes than in fibroblasts. The results of DNase I pro tection assays performed with fibroblast- or monocyte-derived nuclear extracts revealed a difference in the pattern of DNA-binding proteins. One protected region, common to both fibroblasts and monocytes, spans a putative phorbol ester-responsive element (TRE), and binding to the TRE by AP1 was verified with antibodies directed against c-fos and c- jun family members. Mutational analysis revealed that the TRE is requi red for CSF-1 gene expression in proliferating fibroblasts and monocyt es, Binding of a second putative trans-acting factor, preferentially e xpressed in fibroblasts, to the region immediately upstream of the TRE was also detected. Screening a mouse expression library with oligonuc leotides spanning the putative cis-acting element identified cellular nucleic acid-binding protein (CNBP) as the cognate binding activity, a nd antiserum to CNBP disrupted the electromobility shift assay complex . Mutational analysis revealed that loss of CNBP binding leads to a de crease in CSF-1 promoter activity in fibroblasts but has no effect on CSF-1 promoter activity in monocytes, Our results demonstrate that con trol of CSF-1 gene expression in monocytes and fibroblasts is mediated by common and cell type-specific trans-acting factors.