Sp1/Sp3 and PU.1 differentially regulate beta(5) integrin gene expression in macrophages and osteoblasts

Murine osteoclast precursors and osteoblasts express the integrin alpha(v)b eta(5), the appearance of which on the cell surface is controlled by the be ta(5), and not the alpha(v), subunit, Here, we show that a 173-base pair pr oximal region of the beta(5) promoter mediates beta(5) basal transcription in macrophage (osteoclast precursor)-like and osteoblastlike cells. DNase I footprinting reveal four regions (FP1-FP4) within the 173-base pair region , protected by macrophage nuclear extracts. In contrast, osteoblast nuclear extracts protect only FP1, FP2, and FP3, FP1, FP2, and FP3 bind Sp1 and Sp 3 from both macrophage and osteoblast nuclear extracts. FP4 does not bind o steoblast proteins but binds PU.1 from macrophages, Transfection studies sh ow that FP1 and FP2 Sp1/Sp3 sites act as enhancers in both MC3T3-E1 (osteob last-like) and J774 (macrophage-like) cell lines, whereas the FP3 Sp1/Sp3 s ite serves as a silencer. Mutation of the FP2 Sp1/Sp3 site totally abolishe s promoter activity in J774 cells, with only partial reduction in MC3T3-E1 cells, Finally, we demonstrate that PU.1 acts as a beta(5) silencer in J774 cells but plays no role in MC3T3-E1 cells. Thus, three Sp1/Sp3 sites regul ate beta(5) gene expression in macrophages and osteoblast-like cells, with each element exhibiting cell-type and/or activation-suppression specificity .