Leukocyte-specific expression of the pp52 (LSP1) promoter is controlled by the cis-acting pp52 silencer and...

pp52 (LSP1) is a leukocyte-specific phosphoprotein that binds the cytoskeleton and has been implicated in affecting cytoskeletal remodeling in a variety of leukocyte functions, including cell motility and chemotaxis. The expression of pp52 is restricted to leukocytes by a 549 bp tissue-specific promoter. Here, we show that promoter fragments smaller than the 549 bp pp52 promoter have activity in fibroblasts where pp52 is not normally expressed. Specifically, a truncated construct (+1 to -99) functioned as a basal promoter active in leukocytes and fibroblasts. We identified two upstream regions within the 549 bp pp52 promoter responsible for restricting pp52 promoter activity in fibroblasts. These two regions contained a silencer (pp52 NRE) and an anti-silencer (pp52 anti-NRE) with opposing activities controlling pp52 gene expression. The pp52 NRE was active in both leukocytes and fibroblasts while the pp52 anti-NRE was only active in leukocytes, thereby allowing pp52 gene transcription in leukocytes but not in fibroblasts. The pp52 NRE was localized to an 89 bp DNA segment between -324 and -235 in the 549 bp pp52 promoter and functioned as an active silencer element in a position and orientation independent manner. The pp52 anti-NRE was localized to a 33 bp segment between -383 and -350 of the 549 bp pp52 promoter and acted as an anti-silencer element against the pp52 NRE, but lacked any intrinsic enhancing activity on its own. These findings indicate that the tissue specificity of the pp52 promoter is determined by the pp52 anti-NRE anti-silencer which over-rides the general inhibitory activity of the pp52 NRE silencer.