Butyrate, a histone deacetylase inhibitor, activates the human IGF binding protein-3 promoter in breast cancer cells: molecular mechanism involves an Sp1/Sp3 multiprotein complex

Specific cell growth stimulators and inhibitors regulate IGF binding protein-3 (IGFBP-3), where in turn IGFBP-3 mediates their biological effects. The molecular mechanism(s) by which these factors regulate IGFBP-3 are unknown. Sodium butyrate, a histone deacetylase inhibitor causing growth arrest and differentiation, increases IGFBP-3 expression. We investigated the molecular mechanism of this induction using an IGFBP-3 promoter reporter system in MCF-7 and Hs578T breast cancer cells. IGFBP-3 promoter activity was induced up to 40-fold following a 24-h treatment with sodium butyrate and 46-fold in cells treated with trichostatin A, a pure histone deacetylase inhibitor. Deletion analysis of the IGFBP-3 promoter identified key sodium butyrate-responsive element(s) to a 45-bp region containing consensus binding sites for Sp1 and activating protein-2. Sp1 binding to the Sp1 site and Sp3 to the activating protein-2/GA-box played a functional role in sodium butyrate's activation of the IGFBP-3 promoter, however, with no change in binding direct sodium butyrate regulation was attributed to cofactors. The histone acetyltransferase p300 and histone deacetylase-1 were identified in multiprotein complexes containing DNA bound Sp1 and Sp3, with p300 accumulating following sodium butyrate treatment. Taken together, these data suggest that sodium butyrate increases IGFBP-3 expression by activating the IGFBP-3 promoter via an Sp1/Sp3 multiprotein complex, a mechanism that may be important for other key regulators of IGFBP-3.     

Shear stress induces expression of vascular endothelial growth factor receptor Flk-1/KDR through the CT-rich Sp1 binding site

Fluid shear stress is 1 of the major factors that control gene expression in vascular endothelial cells. We investigated the role of shear stress in the regulation of the expression of fetal liver kinase-1/kinase domain region (Flk-1/KDR), a vascular endothelial growth factor receptor, by using human umbilical vein endothelial cells. Laminar shear stress (15 dyne/cm2) elevated Flk-1/KDR mRNA levels by approximately 3-fold for 8 hours, and the expression was upregulated within the range of 5 to 40 dyne/cm2. Deletion analysis of the 5'-flanking region of the Flk-1/KDR gene promoter by use of a luciferase reporter vector revealed that a shear stress-responsive element resided in the sequence between -94 and -31 bp, which contained putative nuclear factor-kappaB, activator protein-2, and GC-rich Sp1 and CT-rich Sp1 binding sites. Electrophoretic mobility shift assay demonstrated that nuclear extract was bound to the GC-rich Sp1 sites and the CT-rich Sp1 site with a similar pattern. However, shear stress enhanced the DNA-protein interactions only on the CT-rich Sp1 site but not on the GC-rich Sp1 sites. A 3-bp mutation in the CT-rich Sp1 site eliminated the response to shear stress in electrophoretic mobility shift assay and luciferase reporter assay. These results suggest that shear stress induces Flk-1/KDR expression through the CT-rich Sp1 binding site.