Upstream stimulating factor-1 mediates the E-box-dependent transcriptional repression of the plasminogen activator inhibitor-1 gene in human mast cells

The Intrinsically Disordered Loop in the USF1 bHLHZ Domain Modulates Its DNA-Binding Sequence Specificity in Hereditary Asthma

USF1, a basic region/helix-loop-helix/leucine zipper (bHLHZ) transcription factor, binds to the E-box in the PAI-1 (plasminogen activator inhibitor) promoter. Two alleles containing the E-box control PAI-1 transcription; these alleles are termed "4G" and "5G" based on the G tract flanking E-box. USF1-governed transcription of PAI-1 is elevated in heritable asthma sufferers: the 4G/4G genotype has the highest plasma levels of PAI-1. While USF1 uses its basic region to bind E-box, we found that it uses its 12 amino-acid loop to recognize the flanking sequence and discern the single-nucleotide difference between the alleles. We used the bacterial one-hybrid and electrophoretic mobility shift assays to assess protein-DNA recognition, and circular dichroism to examine protein secondary structure. We mutated Ser233 and Thr234 in the USF1 bHLHZ loop to Ala to generate S233A and T234A. Interestingly, USF1 bHLHZ, S233A, and T234A prefer the 5G sequence (USF1 bHLHZ K_d values 4.1 ± 0.3 nM and 7.0 ± 0.4 nM for 5G and 4G, respectively), whereas studies in stimulated human mast cells showed a preference for 4G. We replaced the 8 amino-acid loop of transcription factor Max bHLHZ with the 12 amino-acid USF1 loop: this mutant now distinguishes the 4G/5G polymorphism-while Max bHLHZ does not-confirming that USF1 differentiation of the 4G/5G is driven by the loop.

Upstream stimulatory factor-2 mediates quercetin-induced suppression of PAI-1 gene expression in human endothelial cells

The polyphenol quercetin (Quer) represses expression of the cardiovascular disease risk factor plasminogen activator inhibitor-1 (PAI-1) in cultured endothelial cells (ECs). Transfection of PAI-1 promoter-luciferase reporter deletion constructs identified a 251-bp fragment (nucleotides -800 to -549) responsive to Quer. Two E-box motifs (CACGTG), at map positions -691 (E-box1) and -575 (E-box2), are platforms for occupancy by several members of the c-MYC family of basic helix-loop-helix leucine zipper (bHLH-LZ) proteins. Promoter truncation and electrophoretic mobility shift/supershift analyses identified upstream stimulatory factor (USF)-1 and USF-2 as E-box1/E-box2 binding factors. ECs co-transfected with a 251 bp PAI-1 promoter fragment containing the two E-box motifs (p251/luc) and a USF-2 expression vector (pUSF-2/pcDNA) exhibited reduced luciferase activity versus p251/luc alone. Overexpression of USF-2 decreased, while transfection of a dominant-negative USF construct increased, EC growth consistent with the known anti-proliferative properties of USF proteins. Quer-induced decreases in PAI-1 expression and reduced cell proliferation may contribute, at least in part, to the cardioprotective benefit associated with daily intake of polyphenols.

Cyclic adenosine monophosphate induces plasminogen activator inhibitor-1 expression in human mast cells

Plaminogen activator inhibitor-1 (PAI-1), the key physiological inhibitor of the plasmin fibrinolytic system, plays important roles in the pathogenesis of asthma. Mast cells (MCs) are crucial effector cells and a major source of PAI-1 for asthma. Cyclic adenosine monophosphate (cAMP) is the important regulator of MCs; however, its effects on PAI-1 expression in MCs remain unknown. We reported cAMP/protein kinase A pathway positively regulates PAI-1 expression through cAMP-response element binding protein binding to hypoxia response element-1 at -158 to -153bp of human PAI-1 promoter in human MCs. Moreover, cAMP synergistically augments PAI-1 expression with ionomycin- or IgE receptor cross-linking-mediated stimulation.

Plasminogen activator inhibitor-1 and asthma: role in the pathogenesis and molecular regulation

Plasminogen activator inhibitor (PAI)-1 is a major inhibitor of the fibrinolytic system. PAI-1 levels are markedly increased in asthmatic airways, and mast cells (MCs), a pivotal cell type in the pathogenesis of asthma, are one of the main sources of PAI-1 production. Recent studies suggest that PAI-1 may promote the development of asthma by regulating airway remodelling, airway hyperresponsiveness (AHR), and allergic inflammation. The single guanosine nucleotide deletion/insertion polymorphism (4G/5G) at -675 bp of the PAI-1 gene is the major genetic determinant of PAI-1 expression. Plasma PAI-1 level is higher in people with the 4G/4G genotype than in those with the 5G/5G genotype. A strong association between the 4G/5G polymorphism and the risk and the severity of asthma has been suggested. Levels of plasma IgE and PAI-1 and severity of AHR are greater in asthmatic patients with the 4G/4G genotype than in those with the 5G/5G genotype. The PAI-1 promoter with the 4G allele renders higher transcription activity than the PAI-1 promoter with the 5G allele in stimulated MCs. The molecular mechanism for the 4G allele-mediated higher PAI-1 expression is associated with greater binding of upstream stimulatory factor-1 to the E-box adjacent to the 4G site (E-4G) than to the E-5G. In summary, PAI-1 may play an important role in the pathogenesis of asthma. Further studies evaluating the mechanisms of PAI-1 action and regulation may lead to the development of a novel prognostic factor and therapeutic target for the treatment and prevention of asthma and other PAI-1-associated diseases.