Role of transcription factor S p1 and RNA binding protein H u R in the downregulation of D r + E scherichia coli receptor protein decay accelerating factor ( DAF or CD 55) by nitric oxide

We previously reported that nitric oxide ( NO ) reduces the rate of bacteremia and maternal mortality in pregnant rats with uterine infection by E scherichia coli expressing the D r F imbria ( D r + ). The epithelial invasion of D r + E . coli is dependent on the expression level of its cellular receptor decay accelerating factor ( DAF ). NO reduces the rate of bacteremia by downregulating the expression of DAF . In this study, we elucidated the role of transcription factor S p1 and RNA binding protein H u R in the downregulation of human DAF by NO . We generated a series of deletion mutant constructs of DAF gene 5′‐untranslated region and mapped the NO ‐response region upstream to the core promoter region of the DAF gene. One of the several S p1 binding sites in the DAF 5′‐untranslated region was located within the NO ‐response region. The binding of S p1 to this site was inhibited by NO . Furthermore, NO also promoted the degradation of DAF m RNA . The 3′‐untranslated region of DAF harbors an AU ‐rich element and this element destabilized the m RNA transcript. NO promoted the rapid degradation of DAF m RNA by inhibiting the binding of m RNA stabilizing protein H u R to this AU ‐rich region. The inhibition of binding of H u R to the AU ‐rich region was due to the S ‐nitrosylation of one or more cysteine residues by NO . Thus, these data reveal the molecular mediators of transcriptional and post‐transcriptional regulation of DAF by NO with implications in pathophysiology related to DAF .