Lipopolysaccharide down-regulates Sp1 binding activity by promoting Sp1 protein dephosphorylation and degradation.
We examined the in vivo effect of lipopolysaccharide (LPS) on Sp1 (promoter-selective transcription factor 1) DNA binding activity and studied the mechanisms involved in mouse lungs. The Sp1 DNA complex displayed a major band composed of Sp1, Sp2, and Sp3 trimer and a minor band composed of Sp3 homodimer. Compared with control, nuclear proteins from lungs challenged with LPS for 60, 90, 120, 150, 180, and 240 min, respectively, showed a markedly reduced Sp1 binding activity. Down-regulation of Sp1 binding activity was accompanied by a reduced expression of two Sp1-dependent genes (endothelial nitric oxide synthase and cyclooxygenase-1). Immunoprecipitation-Western blot experiments demonstrated that LPS dephosphorylated Sp1 protein at serine and threonine residues but not at the tyrosine residue. Dephosphorylation of Sp1 protein in vitro significantly reduced Sp1 DNA binding activity. Deglycosylation of Sp1 protein also reduced Sp1 binding activity. However, LPS did not cause Sp1 deglycosylation. LPS markedly reduced nuclear Sp1 protein level but had no significant effect on Sp1 mRNA abundance and on Sp1 protein nuclear translocation. Both Sp1 protein dephosphorylation and Sp1 protein degradation are temporally correlated to the reduced Sp1 binding activity. Our results demonstrate that challenge of mice with LPS in vivo down-regulates Sp1 DNA binding activity through promoting Sp1 protein dephosphorylation and degradation.
Ye
Xiaobing
X
Department of Medicine, Division of Pulmonary and Critical Care Medicine, Long Island Jewish Medical Center, Long Island Campus for the Albert Einstein College of Medicine, New Hyde Park, New York 11040, USA.
Liu
Shu Fang
SF
D000818:Animals; D001665:Binding Sites; D051545:Cyclooxygenase 1; D005786:Gene Expression Regulation / Q000187:drug effects; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D007527:Isoenzymes / Q000235:genetics; D008070:Lipopolysaccharides / Q000494:pharmacology*; D008565:Membrane Proteins; D051379:Mice; D019001:Nitric Oxide Synthase / Q000235:genetics; D052247:Nitric Oxide Synthase Type II; D052250:Nitric Oxide Synthase Type III; D010766:Phosphorylation; D011451:Prostaglandin-Endoperoxide Synthases / Q000235:genetics; D016329:Sp1 Transcription Factor / Q000378:metabolism*
D007527:Isoenzymes; D008070:Lipopolysaccharides; D008565:Membrane Proteins; D016329:Sp1 Transcription Factor; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II; D052250:Nitric Oxide Synthase Type III; C496315:Nos3 protein, mouse; D051545:Cyclooxygenase 1; D011451:Prostaglandin-Endoperoxide Synthases; C496512:Ptgs1 protein, mouse