The stimulation of inducible nitric-oxide synthase by the prion protein fragment 106-126 in human microglia is tumor necrosis factor-alpha-dependent and involves p38 mitogen-activated protein kinase

A synthetic peptide consisting of amino acid residues 106-126 of the human prion protein (PrP-(106-126)) has been previously demonstrated to be neurot oxic and to induce microglial activation. The present study investigated th e expression of the inducible form of the nitric-oxide synthase (NOS-II) in human microglial cells treated with PrP-(106-126). Using reverse transcrip tase-polymerase chain reaction, we found that PrP-(106-126) induces NOS-II gene expression after 24 h of treatment and that this effect is accompanied by a peak of nuclear factor kappa B (NF-KB) binding at 30 min as evaluated by electrophoretic mobility shift assay. Since our previous data demonstra ted tumor necrosis factor-alpha (TNF-alpha) to be a potent inducer of NOS-I I in these cells, we analyzed the expression of this cytokine in PrP-(106-1 26)treated microglia, PrP-(106-126) caused the release of TNF-alpha as dete cted by enzyme-linked immunosorbent assay, and a blocking antibody, anti-TN F-alpha, abolished NOS-II induction elicited by this peptide. Moreover, PrP -(106-126) activates p38 mitogen-activated protein kinase, and the inhibiti on of this pathway determines the ablation of NF-kappaB binding induced by this fragment peptide.