Excitotoxic Brain Lesion Modifies Binding to a USF Binding Site Acting as a Negative Regulatory Element in theProtease Nexin-1Promoter

The expression of the serine protease inhibitorProtease nexin-1 (PN-1)is upregulated in glial cells following different types of lesion in the nervous system. A strong negative regulatory element has been shown by the missing nucleoside technique to be a CACGTG site (E-box) in the proximal part of thePN-1promoter. The factor binding to this site is specifically recognized by antibodies directed against the human upstream stimulatory factor (USF). Point mutations in the E-box binding site which abolish USF bindingin vitroincrease the transcriptional activity of thePN-1promoter. Cotransfection of aPN-1promoter/reporter construct together with an expression vector for humanUSF1confirms the negative regulatory function of this site. Finally, we show that the binding to this USF site changed after ibotenic acid-induced lesion of the caudate putamen in the rat brain.