Role of regulatory flanking dinucleotide repeats in the regulation of human nNOS exon 1f gene transcription

초록

NO produced by neuronal NO synthase(nNOS) serves as an important messenger and is involved in physiological and pathological process in the CNS and PNS. Thus, release of NO should be controlled by tightly regulating the transcription of nNOS. In the present study, we report that the repeats of polymorphic dinucleotides (GT)nA(TG)n localized in just upstream to the exon 1f in human nNOS gene transcripts play a suppressive role in the transcription, as shown in the characteristics of Z-DNA motif in other genes. In various neuronal (CATH.a, SH-SY5Y, and PC12) and trophoblast (HT-1) cells transfected transiently with luciferase construct free of the dinucleotide repeats at the 5’-flanking region of exon 1f in nNOS gene, the luciferase activity was increased markedly. However, the luciferase activities in cells containing the dinucleotide repeats were suppressed to the basal level. Furthermore, in cells containing the constructs with the dinuclotide repeats, the suppressive effect on the luciferase activity was length-dependent, that was higher in the longer size. These results suggest that the dinucleotide repeats in the 5’-flanking region of nNOS exon 1f play a regulatory role in the constitutive expression of nNOS in CNS and PNS. Thus, the differential release of NO observed in different individuals may be caused by the differential suppressive mechanisms on the expression of nNOS gene mediated by the polymorphic dinucleotide repeats contained in the DNA structure.