IMPLICATION OF NITRIC-OXIDE SYNTHASE IN CARCINOGENESIS - ANALYSIS OF THE HUMAN INDUCIBLE NITRIC-OXIDE SYNTHASE GENE

Nitric oxide (NO) is a newly identified, multifunctional biological me diator. However, it also has deleterious effects on biological materia ls. For instance, nucleic acids, proteins, and some prosthetic groups of enzymes can be modified by NO or its reaction products with other r eactive oxygen species. Endogenous nitrosamine formation through the r eaction of NO or its oxidized products with amines might be involved i n carcinogenesis. These deleterious effects of NO are often associated with inflammatory processes both in experimental animals and human. W e analysed the molecular mechanism of control of expression of the ind ucible nitric oxide synthase (NOS) gene in mouse cells by cloning its putative promoter region. This promoter responded to various cytokines and endotoxin similarly to the endogenous NOS gene in mouse cells. No appreciable induction of NOS was observed in human peripheral blood c ells, but induction was detected in a human glioblastoma cell line A-1 72. Therefore, the human inducible NOS cDNA was cloned from A-172 cell s and its cDNA-deduced amino acid sequence found to have about 80% sim ilarity to those of both mouse and rat inducible NOSs. The effects of various cytokines on the induction of the gene were somewhat different from those observed in mouse cells, but the mouse promoter responded to these cytokines similarly to the endogenous NOS gene in human cells , indicating functional similarity of cis-elements of the genes encodi ng both human and mouse inducible NOS. Structural analysis of the huma n inducible NOS gene by Southern blot analysis revealed putative genet ic restriction fragment length polymorphism in intron 5. This polymorp hism could be useful for analysis and determinations of the pathophysi ological significance of NOS.