Spontaneous expression of inducible nitric oxide synthase and its possible role in normal human jejunum

초록

It has been demonstrated that inducible nitric oxide synthase (iNOS) is constitutively expressed in some normal human tissues. Here we demonstrate the expression of a specific iNOS in the normal jejunum of human digestive tract. RT-PCR and Northern-blot analyses showed constitutive expression of iNOS mRNA. The size of mRNA expressed was longer (4.5 kb) than that normally seen in other cells like macorphages and hepatocytes (4.2 kb). The larger size iNOS mRNA in the jejunum is a normal characteristic of iNOS seen in digestive tract tissues and is presumed to be due to alternative splicing of iNOS gene. At the translational level, 130 kDa iNOS protein was identified by western-blotting with monoclonal antibodies raised against the purified enzyme. The iNOS actibity in jejunum was measured by employing the Ca++-independent but BH4-dependent with hemoglobin-oxidation assay. Immunohisto-chemistry experiment using anti-mouse iNOS lgG2a monoclonal antibody confirmed the spontaneous expression of iNOS gene. Positive reaction for the antibody was localized only to the macrophages in lamina propria of the jejunum. These results suggest that iNOS is expressed spontaneously in normal jejunum tissue to provide protection against potential infections.