Differential and constitutive expression of neuronal, inducible, and endothelial nitric oxide synthase mRNAs and proteins in pathologically normal human tissues

Nitric oxide (NO) is produced by NO synthases (nNOS, iNOS, and eNOS) expres sed in various human tissues and depending on the amount of NO produced in each tissue, the physiological function of NO is determined. However, due t o the difficulty in obtaining normal human tissues, little is known about t he basal levels of each of the three NOS mRNAs and proteins expressed const itutively in various human tissues. Results of the present study indicate t hat the basal levels of each of the three NOS mRNAs and proteins expressed in various regions of brain and peripheral tissues are different both in th eir sizes and in their contents. In Northern blot analysis, two different-s ized mRNAs were found for each NOS isozymes: for the nNOS, similar to 12 an d <12 kb mRNAs; for the iNOS, 4.2 and 4.5 kb mRNAs; for the eNOS, 4.2 and 4 .4 kb mRNAs, In the Western blot, several different-sized NOS proteins were detected (<similar to>160, similar to 140, and similar to 130 kDa for nNOS ; similar to 130 kDa for iNOS and eNOS) with tissue-specific expression pat terns. These differential expression patterns of NOS mRNAs and proteins wer e caused by alternative splicing in the open-reading frame, and 5'- and/or 3'-untranslated regions of NOS mRNAs. These results suggest that regulation for differential expression of the three NOS genes in various human tissue s may occur by alternative splicing of the NOS mRNAs in tissue-specific pat terns. (C) 2000 Academic Press.