Chapter 7 - Regulation of the Expression of Nitric Oxide Synthase Isoforms

Abstract

There is a large array of regulatory mechanisms for the expression of different nitric oxide synthases (NOS) isoforms. The high-output NOS II is not only turned on transcriptionally, but the stability of the transcripts and their translation can be regulated dynamically. In addition, the expressional levels of the servoregulatory, low-output enzymes, NOS I and NOS III, can also be adjusted to meet local demand. The original paradigm that nitrogen oxide (NO) is synthesized either by constitutive NO synthases or by inducible NOS II is no longer valid. This adds to the diversity of mechanisms controlling NO production in different cells and tissues. Whereas transcriptional regulation of NOS II has been established since about 1990, no expressional regulation was originally known for the other two isoforms. Recent evidence suggests, however, that the expression of NOS I and NOS III can also be regulated under various conditions. Therefore, the mechanisms of expressional regulation of all three NOS isoforms are decribed.