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Inducible nitric-oxide-synthase mRNA is transiently expressed and destroyed by a cycloheximide-sensitive process

T Evans1, A Carpenter, J Cohen

  • 1Department of Infectious Diseases and Bacteriology, Royal Postgraduate Medical School, London, England.

European Journal of Biochemistry
|January 15, 1994
PubMed

Insights

The study reveals that inducible nitric oxide synthase (iNOS) mRNA levels in smooth muscle cells and macrophages are transiently regulated. Protein synthesis inhibition prevents the decay of iNOS mRNA, indicating a shared regulatory mechanism with cytokines.

Area of Science:

  • Molecular Biology
  • Immunology
  • Physiology

Background:

  • Nitric oxide (NO) is a critical physiological mediator produced by nitric-oxide synthases (NOS).
  • A specific form, inducible NOS (iNOS), is upregulated in various cells upon stimulation with cytokines and lipopolysaccharide.
  • Understanding iNOS mRNA regulation is crucial for controlling NO-mediated processes.

Purpose of the Study:

  • To investigate the regulation of inducible nitric-oxide synthase (iNOS) mRNA expression in smooth muscle cells and macrophages.
  • To elucidate the mechanisms underlying the transient expression of iNOS mRNA.
  • To identify conserved sequences and regulatory factors involved in iNOS mRNA stability.

Main Methods:

  • Stimulation of smooth muscle cells and macrophages with cytokines and lipopolysaccharide.
  • Quantitative analysis of iNOS mRNA levels over time using techniques like Northern blotting or RT-qPCR.
  • Bioinformatic analysis of the 3' untranslated region (UTR) of iNOS mRNA for conserved regulatory elements.
  • Experiments involving protein synthesis inhibitors to assess their effect on iNOS mRNA stability.

Main Results:

  • iNOS mRNA levels significantly increased post-stimulation, peaking at 3-6 hours and returning to baseline within 20 hours.
  • Enzyme activity of iNOS remained stable for up to 48 hours, despite transient mRNA levels.
  • A conserved AU-rich octanucleotide sequence was identified in the 3' UTR of both murine and human iNOS mRNA.
  • The half-life of iNOS mRNA was determined to be approximately 6 hours.
  • Protein synthesis inhibition effectively prevented the degradation of iNOS mRNA.

Conclusions:

  • The transient expression of iNOS mRNA is a key regulatory mechanism controlling NO production.
  • The 3' UTR of iNOS mRNA contains instability elements, similar to those found in cytokine and oncogene mRNAs.
  • The decay of iNOS mRNA is dependent on ongoing protein synthesis, suggesting a post-transcriptional regulatory mechanism.
  • iNOS mRNA regulation shares similarities with cytokine mRNA regulation, including transient expression and decay prevention by protein synthesis inhibition.

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