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Posttranscriptional regulation of human iNOS by the NO/cGMP pathway

D Pérez-Sala1, E Cernuda-Morollón, M Díaz-Cazorla

  • 1Departamento de Estructura y Función de Proteínas, Centro de Investigaciones Biológicas, CSIC, Velázquez, 144, 28006 Madrid, Spain. dperezsala@cib.csic.es

American Journal of Physiology. Renal Physiology
|February 22, 2001
PubMed

Insights

Nitric oxide (NO) and cyclic GMP (cGMP) have a dual role in regulating inducible nitric oxide synthase (iNOS) expression in human mesangial cells, influencing both induction and downregulation through complex feedback mechanisms.

Area of Science:

  • Cellular and Molecular Biology
  • Immunology
  • Renal Physiology

Background:

  • Inducible nitric oxide synthase (iNOS) plays a critical role in inflammatory responses within the kidney.
  • The interplay between nitric oxide (NO) and cyclic guanosine monophosphate (cGMP) in modulating iNOS expression is complex and not fully understood.
  • Human mesangial cells are key players in glomerular inflammation and express iNOS.

Purpose of the Study:

  • To investigate the influence of the NO/cGMP pathway on iNOS expression in human mesangial cells.
  • To elucidate the mechanisms by which NO and cGMP regulate iNOS levels, including potential positive and negative feedback loops.
  • To determine the role of soluble guanylyl cyclase (sGC) in mediating these NO/cGMP effects.

Main Methods:

  • Human mesangial cells were stimulated with IL-1beta and TNF-alpha.
  • NOS activity was inhibited, and NO donors were used to assess NO's effect on iNOS induction.
  • Soluble guanylyl cyclase (sGC) activity was inhibited, and cGMP analogs were administered.
  • Transcriptional inhibition and mRNA stability assays were performed to analyze posttranscriptional regulation.

Main Results:

  • Inhibition of NOS activity reduced iNOS levels, while NO donors initially amplified iNOS induction but subsequently inhibited protein and mRNA levels.
  • sGC inhibition attenuated IL-1beta/TNF-alpha-induced iNOS and reduced NO-driven amplification.
  • cGMP analogs exhibited biphasic modulation of iNOS, and 8-bromo-cGMP (8-BrcGMP) reduced iNOS mRNA stability by 50%, indicating posttranscriptional downregulation.

Conclusions:

  • NO exerts a complex, biphasic effect on iNOS expression, contributing to both induction and downregulation in human mesangial cells.
  • The NO/cGMP pathway, involving sGC activation, plays a significant role in modulating iNOS expression.
  • Posttranscriptional mechanisms, particularly mRNA destabilization by NO and cGMP, are crucial for the late-phase downregulation of iNOS.

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