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Nitric oxide increases p21(Waf1/Cip1) expression by a cGMP-dependent pathway that includes activation of

M Gu1, J Lynch, P Brecher

  • 1Department of Biochemistry, Boston University School of Medicine, Boston, Massachusetts 02118, USA.

The Journal of Biological Chemistry
|February 7, 2001
PubMed

Insights

Nitric oxide (NO) rapidly increases p21 expression in fibroblasts via ERK and p70 S6 kinase (p70(S6k)) pathways. This study reveals a novel role for p70(S6k) in p53 activation and p21 regulation.

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Biochemistry

Background:

  • Nitric oxide (NO) is a key signaling molecule regulating gene expression in various cell types.
  • p21(Waf1/Cip1) is a critical regulator of cell cycle progression.
  • The interplay between NO, kinases, and p21 in fibroblast cell cycle regulation requires further elucidation.

Purpose of the Study:

  • To investigate the roles of extracellular signal-regulated kinase (ERK) and p70 S6 kinase (p70(S6k)) in NO-induced p21 expression in adventitial fibroblasts.
  • To elucidate the signaling pathways involved in NO-mediated regulation of p21 during the cell cycle.

Main Methods:

  • Utilized the NO donor S-nitroso-N-acetylpenicillamine (SNAP) to stimulate fibroblasts.
  • Employed selective kinase inhibitors (PD98059 for ERK, Rapamycin for p70(S6k)) and immunoprecipitation.
  • Assessed protein phosphorylation, p21 expression, p53 activation, and p21 mRNA levels.

Main Results:

  • SNAP induced rapid and transient phosphorylation of both ERK and p70(S6k), preceding increased p21 protein.
  • Inhibition of ERK phosphorylation (PD98059) blocked p70(S6k) phosphorylation and subsequent p21 increase.
  • p70(S6k) inhibition (Rapamycin) affected p53 phosphorylation and p21 expression, while PD98059 did not impact p53 or p21 mRNA.
  • A complex between ERK and p70(S6k) was identified.

Conclusions:

  • NO, ERK, and p70(S6k) exhibit a unique signaling relationship in regulating p21 expression in fibroblasts.
  • p70(S6k) plays a novel role in the activation of p53, contributing to p21 regulation.
  • These findings provide insights into the molecular mechanisms of NO-mediated cell cycle control.

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