NADPH oxidase 4 mediates TGF-β-induced smooth muscle α-actin via p38MAPK and serum response factor

Free Radic Biol Med. 2011 Jan 15;50(2):354-62. doi: 10.1016/j.freeradbiomed.2010.11.007. Epub 2010 Nov 11.

Abstract

In contrast to other cell types, vascular smooth muscle cells modify their phenotype in response to external signals. NADPH oxidase 4 (Nox4) is critical for maintenance of smooth muscle gene expression; however, the underlying mechanisms are incompletely characterized. Using smooth muscle α-actin (SMA) as a prototypical smooth muscle gene and transforming growth factor-β (TGF-β) as a differentiating agent, we examined Nox4-dependent signaling. TGF-β increases Nox4 expression and activity in human aortic smooth muscle cells (HASMC). Transfection of HASMC with siRNA against Nox4 (siNox4) abolishes TGF-β-induced SMA expression and stress fiber formation. siNox4 also significantly inhibits TGF-β-stimulated p38MAPK phosphorylation, as well as that of its substrate, mitogen-activated protein kinase-activated protein kinase-2. Moreover, the p38MAPK inhibitor SB-203580 nearly completely blocks the SMA increase induced by TGF-β. Inhibition of either p38MAPK or NADPH oxidase-derived reactive oxygen species impairs the TGF-β-induced phosphorylation of Ser103 on serum response factor (SRF) and reduces its transcriptional activity. Binding of SRF to myocardin-related transcription factor (MRTF) is also necessary, because downregulation of MRTF by siRNA abolishes TGF-β-induced SMA expression. Taken together, these data suggest that Nox4 regulates SMA expression via activation of a p38MAPK/SRF/MRTF pathway in response to TGF-β.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Actins / genetics
  • Actins / metabolism*
  • Aorta / cytology
  • Aorta / metabolism
  • Blotting, Western
  • Cells, Cultured
  • Fluorescent Antibody Technique
  • Humans
  • Imidazoles / pharmacology
  • Luciferases / metabolism
  • Myocytes, Smooth Muscle / drug effects
  • Myocytes, Smooth Muscle / metabolism
  • NADPH Oxidase 4
  • NADPH Oxidases / antagonists & inhibitors
  • NADPH Oxidases / genetics
  • NADPH Oxidases / metabolism*
  • Phosphorylation / drug effects
  • Pyridines / pharmacology
  • RNA, Messenger / genetics
  • RNA, Small Interfering / genetics
  • Reactive Oxygen Species / metabolism
  • Reverse Transcriptase Polymerase Chain Reaction
  • Serum Response Factor / genetics
  • Serum Response Factor / metabolism*
  • Signal Transduction / drug effects
  • Stress Fibers / metabolism*
  • Stress Fibers / pathology
  • Transforming Growth Factor beta / genetics
  • Transforming Growth Factor beta / metabolism*
  • p38 Mitogen-Activated Protein Kinases / antagonists & inhibitors
  • p38 Mitogen-Activated Protein Kinases / genetics
  • p38 Mitogen-Activated Protein Kinases / metabolism*

Substances

  • Actins
  • Imidazoles
  • Pyridines
  • RNA, Messenger
  • RNA, Small Interfering
  • Reactive Oxygen Species
  • Serum Response Factor
  • Transforming Growth Factor beta
  • Luciferases
  • NADPH Oxidase 4
  • NADPH Oxidases
  • NOX4 protein, human
  • p38 Mitogen-Activated Protein Kinases
  • SB 203580