Modulation of pulmonary vascular smooth muscle cell phenotype in hypoxia: role of cGMP-dependent protein kinase and myocardin

Am J Physiol Lung Cell Mol Physiol. 2009 May;296(5):L780-9. doi: 10.1152/ajplung.90295.2008. Epub 2009 Feb 27.


We have previously reported that in ovine fetal pulmonary venous smooth muscle cells (FPVSMC), decreased expression of cGMP-dependent protein kinase (PKG) by hypoxia could explain hypoxia-induced SMC phenotype modulation. In this study, we investigated the role of myocardin, a possible downstream effector of PKG, in SMC phenotype modulation induced by 1 and 24 h of hypoxia. Hypoxia for 1 h induced the phosphorylation of E-26-like protein 1 (Elk-1), indicating a quick activation of Elk-1 after hypoxia. Either hypoxia (1 h) or treatment with DT-3, a PKG inhibitor, increased associations of Elk-1 with myosin heavy chain (MHC) gene and serum response factor (SRF), which was paralleled by a decrease in association of myocardin with MHC gene and SRF. Exposure to hypoxia of FPVSMC for 24 h significantly decreased the promoter activity of multiple SMC marker genes, downregulated protein and mRNA expression of myocardin, and upregulated mRNA expression of Elk-1, but had no significant effects on the phosphorylation of Elk-1. Inhibition of myocardin by siRNA transfection downregulated the expression of SMC marker proteins, while overexpression of myocardin prevented the hypoxia-induced decrease in expression of SMC marker proteins. Inhibition of PKG by siRNA transfection downregulated the expression of myocardin, but upregulated that of Elk-1. Overexpression of PKG prevented hypoxia-induced effects on protein expression of myocardin and Elk-1. These data suggest that PKG induces displacement of myocardin from SRF and upregulates myocardin expression, thus activating the SMC genes transcription. The inhibitory effects of hypoxia on PKG may explain hypoxia-induced SMC phenotype modulation by decreasing the effects of PKG on myocardin.

Publication types

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

MeSH terms

  • Animals
  • Biomarkers / metabolism
  • Cell Hypoxia / drug effects
  • Cyclic GMP-Dependent Protein Kinases / metabolism*
  • Down-Regulation / drug effects
  • Enzyme Inhibitors / pharmacology
  • Lung / cytology*
  • Models, Biological
  • Muscle, Smooth, Vascular / cytology*
  • Myocytes, Smooth Muscle / cytology*
  • Myocytes, Smooth Muscle / drug effects
  • Myocytes, Smooth Muscle / enzymology*
  • Myosin Heavy Chains / genetics
  • Nuclear Proteins / genetics
  • Nuclear Proteins / metabolism*
  • Phenotype
  • Phosphorylation / drug effects
  • Promoter Regions, Genetic / genetics
  • Protein Binding / drug effects
  • RNA, Messenger / genetics
  • RNA, Messenger / metabolism
  • RNA, Small Interfering / metabolism
  • Serum Response Factor / genetics
  • Serum Response Factor / metabolism
  • Sheep
  • Time Factors
  • Trans-Activators / genetics
  • Trans-Activators / metabolism*
  • ets-Domain Protein Elk-1 / genetics
  • ets-Domain Protein Elk-1 / metabolism


  • Biomarkers
  • Enzyme Inhibitors
  • Nuclear Proteins
  • RNA, Messenger
  • RNA, Small Interfering
  • Serum Response Factor
  • Trans-Activators
  • ets-Domain Protein Elk-1
  • myocardin
  • Cyclic GMP-Dependent Protein Kinases
  • Myosin Heavy Chains