The antiproliferative effect of sildenafil on pulmonary artery smooth muscle cells is mediated via upregulation of mitogen-activated protein kinase phosphatase-1 and degradation of extracellular signal-regulated kinase 1/2 phosphorylation.
BACKGROUND
Pulmonary hypertension is a group of diseases comprising vascular constriction and by obstructive changes of the pulmonary vasculature. Phosphodiesterase type 5 inhibitors, e.g., sildenafil, can alleviate vascular remodeling in the monocrotaline pulmonary hypertension model in rats, and inhibit the proliferation of pulmonary vascular smooth muscle cells in vitro. We examined the ability of sildenafil to inhibit platelet-derived growth factor (PDGF)-induced proliferation of porcine pulmonary artery smooth muscle cells.


METHODS
Pulmonary artery smooth muscle cell proliferation and cell cycle analysis were assessed by MTT assay and fluorescence-activated cell sorting. Western blotting was used to examine protein expression of mitogen-activated protein kinase phosphatase-1 (MKP-1) and phosphorylation level of extracellular signal-regulated kinase (ERK1/2).


RESULTS
PDGF increased cell proliferation and the percentage of cells in S phase. These effects were inhibited by pretreatment with sildenafil in a dose-dependent manner. Sildenafil (96 microM) also caused a 67% decrease in PDGF-stimulated ERK1/2 phosphorylation. Sildenafil inhibition of ERK1/2 was accompanied by a rapid induction of MKP-1. Inhibition of the cGMP-dependent kinase I alpha (cGK I alpha) using Rp-8-BrcGMPS (25 microM) blocked sildenafil-induced MKP-1 expression. Either vanadate (12.5 microM), a phosphatase inhibitor, or Rp-8-BrcGMPS abolished the inhibitory effect of sildenafil on PDGF-stimulated phosphorylation of ERK1/2 and restored PDGF-induced cell proliferation.


CONCLUSIONS
This study indicates that sildenafil upregulates MKP-1 expression and promotes degradation of phosphorylation of ERK1/2, which suppresses the proliferation of pulmonary artery smooth muscle cells.
Li
Bingbing
B
Department of Anesthesiology, Zhongshan Hospital affiliated Fudan University, Shanghai, China.
Yang
Lingchao
L
Shen
Jianying
J
Wang
Chunshen
C
Jiang
Zhen
Z
D000818:Animals; D002453:Cell Cycle / Q000187:drug effects; D018797:Cell Cycle Proteins / Q000378:metabolism*; D049109:Cell Proliferation / Q000187:drug effects*; D002478:Cells, Cultured; D017869:Cyclic GMP-Dependent Protein Kinases / Q000378:metabolism; D054638:Dual Specificity Phosphatase 1; D017874:Immediate-Early Proteins / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism*; D009131:Muscle, Smooth, Vascular / Q000166:cytology* / Q000187:drug effects / Q000201:enzymology; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology*; D010749:Phosphoprotein Phosphatases / Q000378:metabolism*; D010766:Phosphorylation; D010879:Piperazines / Q000494:pharmacology*; D054645:Protein Phosphatase 1; D017027:Protein Tyrosine Phosphatases / Q000378:metabolism*; D011651:Pulmonary Artery; D011687:Purines / Q000494:pharmacology; D000068677:Sildenafil Citrate; D013450:Sulfones / Q000494:pharmacology*; D034421:Sus scrofa; D013939:Thymidine Phosphorylase / Q000494:pharmacology; D015854:Up-Regulation
D018797:Cell Cycle Proteins; D017874:Immediate-Early Proteins; D010726:Phosphodiesterase Inhibitors; D010879:Piperazines; D011687:Purines; D013450:Sulfones; D000068677:Sildenafil Citrate; D013939:Thymidine Phosphorylase; D017869:Cyclic GMP-Dependent Protein Kinases; D048052:Mitogen-Activated Protein Kinase 3; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1; D054638:Dual Specificity Phosphatase 1; D017027:Protein Tyrosine Phosphatases