Hypoxia and hypoxia-inducible factor-1alpha promote growth factor-induced proliferation of human vascular smooth muscle cells.
Hypoxia is thought to be a stimulus for the excessive proliferation of vascular smooth muscle cells (VSMC) that contributes to pulmonary hypertension, but the mechanisms involved are unknown. Here we tested whether hypoxia-inducible factor 1-alpha (HIF-1alpha), a master regulator of the transcriptional response to hypoxia, is involved in the enhanced mitogen-induced proliferative responses of hypoxic VSMC. Exposure to moderate hypoxia (5% O(2)) enhanced the proliferative responses of human pulmonary artery SMC (HPASMC) to mitogens including platelet-derived growth factor (PDGF), fibroblast growth factor 2 (FGF-2), and epidermal growth factor (EGF), compared with those in normoxia (20% O(2)). Moderate hypoxia elicited increased cellular HIF-1alpha levels, shown by Western blot analysis, and also enhanced PDGF-, FGF-2-, and EGF-induced expression of HIF-1alpha. Knockdown of HIF-1alpha or HIF-1beta levels in HPASMC with specific small interfering RNAs inhibited FGF-2-stimulated proliferation of HPASMC incubated in either 5% or 20% O(2) but failed to inhibit the comitogenic effect of hypoxia. Knockdown of HIF-1alpha similarly inhibited PDGF-stimulated proliferation, whereas HIF-2alpha knockdown had no effect on HPASMC proliferation. Knockdown of HIF-1alpha expression also inhibited growth factor-induced expression of cyclin A. We conclude that HIF-1alpha promotes proliferative responses of human VSMC to FGF-2, PDGF, and EGF by mechanisms that may involve HIF-1-dependent expression of cyclin A, but HIF is apparently not crucial to the enhancement of FGF-2-, PDGF-, and EGF-induced proliferation of VSMC that occurs during hypoxia.
Schultz
Kelly
K
Molecular Cardiology Research Institute, Department of Medicine, Tufts-New England Medical Center, Box 8486, 750 Washington Street, Boston, MA 02111, USA.
Fanburg
Barry L
BL
Beasley
Debbie
D
D051784:Aryl Hydrocarbon Receptor Nuclear Translocator / Q000235:genetics; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics; D015153:Blotting, Western; D049109:Cell Proliferation / Q000187:drug effects*; D002478:Cells, Cultured; D019925:Cyclin A / Q000096:biosynthesis / Q000235:genetics; D004815:Epidermal Growth Factor / Q000494:pharmacology; D016222:Fibroblast Growth Factor 2 / Q000494:pharmacology; D006801:Humans; D000860:Hypoxia / Q000473:pathology*; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000235:genetics / Q000494:pharmacology*; D008934:Mitogens / Q000494:pharmacology; D009131:Muscle, Smooth, Vascular / Q000166:cytology*; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology; D011651:Pulmonary Artery / Q000166:cytology / Q000187:drug effects; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000494:pharmacology; D014162:Transfection; D000099162:Endothelial PAS Domain-Containing Protein 1
D051784:Aryl Hydrocarbon Receptor Nuclear Translocator; D051792:Basic Helix-Loop-Helix Proteins; D019925:Cyclin A; D004815:Epidermal Growth Factor; D016222:Fibroblast Growth Factor 2; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D008934:Mitogens; D010982:Platelet-Derived Growth Factor; D034741:RNA, Small Interfering; D000099162:Endothelial PAS Domain-Containing Protein 1; C497396:ARNT protein, human