title: Vitamin D inhibits growth of human airway smooth muscle cells through growth factor-induced phosphorylation of retinoblastoma protein and checkpoint kinase 1.
abstract: OBJECTIVE
  Airway remodelling in asthma is manifested, in part, as increased airway smooth muscle (ASM) mass, reflecting myocyte proliferation. We hypothesized that calcitriol, a secosteroidal vitamin D receptor (VDR) modulator, would inhibit growth factor-induced myocyte proliferation.
  
  
  METHODS
  Human ASM cell cultures were derived from bronchial samples taken during surgery. ASM cells were treated with platelet-derived growth factor (PDGF) (10 ng.mL(-1)) for 24 h in the presence of calcitriol, dexamethasone or a checkpoint kinase 1 (Chk1) inhibitor (SB218078). The effects of calcitriol on PDGF-mediated cell proliferation were assessed by thymidine incorporation assay, propidium iodide-based cell cycle analysis, caspase-3 assay and immunoblotting for specific cell cycle modulators.
  
  
  RESULTS
  Calcitriol, but not dexamethasone, inhibited PDGF-induced ASM DNA synthesis concentration dependently (IC(50)= 520 +/- 52 nM). These effects were associated with VDR-mediated expression of cytochrome CYP24A1 with no effects on ASM apoptosis. Calcitriol substantially inhibited (P < 0.01) PDGF-stimulated cell growth in ASM derived from both normal (59 +/- 8%) and asthmatic subjects (57 +/- 9%). Calcitriol inhibited PDGF-induced phosphorylation of retinoblastoma protein (Rb) and Chk1, with no effects on PDGF-mediated activation of extracellular signal-regulated kinases 1/2, PI3-kinase and S6 kinase, or expression of p21(Waf/Cip-1), p27(Kip1), cyclin D and E2F-1. Consistent with these observations, SB218078 also inhibited (IC(50)= 450 +/- 100 pM) PDGF-induced cell cycle progression.
  
  
  CONCLUSIONS
  Calcitriol decreased PDGF-induced ASM cell growth by inhibiting Rb and Chk1 phosphorylation.
authors.affiliation: University of Pennsylvania, Philadelphia, 19104-3403, USA.
authors.forename: G
authors.initials: G
authors.lastname: Damera
authors.forename: H W
authors.initials: HW
authors.lastname: Fogle
authors.forename: P
authors.initials: P
authors.lastname: Lim
authors.forename: E A
authors.initials: EA
authors.lastname: Goncharova
authors.forename: H
authors.initials: H
authors.lastname: Zhao
authors.forename: A
authors.initials: A
authors.lastname: Banerjee
authors.forename: O
authors.initials: O
authors.lastname: Tliba
authors.forename: V P
authors.initials: VP
authors.lastname: Krymskaya
authors.forename: R A
authors.initials: RA
authors.lastname: Panettieri
mesh_terms: D000328:Adult; D056151:Airway Remodeling / Q000187:drug effects*; D001249:Asthma / Q000188:drug therapy / Q000503:physiopathology; D001980:Bronchi / Q000166:cytology / Q000378:metabolism; D002117:Calcitriol / Q000008:administration & dosage / Q000494:pharmacology*; D049109:Cell Proliferation / Q000187:drug effects; D002478:Cells, Cultured; D000071877:Checkpoint Kinase 1; D003907:Dexamethasone / Q000494:pharmacology; D005260:Female; D005938:Glucocorticoids / Q000494:pharmacology; D006801:Humans; D020128:Inhibitory Concentration 50; D008297:Male; D008875:Middle Aged; D032389:Myocytes, Smooth Muscle / Q000187:drug effects* / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology; D011494:Protein Kinases / Q000187:drug effects / Q000378:metabolism; D016160:Retinoblastoma Protein / Q000187:drug effects / Q000378:metabolism; D014815:Vitamins / Q000008:administration & dosage / Q000494:pharmacology*
chemical_list: D005938:Glucocorticoids; D010982:Platelet-Derived Growth Factor; D016160:Retinoblastoma Protein; D014815:Vitamins; D003907:Dexamethasone; D011494:Protein Kinases; C000605867:CHEK1 protein, human; D000071877:Checkpoint Kinase 1; D002117:Calcitriol