title: ERK1/2-dependent vascular endothelial growth factor signaling sustains cyst growth in polycystin-2 defective mice.
abstract: OBJECTIVE
  Severe polycystic liver disease can complicate adult dominant polycystic kidney disease, a genetic disease caused by defects in polycystin-1 (Pkd1) or polycystin-2 (Pkd2). Liver cyst epithelial cells (LCECs) express vascular endothelial growth factor (VEGF) and its receptor, VEGFR-2. We investigated the effects of VEGF on liver cyst growth and autocrine VEGF signaling in mice with Pkd1 and Pkd2 conditional knockouts.
  
  
  METHODS
  We studied mice in which Pkd1 or Pkd2 were conditionally inactivated following exposure to tamoxifen; these mice were called Pkd1(flox/-):pCxCreER (Pkd1KO) and Pkd2(flox/-):pCxCreER (Pkd2KO).
  
  
  RESULTS
  Pkd1KO and Pkd2KO mice developed liver defects; their LCECs expressed VEGF, VEGFR-2, hypoxia-inducible factor (HIF)-1alpha, phosphorylated extracellular signal-regulated kinase 1/2 (pERK1/2), and proliferating cell nuclear antigen (PCNA). In Pkd2KO but not Pkd1KO mice, exposure to the VEGFR-2 inhibitor SU5416 significantly reduced liver cyst development, liver/body weight ratio, and expression of pERK and PCNA. VEGF secretion and phosphorylation of ERK1/2 and VEGFR-2 were significantly increased in cultured LCECs from Pkd2KO compared with Pkd1KO mice. Inhibition of protein kinase A (PKA) reduced VEGF secretion and pERK1/2 expression. Addition of VEGF to LCECs from Pkd2KO mice increased phosphorylated VEGFR-2 and phosphorylated mitogen signal-regulated kinase (MEK) expression and induced phosphorylation of ERK1/2; this was inhibited by SU5416. Expression of HIF-1alpha increased in parallel with secretion of VEGF following LCEC stimulation. VEGF-induced cell proliferation was inhibited by the MEK inhibitor U1026 and by ERK1/2 small interfering RNA.
  
  
  CONCLUSIONS
  The PKA-ERK1/2-VEGF signaling pathway promotes growth of liver cysts in mice. In Pkd2-defective LCECs, PKA-dependent ERK1/2 signaling controls HIF-1alpha-dependent VEGF secretion and VEGFR-2 signaling. Autocrine and paracrine VEGF signaling promotes the growth of liver cysts in Pkd2KO mice. VEGF inhibitors might be used to treat patients with polycystic liver disease.
authors.affiliation: Section of Digestive Diseases, Department of Internal Medicine, Yale University, New Haven, Connecticut 06520, USA.
authors.forename: Carlo
authors.initials: C
authors.lastname: Spirli
authors.forename: Stefano
authors.initials: S
authors.lastname: Okolicsanyi
authors.forename: Romina
authors.initials: R
authors.lastname: Fiorotto
authors.forename: Luca
authors.initials: L
authors.lastname: Fabris
authors.forename: Massimiliano
authors.initials: M
authors.lastname: Cadamuro
authors.forename: Silvia
authors.initials: S
authors.lastname: Lecchi
authors.forename: Xin
authors.initials: X
authors.lastname: Tian
authors.forename: Stefan
authors.initials: S
authors.lastname: Somlo
authors.forename: Mario
authors.initials: M
authors.lastname: Strazzabosco
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D003560:Cysts / Q000378:metabolism* / Q000473:pathology / Q000503:physiopathology; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000378:metabolism; D007211:Indoles / Q000494:pharmacology; D008107:Liver Diseases / Q000378:metabolism* / Q000473:pathology / Q000503:physiopathology; D020935:MAP Kinase Signaling System / Q000502:physiology*; D051379:Mice; D018345:Mice, Knockout; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism*; D010641:Phenotype; D010766:Phosphorylation / Q000502:physiology; D018809:Proliferating Cell Nuclear Antigen / Q000378:metabolism; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D011758:Pyrroles / Q000494:pharmacology; D012097:Repressor Proteins / Q000378:metabolism; D050396:TRPP Cation Channels / Q000235:genetics*; D025521:Tumor Suppressor Proteins / Q000378:metabolism; D042461:Vascular Endothelial Growth Factor A / Q000378:metabolism; D040301:Vascular Endothelial Growth Factor Receptor-2 / Q000037:antagonists & inhibitors / Q000378:metabolism
chemical_list: D017868:Cyclic AMP-Dependent Protein Kinases; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D007211:Indoles; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D018809:Proliferating Cell Nuclear Antigen; D047428:Protein Kinase Inhibitors; D011758:Pyrroles; D012097:Repressor Proteins; D050396:TRPP Cation Channels; D025521:Tumor Suppressor Proteins; D042461:Vascular Endothelial Growth Factor A; D040301:Vascular Endothelial Growth Factor Receptor-2; C497443:Hif1a protein, mouse; C525546:Tip30 protein, mouse; C467480:vascular endothelial growth factor A, mouse; C116890:Semaxinib