ERK1/2-dependent vascular endothelial growth factor signaling sustains cyst growth in polycystin-2 defective mice.

Abstract

BACKGROUND & AIMS:

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: Carlo Spirli, Stefano Okolicsanyi, Romina Fiorotto, Luca Fabris, Massimiliano Cadamuro, Silvia Lecchi, Xin Tian, Stefan Somlo, Mario Strazzabosco
• Journal: Gastroenterology (Gastroenterology) Vol. 138 Issue 1 Pg. 360-371.e7 (Jan 2010) ISSN: 1528-0012 [Electronic] United States
• PMID: 19766642 (Publication Type: Journal Article, Research Support, N.I.H., Extramural, Research Support, Non-U.S. Gov't)
• Copyright: Copyright 2010 AGA Institute. Published by Elsevier Inc. All rights reserved.

Chemical References

• Hif1a protein, mouse
• Hypoxia-Inducible Factor 1, alpha Subunit
• Indoles
• Proliferating Cell Nuclear Antigen
• Protein Kinase Inhibitors
• Pyrroles
• Repressor Proteins
• TRPP Cation Channels
• Tip30 protein, mouse
• Tumor Suppressor Proteins
• Vascular Endothelial Growth Factor A
• polycystic kidney disease 1 protein
• polycystic kidney disease 2 protein
• vascular endothelial growth factor A, mouse
• Semaxinib
• Vascular Endothelial Growth Factor Receptor-2
• Cyclic AMP-Dependent Protein Kinases
• Mitogen-Activated Protein Kinase 1
• Mitogen-Activated Protein Kinase 3

Topics

• Animals
• Cells, Cultured
• Cyclic AMP-Dependent Protein Kinases (metabolism)
• Cysts (metabolism, pathology, physiopathology)
• Hypoxia-Inducible Factor 1, alpha Subunit (metabolism)
• Indoles (pharmacology)
• Liver Diseases (metabolism, pathology, physiopathology)
• MAP Kinase Signaling System (physiology)
• Mice
• Mice, Knockout
• Mitogen-Activated Protein Kinase 1 (metabolism)
• Mitogen-Activated Protein Kinase 3 (metabolism)
• Phenotype
• Phosphorylation (physiology)
• Proliferating Cell Nuclear Antigen (metabolism)
• Protein Kinase Inhibitors (pharmacology)
• Pyrroles (pharmacology)
• Repressor Proteins (metabolism)
• TRPP Cation Channels (genetics)
• Tumor Suppressor Proteins (metabolism)
• Vascular Endothelial Growth Factor A (metabolism)
• Vascular Endothelial Growth Factor Receptor-2 (antagonists & inhibitors, metabolism)