title: FHL-2 suppresses VEGF-induced phosphatidylinositol 3-kinase/Akt activation via interaction with sphingosine kinase-1.
abstract: OBJECTIVE
  In the functional screening of a human heart cDNA library to identify a novel antiangiogenic factor, the prime candidate gene was "four-and-a-half LIM only protein-2" (FHL-2). The goal of this study is to clear the mechanism of antiangiogenic signaling of FHL-2 in endothelial cells (ECs).
  
  
  RESULTS
  Overexpressed FHL-2 strongly inhibited vascular endothelial growth factor (VEGF)-induced EC migration. In the angiogenic signaling, we focused on sphingosine kinase-1 (SK1), which produces sphingosine-1-phosphate (S1P), a bioactive sphingolipid, as a potent angiogenic mediator in ECs. Immunoprecipitation and immunostaining analysis showed that FHL-2 might bind to SK1. Importantly, overexpression of FHL-2 in ECs inhibited VEGF-induced SK1 activity, phosphatidylinositol 3-kinase activity, and phosphorylation of Akt and eNOS. In contrast, overexpression of FHL-2 had no effect on S1P-induced Akt phosphorylation. Interestingly, VEGF stimulation decreased the binding of FHL-2 and SK1. Depletion of FHL-2 by siRNA increased EC migration accompanied with SK1 and Akt activation, and increased the expression of VEGF receptor-2 which further enhanced VEGF signaling. Furthermore, injection of FHL-2 mRNA into Xenopus embryos resulted in inhibition of vascular network development, assessed by in situ hybridization with endothelial markers.
  
  
  CONCLUSIONS
  FHL-2 may regulate phosphatidylinositol 3-kinase/Akt via direct suppression of the SK1-S1P pathway in ECs.
authors.affiliation: Division of Gene Therapy Science, Department of Geriatric Medicine, Osaka University Graduate School of Medicine, 2-2 Yamada-oka, Suita 565-0871, Japan.
authors.forename: Hiroki
authors.initials: H
authors.lastname: Hayashi
authors.forename: Hironori
authors.initials: H
authors.lastname: Nakagami
authors.forename: Yoichi
authors.initials: Y
authors.lastname: Takami
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Koriyama
authors.forename: Masaki
authors.initials: M
authors.lastname: Mori
authors.forename: Katsuto
authors.initials: K
authors.lastname: Tamai
authors.forename: Jianxin
authors.initials: J
authors.lastname: Sun
authors.forename: Kaori
authors.initials: K
authors.lastname: Nagao
authors.forename: Ryuichi
authors.initials: R
authors.lastname: Morishita
authors.forename: Yasufumi
authors.initials: Y
authors.lastname: Kaneda