title: Radiation-induced VEGF-C expression and endothelial cell proliferation in lung cancer.
abstract: BACKGROUND
  The present study was undertaken to investigate whether radiation induces the expression of vascular endothelial growth factor C (VEGF-C) through activation of the PI3K/Akt/mTOR pathway,subsequently affecting endothelial cells.
  
  
  METHODS
  Radiotherapy-induced tumor micro-lymphatic vessel density (MLVD) was determined in a lung cancer xenograft model established in SCID mice. The protein expression and phosphorylation of members of the PI3K/Akt/mTOR pathway and VEGF-C secretion and mRNA expression in irradiated lung cancer cells were assessed by Western blot analysis, enzyme-linked immunosorbent assays (ELISAs), and reverse transcriptase-polymerase chain reaction (RT-PCR). Moreover, specific chemical inhibitors were used to evaluate the role of the PI3K/Akt/mTOR signaling pathway. Conditioned medium (CM) from irradiated control-siRNA or VEGF-C-siRNA-expressing A549 cells was used to evaluate the proliferation of endothelial cells by the MTT assay.
  
  
  RESULTS
  Radiation increased VEGF-C expression in a dose-dependent manner over time at the protein but not at the mRNA level. Radiation also up-regulated the phosphorylation of Akt, mTOR, 4EBP, and eIF4E, but not of p70S6K. Radiation-induced VEGF-C expression was down-regulated by LY294002 and rapamycin (both p < 0.05). Furthermore, CM from irradiated A549 cells enhanced human umbilical vein endothelial cell (HUVEC) and lymphatic endothelial cell (LEC) proliferation, which was not observed with CM from irradiated VEGF-C-siRNA-expressing A549 cells.
  
  
  CONCLUSIONS
  Radiation-induced activation of the PI3K/Akt/mTOR signaling pathway increases VEGF-C expression in lung cancer cells, thereby promoting endothelial cell proliferation.
authors.affiliation: Department of Oncology, National Taiwan University Hospital, Taipei, Taiwan.
authors.forename: Yu-Hsuan
authors.initials: YH
authors.lastname: Chen
authors.forename: Shiow-Lin
authors.initials: SL
authors.lastname: Pan
authors.forename: Jing-Chi
authors.initials: JC
authors.lastname: Wang
authors.forename: Sung-Hsin
authors.initials: SH
authors.lastname: Kuo
authors.forename: Jason Chia-Hsien
authors.initials: JC
authors.lastname: Cheng
authors.forename: Che-Ming
authors.initials: CM
authors.lastname: Teng
mesh_terms: D000818:Animals; D049109:Cell Proliferation / Q000528:radiation effects*; D004307:Dose-Response Relationship, Radiation; D042783:Endothelial Cells / Q000473:pathology* / Q000528:radiation effects*; D015972:Gene Expression Regulation, Neoplastic / Q000528:radiation effects*; D008175:Lung Neoplasms / Q000378:metabolism* / Q000532:radiotherapy*; D008297:Male; D051379:Mice; D016513:Mice, SCID; D011879:Radiotherapy Dosage; D016896:Treatment Outcome; D015854:Up-Regulation / Q000528:radiation effects; D042582:Vascular Endothelial Growth Factor C / Q000378:metabolism*
chemical_list: D042582:Vascular Endothelial Growth Factor C; C467483:vascular endothelial growth factor C, mouse