Participation of the PI-3K/Akt-NF-kappa B signaling pathways in hypoxia-induced mitogenic factor-stimulated Flk-1 [?]expression in endothelial cells.
Tong Q, Zheng L, Lin L, Li B, Wang D, Huang C, Matuschak GM, Li D
Department of Internal Medicine, Saint Louis University, Saint Louis, MO 63110, USA. email@example.com
BACKGROUND: Hypoxia-induced mitogenic factor (HIMF), a lung-specific growth factor, promotes vascular tubule formation in a matrigel plug model. We initially found that HIMF enhances vascular endothelial growth factor (VEGF) expression in lung epithelial cells. In present work, we tested whether HIMFmodulates expression of fetal liver kinase-1 [?] (Flk-1 [?]) in endothelial cells, and dissected the possible signaling pathways that link HIMF to Flk-1 [?] upregulation. METHODS: Recombinant HIMF protein was intratracheally instilled into adult mouse lungs, Flk-1 [?] expression was examined by immunohistochemistry and Western blot. The promoter-luciferase reporter assay and real-time RT-PCR were performed to examine the effects of HIMF on Flk-1 [?] expression in mouse endothelial cell line SVEC 4-10. The activation of NF-kappa B (NF-kappaB) and phosphorylation of Akt, IKK, and IkappaBalpha were examined by luciferase assay and Western blot, respectively. RESULTS: Intratracheal instillation of HIMF protein resulted in a significant increase of Flk-1 [?] production in lung tissues. Stimulation of SVEC 4-10 cells by HIMF resulted in increased phosphorylation of IKK and IkappaBalpha, leading to activation of NF-kappaB. Blocking NF-kappaB signaling pathway by dominant-negative mutants of IKK and IkappaBalpha suppressed HIMF-induced Flk-1 [?]upregulation. Mutation or deletion of NF-kappaB binding site within Flk-1 [?] promoter also abolished HIMF-induced Flk-1 [?] expression in SVEC 4-10 cells. Furthermore, HIMF strongly induced phosphorylation of Akt. A dominant-negative mutant of PI-3K, Deltap85, as well as PI-3K inhibitor LY294002, blocked HIMF-induced NF-kappaB activation and attenuated Flk-1 [?] production. CONCLUSION: These results suggest that HIMF upregulates Flk-1 [?]expression in endothelial cells in a PI-3K/Akt-NF-kappaB signaling pathway-dependent manner, and may play critical roles in pulmonary angiogenesis.
Respir. Res. (2006)
PMID: 16872509 Fulltext – Related articles – Download citation