N-myc is a novel regulator of PI3K-mediated VEGF expression in neuroblastoma.
Angiogenesis in neuroblastoma (NB) correlates with increased expression of vascular endothelial growth factor (VEGF) and a worse clinical outcome. Other cellular markers, such as Akt activation and MYCN amplification, are also associated with poor prognosis in NB; therefore, we sought to determine the role of N-myc in the regulation of the phosphatidylinositol 3-kinase (PI3K)/Akt/VEGF pathway. PI3K inhibition, using small-molecule inhibitors or phosphatase and tensin homolog adenovirus, led to decreased levels of VEGF mRNA and/or protein by reducing phosphorylation of Akt and mammalian target of rapamycin (mTOR), and attenuating hypoxia-inducible factor 1alpha expression. Moreover, PI3K inhibition decreased levels of N-myc expression in MYCN-amplified cells. To further clarify the importance of N-myc as a target of PI3K in VEGF regulation, we inhibited N-myc expression by siRNA transfection. MYCN siRNA significantly blocked VEGF secretion, irrespective of serum conditions, in MYCN-amplified NB cells; this effect was enhanced when combined with rapamycin, an mTOR inhibitor. Interestingly, in cells with low-N-myc expression, MYCN siRNA reduction of VEGF secretion was only effective with MYCN overexpression or insulin-like growth factor-1 stimulation. Our results show that N-myc plays an important role in the PI3K-mediated VEGF regulation in NB cells. Targeting MYCN, as a novel effector of PI3K-mediated angiogenesis, has significant potential for the treatment of highly vascularized, malignant NB.
Kang
J
J
Department of Surgery, The University of Texas Medical Branch, Galveston, TX 77555-0353, USA.
Rychahou
P G
PG
Ishola
T A
TA
Mourot
J M
JM
Evers
B M
BM
Chung
D H
DH
D000256:Adenoviridae / Q000235:genetics; D015971:Gene Expression Regulation, Enzymologic; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000378:metabolism; D008840:Microfilament Proteins / Q000737:chemistry; D009389:Neovascularization, Pathologic; D009447:Neuroblastoma / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D010766:Phosphorylation; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D016271:Proto-Oncogene Proteins c-myc / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D034741:RNA, Small Interfering / Q000378:metabolism; D000070876:Tensins; D042461:Vascular Endothelial Growth Factor A / Q000378:metabolism*
D008840:Microfilament Proteins; D016271:Proto-Oncogene Proteins c-myc; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D000070876:Tensins; D042461:Vascular Endothelial Growth Factor A; D007334:Insulin-Like Growth Factor I; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt