title: Amino acid deprivation promotes tumor angiogenesis through the GCN2/ATF4 pathway.
abstract: As tumors continue to grow and exceed their blood supply, nutrients become limited leading to deficiencies in amino acids (AAD), glucose (GD), and oxygen (hypoxia). These alterations result in significant changes in gene expression. While tumors have been shown to overcome the stress associated with GD or hypoxia by stimulating vascular endothelial growth factor (VEGF)-mediated angiogenesis, the role of AAD in tumor angiogenesis remains to be elucidated. We found that in human tumors, the expression of the general control non-derepressible 2 (GCN2, an AAD sensor) kinase is elevated at both protein and mRNA levels. In vitro studies revealed that VEGF expression is universally induced by AAD treatment in all five cell lines tested (five of five). This is in contrast to two other angiogenesis mediators interleukin-6 (two of five) and fibroblast growth factor 2 (two of five) that have a more restricted expression. Suppressing GCN2 expression significantly decreased AAD-induced VEGF expression. Silencing activating transcription factor 4 (ATF4), a downstream transcription factor of the GCN2 signaling pathway, is also associated with strong inhibition of AAD-induced VEGF expression. PKR-like kinase, the key player in GD-induced unfolded protein response is not involved in this process. In vivo xenograft tumor studies in nonobese diabetic/severe combined immunodeficient mice confirmed that knockdown of GCN2 in tumor cells retards tumor growth and decreases tumor blood vessel density. Our results reveal that the GCN2/ATF4 pathway promotes tumor growth and angiogenesis through AAD-mediated VEGF expression and, thus, is a potential target in cancer therapy.
authors.affiliation: Department of Biologic and Materials Sciences, University of Michigan School of Dentistry, Ann Arbor, MI, USA.
authors.forename: Yugang
authors.initials: Y
authors.lastname: Wang
authors.forename: Yu
authors.initials: Y
authors.lastname: Ning
authors.forename: Goleeta N
authors.initials: GN
authors.lastname: Alam
authors.forename: Brandon M
authors.initials: BM
authors.lastname: Jankowski
authors.forename: Zhihong
authors.initials: Z
authors.lastname: Dong
authors.forename: Jacques E
authors.initials: JE
authors.lastname: Nör
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Polverini
mesh_terms: D051701:Activating Transcription Factor 4 / Q000235:genetics* / Q000378:metabolism; D000596:Amino Acids / Q000172:deficiency* / Q000494:pharmacology; D000818:Animals; D002460:Cell Line; D045744:Cell Line, Tumor; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D015151:Immunoblotting; D061986:MCF-7 Cells; D016688:Mice, Inbred NOD; D016513:Mice, SCID; D009369:Neoplasms / Q000235:genetics / Q000473:pathology / Q000628:therapy; D009389:Neovascularization, Pathologic / Q000235:genetics* / Q000517:prevention & control; D017346:Protein Serine-Threonine Kinases / Q000235:genetics* / Q000378:metabolism; D034622:RNA Interference; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000187:drug effects / Q000235:genetics; D047368:Tumor Burden / Q000235:genetics; D014407:Tumor Cells, Cultured; D042461:Vascular Endothelial Growth Factor A / Q000235:genetics / Q000378:metabolism; D023041:Xenograft Model Antitumor Assays
chemical_list: C497109:ATF4 protein, human; D000596:Amino Acids; D042461:Vascular Endothelial Growth Factor A; D051701:Activating Transcription Factor 4; C529271:EIF2AK4 protein, human; D017346:Protein Serine-Threonine Kinases
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