Abstract
Hypoxia-induced angiogenesis maintains tissue oxygen supply and protects against ischemia but also enhances tumor progression and malignancy. This is mediated through activation of transcription factors like hypoxia-inducible factor 1 (HIF-1) and c-Myc, yet the impact of hypoxia on negative regulators of angiogenesis is unknown. During vascular development, seryl-tRNA synthetase (SerRS) regulates angiogenesis through a novel mechanism by counteracting c-Myc and transcriptionally repressing vascular endothelial growth factor A (VEGFA) expression. Here, we reveal that the transcriptional repressor role of SerRS is inactivated under hypoxia through phosphorylation by ataxia telangiectasia mutated (ATM) and ataxia telangiectasia mutated and RAD3-related (ATR) at Ser101 and Ser241 to attenuate its DNA binding capacity. In zebrafish, SerRSS101D/S241D, a phosphorylation-mimicry mutant, cannot suppress VEGFA expression to support normal vascular development. Moreover, expression of SerRSS101A/S241A, a phosphorylation-deficient and constitutively active mutant, prevents hypoxia-induced binding of c-Myc and HIF-1 to the VEGFA promoter, and activation of VEGFA expression. Consistently, SerRSS101A/S241A strongly inhibits normal and tumor-derived angiogenesis in mice. Therefore, we reveal a key step regulating hypoxic angiogenesis and highlight the importance of nuclear SerRS in post-developmental angiogenesis regulation in addition to vascular development. The role of nuclear SerRS in inhibiting both c-Myc and HIF-1 may provide therapeutic opportunities to correct dysregulation of angiogenesis in pathological settings.
Highlights
Oxygen is critical for the development and growth of most multicellular organisms
To investigate whether seryl-tRNA synthetase (SerRS) is involved in the hypoxia response to regulate vascular endothelial growth factor A (VEGFA) expression, we knocked down SerRS in HEK293 cells with a short hairpin RNA targeting the 30 untranslated region (30UTR) of the SerRS gene
Under normal levels of oxygen, as we observed previously [19], VEGFA expression is up-regulated upon knocking down SerRS, compared with control cells transfected with a nonspecific control short hairpin RNA (shRNA) or an shRNA targeting a different aminoacyl-tRNA synthetases (i.e., glycyl-tRNA synthetase (GlyRS); sh-glycyltRNA synthetase (GlyRS)) (Fig 1A and 1B, S1A Fig)
Summary
Oxygen is critical for the development and growth of most multicellular organisms. Sophisticated molecular mechanisms have been evolved to sense and respond to changes in oxygen levels in order to maintain cell and tissue homeostasis. Nuclear SerRS regulates the vasculature by transcriptionally repressing VEGFA expression and does so through binding to a 27-bp DNA on the VEGFA promoter and recruiting histone deacetylase SIRT2 for epigenetic gene silencing [19] This role of SerRS directly counteracts that of c-Myc, the major transcriptional factor regulating VEGFA during development [19,24,25]. The transcriptional repressor role of SerRS is inactivated during hypoxia through phosphorylation of SerRS by ataxia telangiectasia mutated (ATM) and the related kinase ATR to attenuate its DNA-binding capacity Both c-Myc and HIF-1 cannot bind to the VEGFA promoter without SerRS being phosphorylated and removed from the DNA. Such understanding may provide new opportunities in treating ischemic cardiovascular diseases and cancer
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