ATG7 Knockout Cell Line (HEK293)

Ischemia-induced angiogenesis is critical for blood flow restoration and tissue regeneration, but the underlying molecular mechanism is not fully understood. ATG7 (autophagy related 7) is essential for classical degradative macroautophagy/autophagy and cell cycle regulation. However, whether and how ATG7 influences endothelial cell (EC) function and regulates post-ischemic angiogenesis remain unknown. Here, we showed that in mice subjected to femoral artery ligation, EC-specific deletion of significantly impaired angiogenesis, delayed the recovery of blood flow reperfusion, and displayed reduction in HIF1A (hypoxia inducible factor 1 subunit alpha) expression. In addition, in cultured human umbilical vein endothelial cells (HUVECs), overexpression of prevented deficiency-reduced tube formation. Mechanistically, we identified STAT1 (signal transducer and activator of transcription 1) as a transcription suppressor of and demonstrated that ablation of upregulated STAT1 in an autophagy independent pathway, increased STAT1 binding to promoter, and suppressed expression. Moreover, lack of ATG7 in the cytoplasm disrupted the association between ATG7 and the transcription factor ZNF148/ZFP148/ZBP-89 (zinc finger protein 148) that is required for STAT1 constitutive expression, increased the binding between ZNF148/ZFP148/ZBP-89 and KPNB1 (karyopherin subunit beta 1), which promoted ZNF148/ZFP148/ZBP-89 nuclear translocation, and increased STAT1 expression. Finally, inhibition of STAT1 by fludarabine prevented the inhibition of HIF1A expression, angiogenesis, and blood flow recovery in KO mice. Our work reveals that lack of ATG7 inhibits angiogenesis by suppression of HIF1A expression through upregulation of STAT1 independently of autophagy under ischemic conditions, and suggest new therapeutic strategies for cancer and cardiovascular diseases.: ATG5: autophagy related 5; ATG7: autophagy related 7; KO: endothelial cell-specific knockout; BECN1: beclin 1; ChIP: chromatin immunoprecipitation; CQ: chloroquine; ECs: endothelial cells; EP300: E1A binding protein p300; HEK293: human embryonic kidney 293 cells; HIF1A: hypoxia inducible factor 1 subunit alpha; HUVECs: human umbilical vein endothelial cells; IFNG/IFN-γ: Interferon gamma; IRF9: interferon regulatory factor 9; KPNB1: karyopherin subunit beta 1; MAP1LC3A: microtubule associated protein 1 light chain 3 alpha; MEFs: mouse embryonic fibroblasts; MLECs: mouse lung endothelial cells; NAC: N-acetyl-l-cysteine; NFKB1/NFκB: nuclear factor kappa B subunit 1; PECAM1/CD31: platelet and endothelial cell adhesion molecule 1; RELA/p65: RELA proto-oncogene, NF-kB subunit; ROS: reactive oxygen species; SP1: Sp1 transcription factor; SQSTM1/p62: sequestosome 1; STAT1: signal transducer and activator of transcription 1; ULK1: unc-51 like autophagy activating kinase 1; KO: endothelial cell-specific knockout; VSMCs: mouse aortic smooth muscle cells; WT: wild type; ZNF148/ZFP148/ZBP-89: zinc finger protein 148.

In the setting of virus infection, autophagy regulates the synthesis of type I interferon (IFN) via multiple mechanisms to prevent adverse overreaction. Interferon regulatory factor (IRF) 3, the dominant transcriptional factor of type I IFN, can be degraded via autophagy-lysosomal pathway. However, the exact regulatory mechanism is not yet well elucidated. IRF3 was targeted into autophagosome by interacting with cargo receptors including p62, NDP52 and NBR1. The recent studies have reported the mechanism of p62 and NDP52 sequestrating IRF3. This work aims to investigate the role of NBR1 in the process of IRF3 degradation. We found that blocking autophagy via ATG3/ATG7 knockout and chemical inhibitors both resulted in the accumulation of IRF3 protein and increased synthesis of type I IFN, while enhancing autophagy activity led to more obvious clearance of IRF3 in HEK293T cells infected with Sendai virus (SeV). Our data suggested that NBR1 bound both unphosphorylated and phosphorylated IRF3 through its ubiquitin-associated domain. Meanwhile, viral infection elevated the expression of NBR1, which sequentially formed a negative feedback loop to promote IRF3 degradation and hence optimized the type I IFN signaling. This study expands the knowledge of molecular mechanisms regulating the IRF3 stability and function during viral infection.