Repression of rRNA gene transcription by endothelial SPEN deficiency normalizes tumor vasculature via nucleolar stress
Zi-Yan Yang, … , Tian Xiao, Hua Han
Zi-Yan Yang, … , Tian Xiao, Hua Han
Published August 22, 2023
Citation Information: J Clin Invest. 2023;133(20):e159860. https://doi.org/10.1172/JCI159860.
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Research Article Vascular biology

Repression of rRNA gene transcription by endothelial SPEN deficiency normalizes tumor vasculature via nucleolar stress

Abstract

Human cancers induce a chaotic, dysfunctional vasculature that promotes tumor growth and blunts most current therapies; however, the mechanisms underlying the induction of a dysfunctional vasculature have been unclear. Here, we show that split end (SPEN), a transcription repressor, coordinates rRNA synthesis in endothelial cells (ECs) and is required for physiological and tumor angiogenesis. SPEN deficiency attenuated EC proliferation and blunted retinal angiogenesis, which was attributed to p53 activation. Furthermore, SPEN knockdown activated p53 by upregulating noncoding promoter RNA (pRNA), which represses rRNA transcription and triggers p53-mediated nucleolar stress. In human cancer biopsies, a low endothelial SPEN level correlated with extended overall survival. In mice, endothelial SPEN deficiency compromised rRNA expression and repressed tumor growth and metastasis by normalizing tumor vessels, and this was abrogated by p53 haploinsufficiency. rRNA gene transcription is driven by RNA polymerase I (RNPI). We found that CX-5461, an RNPI inhibitor, recapitulated the effect of Spen ablation on tumor vessel normalization and combining CX-5461 with cisplatin substantially improved the efficacy of treating tumors in mice. Together, these results demonstrate that SPEN is required for angiogenesis by repressing pRNA to enable rRNA gene transcription and ribosomal biogenesis and that RNPI represents a target for tumor vessel normalization therapy of cancer.

Authors

Zi-Yan Yang, Xian-Chun Yan, Jia-Yu-Lin Zhang, Liang Liang, Chun-Chen Gao, Pei-Ran Zhang, Yuan Liu, Jia-Xing Sun, Bai Ruan, Juan-Li Duan, Ruo-Nan Wang, Xing-Xing Feng, Bo Che, Tian Xiao, Hua Han

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Figure 8

Endothelial Spen ablation normalizes functionally tumor vessels.

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Endothelial Spen ablation normalizes functionally tumor vessels. (A) LLC...
(A) LLC tumor sections from control and eSpen–/– mice were stained with CD31 and VE-cadherin or CD31 and ZO-1 immunofluorescence and quantitatively compared (n = 5). Scale bars: 100 μm. (B) Vessel perfusion and leakage in tumors were determined with FITC dextran 2 MD (n = 5 and 4 for control and eSpen–/–, respectively) or Texas Red–dextran 70 KD (n = 4 and 3 for control and eSpen–/–, respectively). Scale bars: 100 μm. (C) Control and eSpen–/– TECs were subjected to RNA-Seq. Cell cycle–associated gene sets were analyzed by GSEA (color-coded gene sets are listed in Supplemental Figure 1H). (D and E) Expression of angiogenesis-related genes in TECs was determined by (D) RT-qPCR (n = 6, except for n = 4 in Hspg2 and Ctgf) or (E) immunoblotting (n = 6 except for n = 5 for VEGFR2). β-Actin served as the loading control. Data represent mean ± SEM. Unpaired 2-tailed Student’s t test was used.