Sidharth Belaguli

Background: Induction of angiogenesis is a hallmark of cancer that begins early in tumor development and correlates strongly with malignant progression.¹ The major pathway by which tumors induce angiogenesis is via hypoxia-induced secretion of vascular endothelial growth factor A (VEGFA), which binds VEGFR2 receptors on endothelial cells in order to promote endothelial proliferation and invasion via PI3K/Akt/mTOR signaling.² Current anti-angiogenic therapies mainly target either secreted VEGFA or receptor tyrosine kinases, but they are approved for a limited number of tumor types, produce resistant tumor cell populations during treatment, and often have systemic adverse effects such as increased bleeding risk and impaired wound healing.³ RNA methylation is a little-explored epigenetic mechanism of angiogenic regulation that holds promise for the development of targeted anti-angiogenic therapies with lower resistance risks. N6-methyladenosine (m6A) is the most abundant eukaryotic RNA modification, and it regulates gene expression on multiple levels via m6A writers (methyltransferases; METTL3-METTL14), readers (m6A-RNA-binding proteins), and erasers (RNA demethylases).⁴

Objective: Here, mechanisms by which m6A modification affects VEGFA-mediated angiogenesis in multiple tumor types are reviewed.

Search methods: The works reviewed here were obtained via PubMed search over the timeframe 2018-2023 with keywords “m6A”, “tumor angiogenesis”, and “VEGFA”.

Results: Bladder tumors harvested from mice with a urothelium-specific knockout of m6A writer METTL3 displayed markedly lower mRNA and protein expression of VEGFA and TEK, which corresponded to lower tumor vascularity and size.⁵ METTL3-mediated m6A methylation of miR-143-3p precursor increased its processing to mature form, indirectly increasing VEGFA protein stability via inhibition of VASH1 in human lung adenocarcinoma cell lines in vitro and in xenografts.⁶ Furthermore, m6A readers mediate many effects of m6A on target mRNAs. For instance, IGF2BP3 was found to increase VEGFA expression by binding m6A-HIF1α mRNA and directly binding and stabilizing m6A-VEGFA mRNA in human gastric carcinoma and colorectal carcinoma cell lines, respectively.^{7, 8} IGF2BP2 was observed to stabilize TRAF1 mRNA in a METTL14-dependent manner, leading to upregulation of HIF1α, VEGFA, and Akt and increased induction of endothelial tube formation in sunitinib-resistant human renal cell carcinoma cell lines.⁹ Moreover, m6A reader YTHDF3 promotes angiogenesis induced by brain-metastatic breast cancer cell lines by binding m6A-modified VEGFA and EGFR mRNA and increasing their translation.¹⁰ Lastly, the m6A methylome and expression of m6A writers and readers is altered in tumors relative to the surrounding tissue, and several of the above studies have observed an association between overexpression of m6A regulators and poorer overall survival in human patients.^{7, 8, 9, 10}

Conclusion: m6A RNA methylation is a potential basis for novel, targeted anti-angiogenic cancer therapies. First, the studies discussed here demonstrate that m6A modification regulates VEGFA expression by cancer cells directly at the post-transcriptional and translational levels and indirectly at the transcriptional and post-translational levels. Therefore, therapies targeting m6A regulators may circumvent resistance by targeting multiple signaling pathways at multiple levels of expression. Secondly, such therapies may be more specific to cancer tissue and thus produce fewer adverse effects, since the m6A RNA methylome and expression of m6A regulators is markedly altered in tumors relative to surrounding tissues.

Works cited:

1. Hanahan D. Hallmarks of Cancer: New Dimensions. Cancer Discov. 2022;12(1):31-46. doi:10.1158/2159-8290.CD-21-1059
2. Jiang X, Wang J, Deng X, et al. The role of microenvironment in tumor angiogenesis. J Exp Clin Cancer Res. 2020;39(1):204. Published 2020 Sep 30. doi:10.1186/s13046-020-01709-5
3. Lugano R, Ramachandran M, Dimberg A. Tumor angiogenesis: causes, consequences, challenges and opportunities. Cell Mol Life Sci. 2020 May;77(9):1745-1770. doi: 10.1007/s00018-019-03351-7. Epub 2019 Nov 6. PMID: 31690961; PMCID: PMC7190605.
4. Zaccara S, Ries RJ, Jaffrey SR. Reading, writing and erasing mRNA methylation. Nat Rev Mol Cell Biol. 2019;20(10):608-624. doi:10.1038/s41580-019-0168-5
5. Wang G, Dai Y, Li K, et al. Deficiency of Mettl3 in Bladder Cancer Stem Cells Inhibits Bladder Cancer Progression and Angiogenesis [published correction appears in Front Cell Dev Biol. 2021 Mar 24;9:675417]. Front Cell Dev Biol. 2021;9:627706. Published 2021 Feb 18. doi:10.3389/fcell.2021.627706
6. Wang H, Deng Q, Lv Z, et al. N6-methyladenosine induced miR-143-3p promotes the brain metastasis of lung cancer via regulation of VASH1. Mol Cancer. 2019;18(1):181. Published 2019 Dec 10. doi:10.1186/s12943-019-1108-x
7. Jiang L, Li Y, He Y, Wei D, Yan L, Wen H. Knockdown of m6A Reader IGF2BP3 Inhibited Hypoxia-Induced Cell Migration and Angiogenesis by Regulating Hypoxia Inducible Factor-1α in Stomach Cancer. Front Oncol. 2021 Sep 21;11:711207. doi: 10.3389/fonc.2021.711207. PMID: 34621671; PMCID: PMC8490730.
8. Yang Z, Wang T, Wu D, Min Z, Tan J, Yu B. RNA N6-methyladenosine reader IGF2BP3 regulates cell cycle and angiogenesis in colon cancer. J Exp Clin Cancer Res. 2020;39(1):203. Published 2020 Sep 29. doi:10.1186/s13046-020-01714-8
9. Chen Y, Lu Z, Qi C, et al. N6-methyladenosine-modified TRAF1 promotes sunitinib resistance by regulating apoptosis and angiogenesis in a METTL14-dependent manner in renal cell carcinoma. Mol Cancer. 2022;21(1):111. Published 2022 May 10. doi:10.1186/s12943-022-01549-1
10. Chang G, Shi L, Ye Y, et al. YTHDF3 Induces the Translation of m6A-Enriched Gene Transcripts to Promote Breast Cancer Brain Metastasis. Cancer Cell. 2020;38(6):857-871.e7. doi:10.1016/j.ccell.2020.10.004