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Published on: December 9, 2016
Atypical E2Fs inhibit tumor angiogenesis
B G M W Weijts1,2, B Westendorp1, B T Hien1
1Department of Pathobiology, Faculty of Veterinary Medicine, Utrecht University, Utrecht, The Netherlands.
Abstract:
Atypical E2F transcription factors (E2F7 and E2F8) function as key regulators of cell cycle progression and their inactivation leads to spontaneous cancer formation in mice. However, the mechanism of the tumor suppressor functions of E2F7/8 remain obscure. In this study we discovered that atypical E2Fs control tumor angiogenesis, one of the hallmarks of cancer. We genetically inactivated atypical E2Fs in epithelial and mesenchymal neoplasm and analyzed blood vessel formation in three different animal models of cancer. Tumor formation was either induced by application of 7,12-Dimethylbenz(a)anthracene/12-O-Tetradecanoylphorbol-13-acetate or by Myc/Ras overexpression. To our surprise, atypical E2Fs suppressed tumor angiogenesis in all three cancer models, which is in a sharp contrast to previous findings showing that atypical E2Fs promote angiogenesis during fetal development in mice and zebrafish. Real-time imaging in zebrafish displayed that fluorescent-labeled blood vessels showed enhanced intratumoral branching in xenografted E2f7/8-deficient neoplasms compared with E2f7/8-proficient neoplasms. DLL4 expression, a key negative inhibitor of vascular branching, was decreased in E2f7/8-deficient neoplastic cells, indicating that E2F7/8 might inhibit intratumoral vessel branching via induction of DLL4.
Insights
Atypical E2F transcription factors (E2F7 and E2F8) suppress tumor angiogenesis, a key cancer hallmark. This contrasts with their role in fetal development, revealing a novel tumor suppressor mechanism involving DLL4 regulation.
Area of Science:
- Oncology
- Molecular Biology
- Developmental Biology
Background:
- Atypical E2F transcription factors (E2F7 and E2F8) are crucial for cell cycle regulation.
- Inactivation of E2F7/8 leads to spontaneous cancer in mice, but their tumor suppressor mechanisms are unclear.
Purpose of the Study:
- To investigate the role of atypical E2Fs in tumor angiogenesis.
- To elucidate the mechanism by which E2F7/8 function as tumor suppressors.
Main Methods:
- Genetic inactivation of E2F7/8 in epithelial and mesenchymal neoplasms.
- Analysis of blood vessel formation in three distinct cancer models (chemical induction and oncogene overexpression).
- Real-time imaging of blood vessel development in zebrafish xenografts.
Main Results:
- Atypical E2Fs suppressed tumor angiogenesis across all three cancer models.
- E2F7/8 deficiency led to enhanced intratumoral blood vessel branching in zebrafish xenografts.
- DLL4 expression, a negative regulator of vascular branching, was decreased in E2F7/8-deficient tumors.
Conclusions:
- Atypical E2Fs (E2F7/8) act as suppressors of tumor angiogenesis, a novel function distinct from their role in fetal development.
- E2F7/8 may inhibit intratumoral vessel branching through the induction of DLL4.
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