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Updated: Apr 28, 2026
Techniques to Induce and Quantify Cellular Senescence
Published on: May 1, 2017
Cellular senescence checkpoint function determines differential Notch1-dependent oncogenic and tumor-suppressor
S Kagawa1, M Natsuizaka2, K A Whelan1
11] Gastroenterology Division, Department of Medicine, University of Pennsylvania, Philadelphia, PA, USA [2] Abramson Cancer Center, University of Pennsylvania, Philadelphia, PA, USA.
Abstract:
Notch activity regulates tumor biology in a context-dependent and complex manner. Notch may act as an oncogene or a tumor-suppressor gene even within the same tumor type. Recently, Notch signaling has been implicated in cellular senescence. Yet, it remains unclear as to how cellular senescence checkpoint functions may interact with Notch-mediated oncogenic and tumor-suppressor activities. Herein, we used genetically engineered human esophageal keratinocytes and esophageal squamous cell carcinoma cells to delineate the functional consequences of Notch activation and inhibition along with pharmacological intervention and RNA interference experiments. When expressed in a tetracycline-inducible manner, the ectopically expressed activated form of Notch1 (ICN1) displayed oncogene-like characteristics inducing cellular senescence corroborated by the induction of G0/G1 cell-cycle arrest, Rb dephosphorylation, flat and enlarged cell morphology and senescence-associated β-galactosidase activity. Notch-induced senescence involves canonical CSL/RBPJ-dependent transcriptional activity and the p16(INK4A)-Rb pathway. Loss of p16(INK4A) or the presence of human papilloma virus (HPV) E6/E7 oncogene products not only prevented ICN1 from inducing senescence but permitted ICN1 to facilitate anchorage-independent colony formation and xenograft tumor growth with increased cell proliferation and reduced squamous-cell differentiation. Moreover, Notch1 appears to mediate replicative senescence as well as transforming growth factor-β-induced cellular senescence in non-transformed cells and that HPV E6/E7 targets Notch1 for inactivation to prevent senescence, revealing a tumor-suppressor attribute of endogenous Notch1. In aggregate, cellular senescence checkpoint functions may influence dichotomous Notch activities in the neoplastic context.
Insights
Notch signaling can act as both an oncogene and tumor suppressor. This study reveals Notch1 induces senescence via the p16INK4A-Rb pathway, but human papillomavirus (HPV) E6/E7 can inactivate Notch1, promoting tumor growth.
Area of Science:
- Oncology
- Cell Biology
- Molecular Biology
Background:
- Notch signaling's role in tumor biology is complex and context-dependent, acting as both an oncogene and tumor suppressor.
- The interplay between Notch signaling and cellular senescence checkpoints is not well understood.
- Investigating this interaction is crucial for understanding tumor development and potential therapeutic strategies.
Purpose of the Study:
- To delineate the functional consequences of Notch activation and inhibition in esophageal cancer.
- To explore the interaction between Notch signaling and cellular senescence pathways.
- To elucidate the role of Notch1 in oncogenesis and tumor suppression within the context of senescence.
Main Methods:
- Utilized genetically engineered human esophageal keratinocytes and esophageal squamous cell carcinoma cells.
- Employed tetracycline-inducible expression of activated Notch1 (ICN1).
- Conducted pharmacological interventions and RNA interference experiments, including assessing p16INK4A and human papillomavirus (HPV) E6/E7 oncogene products.
Main Results:
- Ectopic expression of activated Notch1 (ICN1) induced cellular senescence, characterized by G0/G1 cell-cycle arrest, Rb dephosphorylation, and senescence-associated β-galactosidase activity.
- Notch-induced senescence involves CSL/RBPJ transcriptional activity and the p16INK4A-Rb pathway.
- Loss of p16INK4A or presence of HPV E6/E7 prevented Notch1-induced senescence, promoting anchorage-independent growth, xenograft tumor formation, and reduced differentiation, highlighting Notch1's tumor-suppressor role.
Conclusions:
- Cellular senescence checkpoints significantly influence the dichotomous roles of Notch signaling in cancer.
- Notch1 acts as an oncogene by inducing senescence but functions as a tumor suppressor when inactivated by viral oncogenes like HPV E6/E7.
- Understanding these context-dependent activities is key to targeting Notch signaling in esophageal cancer therapy.
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