While in the majority of mammalian systems, Notch activation is generally thought to promote proliferation and inhibit differentiation, in specific cell types such as keratinocytes, increased Notch signaling results in growth arrest probably through initiation of terminal differentiation program. In addition, Notch1 deficient keratinocytes are sensitive to chemical carcinogenesis, establishing Notch as a tumor growth inhibitor in the epidermis. We have recently identified a novel signaling pathway in keratinocytes involving inhibition of the Notch1 gene downstream of p53, which plays a key role in squamous cell carcinoma (SCC) development. Exploring the downstream effects of activated Notch receptor in the epidermis, we found that the small GTPase RhoE is a new transcriptional target of Notch1, which is essential for the differentiation switch in keratinocytes. RhoE deficiency in vitro and in vivo renders keratinocytes resistant to Notch1-mediated induction of differentiation thereby favoring uncontrolled growth and proliferation. Furthermore, we have strong evidence that RhoE binds to activated Notch1 and mediates the recruitment of the Notch1-transcriptional complex to the promoters of its target genes. Our working hypothesis is that RhoE is a key regulator of Notch1-mediated commitment to differentiation and suppression of carcinogenesis/tumorigenesis in the epidermis. We will explore the molecular mechanism underlying this novel layer of Notch1 regulation by RhoE in keratinocytes in vitro and in vivo. We will dissect in details the functional Notch1-RhoE interaction and will elucidate its functional consequences for non-melanoma tumor development in the skin in vitro, as well as in vivo, in a RhoE knockout mouse model. Further mechanistic understanding of the pathway(s) controlling the Notch-RhoE signaling cascade in the epidermis is expected to eventually translate into the development of therapeutics for the treatment of skin SCCs and other epithelial malignancies with down-modulated Notch signaling.

Public Health Relevance

An aberrant signaling through the Notch1 receptor pathway is closely associated with various steps of carcinogenesis in the skin. Further understanding of the downstream molecular pathways and the target molecules, such as RhoE, responsible for the tumor suppression function of Notch1 in the epidermis is expected to eventually translate into therapeutic benefit in the treatment of non-melanoma skin cancer.

National Institute of Health (NIH)
National Cancer Institute (NCI)
Research Project (R01)
Project #
Application #
Study Section
Cancer Etiology Study Section (CE)
Program Officer
Johnson, Ronald L
Project Start
Project End
Budget Start
Budget End
Support Year
Fiscal Year
Total Cost
Indirect Cost
Massachusetts General Hospital
United States
Zip Code
Neel, Victor A; Todorova, Kristina; Wang, Jun et al. (2016) Sustained Akt Activity Is Required to Maintain Cell Viability in Seborrheic Keratosis, a Benign Epithelial Tumor. J Invest Dermatol 136:696-705
Zhu, Zehua; Todorova, Kristina; Lee, Kevin K et al. (2014) Small GTPase RhoE/Rnd3 is a critical regulator of Notch1 signaling. Cancer Res 74:2082-93
Gurkar, Aditi U; Chu, Kiki; Raj, Lakshmi et al. (2013) Identification of ROCK1 kinase as a critical regulator of Beclin1-mediated autophagy during metabolic stress. Nat Commun 4:2189
Mandinova, Anna; Lee, Sam W (2011) The p53 pathway as a target in cancer therapeutics: obstacles and promise. Sci Transl Med 3:64rv1
Lee, Kevin K; Todorova, Kristina; Mandinova, Anna (2010) Maximizing early detection of esophageal squamous cell carcinoma via SILAC-proteomics. Cancer Biol Ther 10:811-3