Niemann, Catherin - A 5 / CAP 4

Molecular function of Lef1 mutations (E45K/S61P and DNLef1) in epithelial tissues and cancer

Wnt/β-catenin/Lef1 signalling plays a fundamental role in tissue homeostasis and defects in this crucial signalling cascade often result in tumour formation. We have shown that tissue stem cells displaying abnormal Lef1 activity develop tumours caused by interfering with stem cell-specific gatekeeper functions. This project aims to decipher the molecular mechanism of defective Lef1 signalling activity underlying both, the process of tumour initiation and malignant progression of tumours.

Introduction

Development of epithelial cancer is not sufficiently understood to successfully treat this heterogeneous disease. It is widely accepted that genetic lesions play a major role in determining the tumour phenotype. In addition, there is mounting evidence demonstrating that cancers of distinct subtypes within an organ derive from different “cells of origin”. These particular cells acquire the first genetic hits that eventually result in cancer growth. Identification of both, the primary genetic hits and the target cell population would be of great benefit for earlier detection of malignancies and a better prediction of cancer growth and progression. Thus, the important finding, that either stem or progenitor cells can act as targets for tumour initiation in a range of solid tumours, is highly relevant for improving concepts for disease targeting and for designing preventive therapies.

The transcription factor Lef1, an important downstream mediator of canonical Wnt signalling, is crucial for development, differentiation and maintenance of many epithelial tissues. We have shown previously that expression of mutant Lef1 in mouse epidermis, thereby mimicking Lef1 mutations found in human skin cancer patients, leads to impaired hair follicle differentiation and spontaneous skin tumours. It will be important to decipher the molecular and cellular mechanism of mutant Lef1 activity to understand its role in the process of cancer initiation and tumour behaviour.

Tissue stem cells and tumour initiation

Our work uncovered an important role of hair follicle stem cells in mutant Lef1-driven epidermal tumours. Extensive lineage-tracing studies in tumour whole mounts identified hair follicle bulge stem cells as ‘cells-of-origin’ for mutant Lef1-induced tumours. As a ‘proof of concept’ experiment and to further investigate the specific role of epidermal stem cells for tumour initiation, a transgenic mouse line, expressing mutant Lef1 in hair follicle bulge stem cells was generated. Remarkable, stem cell-driven mutant Lef1 mice developed spontaneous tumours supporting our initial finding that bulge stem cells give rise to epidermal tumours.

Stem cell specific mechanisms driving tumourigenesis

To address the question why particular hair follicle bulge stem cells give rise to tumours, molecular and genetic alterations within the stem cell compartment preceding tumour development were investigated in mutant Lef1 mice. Under normal conditions, bulge stem cells are characterised by accelerated DNA repair activity and concomitant attenuation of p53 activation. Intriguingly, mutant Lef1 induced DNA damage (Figure 1) and interfered with these stem cell-specific gatekeeper functions normally protecting against accumulations of DNA lesions and cell loss. Importantly, our work demonstrated that mutant Lef1 abolished p53 activity in stem cells. As a consequence, normal control of stem cell proliferation was disrupted, thereby allowing uncontrolled propagation of tumour-initiating stem cells (Figure 2). Thus, our novel findings point to a crucial function of tissue stem cells for tumour initiation but importantly, our mechanistic results highlights the important role of stem cell-specific surveillance mechanisms for preventing tumour formation.

Perspectives

Our recent data disclose a Lef1-dependent protective mechanism that is specific to (epidermal) stem cells. We will continue investigating how Lef1 regulates DNA damage response and controls p53 activity to better understand how oncogenic pathways affect stem cell-specific surveillance mechanisms. Future research following up on the important finding that cross-regulation between these signalling network is intimately linked to primary events of tumour initiation, could lead to novel therapeutic strategies to successfully interfere with tumour-initiating signals. Given the essential role of Wnt/β-catenin/Lef1 signalling for stem cells of a variety of tissues, the discovery of a mechanistic link between the pathways could be beneficial for malignancies of other organs.

Selected publications

Ali, N.J.A., Dias Gomes, M., Bauer, R., Brodesser, S., Niemann, C., and Iden, S. (2016). Essential role of polarity protein Par3 for epidermal homeostasis through regulation of barrier function, keratinocyte differentiation and stem cell maintenance. J Invest Dermatol. DOI 10.1016/j.jid.2016.07.011

Petersson, M.*, Reuter, K.*, Brylka, H., Schettina, P., Kraus, A., and Niemann, C. (2015). Interfering with stem cell-specific gatekeeper functions controls tumor initiation and malignant progression of skin tumors. Nature Communications 6, 5874. * shared first author.

Frances, D., Sharma, N., Pofahl, R., Maneck, M., Behrendt, K., Reuter, K., Krieg, T., Klein, C.A., Haase, I., and Niemann, C. (2015). A role for Rac1 activity in malignant progression of sebaceous skin tumours. Oncogene 34, 5505-12.

Kloepper, J.E.*, Baris, O.R.*, Reuter, K.*, Kobayashi, K., Weiland, D., Vidali, S., Tobin, D.J., Niemann, C., Wiesner, R.J., and Paus, R. (2015). Mitochondrial function is crucial for hair follicle morphogenesis and epithelial-mesenchymal interactions. J Invest Dermatol. 135, 679-89. * shared first author

Dahlhoff, M., Frances, D., Kloepper, J.E., Paus, R., Schäfer, M., Niemann. C., and Schneider, M.R. (2014). Overexpression of Epigen during embryonic development induces reversible, Epidermal Growth Factor Receptor-dependent sebaceous gland hyperplasia. Mol Cell Biol. 34, 3086-95.

Niemann, C., and Schneider, M.R. (2014). Hair type specific function of canonical wnt activity in adult mouse skin. Exp Dermatol. 23, 881-3.

Former Funding Period 01/2014 - 12/2016

Information from this funding period will not be updated anymore. New research related information is available here.


PD Dr. rer. nat. Catherin Niemann

Institute for Biochemistry and CMMC

PD Dr. rer. nat. Catherin Niemann

Principal Investigator A 7
Co-Coordinator - IPMM Program
Head - Tissue Embedding and Histology Facility

cnieman1@uni-koeln.de

Work +49 221 478 89511

Fax (Work) +49 221 478 86737

CMMC Research Building
Robert-Koch-Str. 21
50931 Cologne

Publications

Link to PubMed

Group Members

Karen Reuter (PostDoc)
Anna Geueke (doctoral student)
Marcel Drews (doctoral student)
Jan-Marc Leonhard (technician)
Peter Schettina (technician)

Figure 1

Figure 1: Mutant Lef1 induces DNA damage in hair follicle bulge stem cells.
Detection of DNA damage (γH2AX, green) and nuclei (PI, red) in epidermal whole mounts of mouse skin from wild-type (control) and mutant Lef1 mice. B: bulge stem cell compartment of hair follicles.

Figure 2

Figure 2: Mutant Lef1 interferes with epidermal stem cell-specific surveillance mechanisms, including fast DNA damage repair, transient p53 activation, protection from apoptosis and strict control of stem cell renewal.