Iden, Sandra - A 3

Intrinsic and extrinsic functions of polarity proteins in melanoma formation and progression

Cell polarization is crucial for a variety of processes such as oriented cell division, adhesion or migration. How cyto-architecture is coordinated in the context of tumor formation and progression is an intriguing question in cancer cell biology. This project aims to investigate how conserved polarity regulators control melanoma skin cancer by extrinsic and intrinsic mechanisms. An ultimate goal is to elucidate clinical strategies targeting the polarity machinery for prevention and treatment of skin malignancies.


Our research aims to understand how molecular control of cell and tissue architecture contributes to cancer. Conserved polarity proteins couple cell shape to control of growth, migration and differentiation. The Par3-atypical PKC-Par6 polarity complex is a key regulatory module of cellular asymmetry and crucial for embryonic development. We previously uncovered Par3 as a crucial rheostat of stem cell maintenance and tumorigenesis. Par3 integrates oncogenic Ras- and aPKC-mediated signalling and serves tumor-type dependent pro-oncogenic and tumor-suppressive roles in formation and invasion of different epidermal cancers (Iden et al., 2012), in line with frequent dysregulation in human cancers (Mescher & Iden, 2015). 

Malignant melanoma is an aggressive skin cancer known for its early metastatic spread associated with poor clinical outcome. With steadily increasing incidence melanoma reflects the most common cancer in young adults. UV-induced damage and genetic predisposition are major risk factors. In this project we ask how polarity protein signalling affects the formation and progression of metastatic melanoma. We combine mouse disease models with cell-based assays and analyses of human cancers to elucidate whether and how targeting the polarity machinery may be used to develop strategies for disease prevention and therapy.

Extrinsic tumor suppression by polarity regulators

Melanoma originates from melanocytes that are in close contact with surrounding epidermal keratinocytes. Though keratinocyte-melanocyte cross-talk is essential for skin photoprotection it is unknown whether the epidermal microenvironment directly controls melanomagenesis. In this project we identified an unexpected non-cell autonomous role of epidermal polarity proteins in malignant melanoma. In an autochthonous mouse melanoma model epidermal Par3 inactivation resulted in increased tumor formation and lung metastasis. Keratinocyte-specific Par3 loss disturbs melanocyte-keratinocyte interactions resulting in melanocyte proliferation and phenotypic switch. In agreement, low epidermal PAR3 levels correlate with human melanoma progression, implying that PAR3 dysfunction also drives human disease. Collectively, reduced Par3 function fosters a permissive niche for melanocyte transformation, invasion and metastasis. This reveals a previously unrecognized extrinsic tumor-suppressive mechanism, whereby epithelial polarity proteins dictate the cyto-architecture and fate of other tissue-resident cells to suppress their malignant outgrowth.

A novel syngeneic model of metastatic melanoma

Next to extrinsic mechanisms underlying melanoma we also aim to understand how polarity regulators control the intrinsic shape and function of melanocytes and melanoma cells. To investigate in vivo processes that direct melanoma invasion and metastasis, in collaboration with the Department of Ophthalmology we developed a novel syngeneic model for metastatic conjunctival melanoma. Immune-competent C57BL/6 mice show tumor-associated lymphangiogenesis with development of metastatic tumors (Schlereth et al., 2015). This model now offers new possibilities to study the pathobiology of tumor growth, invasion, and mechanisms of metastatic tumor spread, and provides a robust system to explore new immune-based and antilymphangiogenic treatment modalities of this malignancy. Ongoing studies address the role of polarity networks therein.

Par3 controls skin barrier and stem cell maintenance

Next to important roles in tumorigenesis we found that Par3 controls the formation of the inside-out skin permeability barrier, epidermal differentiation, mitotic spindle orientation, and hair follicle stem cell maintenance (Ali et al., 2016), thereby preventing premature skin aging. Interestingly, mice with impaired mTORC2 function exhibit skin barrier defects, with Par3 failing to polarize during early stages of barrier formation (Ding et al., 2016). These findings suggest that mTOR signalling acts upstream of polarity protein-mediated skin barrier formation.


Our work has provided new mechanistic insight into cellular cross-talk in the context of formation and progression of melanoma, an aggressive skin malignancy with increasing lifetime risk. Despite recent progress in immune and targeted therapies, diverse resistance mechanisms pose an unresolved major problem preventing long-term treatment success. Melanoma cells display tremendous plasticity to reversibly switch on developmental and differentiation programs, fuelling disease progression. Therefore, future efforts will focus on understanding key principles underlying melanoma plasticity, which will be fundamental to develop effective clinical strategies.

Selected publications

Ding, X., Bloch, W., Iden, S., Rüegg, M.A., Hall, M.N., Leptin, M., Partridge, L., Eming, S.A. (2016).
mTORC1 and mTORC2 regulate skin morphogenesis and epidermal barrier formation. Nat Commun. In press                        

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, pii: S0022-202X(16)32119-4.  

Schlereth, S., Iden, S., Mescher, M., Ksander, B., Bosch, J., Cursiefen, C., and Heindl, L.M. (2015).
A novel model of metastatic conjunctival melanoma in immune competent mice. Invest Ophthalmol Vis Sci. 56(10), 5965-73.

Refaian, N., Schlereth, S., Koch, K., Notara, M., Hos, D., Mescher, M., Iden, S., Bosch, J., Jager, M., Cursiefen, C., and Heindl, L. (2015).
Comparing the Hem- and Lymphangiogenic Profile of Conjunctival and Uveal Melanoma Cell Lines. Invest Ophthalmol Vis Sci. 56(9), 5691-7.

Mescher, M. and Iden, S. (2015).
Par Proteins in Tumor Formation and Progression. Cell Polarity 2. Role in Development and Disease. Springer, VIII. ISBN 978-3-319-144466-5. Book Chapter

Tuncay, H., Brinkmann, B., Steinbacher, T., Schürmann, A., Gerke, V., Iden, S., and Ebnet, K. (2015).
JAM-A regulates cortical dynein localization through Cdc42 to control planar spindle orientation during mitosis. Nat Commun. 6, 8128.

Schlereth, S., Refaian, N., Iden, S., Cursiefen, C., and Heindl, L.M. (2014).
Impact of the Prolymphangiogenic Crosstalk in the Tumor Microenvironment on Lymphatic Cancer Metastasis. BioMed Research International. 2014:639058

Iden, S.*, van Riel, W.E., Schäfer, R., Song, J.-Y., Hirose, T., Ohno, S., and Collard, J.G. (2012).
Tumor Type-Dependent Function of the Par3 Polarity Protein in Skin Tumorigenesis. Cancer Cell 22(3), 389-403
*: corresponding author

Former Funding Period 01/2014 - 12/2016

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

Dr. rer. nat. Sandra Iden

CECAD Cologne

Dr. rer. nat. Sandra Iden

Principal Investigator A 6

Work +49 221 478 89587

CECAD Research Center
Joseph-Stelzmann-Str. 26
50931 Cologne


Link to PubMed

Group Members

Melina Mescher (PhD student)
Sina Knapp (PhD student)
Dominik Kleefisch (PhD student)
Noelle Ali (PhD student)
Soriba Letzian (PhD student)
Martim Dias Gomes (PhD student)
Michael Saynisch (technician)
Alexandra Schwickert (technician)
Peter Jeong (MD student)
Ronja Bauer (MD student)

Figure 1

Figure 1: Epidermal Par3 inactivation (Par3eKO) results in increased melanoma formation and progression in vivo.

Figure 2

Figure 2: Immune-competent syngeneic conjunctival mel-anoma model to study melanoma formation, growth, invasion and metastasis in vivo.

Figure 3

Figure 3: Par3 maintains hair follicle bulge stem cells. Immunostaining for CD34 and Keratin15 (K15) stem cell markers in adult tail epidermis (wholemount).