G. Paolo Dotto (PI) – Laboratory of skin cancer prevention – PhD projects 3 – 4

The three main skin cancers, basal cell carcinoma (BCC), squamous cell carcinoma (SCC), and melanoma have a major impact on human health, with keratinocyte-derived cancers (BCC and SCC) constituting by far the most common type of cancer, and melanoma being among the most aggressive. Overall, the laboratory focuses on biological determinants of pre-malignant to malignant tumor conversion and on field cancerization, a process of major clinical significance that consists of multifocal and recurrent tumors that are associated with widespread changes of surrounding normal tissues.

Field Cancerization : bad seed / bad soil hypothesis. Environmental insults, like UV irradiation or smoke, can target both epithelial and stromal compartments of organs such as skin, head/neck, lung, bladder or breast, with ensuing genetic and/or epigenetic changes. Establishment and spreading of “cancer fields” is the likely result of an interplay between epithelial and stromal alterations, with the latter playing an equally important and possibly primary role. The situation leading to multifocal and recurrent neoplastic lesions may be analogous to that of a bad plant difficult to eradicate.  This may be due to roots deeply embedded in the terrain or the spreading of bad multiple seeds, growing in the presence of a permissive or favorable soil. An alternative possibility with important conceptual implications is that the main problem is the soil itself. A bad soil could corrupt properties of otherwise perfectly good plants or seeds. According to this view, unless the soil is corrected, various forms of prevention and intervention would be of little or no use. 

The incidence of all three skin cancer types  is significantly higher in males than females, and there is a complex interplay between ER and AR signaling in regulating cancer-initiating cells, tumor microenvironments and systemic determinants (immune system and metabolism). Of note, melanoma incidence is increased during pregnancy. We will test the hypothesis that down-modulation of AR signaling in the stromal compartment of the skin, more specifically in dermal fibroblasts, as it occurs as a consequence of aging and/or chronic UV exposure, leads to cancer-associated fibroblast activation and promotes SCC and melanoma development.

Project 3 – Interplay between androgen receptor (AR) signaling, cancer associated fibroblast activation and skin cancer development

Hypothesis: Loss of AR signaling promotes cancer associated fibroblast activation (CAF) activation and skin cancer development.

Background and Significance: As we have recently reviewed , incidence of many cancers in organs with non-reproductive functions is significantly higher in male than female populations, with a complex interplay between estrogens and AR signaling in control of cancer initiating cells, tumor microenvironment and systemic determinants (immune system and metabolism). Levels of estrogens and androgens vary substantially in individuals of the two sexes with age, and may contribute to the aging-associated exponential increase of many cancer types. Conversion of stromal fibroblasts into CAFs plays a key role in skin cancer initiation and progression . This project focuses on the role of AR signaling in this context, as a first milestone to study the complex interplay between sex- and aging-associated cancer risk. 

Objectives: Ongoing studies in the lab indicate that AR expression is down-modulated in dermal fibroblasts of photo-aged skin and underlying premalignant skin cancer lesions (actinic keratoses, AK) and is similarly reduced in CAFs from major skin cancer types, SCC and melanomas . Building on these findings, the objective is to provide training to an ESR on the role of AR in epigenetic / transcriptional control of CAF activation and resulting impact on skin cancer development. The ESR has to assess (1) the functional consequences of AR gene silencing on in vitro properties of primary human dermal fibroblasts (HDFs); (2) the impact of HDFs plus/minus AR knock-down on skin SCC and melanoma development in an orthotopic mouse model of the diseases; (3) perform transcriptomic and AR ChIP-seq analysis to identify genes with CAF effector functions under direct AR control; (4) integrate the transcriptomic results with mRNA expression profiles of skin from identical and di-zygotic twins to identify patterns of androgen responsive genes in the stroma that can be linked to high versus low skin cancer risk.

Project 4 – Prevention of squamous cancer by targeting of transcription / epigenetic regulators

Hypothesis: Genetic and pharmacological targeting of epigenetics regulators in cancer stroma prevents/suppresses skin cancer.

Background and Significance: Conversion of stromal fibroblasts into CAFs and associated chronic inflammation, can play a concurrent or even primary role in cancer initiation and progression. This is of relevance for field cancerization, a condition of major clinical significance consisting of multiple and recurrent premalignant and malignant tumors in many organs, including skin, head/neck, lung, breast, prostate and colon . This condition is very difficult to treat and greater insights into how it develops are urgently needed. We have developed a mouse model of skin field cancerization, based on mesenchymal deletion of the Csl gene, the key effector of canonical Notch signaling and have developed an equivalent in vivo assay for cancer / stromal cell expansion based on mouse ear injection of a combination of cancer and stromal cells . We have further shown that transcriptional control of CAF activation, in vitro and in vivo, is linked to epigenetic alterations that can be overcome by treatment with Brd protein inhibitors, which, at the same time, induce squamous differentiation of adjacent cancer cells . Importantly, treatment of CAFs with Brd protein inhibitors also induces AR expression and activity, which by themselves are sufficient to revert CAF activation.

Related readings

[1] Nosrati, A. & Wei, M. L. Sex disparities in melanoma outcomes: the role of biology. Arch Biochem Biophys 563, 42-50 (2014).

[2] Clocchiatti, A., Cora, E., Zhang, Y. & Dotto, G.P. Sexual dimorphism in cancer. Nat Rev Cancer 16, 330-9 (2016).

[3] Dotto, G.P. Multifocal epithelial tumors and field cancerization: stroma as a primary determinant. J Clin Invest 124, 1446-53 (2014).

[4] Clocchiatti, A. et al. Androgen receptor functions as transcriptional repressor of cancer-associated fibroblast activation. J Clin Invest 128, 5531-5548, (2018).

[5] Dotto, G.P. Multifocal epithelial tumors and field cancerization: stroma as a primary determinant. J Clin Invest 124, 1446-53 (2014).

[6] Hu, B. et al. Multifocal epithelial tumors and field cancerization from loss of mesenchymal CSL signaling. Cell 149, 1207-1220 (2012).

[7] Procopio, M. G. et al. Combined CSL and p53 downregulation promotes cancer-associated fibroblast activation. Nat Cell Biol 17, 1193-1204 (2015).

[8] Kim, D. E. et al. Convergent roles of ATF3 and CSL in chromatin control of cancer-associated fibroblast activation. J Exp Med 214, 2349-2368 (2017).

[9] Clocchiatti, A. et al. Androgen receptor functions as transcriptional repressor of cancer-associated fibroblast activation. J Clin Invest 128, 5531-5548, (2018).