Abstract 4385: Live-imaging the interface between homeostasis and cancer initiation
Authors: Pineda Cristiana , Martone Catherine , Suozzi Katie , Brown Samara , Beronja Slobodan , Greco Valentina 
Published: July 2016

Abstract
While cancer-associated mutations are most frequently found within tumors, it has been established that these same mutations can be present in even phenotypically normal organs, such as the skin. This raises the question as to how the switch from normal to malignant is initiated within the interface between homeostasis and cancer. One challenge to understanding the initiating events towards malignancy is the inability to follow the same cells over time in an intact mammal. Specifically, this roadblock hinders the ability to understand both the role of specific cells and how their location contributes to their growth, whether that growth be normal or cancerous. To overcome this, we have established a novel live imaging approach to track cellular behaviors in normal, healthy skin. This approach has previously enabled our lab to demonstrate that location dictates the fate and behaviors of hair follicle stem cells during skin regeneration (Rompolas et al. Nature 2013). We are now utilizing this approach to capture the emergence of the cellular behaviors that lead to Hras-driven skin tumors in live mice.
To begin to characterize the initiating events of skin cancer, we utilized a model of oncogenic Hras (HrasG12V), which has been established to give rise to skin papillomas. Using targeted, inducible genetic drivers, we activated HrasG12V at low levels and restricted the activation to the cycling, stem-cell rich portion of the hair follicle. Strikingly, we have observed that the presence of HrasG12V cells within the cycling portion of the hair follicle are not only tolerated, but can also be eliminated, supporting the idea that the surrounding wild-type tissue has the capability to both integrate and overcome the presence of a single oncogenic hit. Furthermore, within this targeted genetic system, we found that the initial position of the mutant cell impacted the resultant phenotype of the tissue. To next understand these behaviors at the cellular level, we utilized a viral approach to directly activate and fluorescently tag HrasG12V at clonal levels throughout the skin epithelium allowing us to observe interactions between wild-type and mutant cells. Furthermore, within the upper portion of the hair follicle and epidermis, which (unlike the cycling portion) is immune permissive, we observed the release of exosomes by mutant cells and their subsequent clearing by both epithelial and immune cells. Currently, we are introducing a second mutation, loss of TGFβ signaling, to the oncogenic Hras system which is a mutational combination well established to produce cutaneous Squamous Cell Carcinoma (cSCC). This system will provide us with a spectrum of phenotypes from wild-type, to benign yet aberrant (papillomas), to malignant (cSCC) and allow us to interrogate how interactions among different cell types (wild-type, single mutants, and double mutants) within particular niches influence the overall fate of the tissue to initiate disease.
Citation Format: Cristiana Pineda, Catherine Martone, Katie Suozzi, Samara Brown, Slobodan Beronja, Valentina Greco. Live-imaging the interface between homeostasis and cancer initiation. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4385.