Stem Cell Quiescence acts as a tumor suppressor mechanism in hair follicle initiated squamous tumors

In some organs, adult stem cells are uniquely poised to serve as cancer cells of origin1-4. It is unclear, however, whether tumorigenesis is influenced by the activation state of the adult stem cell. Hair follicle stem cells (HFSCs) act as cancer cells of origin for cutaneous squamous cell carcinoma (SCC) and undergo defined cycles of quiescence and activation. The data presented here show that HFSCs are unable to initiate tumors during the quiescent phase of the hair cycle, indicating that the mechanisms that keep HFSCs dormant are dominant to the gain of oncogenes (Ras) or the loss of tumor suppressors (p53). Furthermore, Pten activity is necessary for quiescence based tumor suppression, as its deletion alleviates tumor suppression without affecting proliferation. These data demonstrate that stem cell quiescence is a form of tumor suppression in HFSCs, and that Pten plays a role in maintaining quiescence in the presence of tumorigenic stimuli. This experiment includes RNA profiling of hair follicle stem cells at various stages of tumorigenesis Briefly: HFSCs were lineage traced with YFP allele, FACS isolated from various genotypes, and then profiled by Affymetrix microarray Cell Isolation and FACS: Whole dorsal and ventral mouse K15-CrePR; LSLYFP, K15-CrePR; KrasG12D; LSLYFP and K15-CrePR; KrasG12D; Ptenff; LSLYFP was extracted, diced and digested with collagenase (20mg/ml) for 2 hours at 37C, then an equal volume of .25% trypsin was added and digestion continued for an additional hour at 37C. Digested tissue was mechanically dispersed via pipette and filtered with a 100uM cell strainer, collected at 300g and washed twice with PBS. The cells were then filtered through a 40uM cell strainer and FACS processed. YFP+ and YFP- cell populations were collected in RNA lysis buffer (Stratagene) and stored at -80C. Gene expression profiling Microarray analyses by GeneSpring software were performed