Cancer stem cell features shift during skin squamous cell carcinoma progression

Cancer stem cells (CSCs) play a key role in tumour growth and metastasis. Although an expansion of CSC population was previously described in advanced cutaneous squamous cell carcinoma (SCC), it remains unknown whether CSC regulatory mechanisms also change through tumour progression to promote malignancy. Here, we generate mouse models of skin SCCs to study alterations in CSC regulation over progression. We found that features of CSCs change at late stage of progression, correlating with a switch from epithelial to mesenchymal tumour shape. beta-catenin and EGFR signalling are down-regulated, whereas autocrine FGFR1 and PDGFR alpha pathways are up-regulated in CSCs of advanced tumours. Inhibition of FGFR and PDGFR signalling repress malignant SCCs growth and metastasis, respectively. An enhanced epithelial-to-mesenchymal transition (EMT) program and over-expression of PDGFR alpha and FGFR1 are observed in malignant human skin SCCs, suggesting that these pathways are also induced over human SCC progression. Therefore, uncover signalling pathways controlling CSCs at specific stage of progression may improve the selection of more accurate targeted therapeutic strategies according to tumour stage, blocking SCC relapse and metastasis. Mouse models of skin SCCs progression were first generated. For that, individual samples of spontaneous or DMBA-TPA induced skin SCCs generated in K14-HPV16 mice were orthotopically engrafted in immunodeficient mice and then serially transplanted, generating lineages in which the progression from WD-SCCs to PD-SCCs was observed. Then, tumour cells expressing CD34 and alpha 6-integrin, previously identified as cutaneous cancer stem cells, were isolated by flow cytometry-sorter from WD-SCCs and PD-SCCs of different tumour lineages. RNA extraction and hybridization on Affymetrix microarrays was carried out to compare whole gene profiling of these populations of CSCs.