Abstract 3372: Mouse keratinocyte side-population plays an important role during malignant progression to skin squamous cell carcinomas

Abstract

Abstract A subset of cells, termed side-population (SP), with characteristics of adult stem cells (SC) has been identified in several tissues, cell lines, as well as human and experimental tumors. The main feature of these putative stem cells is the high efflux capability for antimitotic drugs. The role of this SP in tumorigenesis is controversial; though, a role as cancer stem cells has been reported. Here, we have investigated whether a functionally equivalent SP exists in cell lines derived from mouse epidermis and skin tumors in order to define the extent of which the presence of SP is associated with tumor progression. We observed increased percentage of the SP in cell lines derived from skin squamous cell carcinomas (SCCs; cell lines CH72 and JWF2) compared with those arose from skin papillomas (308 and MT1/2) and mouse epidermis (C50). Side populations were isolated by the high capability to efflux Hoechst upon FACS analysis. Interestingly, qRT-PCR analysis of SP and non-SP shows elevated expression of the ABCG2/BCRP1 transporter -which participates in the dye efflux- in SP; while the expression of the hair follicle stem cell markers keratin 15 (K15), CD34 and Lgr6 were similar between SP and non-SP. These results suggest that the SP is not related to the well characterized stem cells from the bulge region of the hair follicle (BuSC). Importantly, the relevant correlation among the SP size and tumor progression suggests that these cells are positively selected during tumor progression. In order to localize the SP in mouse epidermis and tumors, we performed immunofluorescence analysis of skin papillomas and SCCs generated through the two-stage carcinogenesis protocol. We identified the ABCG2 transporter in a region near and above the BuSC area. Notably, this region was also positive for the thymic epithelial progenitor marker MTS24 which defines a keratinocyte population with characteristic of stem cells. Importantly, the ABCG2 transporter and MTS24 were localized in patches of cells on the proliferative basal cell layer of skin papillomas. Furthermore, we observed an elevated number of putative stem cells expressing ABCG2 and MTS24 in tumors from our previously published K5CDK4 mouse which showed increased malignant progression to SCC. Collectivelly, our results suggest that a putative stem cell population –different from the BuSCs–, play an important role during the malignant progression SCC. Supported by NIH grant CA116328. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3372. doi:1538-7445.AM2012-3372