Endometrial Cancer Side-Population Cells Show Prominent Migration and Have a Potential to Differentiate into the Mesenchymal Cell Lineage

Cancer stem-like cellsubpopulations, referred to as “ side-population” (SP) cells, have been identified in several tumors based on their ability to efflux the fluorescent dye Hoechst 33342. Although SP cellshave been identified in the normal human endometrium and endometrial cancer, little is known about their characteristics. In this study, we isolated and characterized the SP cellsin human endometrial cancer cellsand in rat endometrial cellsexpressing oncogenic human K-Ras protein. These SP cellsshowed i) reduction in the expression levels of differentiation markers; ii) long-term proliferative capacity of the cellcultures; iii) self-renewal capacity in vitro; iv) enhancement of migration, lamellipodia, and, uropodia formation; and v) enhanced tumorigenicity. In nude mice, SP cellsformed large, invasive tumors, which were composed of both tumor cellsand stromal-like cellswith enriched extracellular matrix. The expression levels of vimentin, α-smooth muscle actin, and collagen III were enhanced in SP tumors compared with the levels in non-SP tumors. In addition, analysis of microdissectedsamples and fluorescence in situ hybridization of Hec1-SP-tumors showed that the stromal-like cellswith enriched extracellular matrix contained human DNA, confirming that the stromal-like cellswere derived from the inoculated cells. Moreober, in a Matrigelassay, SP cellsdifferentiated into α-smooth muscle actin-expressing cells. These findings demonstrate that SP cellshave cancer stem-like cellfeatures, including the potential to differentiate into the mesenchymal celllineage.