Relative to conventional two-dimensional (2-D) culture, three-dimensional (3-D) suspension culture of epithelial cells more closely mimics the in vivo cell microenvironment regarding cell architecture, cell to matrix interaction, and osmosis exchange. However, primary normal human keratinocytes (NHKc) rapidly undergo terminal differentiation and detachment-induced cell death (anoikis) upon disconnection from the basement membrane, thus greatly constraining their use in 3-D suspension culture models. Here, we examined the 3-D anchorage-free growth potential of NHKc isolated from neonatal skin explants of 59 different individuals. We found that 40% of all isolates naturally self-assembled into multicellular spheroids within 24 h in anchorage-free culture, while 60% did not. Placing a single spheroid back into 2-D monolayer culture yielded proliferating cells that expressed elevated levels of nuclear P63 and basal cytokeratin 14. These cells also displayed prolonged keratinocyte renewal and a gene expression profile corresponding to cellular heterogeneity, quiescence, and de-differentiation. Notably, spheroid-derived (SD) NHKc were enriched for a P63/K14 double-positive population that formed holoclonal colonies and reassembled into multicellular spheroids during 3-D suspension subculture. This study reveals marked phenotypic differences in neonatal keratinocyte suspension cultures isolated from different individuals. We present here a model system that can be readily employed to study epithelial cell behavior, along with a variety of dermatological diseases.
The role of epidermal basal stem cells in dysplasia is a matter of great interest in the human papillomavirus (HPV)-driven cancers. To assess the relationship between “stemness” and HPV-mediated transformation, we made use of 3-D suspension culture and fluorescence activated cell sorting (FACS) to purify stem/progenitor-like cells from primary normal human keratinocyte (NHKc) cultures. We found that NHKc cells derived from multicellular keratinocyte spheroids were enriched for a basal subpopulation of epidermal stem-like cells, that could be maintained for prolonged time in culture and used to conduct transfection experiments with full-length HPV16 DNA. Thus, by using these stem cell enrichment methods, we set out to investigate in detail the effects of increased and decreased basal stem cell density on keratinocytes’ immortalization and transformation efficiencies. We hypothesized that stem cell properties of NHKc cultures established from neonatal genital skin would positively influence susceptibility to transformation by HPV16 DNA. Our findings reveal that epidermal stem cells (EpSCs) are more effectively immortalized and transformed by oncogenic HPV16 DNA, while terminally differentiated keratinocyte populations fail to successfully immortalize in culture. Tissue stem cell density may prove useful in predicting individual susceptibility to HPV16-mediated transformation in persons with persistent HPV infections, improving on current triage and follow-up measures.