Epidermal stem cells: targets for carcinogenic chemicals

Epidermal stem cells long have been considered a target for carcinogenic chemicals, but these stem cells have never been identified or isolated. Toward this goal, this report examines two-stage carcinogenesis in light of the stem cell model for cellular replacement in the epidermis and considers characteristics that may be useful in the identification and the isolation of epidermal stem cells. Firstly, the carcinogenesis experiments in mice have indicated that the population of target cells normally remains in the epidermis for the life of the animal despite the continual cellular turnover. Hence, the slowly cycling (label-retaining) keratinocytes from the epidermis and hair follicles are potential targets. Secondly, the results of carcinogenesis experiments have also indicated that the target cells are necessarily ones with a high potential for proliferation relative the most of the proliferative population. The keratinocyte colony forming units (kCFU) from the epidermis of normal and treated adult mice are consequently a quantifiable indicator of proliferative potential and another possible target. Further application of the stem cell concepts of quiescence and of self-renewal is expected to yield additional tools for the identification and isolation of the epidermal targets for chemical carcinogens.