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CD34 Expression by Hair Follicle Stem Cells Is Required for Skin Tumor Development in Mice

¹ Cancer Biology Group, Laboratory of Molecular Toxicology, ² Laboratory of Signal Transduction, ³ Laboratory of Experimental Pathology, and ⁴ Biostatistics Branch, National Institute of Environmental Health Sciences; ⁵ National Health and Environmental Effects Research Laboratory, United States Environmental Protection Agency, Research Triangle Park, North Carolina; ⁶ Department of Dermatology, Columbia University Medical Center, New York, New York; ⁷ Integrated Laboratory Systems, Inc., Durham, North Carolina; ⁸ Department of Dermatology, University of Pennsylvania, School of Medicine, Philadelphia, Pennsylvania; ⁹ Department of Dermatology, Leiden University Medical Center, Leiden, the Netherlands; and ¹⁰ Department of Pharmacology, Pennsylvania State Milton S. Hershey Medical Center, Hershey, Pennsylvania

Requests for reprints: Carol S. Trempus, National Institute of Environmental Health Sciences, 111 TW Alexander Drive, Mail Drop F1-05, Research Triangle Park, NC 27709. Phone: 919-541-0240; Fax: 919-541-1460; E-mail: trempus{at}niehs.nih.gov.

The cell surface marker CD34 marks mouse hair follicle bulge cells, which have attributes of stem cells, including quiescence and multipotency. Using a CD34 knockout (KO) mouse, we tested the hypothesis that CD34 may participate in tumor development in mice because hair follicle stem cells are thought to be a major target of carcinogens in the two-stage model of mouse skin carcinogenesis. Following initiation with 200 nmol 7,12-dimethylbenz(a)anthracene (DMBA), mice were promoted with 12-O-tetradecanoylphorbol-13-acetate (TPA) for 20 weeks. Under these conditions, CD34KO mice failed to develop papillomas. Increasing the initiating dose of DMBA to 400 nmol resulted in tumor development in the CD34KO mice, albeit with an increased latency and lower tumor yield compared with the wild-type (WT) strain. DNA adduct analysis of keratinocytes from DMBA-initiated CD34KO mice revealed that DMBA was metabolically activated into carcinogenic diol epoxides at both 200 and 400 nmol. Chronic exposure to TPA revealed that CD34KO skin developed and sustained epidermal hyperplasia. However, CD34KO hair follicles typically remained in telogen rather than transitioning into anagen growth, confirmed by retention of bromodeoxyuridine-labeled bulge stem cells within the hair follicle. Unique localization of the hair follicle progenitor cell marker MTS24 was found in interfollicular basal cells in TPA-treated WT mice, whereas staining remained restricted to the hair follicles of CD34KO mice, suggesting that progenitor cells migrate into epidermis differently between strains. These data show that CD34 is required for TPA-induced hair follicle stem cell activation and tumor formation in mice. [Cancer Res 2007;67(9):4173–81]

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