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]

Recently, the use of selected genetically altered mouse models in the detection of carcinogens after short-term chemical exposures has been evaluated. Studies of several chemicals conducted by the National Toxicology Program in Tg.AC transgenic and heterozygous p53-deficient mice have been completed recently and represent a major contribution to this effort, as well as the largest accumulation to date of toxicologic pathology data in these 2 lines of mice. The purpose of this report is to describe the proliferative target organ effects observed in this set of studies, as well as to present the tumor profile in the control groups of this data set. These findings provide a comprehensive toxicologic assessment of these 2 genetically altered mouse strains, which are of emerging importance in toxicologic pathology.

Stromal interaction molecule 1 (STIM1) is a Ca(2+) sensor protein that initiates store-operated calcium entry (SOCE). STIM1 is known to be involved in the chemoattractant signaling pathway for FPR1 in cell lines, but its role in in vivo functioning of neutrophils is unclear. Plaque-type psoriasis is a chronic inflammatory skin disorder associated with chemoattractants driving neutrophils into the epidermis. We investigated the involvement of STIM1 in neutrophil chemotaxis in vitro, as well as during chronic psoriatic inflammation. To this end, we used conditional knockout (KO) mice lacking STIM1 in cells of myeloid lineage (STIM1(fl/fl) LysM-cre). We demonstrate that STIM1 is required for chemotaxis because of multiple chemoattractants in mouse neutrophils in vitro. Using an imiquimod-induced psoriasis-like skin model, we show that KO mice had less neutrophil infiltration in the epidermis than controls, whereas neither chemoattractant production in the epidermis nor macrophage migration was decreased. KO mice displayed a more rapid reversal of the outward signs of psoriasis (plaques). Thus, KO of STIM1 impairs neutrophil contribution to psoriatic inflammation. Our data provide new insights to our understanding of how STIM1 orchestrates the cellular behavior underlying chemotaxis and illustrate the important role of SOCE in a disease-related pathologic model.

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