Impaired skin regeneration and remodeling after cutaneous injury and chemically induced hyperplasia in taps-transgenic mice.

Recently, we identified an AP-1-dependent target gene in 12-O-tetradecanoylphorbol-13-acetate (TPA)-treated mouse back skin, which encodes a retroviral-like aspartic proteinase (Taps/Asprv1). Taps expression was detected almost exclusively in stratified epithelia of mouse embryos and adult tissues, and enhanced protein levels were present in several non-neoplastic human skin disorders, implicating a crucial role for differentiation and homeostasis of multilayered epithelia. Here, we generated a mouse model in which Taps transgene expression is under the control of the human ubiquitin C promoter (UBC-Taps). Although no obvious phenotype was observed in normal skin development and homeostasis, these mice showed a significant delay in cutaneous wound closure compared with control animals. Shortly after re-epithelialization, we found an increase in keratinocytes in the stratum granulosum, which express Filaggrin, a late differentiation marker. A hypergranulosum-like phenotype with increased numbers of Filaggrin-positive keratinocytes was also observed in UBC-Taps mice after administration of TPA. In summary, these data show that aberrant Taps expression causes impaired skin regeneration and skin remodeling after cutaneous injury and chemically induced hyperplasia.

A novel aspartic proteinase-like gene expressed in stratified epithelia and squamous cell carcinoma of the skin.

Homeostasis of stratified epithelia, such as the epidermis of the skin, is a sophisticated process that represents a tightly controlled balance between proliferation and differentiation. Alterations of this balance are associated with common human diseases including cancer. Here, we report the cloning of a novel cDNA sequence, from mouse back skin, that is induced by the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) and codes for a hitherto unknown aspartic proteinase-like protein (Taps). Taps represents a potential AP-1 target gene because TPA-induced expression in epidermal keratinocytes critically depends on c-Fos, and co-treatment with dexamethasone, a potent inhibitor of AP-1-mediated gene regulation, resulted in impaired activation of Taps expression. Taps mRNA and protein are restricted to stratified epithelia in mouse embryos and adult tissues, implicating a crucial role for this aspartic proteinase-like gene in differentiation and homeostasis of multilayered epithelia. During chemically induced carcinogenesis, transient elevation of Taps mRNA and protein levels was detected in benign skin tumors. However, its expression is negatively associated with dedifferentiation and malignant progression in squamous cell carcinomas of the skin. Similar expression was observed in squamous skin tumors of patients, suggesting that detection of Taps levels represents a novel strategy to discriminate the progression state of squamous skin cancers.