Indian Hedgehog Controls Proliferation and Differentiation in Skin Tumorigenesis and Protects against Malignant Progression

• Ihh is a crucial regulator of skin tumorigenesis and has context-dependent functions
• Ihh drives keratinocyte differentiation and protects against malignant tumor progression
• Ihh inhibits keratinocyte migration and blocks metastasis of skin cancer in vivo
• Stimulation of proliferation by Ihh in human skin cancer is mediated by Gli2

SummaryMutations in the hedgehog pathway drive the formation of tumors in many different organs, including the development of basal cell carcinoma in the skin. However, little is known about the role of epidermal Indian hedgehog (Ihh) in skin physiology. Using mouse genetics, we identified overlapping and distinct functions of Ihh in different models of epidermal tumorigenesis. Epidermal deletion of Ihh resulted in increased formation of benign squamous papilloma. Strikingly, Ihh-deficient mice showed an increase in malignant squamous cell carcinoma and developed lung and lymph node metastases. In a sebaceous gland tumor model, Ihh deficiency inhibited tumor cell differentiation. More mechanistically, IHH stimulated cell proliferation by activating the transcription factor GLI2 in human keratinocytes and human tumors. Thus, our results uncover important functions for Ihh signaling in controlling proliferation, differentiation, malignant progression, and metastasis of epithelial cancer, establishing Ihh as a gatekeeper for controlling the grade of tumor malignancy.Video Abstract To view the video inline, enable JavaScript on your browser. However, you can download and view the video by clicking on the icon belowHelp with MPG filesOptionsDownload video (55047 K)

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