Identification and dissection of an enhancer controlling epithelial gene expression in skin

摘要

Keratins 14 and 5 are the structural hallmarks of the basal kera- tinocytes of the epidermis and outer root sheath (ORS) of the hair follicle. Their genes are controlled in a tissue-specific manner and thus serve as useful tools to elucidate the regulatory mechanisms involved in keratinocyte-specific transcription. Previously we iden- tified several keratinocyte-specific DNase l hypersensitive sites (HSs) in the 5' regulatory sequences of the K14 gene and showed that a 700-bp regulatory domain encompassing HSs Ⅲ and Ⅲ can confer epidermal and ORS-specific gene expression in transgenic mice in vivo. Although HS Ⅱ harbored much of the transactivation activity in vitro, it was not sufficient to restrict expression to keratinocytes in vivo. We now explore the HS Ⅲ regulatory ele- ment. Surprisingly. this element on its own confers gene expres- sion to the keratinocytes of the inner root sheath (IRS) of the hair follicle, whereas a 275-bp DNA fragment containing both HSs Ⅱ and Ill shifts the expression from the IRS to the basal keratinocytes and 0RS in vivo. Electrophoretic mobility-shift assays and mutational studies of HSs Ⅲ reveal a role for CACCC-box binding proteins, Sp1 family members, and other factors adding to the list of previously described factors that are involved in keratinocyte-specific gene expression. These studies highlight a cooperative interaction of the two HSs domains and strengthen the importance of combinatorial play of transcription factors that govern keratinocyte-specific gene regulation.