Regulation of a hair follicle keratin intermediate filament gene promoter

During hair growth, cortical cells emerging from the proliferative follicle bulb rapidly undergo a differentiation program and synthesise large amount s of hair keratin proteins. To identify some of the controls that specify e xpression of hair genes we have defined the minimal promoter of the wool ke ratin intermediate filament gene K2.10. The region of this gene spanning nu cleotides -350 to +53 was sufficient to direct expression of the lacZ gene to the follicle cortex of transgenic mice but deletion of nucleotides -350 to -150 led to a complete loss of promoter activity. When a four base subst itution mutation was introduced into the minimal functional promoter at the binding site for lymphoid enhancer factor 1 (LEF-1), promoter activity in transgenic mice was decreased but specificity was not affected. To investig ate the interaction of trails-acting factors within the minimal K2.10 promo ter we performed DNase I footprinting analyses and electrophoretic mobility shift assays. In addition to LEF-1, Spl, AP2-like and NF1-like proteins bo und to the promoter. The Spl and AP2-like proteins bound sequences flanking the LEF-1 binding site whereas the NF1-like proteins bound closer to the t ranscription start site. We conclude that the LEF-1 binding site is an enha ncer element of the K2.10 promoter in the hair follicle cortex and that fac tors other than LEF-1 regulate promoter tissue- and differentiation-specifi city.