THE PROXIMAL PROMOTER OF THE HUMAN TRANSGLUTAMINASE-3 GENE - STRATIFIED SQUAMOUS EPITHELIAL-SPECIFIC EXPRESSION IN CULTURED-CELLS IS MEDIATED BY BINDING OF SP1 AND ETS TRANSCRIPTION FACTORS TO A PROXIMAL PROMOTER ELEMENT

The transglutaminase 3 enzyme is expressed during the late stages of t he terminal differentiation of the epidermis and in certain cell types of the hair follicle. The enzyme is thought to be critically involved in the crosslinking of structural proteins and in the formation of th e cornified cell envelope, thereby contributing to rigid structures th at play vital roles in shape determination and/or barrier functions. T o explore the mechanisms regulating the expression of the transglutami nase 3 gene (TGM3), 3.0 kilobase pairs of sequences upstream from the transcription start site were assessed for their ability to control th e expression of a chloramphenicol acetyltransferase reporter gene. Del etion analyses in transiently transfected epidermal keratinocytes defi ned sequences between -126 and -91 as the proximal promoter region of the gene, and which can confer epithelial-specific expression to the T GM3 gene in vitro. Mutation and DNA-protein binding analyses indicated that a complex interaction between adjacent Sp1- and ets-like recogni tion motifs with their cognate binding factors is required for the fun ction of the TGM3 promoter. As these TGM3 sequences can confer promote r/enhancer activity to reporter genes at a level comparable to the pow erful SV40 promoter, they may be useful for gene therapy in keratinocy tes.