ABSTRACT
The genes encoding keratin 5 and 14 are highly expressed in the basal cell layer keratinocytes of the epidermis, but both genes are silenced when keratinocytes move into the suprabasal compartment. The POU homeodomain factors Skn-1a and Tst-1, which are expressed in epidermis, may play a role in the suprabasal repression of the keratin 5 and 14 genes because keratin 14 mRNA expression persists in suprabasal cells in Skn-1/Tst-1 double knockout mice. In transfection experiments, both Skn-1a and Tst-1 repress the keratin 14 promoter, with the POU domain being sufficient for repression. The region of the keratin 14 gene sufficient and required for repression by Skn-1a is a 100-base pair sequence lacking POU-binding sites adjacent to the transcription start site. DNA-binding defective mutants of Skn-1a and Tst-1 are as effective at mediating repression as the wild type proteins, suggesting that protein-protein interactions rather than direct DNA binding are important for repression. We also show that CREB-binding protein (CBP)/p300 co-activators are strong activators of keratin 14 gene expression, acting through sequences close to the keratin 14 promoter. Further, CBP interacts directly with the POU domain of Skn-1a, and increasing concentrations of CBP can overcome Skn-1a-mediated repression, suggesting that POU domain factors may repress keratin 14 gene expression by interfering with the activity of co-activators such as CBP/p300.
Subject(s)
Gene Expression Regulation , Keratinocytes/metabolism , Keratins/genetics , Nuclear Proteins/metabolism , Promoter Regions, Genetic , Repressor Proteins/metabolism , Trans-Activators/metabolism , Transcription, Genetic , Animals , Animals, Newborn , Base Pairing , Binding Sites , CREB-Binding Protein , Cell Line , Cells, Cultured , Epidermal Cells , Epidermis/metabolism , Genes, Reporter , HeLa Cells , Humans , Keratin-14 , Keratin-15 , Keratin-5 , Keratinocytes/cytology , Luciferases/genetics , Mice , Octamer Transcription Factor-6 , RNA, Messenger/genetics , Recombinant Proteins/biosynthesis , Repressor Proteins/chemistry , Repressor Proteins/genetics , Skin/cytology , Skin/metabolism , Transcription Factors/genetics , Transcription Factors/metabolism , TransfectionABSTRACT
The human adenovirus 5 E1B 55-kDa protein is required for efficient nucleocytoplasmic transport of late viral mRNAs. This protein is shown to have RNA-binding activity which maps to a region of the protein with homology to a family of RNA-binding proteins and which has been shown previously to be essential for functionality of the protein in vivo.
