Filaggrin, the processed form of profilaggrin, is a major product of terminally differentiating mammalian epidermal cells which, based on in vitro studies, is thought to be involved in the aggregation and specific alignment of keratin intermediate filaments during the final stages of development in vivo. In order to explore this possibility, a vector containing one filaggrin repeat was coupled to an inducible heat shock promoter, and stably transfected keratinocyte cell lines were developed. Upon activation of the promoter, the expressed filaggrin quickly disrupts the keratin cytoskeleton due to aggregation of the filaments in the vicinity of the nucleus by causing their collapse. We have also explored the proximal promoter region of the human profilaggrin gene. This consists of a complex of an Sp1 site modulated by nearby interacting ets, NF-KB and AP-1 like consensus transcription sequences. All of these elements are functional, based on gel shift, foot printing and mutational analyses. The ets element is different from the ets-1 and ets-2 sequences heretofore characterized. Since this same ets motif is present in two other epidermally-expressed genes (transglutaminase 3 and trichohyalin), we have initated a detailed analysis of the ets-like transcription factors expressed in epidermal keratinocytes.
