Redistribution of transcription factor AP-2 alpha in differentiating cultured human epidermal cells

Expression of the transcription factor AP-2 alpha was examined in cultured human epidermal cells. Levels of AP-2 alpha mRNA increased substantially af ter the cultures reached confluence, similar to the expression pattern of t he differentiation markers involucrin and keratinocyte transglutaminase. Th e level of AP-2 alpha, protein in nuclear extracts declined markedly after confluence, however, along with its ability to form complexes with oligonuc leotides containing the AP-2 response element. In contrast, the levels of A P-2 alpha protein in cytoplasmic extracts increased dramatically after conf luence, but these extracts had low DNA binding activity. Supershift experim ents with specific antisera detected only AP-2 alpha and not the beta or ga mma isoforms. Examination of its localization by confocal microscopy reveal ed that AP-2 alpha was primarily in the nucleus of basal cells and largely cytoplasmic in the most superficial cells. Localization was a dynamic pheno menon in that changing the medium resulted in accumulation of this transcri ption factor in the nucleus after several hours. Overall, the data indicate that AP-2 alpha transcriptional activity is regulated in a differentiation -dependent manner in cultured keratinocytes and that this occurs by relocal ization of the protein. Nuclear localization of the AP-2 alpha protein in b asal cells permits its accessibility to response elements in gene promoters , whereas sequestration in the cytoplasm as the differentiation program pro gresses curtails its transcriptional activity. This regulatory scheme may p rovide keratinocytes with the ability to restore AP-2 transcriptional activ ity rapidly by redistribution to the nucleus after receiving an appropriate growth signal, such as a medium change.