AbstractTGFβis an important regulator of epidermal keratinocyte function because it suppresses cell proliferation, while it induces synthesis of extracellular matrix proteins and their cells surface receptors. To examine whether TGFβaffects synthesis of intracellular proteins as well, specifically the transcription of keratin genes, we transfected a series of DNA constructs that contain keratin gene promoters into human epidermal keratinocytes. The transfected cells were grown in the presence and absence of TGFβ. We found that TGFβspecifically induces transcription controlled by the promoters of K#5 and K#14 keratin genes, markers of basal cells. No other keratin gene promoters were induced. The effect of TGFβis concentration-dependent, can be demonstrated in HeLa cells, does not depend on keratinocyte growth conditions and can be elicited by both TGFβ1and TGFβ2. We conclude that TGFβpromotes the basal cell phenotype in stratified epithelia such as the epidermis.