DISTINCT POSITIVE AND NEGATIVE REGULATORY ELEMENTS CONTROL NEURONAL AND HEPATIC TRANSCRIPTION OF THE HUMAN TRANSFERRIN GENE

Transferrin (Tf), the iron-transport protein, plays an essential role in the central nervous system development, plasticity, and aging. As a first step toward elucidating the role of each transcription factor i nvolved in the regulation of Tf gene expression, we have recently show n that similar promoter elements direct cell-type specific transcripti on in oligodendrocytes, epithelial choroid plexus cells, and in the ne uronal cell line B103. Here we have analyzed the regulatory elements t hat control the level of expression of the Tf gene in neuronal cells. Transient expression experiments in B103 cells revealed that the -164/ +1 promoter region is stimulated by a position-dependent -1140/-1000 u pstream region. DNase I footprinting, gel retardation assays, and anti body reactivity data allowed us to characterize the nuclear factors in teracting with this region, The upstream region I-binding protein (URI -BP) belongs to the steroid/ retinoid receptor family, while URII-BP i s a member of the nuclear factor I (NF-I) family. Interestingly, no en hancer nor silencer activity is detected in B103 cells. This contrasts with our findings in hepatoma cells, where the activity of the -125/1 promoter can be repressed by a -1000/-819 upstream negative-acting r egion and stimulated by the -3600/-3300 enhancer. We demonstrate that the negative-acting region presents the characteristics of a silencer that interacts with a nuclear protein present in liver and absent in B 103 cells, Similarly, B103 cells lack a nuclear protein able to bind t o an essential site of the enhancer. This shows that in B103 cells, th e inactivity of the silencer and the enhancer regions results from the absence of at least one essential nuclear protein. (C) 1996 Wiley-Lis s, Inc.