Binding of a 100‐kDa ubiquitous factor to the human prolactin promoter is required for its basal and hormone‐regulated activity

Abstract

CAMP strongly stimulates the activity of the human prolactin (hPRL) promoter. We have previously shown that two types of cis-element are required for this cAMP regulation; binding sites for the pituitary-specific factor Pit-1, and the sequence spanning nucleotides -115 to -85 (named sequence A). Sequence A contains the TGACG motif found in the consensus sequence of the cAMP-responsive element (CRE). In this study, we show that a mutation in the TGACG motif of sequence A strongly reduces not only the cAMP regulation but also the Ca2+ regulation and basal activity of the hPRL promoter. Furthermore, gel-shift assays indicate that the mutation prevents binding of a ubiquitous factor which is not the CRE-binding protein. Southwestern experiments suggest that this ubiquitous factor's molecular mass is approximately 100 kDa. We conclude that binding of a 100-kDa ubiquitous factor to sequence A is required for full basal and hormonal regulation of hPRL-promoter activity.