Helix-loop-helix proteins are present and differentially expressed in different cell lines from the anterior pituitary.

The basic-helix-loop-helix (bHLH) class of transcriptional activators, important in the establishment of many different cell lineages, share two important properties: the ability to heterodimerize with other members of this family and to bind DNA containing the loose consensus sequence CANNTG. This study takes advantage of these shared characteristics to begin to address whether or not bHLH proteins are present in pituitary cells. Gel-shift and Southwestern assays using an oligonucleotide containing a bHLH binding consensus sequence demonstrate that pituitary-specific proteins are present in extracts from adult pituitary tissue and pituitary cell lines and bind specifically to this sequence. Pituitary extracts were also found to contain several factors which interact with Id protein, a negative regulator of bHLH activity, in Far-Western assays of protein-protein interactions. Finally, messenger RNA for Id is present in pituitary cell lines but is absent in adult pituitary tissue. Together, these studies indicate that bHLH proteins are present in pituitary cells and their levels are differentially regulated in the separate cell types.