HELIX-LOOP-HELIX PROTEINS ARE PRESENT AND DIFFERENTIALLY EXPRESSED INDIFFERENT 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 me mbers of this family and to bind DNA containing the loose consensus se quence CANNTG. This study takes advantage of these shared characterist ics to begin to address whether or not bHLH proteins are present in pi tuitary cells. Gel-shift and Southwestern assays using an oligonucleot ide containing a bHLH binding consensus sequence demonstrate that pitu itary-specific proteins are present in extracts from adult pituitary t issue and pituitary cell lines and bind specifically to this sequence. Pituitary extracts were also found to contain several factors which i nteract with Id protein, a negative regulator of bHLH activity, in Far -Western assays of protein-protein interactions. Finally, messenger RN A for Id is present in pituitary cell lines but is absent in adult pit uitary tissue. Together, these studies indicate that bHLH proteins are present in pituitary cells and their levels are differentially regula ted in the separate cell types.