Presence of activating transcription factor 4 (ATF4) in the porcine anterior pituitary.

The two-hybrid system that identifies protein-protein interactions in a yeast expression system was used to investigate porcine anterior pituitary transcription factors. Four cDNA clones of a protein interacting with the leucine zipper domain of porcine cJun were obtained. Their nucleotide sequences revealed that they encode activating transcription factor 4 (ATF4). A full-length cDNA of porcine ATF4 was obtained by the polymerase chain reaction, and its deduced amino acid sequence showed 88 and 83% identity to human and mouse ATF4, respectively. Reverse transcription-polymerase chain reaction analysis of mRNAs prepared from 11 porcine tissues demonstrated that ATF4 is ubiquitous. Immunohistochemistry showed that ATF4 is present in the hormone producing cells of the anterior pituitary, but absent in some cells of the anterior pituitary. Further binding analysis revealed that ATF4 also interacts with itself and cFos. This evidence of ATF4 homodimerization, as well as heterodimerization with cJun and cFos in the anterior pituitary suggests a novel mechanism for the regulation of gene expression in this tissue.