Heterodimeric interactions between chicken ovalbumin upstream promoter-transcription factor family members ARP1 and Ear2

Members of the chicken ovalbumin upstream promoter-transcription factor (CO UP-TF) subfamily of orphan nuclear receptors, which minimally includes COUP -TFI and ARP1, are highly expressed in brain and are generally considered t o be constitutive repressors of transcription. We have used a yeast two-hyb rid system to isolate proteins expressed in brain that interact with ARP1. One of the proteins isolated in this screen was Ear2, another orphan recept or that has been suggested to be a member of the COUP-TF subfamily. Here we demonstrate that ARP1 and Ear2 form heterodimers in solution and on direct ly repeated response elements with high efficiency and a specificity differ ing from that of homodimeric complexes composed of either receptor. ARP1 an d Ear2 were observed to interact in mammalian cells, and the tissue distrib ution of Ear2 transcripts was found to overlap precisely with the expressio n pattern of ARP1 in several mouse tissues and embryonal carcinoma cell lin es. Heterodimeric interactions between ARP1 and Ear2 may define a distinct pathway of orphan receptor signaling.