TRANSCRIPTIONALLY ACTIVE HETERODIMER FORMATION OF AN ARNT-LIKE PAS PROTEIN, ARNT3, WITH HIF-1A, HLF, AND CLOCK

We isolated a cDNA clone encoding a polypeptide of 626 amino acids con taining basic helix-loop-helix (bHLH) and PAS domains from a mouse cDN A library of P19 cells. This protein, termed Arnt3, showed the highest similarity to Arnt and Arnt2 in the bHLH and PAS regions. Arnt3 mRNA was expressed in brain, skeletal muscle, 13.5-day embryos, and P19 cel ls treated with retinoic acid. The partner PAS proteins of Arnt8 were searched for by the two-hybrid system in yeast, and HIF-1 alpha, HLF, and Clock among various bHLH/PAS proteins were found. Gel mobility shi ft analysis using nuclear extracts from 293T cells cotransfected with Arnt3 and HIF-1 alpha (or HLF) expression plasmids revealed that these complexes specifically bound the hypoxia-response element (HRE). Coex pression of Arnt3 and HIF-1 alpha (or HLF) in Arnt-deficient c4 cells enhanced transcription of a reporter gene driven by the HRE sequences. We also showed that Arnt3 contained an activation domain at the C-ter minal region and a repression domain between the PAS-A and PAS-B regio ns. (C) 1998 Academic Press.