The stem cell pluripotency factor NANOG activates transcription with two unusually potent subdomains at its C terminus

Abstract

Embryonic stem cells are pluripotent progenitors for virtually all cell types in our body and thus possess unlimited therapeutic potentials for regenerative medicine. NANOG, an NK-2 type homeodomain gene, has been proposed to play a key role in maintaining stem cell pluripotency presumably by regulating the expression of genes critical to stem cell renewal and differentiation. Here, we provide the evidence that NANOG behaves as a transcription activator with two unusually strong activation domains embedded in its C terminus. First, we identified these two transactivators by employing the Gal4-DNA binding domain fusion and reporter system and named them WR and CD2. Whereas CD2 contains no obvious structural motif, the WR or Trp repeat contains 10 pentapeptide repeats starting with a Trp in each unit. Substitution of Trp with Ala in each repeat completely abolished its activity, whereas mutations at the conserved Ser, Gln, and Asn had relatively minor or no effect on WR activity. We then validated the activities of WR and CD2 in NANOG by constructing a reporter plasmid bearing five NANOG binding sites. Deletion of both WR and CD2 from NANOG completely eliminated its transactivation function. Paradoxically, whereas the removal of CD2 reduced NANOG activity by ∼30-70%, the removal of WR not only did not diminish but actually enhanced its activity by ∼50-100% depending on the cell lines analyzed. These data suggest that either WR or CD2 is sufficient for NANOG to function as a transactivator.