NK2 Homeobox Protein 5 (NKX2-5)

The cardiac homeobox protein Nkx2.5 is essential in cardiac development, and mutations in CSX (which encodes Nkx2.5) cause various congenital heart malformations. Cotransfection of Nkx2.5 and Tbx5 into COS-7 cells showed that they also associate with each other in mammalian cells. Glutathionine S-transferase (GST) pull-down assays indicated that the N-terminal domain and N-terminal part of the T box of Tbx5 and the homeodomain of Nkx2.5 are necessary for their interaction. Tbx5 and Nkx2.5 directly bound to the promoter of the gene encoding cardiac-specific natriuretic peptide precursor type A (NPPA) in tandem, and both transcription factors showed synergistic activation. Deletion analysis showed that both the N-terminal domain and the T box of Tbx5 are important for this transactivation.