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Transcriptional Antagonism between Hmx1 and Nkx2.5 for a Shared DNA-binding Site
Journal article   Open access   Peer reviewed

Transcriptional Antagonism between Hmx1 and Nkx2.5 for a Shared DNA-binding Site

Brad A Amendt, Lillian B Sutherland and Andrew F Russo
The Journal of biological chemistry, Vol.274(17), pp.11635-11642
04/23/1999
DOI: 10.1074/jbc.274.17.11635
PMID: 10206974
url
https://doi.org/10.1074/jbc.274.17.11635View
Published (Version of record) Open Access

Abstract

The recently described Hmx family of homeodomain proteins is predominately expressed in discrete regions of developing sensory tissues. In this report, we have identified the preferred DNA-binding site of the murine Hmx3 homeodomain protein by the selection and amplification binding (SAAB) technique. The consensus Hmx-binding site contained the sequence 5'-CAAGTG-3', which differs from the 5'-TAAT-3' motif commonly associated with homeodomain proteins. Instead, the Hmx consensus is similar to the 5'-CAAGTG-3'-binding sites of Nkx2.1 and Nkx2.5 homeodomain proteins. Based on mutation studies, both the 5'-CAAG-3' core and the 3'-TG dinucleotide are required for high affinity binding by Hmx3 and the homologous Hmx1 protein. A critical determinant of this specificity is the glutamine at position 50 in the third helix of the Hmx homeodomain. Hmx1 binds to the 5'-CAAGTG-3' element with an apparent dissociation constant of 20 nM. Unexpectedly, the human Hmx1 protein specifically repressed transcription from a luciferase reporter gene containing 3 copies of the 5'-CAAGTG-3' sequence. In contrast, the Nkx2.5 protein transactivated this luciferase reporter. Interestingly, co-expression of Hmx1 and Nkx2.5 attenuated each others activity, suggesting that genes containing the CAAGTG element can integrate signals from these proteins. Therefore, Hmx1 and Nkx2. 5 proteins bind a unique DNA sequence and act as transcriptional antagonists.

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