PBX and MEIS as non-DNA-binding partners in trimeric complexes with HOX proteins.
HOX, PBX, and MEIS transcription factors bind DNA through a homeodomain. PBX proteins bind DNA cooperatively as heterodimers with MEIS family members and also with HOX proteins from paralog groups 1 to 10. MEIS proteins cooperatively bind DNA with ABD-B class HOX proteins of groups 9 and 10. Here, we examine aspects of dimeric and higher-order interactions between these three homeodomain classes. The most significant results can be summarized as follows. (i) Most of PBX N terminal to the homeodomain is required for efficient cooperative binding with HOXD4 and HOXD9. (ii) MEIS and PBX proteins form higher-order complexes on a heterodimeric binding site. (iii) Although MEIS does not cooperatively bind DNA with ANTP class HOX proteins, it does form a trimer as a non-DNA-binding partner with DNA-bound PBX-HOXD4. (iv) The N terminus of HOXD4 negatively regulates trimer formation. (v) MEIS forms a similar trimer with DNA-bound PBX-HOXD9. (vi) A related trimer (where MEIS is a non-DNA-binding partner) is formed on a transcriptional promoter within the cell. (vii) We observe an additional trimer class involving non-DNA-bound PBX and DNA-bound MEIS-HOXD9 or MEIS-HOXD10 heterodimers that is enhanced by mutation of the PBX homeodomain. (viii) In this latter trimer, PBX is likely to contact both MEIS and HOXD9/D10. (ix) The stability of DNA binding by all trimers is enhanced relative to the heterodimers. These findings suggest novel functions for PBX and MEIS in modulating the function of DNA-bound MEIS-HOX and PBX-HOX heterodimers, respectively.
Shanmugam
K
K
McGill Cancer Centre, McGill University, Montreal, Quebec, Canada H3G 1Y6.
Green
N C
NC
Rambaldi
I
I
Saragovi
H U
HU
Featherstone
M S
MS
D051943:Antennapedia Homeodomain Protein; D001665:Binding Sites; D004268:DNA-Binding Proteins / Q000378:metabolism; D019281:Dimerization; D018398:Homeodomain Proteins / Q000145:classification / Q000378:metabolism*; D046911:Macromolecular Substances; D008957:Models, Genetic; D005810:Multigene Family; D000075064:Myeloid Ecotropic Viral Integration Site 1 Protein; D009363:Neoplasm Proteins / Q000378:metabolism; D009687:Nuclear Proteins; D000075062:Pre-B-Cell Leukemia Transcription Factor 1; D011485:Protein Binding; D020836:Protein Structure, Quaternary; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D014157:Transcription Factors / Q000145:classification / Q000378:metabolism*
D051943:Antennapedia Homeodomain Protein; D004268:DNA-Binding Proteins; D018398:Homeodomain Proteins; D046911:Macromolecular Substances; D000075064:Myeloid Ecotropic Viral Integration Site 1 Protein; D009363:Neoplasm Proteins; D009687:Nuclear Proteins; D000075062:Pre-B-Cell Leukemia Transcription Factor 1; D011518:Proto-Oncogene Proteins; D014157:Transcription Factors; C083400:PBX1 protein, human