Changing homeodomain residues 2 and 3 of Hoxa1 alters its activity in a cell-type and enhancer dependent manner.
The second and third amino acid residues of the N-terminal arm of most Hox protein homeodomains are basic (lysine or arginine), whereas they are asparagine and alanine, respectively, in the Hoxa1 homeodomain. Previous reports pinpointed these residues as specificity determinants in the function of Hoxa1 when it is acting as a monomer. However, in vitro data supported that these residues do not influence the target specificity of Hoxa1 in Pbx1a-Hoxa1 heterodimers. Here, we have analysed the transcriptional activity of a Hoxa1(NA-KR) mutant for which the asparagine and alanine residues of the homeodomain have been replaced by lysine and arginine, respectively. Comparison between the wild-type and mutant Hoxa1 reveals that they show distinct activity on the TSEII enhancer of the somatostatin gene, but that they are equally active in the presence of Pbx and Prep cofactors. This therefore corroborates the biochemical evidence having shown that the second and third residues of the homeodomain do not contribute to the DNA binding of Hoxa1-Pbx dimers. However, on the hoxb1 autoregulatory enhancer, Hoxa1 and Hoxa1(NA-KR) may display distinct activity despite the presence of Pbx, in a cell-type dependent manner. Therefore, our data suggest that, depending on the enhancer, these residues may contribute to the functional specificity of Hoxa1 and that this contribution may not be abrogated by the interaction with Pbx.
Remacle
Sophie
S
Unité de Génétique du Développement, UCL 7382, Université Catholique de Louvain, B-1200 Bruxelles, Belgium.
Shaw-Jackson
Chloë
C
Matis
Christelle
C
Lampe
Xavier
X
Picard
Jacques
J
Rezsöhazy
René
R
D019943:Amino Acid Substitution; D000818:Animals; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000378:metabolism; D004742:Enhancer Elements, Genetic; D017405:Herpes Simplex Virus Protein Vmw65 / Q000235:genetics; D018398:Homeodomain Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D000075062:Pre-B-Cell Leukemia Transcription Factor 1; D017434:Protein Structure, Tertiary; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D013004:Somatostatin / Q000235:genetics; D013329:Structure-Activity Relationship; D015534:Trans-Activators / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D015533:Transcriptional Activation; D000099261:Homeobox A1 Protein
D004268:DNA-Binding Proteins; D017405:Herpes Simplex Virus Protein Vmw65; D018398:Homeodomain Proteins; D000075062:Pre-B-Cell Leukemia Transcription Factor 1; D011518:Proto-Oncogene Proteins; D011993:Recombinant Fusion Proteins; D013004:Somatostatin; D015534:Trans-Activators; D014157:Transcription Factors; D000099261:Homeobox A1 Protein; C101121:HOXB1 homeodomain protein; C106682:PKNOX1 protein, human; C083400:PBX1 protein, human