The truncated Hoxa1 protein interacts with Hoxa1 and Pbx1 in stem cells.
Hox genes contain a homeobox encoding a 60-amino acid DNA binding sequence. The Hoxa1 gene (Hox1.6, ERA1) encodes two alternatively spliced mRNAs that encode distinct proteins, one with the homeodomain (Hoxa1-993), and another protein lacking this domain (Hoxa1-399). The functions of Hoxa1-399 are unknown. We detected Hoxa1-993 and Hoxa1-399 by immunoprecipitation using Hoxa1 antibodies. To assess whether Hoxa1-399 functions in cellular differentiation, we analyzed Hoxb1, a Hoxa1 target gene. Hoxa1-993 and its cofactor, Pbx1, bind to the Hoxb1 SOct-R3 promoter to transcriptionally activate a luciferase reporter. Results from F9 stem cells that stably express ectopic Hoxa1-399 (the F9-399 line) show that Hoxa1-399 reduces this transcriptional activation. Gel shift assays demonstrate that Hoxa1-399 reduces Hoxa1-993/Pbx1 binding to the Hoxb1 SOct-R3 region. GST pull-down experiments suggest that Hoxa1-399, Hoxa1-993, and Pbx1 form a trimer. However, the F9-399 line exhibits no differences in RA-induced proliferation arrest or endogenous Hoxb1, Pbx1, Hoxa5, Cyp26a1, GATA4, or Meis mRNA levels when compared to F9 wild-type.
Fernandez
Cristina C
CC
Department of Pharmacology, Weill Cornell Medical College, 1300 York Avenue, New York, New York 10065, USA.
Gudas
Lorraine J
LJ
D017398:Alternative Splicing / Q000235:genetics; D020816:Amino Acid Motifs; D000818:Animals; D002460:Cell Line; D049109:Cell Proliferation; D002522:Chlorocebus aethiops; D004247:DNA / Q000378:metabolism; D017930:Genes, Reporter / Q000235:genetics; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D000075062:Pre-B-Cell Leukemia Transcription Factor 1; D011401:Promoter Regions, Genetic / Q000235:genetics; D011485:Protein Binding; D013234:Stem Cells / Q000166:cytology / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D019076:Transgenes / Q000235:genetics; D000099261:Homeobox A1 Protein
D004247:DNA; D018398:Homeodomain Proteins; D000075062:Pre-B-Cell Leukemia Transcription Factor 1; D014157:Transcription Factors; D000099261:Homeobox A1 Protein; C481797:Pbx1 protein, mouse