PBX and MEIS as Non-DNA-Binding Partners in Trimeric Complexes with HOX Proteins

Abstract

These related genes fall into 13 paralogous groups. The products of groups 1 to 8 are more similar to the fly HOX protein Antennapedia (ANTP class), while 9 to 13 are related to the fly Abdominal-B (ABD-B class).Hox gene products function as sequence-specific DNA-binding transcription factors, as evidenced by their ability to regulate natural and artificial promoters in cell culture (18,48,49,53,61,63) and in the animal embryo (3,12,21,33,45,47,51,64).Homeodomain-DNA interactions are facilitated through residues in the flexible N-terminal arm and the recognition helix in the homeodomain (20), with the majority of HOX proteins binding a TAAT core motif. Asparagine 51 in the recognition helix plays a key role in the specificity of target site recognition, both in monomeric and in heterodimeric complexes (7,8,25,41,46,62). The size of the HOX family and their relatively poor discrimination in target site recognition suggest that they may interact with cofactors.Recently, it has been shown that the affinity and specificity of DNA binding by HOX proteins is indeed augmented by cofactor interactions. HOX cofactors in mammals include PBX (15,32,39,44,47) and MEIS (37, 57), members of the TALE family (9) of homeodomain proteins. The Drosophila homologs of mammalian PBX and MEIS are Extradenticle (EXD) (50) and Homothorax (HTH) (52), respectively. In mammals, while the majority of HOX proteins interact with PBX (HOX paralogs 1 to 10) (13), only the group 9 and 10 ABD-B class HOX proteins complex with MEIS (57).We and others have shown that a conserved motif present N terminal to the homeodomain of HOX proteins (11,15,23,27,39,43,44,54,55) and residues in the homeodomain of PBX (14,15,22,31,46) contact each other within the PBX-HOX cooperative complex. These results have been confirmed and extended through the resolution of the crystal structure of the cooperative complex (41,46). Systematic deletions carried out in HOXA9 and MEIS proteins have mapped amino acids (aa) 1 to 61 in HOXA9 and a region C terminal to the homeodomain of MEIS as responsible for mediating .In addition to their interaction with HOX proteins, MEIS and PBX form stable heterodimers that cooperatively bind DNA (16). The MEIS-related protein PREP1 interacts with PBX in a similar fashion (6). This interaction requires a portion of the first 89 aa in PBX and conserved N-terminal regions of MEIS or PREP. The chimeric oncoprotein E2A-PBX (24, 40) lacks the first 89 residues of PBX1 and is unable to interact with MEIS (16).Recently, a number of groups have reported on the formation of trimeric complexes involving proteins of the HOX, PBX, and MEIS extended families. In each case, a DNAbound PBX-HOX (or HOX-like) heterodimer tethers a member of the MEIS/PREP family via protein-protein interactions. Thus, PREP1 associates with DNA-bound HOXB1 and PBX, thereby modulating transcriptional activity (6). Mutation of the PREP1 homeodomain actually improves formation of the tri-* Corresponding author. Mailing address:

Homeobox gene methylation in lung cancer studied by genome-wide analysis with a microarray-based methylated CpG island recovery assay

“…However, by interacting with other transcription factors they can diversify their binding targets. Interacting partners for HOX proteins can be other homeodomain-containing factors (32)(33)(34)(35), and they synergistically govern the expression of downstream target genes. We noticed that nonclustered homeobox genes are also frequent targets of hypermethylation (Fig.…”

Xmeis1, a protooncogene involved in specifying neural crest cell fate in Xenopus embryos

“…Recently, it has shown that the Meis protein and other homeobox-containing proteins, such as Pbx and Hox family proteins form trimeric complexes in vivo and augment the a nity and speci®city of DNA binding (Chang et al, 1996(Chang et al, , 1997Ryoo et al, 1999;Lu et al, 1995;Neuteboom et al, 1995;Phelan et al, 1995;Berthelsen et al, 1998;Swift et al, 1998;Jacobs et al, 1999;Shanmugam et al, 1999;Shen et al, 1999). Since Xmeis1a did show a weak ability to induce XGli-3, it was a possibility that the two alternatively spliced forms of Xmeis1 (Xmeis1a and Xmeis1b) may cooperate with each other to induce XZic gene expression.…”

“…In mammals, while the majority of Hox proteins interact with Pbx (Hox paralogs 1 ± 10) (Chang et al, 1995;Neuteboom et al, 1995;Phelan et al, 1995), only the group 9 and 10 Abd-B class Hox proteins complex with Meis (Shen et al, 1997). Meis, Pbx, and Hox family members have also been reported to form trimeric complexes in vivo (Berthelsen et al, 1998;Swift et al, 1998;Jacobs et al, 1999;Shanmugam et al, 1999;Shen et al, 1999).…”

Transplantable cell lines generated with NUP98–Hox fusion genes undergo leukemic progression by Meis1 independent of its binding to DNA

“…The MSCV-HAMeis1(N51S)-YFP (Meis1(N51S) virus) was constructed by replacing the HA-Meis1 portion of the Meis1 virus by a HAMeis1 cDNA containing an asparagine to serine substitution at position 51 of the homeodomain (kindly provided by Dr Mark Featherstone, McGill University, Montreal, Quebec). 19 …”

“…This was directly tested by transducing the ND13 and NA10 lines with a Meis1 mutant, Meis1(N51S), previously shown to be incapable of binding to DNA, due to an asparagines-to-serine substitution in the residue 51 of its homeodomain. 19 The subclones ND13-2.15 and NA10-3.4 lines were first used to Southern blot analysis of genomic DNA from the bm of moribund mice confirmed the presence of NUP98-Hox and Meis1 proviruses (total time spent in culture prior to injection also shown). Genomic DNA was digested with XbaI, which cuts in both retroviral LTRs, and the eGFP cDNA was used as proviral probe.…”