The Abd-B-like Hox Homeodomain Proteins Can Be Subdivided by the Ability to Form Complexes with Pbx1a on a Novel DNA Target

Shen, Wen Hong; Rozenfeld, Sophia; Helson, Lawrence; Largman, Corey

doi:10.1074/jbc.272.13.8198

Cited by 131 publications

(143 citation statements)

References 37 publications

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“…38 PBX1a is involved in translocations in human ALL and is a known binding partner for many HOX genes including those studied here. 13 Interestingly, the pattern of PBX1a expression in subpopulations of normal cells was similar to that for the four HOX genes and MEIS1. However, its expression was difficult to detect in AML blasts.…”

Section: Figurementioning

confidence: 82%

“…10 Transcripts for HOXA9, A10, B3 and B4 are detected in malignant cells from various subtypes of AML, but interestingly, expression of at least one of these (A10) is not seen in acute promyelocytic leukemia. 11,12 PBX1a, a DNA binding partner of several HOX gene family members, 13 is fused to E2A in acute lymphoblastic leukemia (ALL) containing the t(1;19). 14 Another HOX binding partner, Meis1, 15 is activated by retroviral insertion together with Hoxa7 and Hoxa9 in myeloid leukemia in BXH-2 mice.…”

Section: Introductionmentioning

confidence: 99%

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Expression of HOX genes, HOX cofactors, and MLL in phenotypically and functionally defined subpopulations of leukemic and normal human hematopoietic cells

et al. 1999

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To explore the possibility that deregulated HOX gene expression might commonly occur during leukemic hematopoiesis, we compared the relative levels of expression of these and related genes in phenotypically and functionally defined subpopulations of AML blasts and normal hematopoietic cells. Initially, a semi-quantitative RT-PCR technique was used to amplify total cDNA from total leukemic blast cell populations from 20 AML patients and light density cells from four normal bone marrows. Expression of HOX genes (A9, A10, B3 and B4), MEIS1 and MLL was easily detected in the majority of AML samples with the exception of two samples from patients with AML subtype M3 (which expressed only MLL). Low levels of HOXA9 and A10 but not B3 or B4 were seen in normal marrow while MLL was easily detected. PBX1a was difficult to detect in any AML sample but was seen in three of four normal marrows. Cells from nine AML patients and five normal bone marrows were FACS-sorted into CD34 ؉ CD38 ؊ , CD34 ؉ CD38 ؉ and CD34 ؊ subpopulations, analyzed for their functional properties in long-term culture (LTC) and colony assays, and for gene expression using RT-PCR. 93 ؎ 14% of AML LTC-initiating cells, 92 ± 14% AML colony-forming cells, and Ͼ99% of normal LTC-IC and CFC were CD34 ؉ . The relative level of expression of the four HOX genes in amplified cDNA from CD34 ؊ as compared to CD34 ؉ CD38 ؊ normal cells was reduced Ͼ10-fold. However, in AML samples this down-regulation in HOX expression in CD34 ؊ as compared to CD34 ؉ CD38 ؊ cells was not seen (P Ͻ 0.05 for comparison between AML and normal). A similar difference between normal and AML subpopulations was seen when the relative levels of expression of MEIS1, and to a lesser extent MLL, were compared in CD34 ؉ and CD34 ؊ cells (P Ͻ 0.05). In contrast, while some evidence of down-regulation of PBX1a was found in comparing CD34 ؊ to CD34 ؉ normal cells it was difficult to detect expression of this gene in any subpopulation from most AML samples. Thus, the down-regulation of HOX, MEIS1 and to some extent MLL which occurs with normal hematopoietic differentiation is not seen in AML cells with similar functional and phenotypic properties.

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Section: Figurementioning

confidence: 82%

Section: Introductionmentioning

confidence: 99%

Expression of HOX genes, HOX cofactors, and MLL in phenotypically and functionally defined subpopulations of leukemic and normal human hematopoietic cells

et al. 1999

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“…Competition for binding sites has in the past seemed unlikely because of varying binding-site preference among anterior and posterior Hox proteins. Anterior Hox proteins prefer a G at the second position of the 5Ј-TNAT/CNNN-3Ј half-site, middle Hox proteins accept a G or A, whereas the more posterior proteins bind G, A, or T. A preference for C in the fourth position is exhibited by the most posterior Hox proteins (Shen et al 1997). Given that Hox proteins contain the same four helix-3 residues that make direct DNA base contacts in the major groove, this specificity has been postulated to be determined by residues in the N-terminal arm through interactions with the minor groove of DNA (Ekker et al 1994) and modulated by the interaction with PBC proteins Passner et al 1999;Piper et al 1999).…”

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confidence: 96%

“…The PBC family, which includes human Pbx1 and Drosophila Exd, belongs to a class of proteins that contains the TALE (three-aminoacid loop extension)-type homeodomain, so named because of a three-amino-acid insertion between homeodomain residues 23 and 24 in the loop between helices 1 and 2 (Mann 1995;Mann and Chan 1996;Bü rglin 1997). A subset of vertebrate Hox proteins interacts with Pbx1 via a conserved six-amino-acid motif, or hexapeptide, enabling cooperative DNA binding (Chang et al 1995;Neuteboom et al 1995;Peltenburg and Murre 1996;Shen et al 1996Shen et al , 1997Passner et al 1999;Piper et al 1999).…”

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confidence: 99%

Structure of HoxA9 and Pbx1 bound to DNA: Hox hexapeptide and DNA recognition anterior to posterior

LaRonde-LeBlanc¹,

Wolberger²

2003

Genes Dev.

205

233

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The large family of Hox transcription factors has critical roles in early morphological development and later cell differentiation (McGinnis and Krumlauf 1992;Krumlauf 1994;Lawrence et al. 1996;Magli et al. 1997). Humans have 39 Hox genes arranged in four clusters (HoxAHoxD). The linear arrangement of genes within each cluster facilitates controlled spatial and temporal expression along the anterior-posterior axis of the body (Fig. 1A). Expression of Hox genes in the wrong segment at the wrong time often results in homeotic transformation of that segment (Lamka et al. 1992;Morgan et al. 1992;Duboule 1994a). Hox homeodomains contain identical DNA-base-contacting residues (Fig. 1B) and have very similar DNA sequence specificity, generally preferring a core DNA-binding site containing the sequence 5Ј-TTNAT-3Ј, whose third base depends on the particular Hox protein (Laughon 1991). Cooperative DNA binding with other protein cofactors, such as the PBC family of homeodomain proteins, is thought to enhance the specificity of Hox proteins and thereby allow them to carry out distinct functions (Chan et al. 1994;Chang et al. 1995;Mann and Chan 1996). The PBC family, which includes human Pbx1 and Drosophila Exd, belongs to a class of proteins that contains the TALE (three-aminoacid loop extension)-type homeodomain, so named because of a three-amino-acid insertion between homeodomain residues 23 and 24 in the loop between helices 1 and 2 (Mann 1995;Mann and Chan 1996;Bü rglin 1997). A subset of vertebrate Hox proteins interacts with Pbx1 via a conserved six-amino-acid motif, or hexapeptide, enabling cooperative DNA binding (Chang et al. 1995;Neuteboom et al. 1995;Peltenburg and Murre 1996;Shen et al. 1996Shen et al. , 1997Passner et al. 1999;Piper et al. 1999).Hox proteins required for anterior development are expressed earliest and are restricted to anterior domains. The more posterior proteins are expressed later in development and in more posterior domains (Duboule 1994b;Krumlauf 1994). This character is critical to their in vivo function. In general, when posterior proteins are ex-

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“…A number of studies have demonstrated that Pbx and exd proteins increase the in vitro DNA binding affinities of many Hox and several non-Hox homeodomain proteins (6-8, 16, 20, 28, 37, 39, 41, 43, 49, 50, 53). Pbx-Hox cooperative DNA binding occurs through adjacent DNA half sites and requires highly conserved motifs flanking the Hox and Pbx homeodomains (7,20,25,37,43,50). Interactions with Pbx also result in enhanced DNA binding specificities by Hox proteins due to modulation of the Hox homeodomain N-terminal arm, which contacts nucleotides in the DNA minor groove (8, 26).…”

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confidence: 99%

Meis Proteins are Major In Vivo DNA Binding Partners for Wild-Type but Not Chimeric Pbx Proteins

Chang

Jacobs

Nakamura

et al. 1997

Molecular and Cellular Biology

241

263

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The Pbx1 and Meis1 proto-oncogenes code for divergent homeodomain proteins that are targets for oncogenic mutations in human and murine leukemias, respectively, and implicated by genetic analyses to functionally collaborate with Hox proteins during embryonic development and/or oncogenesis. Although Pbx proteins have been shown to dimerize with Hox proteins and modulate their DNA binding properties in vitro, the biochemical compositions of endogenous Pbx-containing complexes have not been determined. In the present study, we demonstrate that Pbx and Meis proteins form abundant complexes that comprise a major Pbx-containing DNA binding activity in nuclear extracts of cultured cells and mouse embryos. Pbx1 and Meis1 dimerize in solution and cooperatively bind bipartite DNA sequences consisting of directly adjacent Pbx and Meis half sites. Pbx1-Meis1 heterodimers display distinctive DNA binding specificities and cross-bind to a subset of Pbx-Hox sites, including those previously implicated as response elements for the execution of Pbx-dependent Hox programs in vivo. Chimeric oncoprotein E2a-Pbx1 is unable to bind DNA with Meis1, due to the deletion of amino-terminal Pbx1 sequences following fusion with E2a. We conclude that Meis proteins are preferred in vivo DNA binding partners for wild-type Pbx1, a relationship that is circumvented by its oncogenic counterpart E2a-Pbx1.Hox proteins make critical contributions to cell fate and segmental patterning during embryonic development (30). As targets of oncogenic mutations in human and murine leukemias, they are also implicated in cancer pathogenesis (3,4,21,34,35), which likely reflects perturbations of their roles in normal hematopoietic cell differentiation (23). In these capacities, they are presumed to function as transcription factors whose DNA binding activities are mediated through a conserved motif known as the homeodomain, which is structurally related to the bacterial helix-turn-helix motif (48). However, at a molecular level, the contributions of Hox proteins to developmental processes and disease pathogenesis are inadequately explained, given their disappointingly poor in vitro DNA binding affinities and specificities as monomeric proteins. This has led to the proposal that additional factors are required to modulate the DNA binding and transcriptional properties of Hox proteins (13), which would be consistent with models for achievement of specificity by other classes of transcriptional proteins.Genetic and biochemical studies support the argument for a role for members of the Pbx, exd, and ceh-20 subfamily (5) of divergent homeodomain proteins as potential Hox cofactors. In Drosophila melanogaster, exd is required for the execution of genetic programs that are also dependent on Hox proteins for appropriate segment-specific expression (40,45,46). A similar role for mammalian Pbx proteins is suggested by genetic analyses demonstrating that sequence elements with features of Pbx-Hox consensus sites are required for appropriate expression of murine Hoxb-1 in th...

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The Abd-B-like Hox Homeodomain Proteins Can Be Subdivided by the Ability to Form Complexes with Pbx1a on a Novel DNA Target

Cited by 131 publications

References 37 publications

Expression of HOX genes, HOX cofactors, and MLL in phenotypically and functionally defined subpopulations of leukemic and normal human hematopoietic cells

Expression of HOX genes, HOX cofactors, and MLL in phenotypically and functionally defined subpopulations of leukemic and normal human hematopoietic cells

Structure of HoxA9 and Pbx1 bound to DNA: Hox hexapeptide and DNA recognition anterior to posterior

Meis Proteins are Major In Vivo DNA Binding Partners for Wild-Type but Not Chimeric Pbx Proteins

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