Animal-specific C-terminal domain links myeloblastosis oncoprotein (Myb) to an ancient repressor complex

Abstract

Members of the Myb oncoprotein and E2F-Rb tumor suppressor protein families are present within the same highly conserved multiprotein transcriptional repressor complex, named either as Myb and synthetic multivuval class B (Myb-MuvB) or as Drosophila Rb E2F and Myb-interacting proteins (dREAM). We now report that the animal-specific C terminus of Drosophila Myb but not the more highly conserved N-terminal DNA-binding domain is necessary and sufficient for (i) adult viability, (ii) proper localization to chromosomes in vivo, (iii) regulation of gene expression in vivo, and (iv) interaction with the highly conserved core of the MuvB/dREAM transcriptional repressor complex. In addition, we have identified a conserved peptide motif that is required for this interaction. Our results imply that an ancient function of Myb in regulating G2/M genes in both plants and animals appears to have been transferred from the DNA-binding domain to the animal-specific C-terminal domain. Increased expression of B-MYB/MYBL2, the human ortholog of Drosophila Myb, correlates with poor prognosis in human patients with breast cancer. Therefore, our results imply that the specific interaction of the C terminus of Myb with the MuvB/dREAM core complex may provide an attractive target for the development of cancer therapeutics.oncogene | transcription | repression | evolution T he Myb oncogene family was discovered because of the retroviral transduction of the chicken cellular myb protooncogene that generated the avian myeloblastosis virus (1, 2). Both the cellular Myb and viral Myb proteins are present within the nucleus of the cell, bind to specific DNA sequences, and can regulate gene expression (3-9). The Myb DNA-binding domain is present in members of all major classes of eukaryotic organisms, including plants, animals, fungi, cellular slime molds, and protists (10, 11). Simpler plants have only one or a few Myb transcription factors, whereas all flowering plant species have hundreds of related Myb transcription factors that arose via massive gene duplication and divergence (12). The picture in animals is simpler. All vertebrates have three closely related Myb transcription factors, whereas most invertebrates have only one Myb transcription factor. In addition to the presence of an aminoterminal Myb DNA-binding domain, most of these Myb transcription factors of animals share a conserved C-terminal domain that appears to be animal-specific. We have recently reported that, rather surprisingly, this C-terminal Myb domain is sufficient to rescue the lethality of a Myb null mutation in Drosophila when expressed via a heterologous promoter (13). We have now used a combination of genetic, cell biological, and biochemical approaches to explore the function of this animal-specific C-terminal Myb domain. We find that this domain is both necessary and sufficient for interaction with the synthetic multivulval class B (MuvB) core, a highly conserved transcriptional repressor complex that also interacts with the E2F-Rb tumor suppressor proteins (14-16...

Epigenetic regulation of olfactory receptor gene expression by the Myb–MuvB/dREAM complex

“…Myb is required for expression in the antenna, and its absence substantially reduces activity of ab1C neurons and behavioral avoidance to low levels of CO 2 . Interestingly, the DNA-binding domain of Myb is not required for receptor regulation, consistent with the previous observation that Myb can bind to chromatin indirectly via other members of the MMB/dREAM complex (Andrejka et al 2011). Expression of the receptor genes tested in the antenna show a pattern of repressive histone methylation (H3K9me2), an enrichment that has been previously seen in developing olfactory neurons in mammals (Magklara et al 2011).…”

“…S1B). Despite lacking all three repeats of the highly conserved Myb DNA-binding domain (Peters et al 1987), this Myb C-terminal domain is sufficient to assemble into the MMB/dREAM complex and localize to specific regions in the genome to regulate gene expression (Wen et al 2008;Andrejka et al 2011). Thus, the rescue of receptor expression in the absence of the highly conserved Myb DNA-binding domain suggests that Myb is acting via the complex at the receptor loci.…”

The Complex Containing Drosophila Myb and RB/E2F2 Regulates Cytokinesis in a Histone H2Av-Dependent Manner

“…We used the following mutant and transgenic fly strains: Myb MH107 (20), mip130 (15), mip120 67-9A-9 and mip120 67-21-6 (16), mip40 EY16520 (16), E2f2 329/DS8-78A (23), Caf1 9-2⌬ (C. Geng and J. S. Lipsick, unpublished data) and Caf1 short (24) (26), Ubi-GFP-Polo and Ubi-GFP-AurB (described below), GFP-Myb (19), GFP-Myb-KW606AA and GFP-Myb C terminus (27), P[mip120-1F] (16), and P[His2Av-mRFP1] strains (28 . Two-to 4-day-old females were incubated at 37°C for 1 h on 2 successive days to induce FLP expression by the Hsp70 promoter.…”

Structural mechanisms of DREAM complex assembly and regulation

“…The evolutionarily conserved MuvB proteins in the Drosophila melanogaster DREAM complex were found to interact with the C terminus of BMyb (Andrejka et al 2011). To test whether this association is direct and conserved in the human proteins, we performed a series of precipitation experiments with recombinant B-Myb and MuvB proteins from Sf9 cells (Fig.…”