A-MYB substitutes for B-MYB in activating cell cycle genes and in stimulating proliferation
Ontology highlight
ABSTRACT: A-MYB (MYBL1) is a transcription factor with a role in meiosis in spermatocytes. The related B-MYB protein is a key proto-oncogene and a master regulator activating late cell cycle genes. To activate genes, B-MYB forms a complex with MuvB and is recruited indirectly to cell cycle genes homology region (CHR) promoter sites of target genes. Activation through the B-MYB-MuvB (MMB) complex is essential for successful mitosis. Here, we discover that A-MYB has a function in transcriptional regulation of the mitotic cell cycle and can substitute for B-MYB. Knockdown experiments in cells not related to spermatogenesis show that B-MYB loss alone only delays cell cycle progression. Only dual knockdown of B-MYB and A-MYB causes cell cycle arrest. A-MYB can substitute for B-MYB in binding to MuvB. The resulting A-MYB-MuvB complex activates genes through CHR sites. We find that A-MYB activates the same target genes as B-MYB. Many of the corresponding proteins are central regulators of the cell division cycle. In summary, we demonstrate that A-MYB is an activator of the mitotic cell cycle by activating late cell cycle genes.
Project description:The core cell cycle machinery genes are transcriptionally regulated by the MuvB family of protein complexes in a cell cycle specific manner. During cell cycle exit in quiescence or senescence, the DREAM complex, which is the repressive form of MuvB, directs transcriptional repression of cell cycle genes; conversely during cell proliferation, the complex of MuvB with the transcription factors (TFs) B-MYB and FOXM1 activate mitotic genes during the G2 phase of the cell cycle. The mechanisms of transcriptional regulation of these complexes are still poorly characterised. Here we combine biochemical analysis and in vitro reconstitution, with structural analysis by cryo-electron microscopy (cryo-EM) and cross-linking mass spectrometry (XL-MS), to functionally examine these complexes. Our data suggests that MuvB is a chromatin regulator whereby a core region binds the nucleosome and remodels it, thereby exposing nucleosomal DNA. This remodelling activity is supported by B-MYB which directly binds the remodelled DNA. Given the remodelling activity on the nucleosome, we propose that the MuvB complex with B-MYB (MMB) function as a pioneer transcription factor complex. Our data rationalises prior biochemical and cellular studies and provides a molecular framework of interactions on a protein complex, which is key for cell cycle regulation.
Project description:To identify genomic regions bound by B-Myb and LIN9 (a subunit of the MuvB complex), we performed ChIP-Sequencing (ChIP-Seq) using chromatin from proliferating HeLa cells in which we can detect a robust association between B-Myb and subunits of the MuvB complex. This analysis allowed us identify late cell cycle or G2/M expressed genes as specific targets of the B-Myb-MuvB complex. Examination of B-Myb and LIN9 binding in asynchronously growing HeLa cells
Project description:To identify genomic regions bound by B-Myb and LIN9 (a subunit of the MuvB complex), we performed ChIP-Sequencing (ChIP-Seq) using chromatin from proliferating HeLa cells in which we can detect a robust association between B-Myb and subunits of the MuvB complex. This analysis allowed us identify late cell cycle or G2/M expressed genes as specific targets of the B-Myb-MuvB complex.
Project description:This SuperSeries is composed of the following subset Series: GSE26922: Cell cycle expression profiles in HeLa cells GSE27030: Genome-wide binding profiles of the B-Myb-MuvB complex in HeLa cells Refer to individual Series
Project description:YAP, a major downstream effector of the Hippo signaling pathway, is an important regulator of cell proliferation. Previous studies have shown that YAP cooperates with the two transcription factors E2F and MYC to mediate G1 to S transition by regulating early cell cycle gene expression. On the other hand, the ability of YAP to regulate G2/M gene expression is dependent on the Myb-MuvB (MMB) complex, consisting of the evolutionary MuvB core complex of five proteins and the facultative subunit B-MYB, a transcription factor. We now carried out interaction studies and found that YAP directly binds to the B-MYB subunit of MMB. Disruption of the YAP/B-MYB interaction by overexpression of the YAP binding domain of B-MYB results in errors in cell division. We also show that YAP and MMB interact in vivo in the developing heart. Genome wide expression and binding studies revealed that YAP and MMB regulate an overlapping set of cell cycle genes in cardiomyocytes. Cardiac specific deletion of the LIN9 subunit of MMB prevents the upregulation of cell cycle genes and the increased proliferation of cardiomyocytes lacking the hippo-signaling component SAV1. Similarly, we find that proliferation of postnatal cardiomyocytes induced by constitutive active YAP depends on MMB. Our findings provide new insights in the mechanisms of cell cycle regulation by the Hippo pathway in cardiomyocytes and suggests that YAP and MMB interact to induce genes critical for cell cycle regulation.
Project description:Myb-MuvB (MMB)/dREAM is a nine subunit complex first described in Drosophila as a repressor of transcription, dependent upon E2F2 and the RBFs. Myb, an integral member of MMB, curiously plays no role in the silencing of the test genes previously analyzed. Moreover, Myb plays an activating role in DNA replication in Drosophila egg chamber follicle cells. The essential functions for Myb are executed as part of MMB. This duality of function lead to the hypothesis that MMB, which contains both known activator and repressor proteins, might function as part of a switching mechanism that is dependent upon DNA sites and developmental context. Here, we used proliferating Drosophila Kc tissue culture cells to explore both the network of genes regulated by MMB (employing RNAi and micro-array expression analysis) and the genomic locations of MMB following chromatin immunoprecipitation (ChIP) and tiling array analysis. MMB occupies thousands of chromosomal sites where a substantial number are proximal to repressed genes that are normally expressed in a wide range of developmental pathways. At many of these sites, E2F2 was critical for repression whereas at other non-overlapping sites, Myb was critical for repression. These data highlight that the MMB factors are utilized in a combinatorial way for targeting gene regulation. We also found sites where MMB was a positive regulator of transcript levels that included genes required for mitotic functions (G2/M), which may explain some of the chromosome instability phenotypes attributed to loss of Myb function in myb mutants. Keywords: Drosophila Myb-MuvB/dREAM, RNAi, ChIP-chip
Project description:Myb-MuvB (MMB)/dREAM is a nine subunit complex first described in Drosophila as a repressor of transcription, dependent upon E2F2 and the RBFs. Myb, an integral member of MMB, curiously plays no role in the silencing of the test genes previously analyzed. Moreover, Myb plays an activating role in DNA replication in Drosophila egg chamber follicle cells. The essential functions for Myb are executed as part of MMB. This duality of function lead to the hypothesis that MMB, which contains both known activator and repressor proteins, might function as part of a switching mechanism that is dependent upon DNA sites and developmental context. Keywords: Drosophila Myb-MuvB/dREAM, ChIP-chip
Project description:YAP/TAZ, downstream effectors of the Hippo pathway, are important regulators of proliferation. Here we show that the ability of YAP to activate mitotic gene expression is dependent on the Myb-MuvB (MMB) complex, a master regulator of genes expressed in the G2/M phase of the cell cycle. By carrying out genome-wide expression and binding analyses, we found that YAP promotes binding of the MMB subunit B-MYB to the promoters of mitotic target genes. YAP binds to B-MYB and stimulates B-MYB chromatin-association through distal enhancer elements that interact with MMB-regulated promoters through chromatin looping. The cooperation between YAP and B-MYB is critical for YAP-mediated entry into mitosis. Furthermore, the expression of genes co-activated by YAP and B-MYB is associated with poor survival of cancer patients. Together, our findings provide a molecular mechanism by which YAP and MMB regulate mitotic gene expression and suggest a link between two cancer-relevant signaling pathways.
Project description:Myb-MuvB (MMB)/dREAM is a nine subunit complex first described in Drosophila as a repressor of transcription, dependent upon E2F2 and the RBFs. Myb, an integral member of MMB, curiously plays no role in the silencing of the test genes previously analyzed. Moreover, Myb plays an activating role in DNA replication in Drosophila egg chamber follicle cells. The essential functions for Myb are executed as part of MMB. This duality of function lead to the hypothesis that MMB, which contains both known activator and repressor proteins, might function as part of a switching mechanism that is dependent upon DNA sites and developmental context. Here, we used proliferating Drosophila Kc tissue culture cells to explore both the network of genes regulated by MMB (employing RNAi and micro-array expression analysis) and the genomic locations of MMB following chromatin immunoprecipitation (ChIP) and tiling array analysis. MMB occupies thousands of chromosomal sites where a substantial number are proximal to repressed genes that are normally expressed in a wide range of developmental pathways. At many of these sites, E2F2 was critical for repression whereas at other non-overlapping sites, Myb was critical for repression. These data highlight that the MMB factors are utilized in a combinatorial way for targeting gene regulation. We also found sites where MMB was a positive regulator of transcript levels that included genes required for mitotic functions (G2/M), which may explain some of the chromosome instability phenotypes attributed to loss of Myb function in myb mutants. Experiment Overall Design: RNAi to deplete Lin-52, Mip40, Myb, Mip120, Mip130, E2F2, both RBFs (RBF1 and RBF2) and L(3)MBT were performed in triplicate. RNAi with a nonspecific RNA derived from a pBSK+ plasmid (named SK+) was used as control. Total RNA was extracted from RNAi-transfected cells after 4 days using RNeasy Mini Kit (QIAGEN).