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MYC-Associated Factor MAX is a Regulator of the Circadian Clock.

ABSTRACT: The circadian transcriptional network is based on a competition between transcriptional activator and repressor complexes regulating the rhythmic expression of clock-controlled genes. We show here that the MYC-associated factor X, MAX, plays a repressive role in this network and operates through a MYC-independent binding to E-box-containing regulatory regions within the promoters of circadian BMAL1 targets. We further show that this "clock" function of MAX is required for maintaining a proper circadian rhythm and that MAX and BMAL1 contribute to two temporally alternating transcriptional complexes on clock-regulated promoters. We also identified MAX network transcriptional repressor, MNT, as a fundamental partner of MAX-mediated circadian regulation. Collectively, our data indicate that MAX regulates clock gene expression and contributes to keeping the balance between positive and negative elements of the molecular clock machinery.

SUBMITTER: Blazevits O

PROVIDER: S-EPMC7177918 | biostudies-literature | 2020 Mar

REPOSITORIES: biostudies-literature

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MYC-Associated Factor MAX is a Regulator of the Circadian Clock.

Blaževitš Olga O Bolshette Nityanand N Vecchio Donatella D Guijarro Ana A Croci Ottavio O Campaner Stefano S Grimaldi Benedetto B

International journal of molecular sciences 20200326 7

The circadian transcriptional network is based on a competition between transcriptional activator and repressor complexes regulating the rhythmic expression of clock-controlled genes. We show here that the MYC-associated factor X, MAX, plays a repressive role in this network and operates through a MYC-independent binding to E-box-containing regulatory regions within the promoters of circadian BMAL1 targets. We further show that this "clock" function of MAX is required for maintaining a proper ci ...[more]

PMID: 32225100

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MYC-associated Factor X, MAX, controls the clock transcriptional network [RNA-Seq]

Project description:Purpose: Quantitative RT-PCR and ChIP analyses identified MAX as a transcriptional repressor of circadian BMAL1 target genes. The goal of this study is to compare the transcriptional effect of a knockdown of either MAX and BMAL1 in a human cell line (MDA-MB-231) Methods: Polyadenylated mRNA profiles of human breast cancer MDA-MB-231 cells with knocked down MAX or BMAL1 were generated by deep sequencing, in triplicate, using Illumina HiSeq 2000 sequencer. Cells transfected with a non-targeting siRNA sequence were used as a control. RNA sequencing counts were used to determine differentially expressed genes with DeSeq2 package included in the Galaxy web platform (usergalaxy.org). Differentially expressed genes (DEGs) were defined adopting an adjust P < 0.001 as a statistical cut-off value. Results: Transcript assembly and quantification of RNA-sequencing reads identified 4863 and 4247 differentially expressed genes (DEGs) upon knockdown of BMAL1 or MAX, respectively. The comparison of the two set of genes revealed that 2391 of siBMAL1 DEGs (almost 50%) were also differentially expressed in MAX-silenced cells. Heat map and clustering analysis of this sub-set of genes revealed that more than 90% (2241 out of 2391) were coherently altered in both conditions (i.e. their expression was altered in the same direction). Consistent with our quantitative RT-PCR experiments, genes belonging to the circadian rhythm signalling were altered by both MAX and BMAL1 silencing. Conclusion: This study indicate that MAX is a part of the molecular clock transcriptional network.

2020-04-29 | GSE127212 | GEO

MYC-associated factor X, MAX

Project description:This SuperSeries is composed of the SubSeries listed below.

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Project description:MYC-associated factor X, MAX

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Circadian regulator CLOCK promotes tumor angiogenesis in glioblastoma.

Project description:Glioblastoma (GBM) is one of the most aggressive tumors in the adult central nervous system. We previously revealed that circadian regulation of glioma stem cells (GSCs) affects GBM hallmarks of immunosuppression and GSC maintenance in a paracrine and autocrine manner. Here, we expand the mechanism involved in angiogenesis, another critical GBM hallmark, as a potential basis underlying CLOCK's pro-tumor effect in GBM. Mechanistically, CLOCK-directed olfactomedin like 3 (OLFML3) expression results in hypoxia-inducible factor 1-alpha (HIF1α)-mediated transcriptional upregulation of periostin (POSTN). As a result, secreted POSTN promotes tumor angiogenesis via activation of the TANK-binding kinase 1 (TBK1) signaling in endothelial cells. In GBM mouse and patient-derived xenograft models, blockade of the CLOCK-directed POSTN-TBK1 axis inhibits tumor progression and angiogenesis. Thus, the CLOCK-POSTN-TBK1 circuit coordinates a key tumor-endothelial cell interaction and represents an actionable therapeutic target for GBM.

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The MNT transcription factor autoregulates its expression and supports proliferation in MYC-associated factor X (MAX)-deficient cells.

Project description:The MAX network transcriptional repressor (MNT) is an MXD family transcription factor of the basic helix-loop-helix (bHLH) family. MNT dimerizes with another transcriptional regulator, MYC-associated factor X (MAX), and down-regulates genes by binding to E-boxes. MAX also dimerizes with MYC, an oncogenic bHLH transcription factor. Upon E-box binding, the MYC-MAX dimer activates gene expression. MNT also binds to the MAX dimerization protein MLX (MLX), and MNT-MLX and MNT-MAX dimers co-exist. However, all MNT functions have been attributed to MNT-MAX dimers, and no functions of the MNT-MLX dimer have been described. MNT's biological role has been linked to its function as a MYC oncogene modulator, but little is known about its regulation. We show here that MNT localizes to the nucleus of MAX-expressing cells and that MNT-MAX dimers bind and repress the MNT promoter, an effect that depends on one of the two E-boxes on this promoter. In MAX-deficient cells, MNT was overexpressed and redistributed to the cytoplasm. Interestingly, MNT was required for cell proliferation even in the absence of MAX. We show that in MAX-deficient cells, MNT binds to MLX, but also forms homodimers. RNA-sequencing experiments revealed that MNT regulates the expression of several genes even in the absence of MAX, with many of these genes being involved in cell cycle regulation and DNA repair. Of note, MNT-MNT homodimers regulated the transcription of some genes involved in cell proliferation. The tight regulation of MNT and its functionality even without MAX suggest a major role for MNT in cell proliferation.

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Project description:MYC-associated Factor X, MAX, controls the clock transcriptional network [RNA-Seq]

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Circadian Regulator CLOCK Recruits Immune-Suppressive Microglia into the GBM Tumor Microenvironment.

Project description:Glioblastoma (GBM) is a lethal brain tumor containing a subpopulation of glioma stem cells (GSC). Pan-cancer analyses have revealed that stemness of cancer cells correlates positively with immunosuppressive pathways in many solid tumors, including GBM, prompting us to conduct a gain-of-function screen of epigenetic regulators that may influence GSC self-renewal and tumor immunity. The circadian regulator CLOCK emerged as a top hit in enhancing stem-cell self-renewal, which was amplified in about 5% of human GBM cases. CLOCK and its heterodimeric partner BMAL1 enhanced GSC self-renewal and triggered protumor immunity via transcriptional upregulation of OLFML3, a novel chemokine recruiting immune-suppressive microglia into the tumor microenvironment. In GBM models, CLOCK or OLFML3 depletion reduced intratumoral microglia density and extended overall survival. We conclude that the CLOCK-BMAL1 complex contributes to key GBM hallmarks of GSC maintenance and immunosuppression and, together with its downstream target OLFML3, represents new therapeutic targets for this disease. SIGNIFICANCE: Circadian regulator CLOCK drives GSC self-renewal and metabolism and promotes microglia infiltration through direct regulation of a novel microglia-attracting chemokine, OLFML3. CLOCK and/or OLFML3 may represent novel therapeutic targets for GBM.This article is highlighted in the In This Issue feature, p. 327.

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