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MYC regulates ribosome biogenesis and mitochondrial gene expression programs through its interaction with Host Cell Factor-1

ABSTRACT: MYC is an oncoprotein transcription factor that is overexpressed in the majority cancers. Although MYC itself is considered undruggable, it may be possible to inhibit MYC by targeting the co-factors it uses to drive oncogenic gene expression patterns. Here, we use loss- and gain- of function approaches to interrogate how one MYC co-factor—Host Cell Factor (HCF)-1—contributes to MYC activity in a Burkitt lymphoma setting. We identify high-confidence direct targets of the MYC–HCF-1 interaction that are regulated through a recruitment-independent mechanism, including genes that control mitochondrial function and rate-limiting steps for ribosome biogenesis and translation. We describe how these gene expression events impact cell growth and metabolism, and demonstrate that the MYC–HCF-1 interaction is essential for tumor maintenance in vivo. This work highlights the MYC–HCF-1 interaction as a focal point for development of novel anti-cancer therapies.

ORGANISM(S): Human Homo Sapiens

TISSUE(S): Lymphoma Cells

DISEASE(S): Cancer

SUBMITTER: Simona Codreanu

PROVIDER: ST001429 | MetabolomicsWorkbench | Wed Jul 15 00:00:00 BST 2020

REPOSITORIES: MetabolomicsWorkbench

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Project description:Medulloblastoma (MB) is the most common malignant brain tumor. MB is a cerebellar tumor that occurs mostly in children between the ages of 3-7 years but also in adults. Human MBs are classified into four subgroups: Wingless (WNT), Sonic Hedgehog (SHH), Group 3 (G3) and G4, each of which with distinct molecular signatures. SHH MBs with MYCN amplification and TP53 mutations and G3 MBs characterized by C-MYC (MYC) overexpression in ~17% of cases from gene amplification with stem like properties, are the most aggressive and least curable with current therapeutic regimen. Using an orthotopic transplant approach, we found that enforced expression of MYCN in cerebellar granule neural progenitors (CGNPs) from 5-7 days old Trp53-null mice induced SHH MBs after transfer in the cortices or cerebella of naive recipient mice. In contrast, overexpression of MYC induced G3 MBs. Because MYCN and MYC bind to the same E-box DNA sequences, we hypothesized that the difference between MYC and MYCN-induced gene expression and tumor identity might be due to their interaction with different partners in CGNPs. In this study, we investigated the role of the Myc interacting zinc finger protein 1 (MIZ1). We found that MIZ1 binds with higher affinity to MYC than to MYCN and that MIZ1 and MYC co-occupy thousands of promoters in G3 MB. Remarkably, enforced expression of a MYC mutant (MYCV394D) that no longer binds to MIZ1 in Trp53-null CGNPs or expression of wild type MYC in CGNPs that lack functional Miz1 resulted in massive changes of the resulting tumorâ??s transcriptional program. Tumors differed from both SHH and G3 medulloblastoma and had a later time of onset compared to MYC-driven G3 medulloblastoma. Our data demonstrate that interaction of MYC with MIZ1 is required for the development of G3 medulloblastoma. ChIP-Seq experiments for Miz1, c-Myc and NMyc from murine medulloblastoma material. Either sorted tumor cells (Miz1 and c-Myc) or spheres from tumor cells (Miz1 and NMyc) were used. Input-samples were sequenced as controls. RNA-Seq from G3 medulloblastomas after restoration of Atoh1 expression.

Project description:The nucleolus is a subnuclear compartment with a key role in ribosome biogenesis and cellular stress responses. These mechanisms are governed by a complex interaction of proteins, including the NOC1 network. This study reveals a novel relationship between NOC1 and MYC transcription factor, known for its key role in controlling ribosomal biogenesis and cell growth and proliferation. Here, we demonstrate that NOC1 functions as a direct target of MYC, as it is transcriptionally induced through a functional MYC-binding E-box sequence in the NOC1 promoter region. Furthermore, interactome analysis reveals that NOC1-complex includes the nucleolar proteins NOC2 and NOC3 and other nucleolar components such as Nucleostemin1 Ns1 and mainly components for the transport of ribosomal subunits and maturation and with components for rRNA processing. In response to MYC, NOC1 expression and localization within the nucleolus significantly increase, suggesting a direct functional link between MYC activity and NOC1 function. Notably, NOC1 over-expression leads to the formation of large nuclear granules and enlarged nucleoli, which co-localize with nucleolar fibrillarin and Ns1. Additionally, we demonstrate that NOC1 expression is necessary for Ns1 nucleolar localization, suggesting a role for NOC1 in maintaining nucleolar structure. Finally, the co-expression of NOC1 and MYC enhances the formation of abnormal structures formed by NOC1 within the nucleolus, outlining another aspect of NOC1 and MYC cooperation in nucleolar dynamics. This study reveals NOC1's interactions with proteins involved in RNA processing, modification, and splicing, such as Ythdc1, Flacc, and spenito. These proteins play key roles in mediating N6-methyladenosine (m6A) methylation of mRNAs. NOC1's potential involvement in coordinating RNA splicing and nuclear mRNA export highlights its significance in regulating gene expression. In summary, our study uncovers novel roles for NOC1 in nucleolar homeostasis and establishes its direct connection with MYC in the network governing nucleolar structure and function. These findings also highlight NOC1's interaction with proteins relevant for RNA processing, modification, and splicing, suggesting a broader role in addition to its control of nucleolar homeostasis, providing new insight into NOC1 function that can be further investigated into its function in regulating cellular growth and proliferation.

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MYC regulates ribosome biogenesis and mitochondrial gene expression programs through its interaction with Host Cell Factor-1

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