Project description:The suppression of oncogenic levels of MYC is sufficient to induce sustained tumor regression associated with proliferative arrest, differentiation, cellular senescence and/or apoptosis, a phenomenon known as oncogene addiction. However, after prolonged inactivation of MYC in a conditional transgenic mouse model of Em-tTA/tetO-MYC T-acute lymphomablastic lymphoma (T-ALL), some of the tumors recur, recapitulating what is frequently observed in human tumors in response to targeted therapies. Here we report that these recurring lymphomas express high levels of either transgenic or endogenous Myc suggesting that tumors continue to be addicted to oncogenic levels of MYC. Many of the recurring lymphomas (76%) harbored mutations in the tetracycline transactivator (tTA) resulting in expression of the MYC transgene even in the presence of doxycycline. Many of the remaining recurring tumors expressed high levels of endogenous Myc which was in some cases associated with a genomic rearrangement of the endogenous Myc locus or overexpression of Notch1. Gene expression profiling confirmed that the primary and recurring tumors have highly similar transcriptomes. Importantly, shRNA-mediated suppression of the high levels of MYC in recurring tumors elicited both suppression of proliferation and increased apoptosis confirming that these tumors remain oncogene addicted. These results suggest that tumors caused by MYC overexpression remain addicted to high levels of expression of this oncogene. 13 samples, no replicates included
Project description:Tumors driven by activation of the transcription factor Myc generally show oncogene addiction. However, the gene-expression programs that depend upon sustained Myc activity in those tumors remain unknown. We have addressed this issue in a model of liver carcinoma driven by a reversible tet-Myc transgene, combining gene expression profiling with the mapping of Myc and RNA Polymerase II on chromatin. Switching off the oncogene in advanced carcinomas revealed that Myc is required for the continuous activation and repression of distinct sets of genes, constituting no more than half of those deregulated during tumor progression, and an even smaller subset of all Myc-bound genes. We further showed that a Myc mutant unable to associate with the co-repressor protein Miz1 is defective in the initiation of liver tumorigenesis. Altogether, our data provide the first detailed analysis of a Myc-dependent transcriptional program in a fully developed carcinoma, revealing that the critical effectors of Myc in tumor maintenance must be included within defined subsets (ca. 1,300 each) of activated and repressed genes.
Project description:Tumors driven by activation of the transcription factor Myc generally show oncogene addiction. However, the gene-expression programs that depend upon sustained Myc activity in those tumors remain unknown. We have addressed this issue in a model of liver carcinoma driven by a reversible tet-Myc transgene, combining gene expression profiling with the mapping of Myc and RNA Polymerase II on chromatin. Switching off the oncogene in advanced carcinomas revealed that Myc is required for the continuous activation and repression of distinct sets of genes, constituting no more than half of those deregulated during tumor progression, and an even smaller subset of all Myc-bound genes. We further showed that a Myc mutant unable to associate with the co-repressor protein Miz1 is defective in the initiation of liver tumorigenesis. Altogether, our data provide the first detailed analysis of a Myc-dependent transcriptional program in a fully developed carcinoma, revealing that the critical effectors of Myc in tumor maintenance must be included within defined subsets (ca. 1,300 each) of activated and repressed genes.
Project description:The suppression of oncogenic levels of MYC is sufficient to induce sustained tumor regression associated with proliferative arrest, differentiation, cellular senescence and/or apoptosis, a phenomenon known as oncogene addiction. However, after prolonged inactivation of MYC in a conditional transgenic mouse model of Em-tTA/tetO-MYC T-acute lymphomablastic lymphoma (T-ALL), some of the tumors recur, recapitulating what is frequently observed in human tumors in response to targeted therapies. Here we report that these recurring lymphomas express high levels of either transgenic or endogenous Myc suggesting that tumors continue to be addicted to oncogenic levels of MYC. Many of the recurring lymphomas (76%) harbored mutations in the tetracycline transactivator (tTA) resulting in expression of the MYC transgene even in the presence of doxycycline. Many of the remaining recurring tumors expressed high levels of endogenous Myc which was in some cases associated with a genomic rearrangement of the endogenous Myc locus or overexpression of Notch1. Gene expression profiling confirmed that the primary and recurring tumors have highly similar transcriptomes. Importantly, shRNA-mediated suppression of the high levels of MYC in recurring tumors elicited both suppression of proliferation and increased apoptosis confirming that these tumors remain oncogene addicted. These results suggest that tumors caused by MYC overexpression remain addicted to high levels of expression of this oncogene.
Project description:To identify proteomic signatures associated with hepatocellular carcinoma driven by MYC overexpression, proteomics was performed on the LAP-tTA/tetO-MYC mouse conditional liver cancer model. Upon MYC activation, mice form liver cancer. Differential proteomics was performed in "MYC on" (MYC-HCC) mouse liver tumors versus mouse control normal liver tissue (where MYC was not overexpressed to drive tumorigenesis -- "MYC off").
Project description:Deregulated expression of MYC enhances glutamine utilization and renders cell survival dependent on glutamine, inducing “glutamine addiction”. Surprisingly, colon cancer cells that express high levels of MYC due to WNT pathway mutations, are not glutamine-addicted but undergo a reversible cell cycle arrest upon glutamine deprivation. We show here that glutamine deprivation suppresses translation of endogenous MYC via the 3’-UTR of the MYC mRNA, enabling escape from apoptosis. This regulation is mediated by glutamine-dependent changes in adenosine nucleotide levels. Glutamine deprivation causes a global reduction in promoter association of RNA Polymerase II (RNAPII) and slows transcriptional elongation. While activation of MYC restores binding of MYC and RNAPII function on most promoters, restoration of elongation is imperfect and activation of MYC in the absence of glutamine causes stalling of RNAPII on multiple genes, correlating with R-loop formation. Stalling of RNAPII and R-loop formation can cause DNA damage, arguing that the MYC 3’-UTR is critical for maintaining genome stability when ribonucleotide levels are low.
Project description:MYC and RAS signaling are two oncogene pathways important in human liver cancer. We sought to model liver cancer driven by either MYC or RAS using conditional LAP-tTA crossed to either TRE-MYC or TRE-HRAS models in the FVB/N background, and to understand oncogenic signaling pathways that are distinct between each model. Non-tumor tissue, from LAP-tTTA (LT2) mice were used as controls. In this study, we generated tumors from either MYC or RAS driven tumors and compared global gene expression changes to each other and control samples.