Putting p53 in Context Kastenhuber, Edward R.; Lowe, Scott W.
Cell,
09/2017, Volume:
170, Issue:
6
Journal Article
Peer reviewed
Open access
TP53 is the most frequently mutated gene in human cancer. Functionally, p53 is activated by a host of stress stimuli and, in turn, governs an exquisitely complex anti-proliferative transcriptional ...program that touches upon a bewildering array of biological responses. Despite the many unveiled facets of the p53 network, a clear appreciation of how and in what contexts p53 exerts its diverse effects remains unclear. How can we interpret p53’s disparate activities and the consequences of its dysfunction to understand how cell type, mutation profile, and epigenetic cell state dictate outcomes, and how might we restore its tumor-suppressive activities in cancer?
The most frequently mutated gene in human cancer, p53, governs a complex anti-proliferative program that in turn impacts an array of biological responses in a context-specific manner.
The microcosmos of cancer LUJAMBIO, Amaia; LOWE, Scott W
Nature (London),
02/2012, Volume:
482, Issue:
7385
Journal Article
Peer reviewed
Open access
The discovery of microRNAs (miRNAs) almost two decades ago established a new paradigm of gene regulation. During the past ten years these tiny non-coding RNAs have been linked to virtually all known ...physiological and pathological processes, including cancer. In the same way as certain key protein-coding genes, miRNAs can be deregulated in cancer, in which they can function as a group to mark differentiation states or individually as bona fide oncogenes or tumour suppressors. Importantly, miRNA biology can be harnessed experimentally to investigate cancer phenotypes or used therapeutically as a target for drugs or as the drug itself.
The adenomatous polyposis coli (APC) tumor suppressor is mutated in the vast majority of human colorectal cancers (CRC) and leads to deregulated Wnt signaling. To determine whether Apc disruption is ...required for tumor maintenance, we developed a mouse model of CRC whereby Apc can be conditionally suppressed using a doxycycline-regulated shRNA. Apc suppression produces adenomas in both the small intestine and colon that, in the presence of Kras and p53 mutations, can progress to invasive carcinoma. In established tumors, Apc restoration drives rapid and widespread tumor-cell differentiation and sustained regression without relapse. Tumor regression is accompanied by the re-establishment of normal crypt-villus homeostasis, such that once aberrantly proliferating cells reacquire self-renewal and multi-lineage differentiation capability. Our study reveals that CRC cells can revert to functioning normal cells given appropriate signals and provide compelling in vivo validation of the Wnt pathway as a therapeutic target for treatment of CRC.
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•Apc suppression in mouse colon recapitulates the molecular features of human CRC•Apc restoration triggers differentiation and restores crypt homeostasis•CRCs harboring Kras and p53 mutations remain strictly dependent on Apc loss•In vivo validation of the Wnt pathway as an effective therapeutic target in CRC
Colorectal cancer cells can revert to functioning normal cells in vivo when Apc levels are restored, even if potent oncogenic insults such as Kras and p53 mutations are present.
p53 is a frequent target for mutation in human tumors, and mutant p53 proteins can actively contribute to tumorigenesis. We employed a three-dimensional culture model in which nonmalignant breast ...epithelial cells form spheroids reminiscent of acinar structures found in vivo, whereas breast cancer cells display highly disorganized morphology. We found that mutant p53 depletion is sufficient to phenotypically revert breast cancer cells to a more acinar-like morphology. Genome-wide expression analysis identified the mevalonate pathway as significantly upregulated by mutant p53. Statins and sterol biosynthesis intermediates reveal that this pathway is both necessary and sufficient for the phenotypic effects of mutant p53 on breast tissue architecture. Mutant p53 associates with sterol gene promoters at least partly via SREBP transcription factors. Finally, p53 mutation correlates with highly expressed sterol biosynthesis genes in human breast tumors. These findings implicate the mevalonate pathway as a therapeutic target for tumors bearing mutations in p53.
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► Depletion of mutant p53 phenotypically reverts breast cancer cells in 3D culture ► Mutant p53 upregulates mevalonate pathway genes via SREBP transcription factors ► HMG-CoA reductase inhibitors mimic the phenotypic effects of mutant p53 depletion ► TP53 mutation correlates with elevation of mevalonate pathway genes in human tumors
Metastasis-associated p53 mutations disrupt breast tissue organization by upregulating transcription of sterol biosynthesis genes, highlighting p53 status as a predictive marker for responsiveness to statin therapy in cancer.
We screened 124 genes that are amplified in human hepatocellular carcinoma (HCC) using a mouse hepatoblast model and identified 18 tumor-promoting genes, including
CCND1 and its neighbor on 11q13.3,
...FGF19. Although it is widely assumed that
CCND1 is the main driving oncogene of this common amplicon (15% frequency in HCC), both forward-transformation assays and RNAi-mediated inhibition in human HCC cells established that
FGF19 is an equally important driver gene in HCC. Furthermore, clonal growth and tumorigenicity of HCC cells harboring the 11q13.3 amplicon were selectively inhibited by RNAi-mediated knockdown of
CCND1 or
FGF19, as well as by an anti-FGF19 antibody. These results show that 11q13.3 amplification could be an effective biomarker for patients most likely to respond to anti-FGF19 therapy.
► An oncogenomic-based screen identifies 18 amplified tumor-promoting genes in HCC ► In HCC,
FGF19 is a codriver gene, along with
CCND1, of the 11q13.3 amplicon ► Amplification of 11q13.3 in human HCC cells predicts response to anti-FGF19 treatment
RNA interference is a powerful tool for studying gene function, however, the reproducible generation of RNAi transgenic mice remains a significant limitation. By combining optimized ...fluorescence-coupled miR30-based shRNAs with high efficiency ES cell targeting, we developed a fast, scalable pipeline for the production of shRNA transgenic mice. Using this system, we generated eight tet-regulated shRNA transgenic lines targeting Firefly and Renilla luciferases, Oct4 and tumor suppressors p53, p16INK4a, p19ARF and APC and demonstrate potent gene silencing and GFP-tracked knockdown in a broad range of tissues in vivo. Further, using an shRNA targeting APC, we illustrate how this approach can identify predicted phenotypes and also unknown functions for a well-studied gene. In addition, through regulated gene silencing we validate APC/Wnt and p19ARF as potential therapeutic targets in T cell acute lymphoblastic leukemia/lymphoma and lung adenocarcinoma, respectively. This system provides a cost-effective and scalable platform for the production of RNAi transgenic mice targeting any mammalian gene.
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► shRNA transgenics enable potent and reversible fluorescence-marked gene silencing ► Transgenic mouse production is fast, efficient, and scalable ► “Speedy” ES cells accelerate the evaluation of gene function in mouse models ► Reversible gene suppression can pinpoint pathways for therapeutic intervention
Mutation of the TP53 tumor suppressor gene is the most common genetic alteration in cancer, and almost 1000 alleles have been identified in human tumors. While virtually all TP53 mutations are ...thought to compromise wild type p53 activity, the prevalence and recurrence of missense TP53 alleles has motivated countless research studies aimed at understanding the function of the resulting mutant p53 protein. The data from these studies support three distinct, but perhaps not necessarily mutually exclusive, mechanisms for how different p53 mutants impact cancer: first, they lose the ability to execute wild type p53 functions to varying degrees; second, they act as a dominant negative (DN) inhibitor of wild type p53 tumor-suppressive programs; and third, they may gain oncogenic functions that go beyond mere p53 inactivation. Of these possibilities, the gain of function (GOF) hypothesis is the most controversial, in part due to the dizzying array of biological functions that have been attributed to different mutant p53 proteins. Herein we discuss the current state of understanding of TP53 allele variation in cancer and recent reports that both support and challenge the p53 GOF model. In these studies and others, researchers are turning to more systematic approaches to profile TP53 mutations, which may ultimately determine once and for all how different TP53 mutations act as cancer drivers and whether tumors harboring distinct mutations are phenotypically unique. From a clinical perspective, such information could lead to new therapeutic approaches targeting the effects of different TP53 alleles and/or better sub-stratification of patients harboring TP53 mutant cancers.
RNA interference has become an indispensable tool for loss-of-function studies across eukaryotes. By enabling stable and reversible gene silencing, shRNAs provide a means to study long-term ...phenotypes, perform pool-based forward genetic screens and examine the consequences of temporary target inhibition in vivo. However, efficient implementation in vertebrate systems has been hindered by technical difficulties affecting potency and specificity. Focusing on these issues, we analyse current strategies to obtain maximal knockdown with minimal off-target effects.
The induction of cellular senescence is an important mechanism by which p53 suppresses tumorigenesis. Using a mouse model of liver carcinoma, where cellular senescence is triggered in vivo by ...inducible p53 expression, we demonstrated that NK cells participate in the elimination of senescent tumors. The elimination of senescent tumor cells is dependent on NKG2D. Interestingly, p53 restoration neither increases ligand expression nor increases the sensitivity to lysis by NK cells. Instead, p53 restoration caused tumor cells to secrete various chemokines with the potential to recruit NK cells. Antibody-mediated neutralization of CCL2, but not CCL3, CCL4 or CCL5, prevented NK cell recruitment to the senescent tumors and reduced their elimination. Our findings suggest that elimination of senescent tumors by NK cells occurs as a result of the cooperation of signals associated with p53 expression or senescence, which regulate NK cell recruitment, and other signals that induce NKG2D ligand expression on tumor cells.
The p53 tumor suppressor can restrict malignant transformation by triggering cell-autonomous programs of cell-cycle arrest or apoptosis. p53 also promotes cellular senescence, a tumor-suppressive ...program that involves stable cell-cycle arrest and secretion of factors that modify the tissue microenvironment. In the presence of chronic liver damage, we show that ablation of a p53-dependent senescence program in hepatic stellate cells increases liver fibrosis and cirrhosis associated with reduced survival and enhances the transformation of adjacent epithelial cells into hepatocellular carcinoma. p53-expressing senescent stellate cells release factors that skew macrophage polarization toward a tumor-inhibiting M1-state capable of attacking senescent cells in culture, whereas proliferating p53-deficient stellate cells secrete factors that stimulate polarization of macrophages into a tumor-promoting M2-state and enhance the proliferation of premalignant cells. Hence, p53 can act non-cell autonomously to suppress tumorigenesis by promoting an antitumor microenvironment, in part, through secreted factors that modulate macrophage function.
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► p53 promotes senescence in hepatic stellate cells, limiting fibrosis, cirrhosis, and liver cancer ► Senescent stellate cells secrete factors that promote M1 macrophage polarization ► M1 macrophages eliminate senescent cells and support an antitumor microenvironment ► p53 acts non-cell autonomously to maintain organ integrity and suppress cancer
p53 acts both cell autonomously and nonautonomously in liver stellate cells to limit their tumorigenic activity. p53 expression promotes stellate cell senescence and also induces secretion of factors that influence macrophage polarization, leading to the generation of macrophages that eliminate senescent cells.
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