Keeping p53 in check: essential and synergistic functions of Mdm2 and Mdm4.
TL;DR: This work presents a novel and scalable approach to gene expression engineering that allows for real-time annotation of gene expression changes in response to cancerigenicity and shows promise in finding novel and efficient treatments for cancer.
Abstract: 1 Laboratory For Molecular Cancer Biology, Flanders Interuniversity Institute for Biotechnology (VIB), University of Ghent, Technologiepark, 927, Ghent B9052, Belgium 2 Salk Institute for Biological Studies, Gene Expression Laboratory, La Jolla, CA 92037, USA 3 Gene Expression and Diseases Unit, Institut Pasteur, Paris, France 4 The University of Texas Graduate School of Biomedical Sciences and department of Molecular Genetics, Section of Cancer Genetics, The University of Texas MD Anderson Cancer Center, Houston, Texas 77030, USA * Corresponding author: J-C Marine, Laboratory For Molecular Cancer Biology, VIB, Technologiepark, 927, Ghent B-9052, Belgium. Tel: þ 32-93-313-640; Fax: þ 32-93-313-516; E-mail: chris.marine@dmbr.ugent.be
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01 Jan 2007
TL;DR: Newly discovered ligand-receptor interactions between cancer cells and these host elements offer a molecular explanation for Paget’s “seed and soil” hypothesis, and indicate new targets for possible anti-metastatic therapeutic agents.
Abstract: Motility and invasion of breast cancer cells are the result of the concerted action of a number of cell activities: directional migration underpinned by the dynamic organisation of cytoskeletal components (actin micro-filaments and microtubules), establishment and disruption of cell-matrix and homotypic/heterotypic cell-cell adhesions, and extracellular proteolysis. Metastasis formation is not only related to cancer cell motility, but also necessitates the collaboration of other, coined “host” cells. Newly discovered ligand-receptor interactions between cancer cells and these host elements offer a molecular explanation for Paget’s “seed and soil” hypothesis, and indicate new targets for possible anti-metastatic therapeutic agents
2 citations
01 Jan 2015
TL;DR: It is suggested that children under the age of 13 should be supervised by an adult rather than a stranger, as is the case with children aged under 14 and under 15.
Abstract: ......................................................................................................................................v Table of
2 citations
Cites background from "Keeping p53 in check: essential and..."
...In physiological conditions, p53 is degraded or inhibited upon binding of MDM2 ubiquitinase [59]....
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Dissertation•
01 Jan 2011
TL;DR: A regulatory crosstalk may be revealed between the MST2 apoptotic pathway and the Raf-1 proliferative pathway through CNK1 by coordinating assembly of appropriate pathway components to possibly drive discrete stimulus-specific responses.
Abstract: An emerging concept in the regulation of signal transduction specificity is the mediation
of scaffold proteins embedded in the circuitry of signalling pathways. The multidomainbased
architecture of scaffold proteins facilitates the assembly and modulation of protein
complexes to regulate cellular signals to bring about an exacting biological output. The
work presented in this thesis aimed to investigate the mechanisms of the protein scaffold
CNK1 (connector enhancer of Ras 1) in the pro-apoptotic MST2 pathway and the prooncogenic
Raf-1 signalling pathways. Here, by using several molecular, biochemical and
cell biology techniques, I demonstrated that CNK1 regulates the interaction of the protooncogene
Raf-1 and the tumour suppressor MST2 kinase. Perturbations of CNK1 levels
exhibit a biphasic signalling response typical of a scaffold protein. Transient expression
of CNK1 upon growth factor withdrawal results in a concentration-dependent increase
of the Raf-1/MST2 complex, thus preventing apoptosis, but this complex dissociates at
higher expression levels, hence promoting an apoptotic response. Moreover, CNK1 is
involved in the regulation of Fas-induced apoptosis via the MST2/RASSF1A pathway
by influencing the time-scale kinetics of MST2 docking and release from the Raf-
1/CNK1 complex and its eventual activation. SiRNA-silencing of CNK1 destabilizes the
Raf-1 and MST2 interaction, and enhanced MST2/LATS1 interaction that promotes
apoptosis. Thus, CNK1 is required for Raf-1 inhibitory function, but is also necessary
for MST2-mediated apoptosis. Remarkably, CNK1 selects and switches complex
formation of opposing anchored proteins depending on the stimulus. In response to Fas
ligand stimulation, MST2 is released, whereas Raf-1 is retained in complex with CNK1.
Conversely, CNK1 retains MST2 and whilst releasing Raf-1 from the complex following
growth factor treatment. Mapping the multidomain binding sites of CNK1 using peptide
array demonstrates specific interaction sites of client protein complexes. Specific CNK1
point mutants were generated, and found to alter wild-type regulation of client protein
complexes. Thus, the work described in this thesis may reveal a regulatory crosstalk
between the MST2 apoptotic pathway and the Raf-1 proliferative pathway through
CNK1 by coordinating assembly of appropriate pathway components to possibly drive
discrete stimulus-specific responses.
2 citations
Cites background from "Keeping p53 in check: essential and..."
...As it plays a crucial role in cell cycle regulation (growth arrest, DNA recognition, transcription of repair genes) (Marine et al., 2006) and apoptosis (suppress replication of damaged DNA, induce cell death of damaged cells) (Zhang et al, 2007), loss of p53 function or inactivation abolishes apoptosis and allows abnormal cell division (genomic instability) (Rivlin et al....
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01 Jan 2008
2 citations
Dissertation•
01 Nov 2011
TL;DR: The focus of this thesis was to evaluate the mechanisms whereby myeloma cells develop intrinsic resistance with a focus on resistance in the context of bortezomib treatment and found that that overexpression of P-gp attenuates bortzomib activity.
Abstract: The focus of this thesis was to evaluate the mechanisms whereby myeloma cells develop intrinsic resistance with a focus on resistance in the context of bortezomib treatment. The aims of this thesis were to examine multidrug resistance pumps as a mechanism of resistance in MM, to investigate the contribution of p53 signalling perturbations in resistance mechanism in MM, to study the AMPK pathway as an alternative target to overcome MM resistance and finally to characterise myeloma resistance to bortezomib treatment using 2D-DIGE analysis.
Focussing on bortezomib resistance models, we found that that overexpression of P-gp attenuates bortezomib activity. Bortezomib is a P-gp substrate and a combination of P-gp inhibitor and bortezomib is able to overcome resistance. Bortezomib is also able to downregulate the expression and function of P-gp. Our findings therefore suggest that combination of a P-gp inhibitor and bortezomib in P-gp positive myeloma would be a reasonable treatment combination to extend use of the drug.
We have shown that p53 apoptotic signalling pathways can be accentuated when bortezomib is combined with a Mdm2 inhibitor. In p53 WT cells, nutlin-3 in combination with bortezomib generates additive toxicity in MM cells but is highly synergistic in epithelial models and p53-mutated cell lines. This synergy persists in the presence of BMSCs. This observation has implications more so in epithelial cancers and p53 mutated cancers where single agent bortezomib activity is mild. We have also shown that bortezomib-treated patients who had high expression of nutlin-3-suppressed genes had significantly shorter progression-free (p=0.001, log-rank test) and overall survival (p=0.002, log-rank test) compared to those with low expression levels.
AMPK activation is promising as an anticancer pathway and may also be a chemoprevention target. Metformin and AICAR, which activate this pathway, both have demonstrated useful preclinical anticancer properties and have a good therapeutic index in patients. We explored mechanism of cell death and showed that AICAR was able to activate the apoptotic pathway. These agents also synergise with glycolysis inhibitors to further increase cytotoxicity in cancer cells.
Identification of proteins whose expression is altered in differing states of sensitivity and resistance provides candidates for better understanding of resistance mechanisms so we also investigated bortezomib resistance in cellular models using proteomic techniques and isolated and identified several novel proteins which may play a role in this phenomenon. Our findings are mechanistically consistent since two of the identified proteins Hsp70 and caspase-3 are known in the literature to be affected by bortezomib treatment.
2 citations
References
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TL;DR: A gene is identified, named WAF1, whose induction was associated with wild-type but not mutant p53 gene expression in a human brain tumor cell line and that could be an important mediator of p53-dependent tumor growth suppression.
8,339 citations
TL;DR: In this article, the authors identify potent and selective small-molecule antagonists of MDM2 and confirm their mode of action through the crystal structures of complexes, leading to cell cycle arrest, apoptosis, and growth inhibition of human tumor xenografts.
Abstract: MDM2 binds the p53 tumor suppressor protein with high affinity and negatively modulates its transcriptional activity and stability. Overexpression of MDM2, found in many human tumors, effectively impairs p53 function. Inhibition of MDM2-p53 interaction can stabilize p53 and may offer a novel strategy for cancer therapy. Here, we identify potent and selective small-molecule antagonists of MDM2 and confirm their mode of action through the crystal structures of complexes. These compounds bind MDM2 in the p53-binding pocket and activate the p53 pathway in cancer cells, leading to cell cycle arrest, apoptosis, and growth inhibition of human tumor xenografts in nude mice.
4,397 citations
TL;DR: It is proposed that the Mdm2-promoted degradation of p53 provides a new mechanism to ensure effective termination of the p53 signal.
Abstract: The p53 tumour-suppressor protein exerts antiproliferative effects, including growth arrest and apoptosis, in response to various types of stress. The activity of p53 is abrogated by mutations that occur frequently in tumours, as well as by several viral and cellular proteins. The Mdm2 oncoprotein is a potent inhibitor of p53. Mdm2 binds the transcriptional activation domain of p53 and blocks its ability to regulate target genes and to exert antiproliferative effects. On the other hand, p53 activates the expression of the mdm2 gene in an autoregulatory feedback loop. The interval between p53 activation and consequent Mdm2 accumulation defines a time window during which p53 exerts its effects. We now report that Mdm2 also promotes the rapid degradation of p53 under conditions in which p53 is otherwise stabilized. This effect of Mdm2 requires binding of p53; moreover, a small domain of p53, encompassing the Mdm2-binding site, confers Mdm2-dependent detstabilization upon heterologous proteins. Raised amounts of Mdm2 strongly repress mutant p53 accumulation in tumour-derived cells. During recovery from DNA damage, maximal Mdm2 induction coincides with rapid p53 loss. We propose that the Mdm2-promoted degradation of p53 provides a new mechanism to ensure effective termination of the p53 signal.
4,311 citations
TL;DR: It is shown that interaction with Mdm2 can also result in a large reduction in p53 protein levels through enhanced proteasome-dependent degradation, which may contribute to the maintenance of low p53 concentrations in normal cells.
Abstract: The tumour-suppressor p53 is a short-lived protein that is maintained at low, often undetectable, levels in normal cells. Stabilization of the protein in response to an activating signal, such as DNA damage, results in a rapid rise in p53 levels and subsequent inhibition of cell growth. Tight regulation of p53 function is critical for normal cell growth and development, and one mechanism by which p53 function is controlled is through interaction with the Mdm2 protein. Mdm2 inhibits p53 cell-cycle arrest and apoptic functions and we show here that interaction with Mdm2 can also result in a large reduction in p53 protein levels through enhanced proteasome-dependent degradation. Endogenous levels of Mdm2 are sufficient to regulate p53 stability, and overexpression of Mdm2 can reduce the amount of endogenous p53. Because mdm2 is transcriptionally activated by p53, this degradative pathway may contribute to the maintenance of low p53 concentrations in normal cells. Furthermore, mechanisms regulating the Mdm2-induced degradation of p53 may play a role in controlling the extent and duration of the p53 response.
3,298 citations
TL;DR: The data suggest that the MDM2 protein, which is induced by p53, functions as a ubiquitin ligase, E3, in human papillomavirus‐uninfected cells which do not have E6 protein.
1,962 citations