Mdm4 and Mdm2 cooperate to inhibit p53 activity in proliferating cells in vivo

The Mdm2 and Mdm4 oncoproteins are key negative regulators of the p53 tumor suppressor. However, their physiological contributions to the regulation of p53 stability and activity remain highly controversial. Here, we combined a p53 knock-in allele, in which p53 is silenced by a transcriptional stop element flanked by loxP sites, with the Mdm2- and Mdm4-null alleles. This approach allows Cre-mediated conditional p53 expression in tissues in vivo and cells in vitro lacking Mdm2, Mdm4, or both. Using this strategy, we show that Mdm2 and Mdm4 are essential in a nonredundant manner for preventing p53 activity in the same cell type (Mouse Embryonic Fibroblasts (MEFs), neuronal progenitor cells and postmitotic neurons) and irrespective of the proliferation/differentiation status of the cells. Although Mdm2 prevents accumulation of the p53 protein, Mdm4 contributes to the overall inhibition of p53 activity independent of Mdm2. We propose a model in which Mdm2 is critical for the regulation of p53 levels and Mdm4 is critical for the fine-tuning of p53 transcriptional activity, both proteins acting synergistically to keep p53 in check. Finally, we show that neither Mdm2 nor Mdm4 regulate cell cycle progression independently of its ability to modulate p53 function.Doctorat en sciences, Spécialisation biologie moléculaireinfo:eu-repo/semantics/nonPublishe

Identification of cancer initiating cells in K-Ras driven lung adenocarcinoma

Ubiquitous expression of a resident K-RasG12V oncogene in adult mice revealed that most tissues are resistant to K-Ras oncogenic signals. Indeed, K-RasG12V expression only induced overt tumors in lungs. To identify these transformation-permissive cells, we induced K-RasG12V expression in a very limited number of adult lung cells (0.2%) and monitored their fate by X-Gal staining, a surrogate marker coexpressed with the K-Ras G12V oncoprotein. Four weeks later, 30% of these cells had proliferated to form small clusters. However, only SPC+ alveolar type II (ATII) cells were able to form hyperplastic lesions, some of which progressed to adenomas and adenocarcinomas. In contrast, induction of K-Ras G12V expression in lung cells by intratracheal infection with adenoviral-Cre particles generated hyperplasias in all regions except the proximal airways. Bronchiolar and bronchioalveolar duct junction hyperplasias were primarily made of CC10+ Clara cells. Some of them progressed to form benign adenomas. However, only alveolar hyperplasias, exclusively made up of SPC+ ATII cells, progressed to yield malignant adenocarcinomas. Adenoviral infection induced inflammatory infiltrates primarily made of T and B cells. This inflammatory response was essential for the development of K-RasG12V-driven bronchiolar hyperplasias and adenomas, but not for the generation of SPC+ ATII lesions. Finally, activation of K-RasG12V during embryonic development under the control of a Sca1 promoter yielded CC10+, but not SPC+, hyperplasias, and adenomas. These results, taken together, illustrate that different types of lung cells can generate benign lesions in response to K-Ras oncogenic signals. However, in adult mice, only SPC+ ATII cells were able to yield malignant adenocarcinomas.Work was supported by European Research Council Grant ERC-AG/250297-RAS AHEAD; EU-Framework Programme Grants LSHG-CT-2007-037665/CHEMORES, HEALTH-F2-2010-259770/LUNGTARGET, and HEALTH-010-260791/EUROCANPLATFORM; Spanish Ministry of Economy and Competitiveness Grant SAF2011-30173; Autonomous Community of Madrid S2011/BDM-2470/ONCOCYCLE (to M.B.); National Institutes of Health Grant R01 CA109335-04A1; Spanish Ministry of Economy and Competitivenes Grant SAF2012-32810; and EU-Framework Programme Grant FP7-ENV-2011/ARIMMORA (to I.S.-G.). S.M. was supported by a predoctoral fellowship from Fundación La Caixa.Peer Reviewe

Distinct roles of Mdm2 and Mdm4 in red cell production

info:eu-repo/semantics/publishe

A critical role for p53 in the control of NF-kappa B-dependent gene expression in TLR4-stimulated dendritic cells exposed to genistein

Considerable research has focused on the anti-inflammatory and antiproliferative activities exhibited by the soy isoflavone genistein. We previously demonstrated that genistein suppresses TNF-alpha-induced NF-kappaB-dependent IL-6 gene expression in cancer cells by interfering with the mitogen- and stress-activated protein kinase 1 activation pathway. However, effects of isoflavones on immune cells, such as dendritic cells, remain largely unknown. Here we show that genistein markedly reduces IL-6 cytokine production and transcription in LPS-stimulated human monocyte-derived dendritic cells. More particularly, we observe that genistein inhibits IL-6 gene expression by modulating the transcription factor NF-kappaB. Examination of NF-kappaB-related events downstream of TLR4 demonstrates that genistein affects NF-kappaB subcellular localization and DNA binding, although we observe only a minor inhibitory impact of genistein on the classical LPS-induced signaling steps. Interestingly, we find that genistein significantly increases p53 protein levels. We also show that overexpression of p53 in TLR4/MD2 HEK293T cells blocks LPS-induced NF-kappaB-dependent gene transcription, indicating the occurrence of functional cross-talk between p53 and NF-kappaB. Moreover, analysis of IL-6 mRNA levels in bone marrow-derived p53 null vs wild-type dendritic cells confirms a role for p53 in the reduction of NF-kappaB-dependent gene expression, mediated by genistein.info:eu-repo/semantics/publishe

c-RAF Ablation Induces Regression of Advanced Kras/Trp53 Mutant Lung Adenocarcinomas by a Mechanism Independent of MAPK Signaling

A quarter of all solid tumors harbor KRAS oncogenes. Yet, no selective drugs have been approved to treat these malignancies. Genetic interrogation of the MAPK pathway revealed that systemic ablation of MEK or ERK kinases in adult mice prevent tumor development but are unacceptably toxic. Here, we demonstrate that ablation of c-RAF expression in advanced tumors driven by KrasG12V/Trp53 mutations leads to significant tumor regression with no detectable appearance of resistance mechanisms. Tumor regression results from massive apoptosis. Importantly, systemic abrogation of c-RAF expression does not inhibit canonical MAPK signaling, hence, resulting in limited toxicities. These results are of significant relevance for the design of therapeutic strategies to treat K-RAS mutant cancers.We thank David Kirsch for providing theTrp53F/Fstrain. We thank Dr. ManuelMorente for his advice in histopathological analysis. We also thank M. SanRoman, C. Lechuga, R. Villar, P. Villanueva, N. Cabrera, J. Condo, M. Munoz,and R. Blasco for excellent technical support. This work was supported bygrants from the European Research Council (ERC-2009-AdG/250297-RASAHEAD and ERC-2015-AdG/695566,THERACAN), EU-Framework Program(HEALTH-F2-2010-259770/LUNGTARGET and HEALTH-2010-260791/EUROCANPLATFORM), Spanish Ministry of Economy and Competitiveness(SAF2011-30173 and SAF2014-59864-R) and Autonomous Community ofMadrid (S2011/BDM-2470/ONCOCYCLE) to M.B. M.B. is a recipient of anEndowed Chair from the AXA Research Fund. M.S. is the recipient of anFPU fellowship from the Spanish Ministry of Education. S.F. was supportedby a FEBS Long-Term Fellowship and a Sara Borrell grant from the Institutode Salud Carlos III. L.E.-B. is the recipient of an FPI fellowship from the Span-ish Ministry of Economy and Competitiveness

Erratum: Correction for Danovi et al. "Amplification of Mdmx (or Mdm4) Directly Contributes to Tumor Formation by Inhibiting p53 Tumor Suppressor Activity" (Molecular and cellular biology (2004) 24 13 (5835-5843) PII: e00150-19)

SCOPUS: er.jDecretOANoAutActifinfo:eu-repo/semantics/publishe