Resistance mechanisms to TP53-MDM2 inhibition identified by in vivo piggyBac transposon mutagenesis screen in an Arf mouse model.

Inhibitors of double minute 2 protein (MDM2)-tumor protein 53 (TP53) interaction are predicted to be effective in tumors in which the gene is wild type, by preventing TP53 protein degradation. One such setting is represented by the frequent deletion in human cancer that, through inactivation of , activates MDM2 protein, which in turn degrades TP53 tumor suppressor. Here we used piggyBac (PB) transposon insertional mutagenesis to anticipate resistance mechanisms occurring during treatment with the MDM2-TP53 inhibitor HDM201.

HIF prolyl hydroxylase 2 (PHD2) is a critical regulator of hematopoietic stem cell maintenance during steady-state and stress.

Hypoxia is a prominent feature in the maintenance of hematopoietic stem cell (HSC) quiescence and multipotency. Hypoxia-inducible factor (HIF) prolyl hydroxylase domain proteins (PHDs) serve as oxygen sensors and may therefore regulate this system. Here, we describe a mouse line with conditional loss of HIF prolyl hydroxylase 2 (PHD2) in very early hematopoietic precursors that results in self-renewal of multipotent progenitors under steady-state conditions in a HIF1α- and SMAD7-dependent manner.

MDM4 is a key therapeutic target in cutaneous melanoma.

The inactivation of the p53 tumor suppressor pathway, which often occurs through mutations in TP53 (encoding tumor protein 53) is a common step in human cancer. However, in melanoma-a highly chemotherapy-resistant disease-TP53 mutations are rare, raising the possibility that this cancer uses alternative ways to overcome p53-mediated tumor suppression. Here we show that Mdm4 p53 binding protein homolog (MDM4), a negative regulator of p53, is upregulated in a substantial proportion (∼65%) of stage I-IV human melanomas and that melanocyte-specific Mdm4 overexpression enhanced tumorigenesis in a mouse model of melanoma induced by the oncogene Nras.

Widespread overexpression of epitope-tagged Mdm4 does not accelerate tumor formation in vivo.

Mdm2 and Mdm4 are critical negative regulators of p53. A large body of evidence indicates that elevated expression of either Mdm2 or Mdm4 may favor tumor formation by inhibiting p53 tumor suppression function. To explore this possibility in vivo, we generated conditional Mdm2 and Mdm4 transgenic mice.

Efficient mouse transgenesis using Gateway-compatible ROSA26 locus targeting vectors and F1 hybrid ES cells.

The ability to rapidly and efficiently generate reliable Cre/loxP conditional transgenic mice would greatly complement global high-throughput gene targeting initiatives aimed at identifying gene function in the mouse. We report here the generation of Cre/loxP conditional ROSA26-targeted ES cells within 3-4 weeks by using Gateway cloning to build the target vectors. The cDNA of the gene of interest can be expressed either directly by the ROSA26 promoter providing a moderate level of expression or by a CAGG promoter placed in the ROSA26 locus providing higher transgene expression.

Negative and positive regulation of MAPK phosphatase 3 controls platelet-derived growth factor-induced Erk activation.

MAPK phosphatases (MKPs) are dual specificity phosphatases that dephosphorylate and thereby inactivate MAPKs. In the present study, we provide evidence that platelet-derived growth factor BB (PDGF-BB) regulates MKP3 (DUSP6), which is considered to be a phosphatase highly selective for Erk. Intriguingly, we observed that Mek is positively regulated by MKP3, whereas Erk itself is negatively regulated.